4.5V to 18V Input Voltage, 3A/2A/2A Output Current Triple

LX1

FB1

LX2

FB2

LX3

FB3

PVINx

VIN

ENx

PGOOD

MODE

SSx

ROSC

VDIV

RESET

PGND

AGND

Vin Vout1

Vout3

TPS65261

TPS65261-1

Vout2

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1

Effic

iency

(%)

Output Load (A)

TPS65261

C001

VIN = 12 VVOUT = 3.3 V

Product

Folder

Sample &Buy

Technical

Documents

Tools &

Software

Support &Community

TPS65261, TPS65261-1SLVSCD3B –DECEMBER 2013–REVISED MAY 2014

TPS6526x 4.5V to 18V Input Voltage, 3A/2A/2A Output CurrentTriple Synchronous Step-Down Converter

1 Features 3 DescriptionThe TPS65261, TPS65261-1 is a monolithic triple

1• Operating Input Supply Voltage Rangesynchronous step-down (buck) converter with(4.5 V to 18 V)3A/2A/2A output currents. A wide 4.5V to 18V input

• Feedback Reference Voltage 0.6V±1% supply voltage range encompasses the most• Maximum Continuous Output Current 3A/2A/2A intermediate bus voltages operating off 5V, 9V, 12V

or 15V power bus. The converter, with constant• Adjustable Clock Frequency from 250kHz tofrequency peak current mode, is designed to simplify2MHzits application while giving designers options to

• Dedicated Enable and Soft Start Pins for Each optimize the system according to targetedBuck applications. The switching frequency of the

• Automatic Power-up/Power-down Sequence converters can be adjusted from 250kHz to 2MHzwith an external resistor. The 180° out-of-phase• Pulse Skipping Mode (PSM) at Light Loadoperation between Buck1 and Buck2, 3 (Buck2 and 3(TPS65261 only)run in phase) minimizes the input filter requirements.

• Output Voltage Power Good IndicatorThe TPS65261, TPS65261-1 features an automatic• Input Voltage Power Failure Indicator power sequence with connecting MODE pin to V7V

• Thermal Overloading Protection and configuring EN1/2/3 pins. The device alsofeatures an open drain RESET signal to monitor

2 Applications power down.• DTV At light load, the TPS65261 automatically operates in

pulse skipping mode (PSM) and the TPS65261-1• Set Top Boxesoperates in force continuous current mode (FCC).• Home Gateway and Access Point Networks PSM mode provides high efficiency by reducing

• Wireless Routers switching losses at light loads and FCC mode• Surveillance reduces noise susceptibility and RF interference.• POS Machine The device features overvoltage protection,

overcurrent and short-circuit protection and over-temperature protection. A power good pin assertswhen any output voltages are out of regulation.

Device Information (1)

PART NUMBER PACKAGE BODY SIZE (NOM)TPS65261, VQFN (32) 5.00 mm × 5.00 mmTPS65261-1

(1) For all available packages, see the orderable addendum atthe end of the datasheet.

4 Typical Application

1

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,intellectual property matters and other important disclaimers. PRODUCTION DATA.

TPS65261, TPS65261-1SLVSCD3B –DECEMBER 2013–REVISED MAY 2014 www.ti.com

Table of Contents8.3 Feature Description................................................. 131 Features .................................................................. 18.4 Device Functional Modes........................................ 222 Applications ........................................................... 1

9 Application and Implementation ........................ 243 Description ............................................................. 19.1 Application Information............................................ 244 Typical Application ................................................ 19.2 Typical Application ................................................. 245 Revision History..................................................... 2

10 Power Supply Recommendations ..................... 346 Pin Configuration and Functions ......................... 311 Layout................................................................... 347 Specifications......................................................... 4

11.1 Layout Guidelines ................................................. 347.1 Absolute Maximum Ratings ...................................... 411.2 Layout Example .................................................... 357.2 Handling Ratings ...................................................... 5

12 Device and Documentation Support ................. 367.3 Recommended Operating Conditions....................... 512.1 Documentation Support ....................................... 367.4 Thermal Information .................................................. 512.2 Related Links ........................................................ 367.5 Electrical Characteristics........................................... 612.3 Trademarks ........................................................... 367.6 Typical Characteristics .............................................. 812.4 Electrostatic Discharge Caution............................ 368 Detailed Description ............................................ 1212.5 Glossary ................................................................ 368.1 Overview ................................................................. 12

13 Mechanical, Packaging, and Orderable8.2 Functional Block Diagram ....................................... 13Information ........................................................... 36

5 Revision History

Changes from Revision A (December 2013) to Revision B Page

• Changed all text, tables and graphics to match the new data sheet template. ..................................................................... 1• Changed Figure 70............................................................................................................................................................... 35

2 Submit Documentation Feedback Copyright © 2013–2014, Texas Instruments Incorporated

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http://www.go-dsp.com/forms/techdoc/doc_feedback.htm?litnum=SLVSCD3B&partnum=TPS65261

EN3

PGOOD

MODE

RESET

FB2

V7V

SS2

COMP2

32

9

31

10

30

11

29

12

28

13

27

14

26

15

25

16

241

232

223

214

205

196

187

178

EN

2

EN

1

FB1

VD

IV

VIN

COMP1

SS1

BS

T1

LX

1

PG

ND

1

PV

IN1

LX

3

SS3

BS

T3

BS

T2

LX

2

PG

ND

2

PV

IN3

ROSC

AGND

FB3

PV

IN2

COMP3

PG

ND

3

Thermal Pad

TPS65261, TPS65261-1www.ti.com SLVSCD3B –DECEMBER 2013–REVISED MAY 2014

6 Pin Configuration and Functions

RHB PACKAGE(TOP VIEW)

(There is no electric signal down bonded to thermal pad inside IC.Exposed thermal pad must be soldered to PCB for optimal thermal performance.)

Pin FunctionsPIN

DESCRIPTIONNO. NAME

Enable for buck3. Float to enable. Can use this pin to adjust the input under-voltage lockout of buck3 with a resistor1 EN3 divider.An open drain output, asserts low if output voltage of any buck beyond regulation range due to thermal shutdown,2 PGOOD over-current, under-voltage or ENx shut down.

3 RESET Open drain power failure output signal.When high, an automatic power-up/power-down sequence is provided according to states of EN1, EN2 and EN34 MODE pins.

5 V7V Internal LDO for gate driver and internal controller. Connect a 1µF capacitor from the pin to power ground6 FB2 Feedback Kelvin sensing pin for buck2 output voltage. Connect this pin to buck2 resistor divider.

Error amplifier output and Loop compensation pin for buck2. Connect a series resistor and capacitor to compensate7 COMP2 the control loop of buck2 with peak current PWM mode.Soft-start and tracking input for buck2. An internal 5µA pull-up current source is connected to this pin. The soft-start8 SS2 time can be programmed by connecting a capacitor between this pin and ground.Boot strapped supply to the high side floating gate driver in buck2. Connect a capacitor (recommend 47nF) from9 BST2 BST2 pin to LX2 pin.Switching node connection to the inductor and bootstrap capacitor for buck2. The voltage swing at this pin is from a10 LX2 diode voltage below the ground up to PVIN2 voltage.Power ground connection of buck2. Connect PGND2 pin as close as practical to the (–) terminal of VIN2 input11 PGND2 ceramic capacitor.Input power supply for buck2. Connect PVIN2 pin as close as practical to the (+) terminal of an input ceramic12 PVIN2 capacitor (suggest 10µF).Input power supply for buck3. Connect PVIN3 pin as close as practical to the (+) terminal of an input ceramic13 PVIN3 capacitor (suggest 10µF).Power ground connection of buck3. Connect PGND3 pin as close as practical to the (–) terminal of VIN3 input14 PGND3 ceramic capacitor.Switching node connection to the inductor and bootstrap capacitor for buck3. The voltage swing at this pin is from a15 LX3 diode voltage below the ground up to PVIN3 voltage.

Copyright © 2013–2014, Texas Instruments Incorporated Submit Documentation Feedback 3

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Pin Functions (continued)PIN

DESCRIPTIONNO. NAME

Boot strapped supply to the high side floating gate driver in buck3. Connect a capacitor (recommend 47nF) from16 BST3 BST3 pin to LX3 pin.Soft-start and tracking input for buck3. An internal 5µA pull-up current source is connected to this pin. The soft-start17 SS3 time can be programmed by connecting a capacitor between this pin and ground.Error amplifier output and Loop compensation pin for buck3. Connect a series resistor and capacitor to compensate18 COMP3 the control loop of buck3 with peak current PWM mode.

19 FB3 Feedback Kelvin sensing pin for buck3 output voltage. Connect this pin to buck3 resistor divider.20 ROSC Oscillator frequency programmable pin. Connect an external resistor to set the switching frequency.

Analog ground common to buck controllers and other analog circuits. It must be routed separately from high current21 AGND power grounds to the (–) terminal of bypass capacitor of input voltage VIN.22 FB1 Feedback Kelvin sensing pin for buck1 output voltage. Connect this pin to buck1 resistor divider.

Error amplifier output and Loop compensation pin for buck1. Connect a series resistor and capacitor to compensate23 COMP1 the control loop of buck1 with peak current PWM mode.Soft-start and tracking input for buck1. An internal 5µA pull-up current source is connected to this pin. The soft-start24 SS1 time can be programmed by connecting a capacitor between this pin and ground.Boot strapped supply to the high side floating gate driver in buck1. Connect a capacitor (recommend 47nF) from25 BST1 BST1 pin to LX1 pin.Switching node connection to the inductor and bootstrap capacitor for buck1. The voltage swing at this pin is from a26 LX1 diode voltage below the ground up to PVIN1 voltage.Power ground connection of Buck1. Connect PGND1 pin as close as practical to the (–) terminal of VIN1 input27 PGND1 ceramic capacitor.Input power supply for buck1. Connect PVIN1 pin as close as practical to the (+) terminal of an input ceramic28 PVIN1 capacitor (suggest 10µF).

29 VIN Buck controller power supply.30 VDIV Input voltage threshold for power failure detection of input voltage.

Enable for buck1. Float to enable. Can use this pin to adjust the input under-voltage lockout of buck1 with a resistor31 EN1 divider.Enable for buck2. Float to enable. Can use this pin to adjust the input under-voltage lockout of buck2 with a resistor32 EN2 divider.There is no electric signal down bonded to thermal pad inside IC. Exposed thermal pad must be soldered to PCB forPAD optimal thermal performance.

7 Specifications

7.1 Absolute Maximum Ratingsover operating free-air temperature range (unless otherwise noted) (1)

MIN MAX UNITPVIN1, PVIN2, PVIN3,VIN –0.3 20 VLX1, LX2, LX3 (Maximum withstand voltage transient < 20 ns) –1.0 20 VBST1, BST2, BST3 referenced to LX1, LX2, LX3 pins respectively –0.3 7 VEN1, EN2, EN3, PGOOD, V7V, MODE, RESET, VDIV –0.3 7 VFB1, FB2, FB3, COMP1 , COMP2, COMP3, SS1, SS2, SS3, ROSC –0.3 3.6 VAGND, PGND1, PGND2, PGND3 –0.3 0.3 VOperating junction temperature, TJ –40 125 °C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratingsonly, which do not imply functional operation of the device at these or any other conditions beyond those indicated under RecommendedOperating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.


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7.2 Handling RatingsMIN MAX UNIT

Tstg Storage temperature range –55 150 °CHuman body model (HBM), per ANSI/ESDA/JEDEC JS-001, all -2000 2000pins (1)

V(ESD) Electrostatic discharge VCharged device model (CDM), per JEDEC specification -500 500JESD22-C101, all pins (2)

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

7.3 Recommended Operating Conditionsover operating free-air temperature range (unless otherwise noted)

MIN NOM MAX UNITPVIN1, PVIN2, PVIN3,VIN 4.5 18 VLX1, LX2, LX3 (Maximum withstand voltage transient < 20 ns) -0.8 18 VBST1, BST2, BST3 referenced to LX1, LX2, LX3 pins respectively -0.1 6.8 VEN1, EN2, EN3, PGOOD, V7V, MODE, RESET, VDIV -0.1 6.3 VFB1, FB2, FB3, COMP1 , COMP2, COMP3, SS1, SS2, SS3, ROSC -0.1 3 V

TA Operating junction temperature -40 85 °CTJ Operating junction temperature -40 125 °C

7.4 Thermal InformationTPS65261

THERMAL METRIC (1) UNITRHB (32 PINS)

RθJA Junction-to-ambient thermal resistance 31.6RθJC(top) Junction-to-case (top) thermal resistance 23.4RθJB Junction-to-board thermal resistance 6.1

°C/WψJT Junction-to-top characterization parameter 0.2ψJB Junction-to-board characterization parameter 6.1RθJC(bot) Junction-to-case (bottom) thermal resistance 0.9

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.


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7.5 Electrical CharacteristicsTA = 25°C, VIN = 12 V, fSW = 600 kHz (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNITINPUT SUPPLY VOLTAGEVIN Input voltage range 4.5 18 V

VIN rising 4 4.25 4.5V

UVLO VIN under-voltage lockout VIN falling 3.5 3.75 4Hysteresis 500 mV

IDDSDN Shutdown supply current EN1=EN2=EN3=MODE=0V 9.2 µAEN1=EN2=EN3=5V,IDDQ_NSW 605 µAFB1=FB2=FB3=0.8V

Input quiescent current withoutIDDQ_NSW1 EN1=5V, EN2=EN3=0V, FB1=0.8V 330 µAbuck1/2/3 switching

IDDQ_NSW2 EN2=5V, EN1=EN3=0V, FB2=0.8V 330 µAIDDQ_NSW3 EN3=5V, EN1=EN2=0V, FB3=0.8V 330 µAV7V V7V LDO output voltage V7V load current=0A 6 6.3 6.6 VIOCP_V7V V7V LDO current limit 175 mAFEEDBACK VOLTAGE REFERENCE

VCOMP = 1.2 V, TJ = 25°C 0.596 0.6 0.605 VVFB Feedback voltage

VCOMP = 1.2 V, TJ = -40°C to 125°C 0.594 0.6 0.606 VIOUT1 = 1.5A, IOUT2 = 1A, IOUT3 = 1AVLINEREG_BUCK Line regulation-DC 0.002 %/V5V < PVINx < 18V

VLOADREG_BUCK Load regulation-DC IOUTx = (10–100%) × IOUTx_max 0.02 %/ABuck1, Buck2, Buck3VENXH EN1/2/3 high level input voltage 1.2 1.26 VVENXL EN1/2/3 low level input voltage 1.1 1.15 VIENX1 EN1/2/3 pull-up current ENx = 1V 3.6 µAIENX2 EN1/2/3 pull-up current ENx = 1.5V 6.6 µAIENhys Hysteresis current 3 µAISSX Soft start charging current 4.3 5 6 µATON_MIN Minimum on time 80 100 nsGm_EA Error amplifier trans-conductance –2 µA < ICOMPX < 2 µA 300 µS

COMP1/2/3 voltage to inductor currentGm_PS1/2/3 ILX = 0.5 A 7.4 A/VGmILIMIT1 Buck1 peak inductor current limit 4.33 5.1 6.02 AILIMITSOURCE1 Buck1 low side source current limit 4.3 AILIMITSINK1 Buck1 low side sink current limit 1.3 AILIMIT2/3 Buck2/3 peak inductor current limit 2.6 3.1 3.73 AILIMITSOURCE2/3 Buck2/3 low side source current limit 2.7 AILIMITSINK2/3 Buck2/3 low side sink current limit 1 ATHiccup_wait Over current wait time 256 cyclesTHiccup_re Hiccup time before re-start 8192 cyclesRdson_HS1 Buck1 High-side switch resistance VIN = 12V 100 mΩRdson_LS1 Buck1 low-side switch resistance VIN = 12V 65 mΩRdson_HS2 Buck2 High-side switch resistance VIN = 12V 140 mΩRdson_LS2 Buck2 low-side switch resistance VIN = 12V 95 mΩRdson_HS3 Buck3 High-side switch resistance VIN = 12V 140 mΩRdson_LS3 Buck3 low-side switch resistance VIN = 12V 95 mΩ


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Electrical Characteristics (continued)TA = 25°C, VIN = 12 V, fSW = 600 kHz (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNITPOWER GOOD, MODE, POWER SEQUENCE

FBx under-voltage Falling 92.5 %VREF

FBx under-voltage Rising 95 %VREFVth_PG Feedback voltage thresholdFBx over-voltage Rising 107.5 %VREF

FBx over-voltage Falling 105 %VREF

TDEGLITCH(PG)_F PGOOD falling edge deglitch time 128 cyclesTRDEGLITCH(PG)_R PGOOD rising edge deglitch time 512 cyclesIPG PGOOD pin leakage 0.05 µAVLOW_PG PGOOD pin low voltage ISINK = 1 mA 0.4 VVMODEH MODE high level input voltage 1.2 1.26 VVMODEL MODE low level input voltage 1.1 1.15 VIMODE1 MODE pull-up current MODE = 1V 3.6 µAIMODE2 MODE pull-up current MODE = 1.5V 6.6 µA

Delay time between bucks at automaticTpsdelay MODE = 1.5V 1024 cyclespower sequencing modePOWER FAILURE DETECTORVDIVth VDIV threshold 1.18 1.23 1.26 V

VDIV = 1V 1 µAIVDIV VDIV pull-up current

VDIV = 1.5V 2 µAIVDIVhys VDIV hysteresis current 1 µATdeglitch_R RESET deglitch on the rising edge 534 cyclesTdeglitch_F RESET deglitch on the falling edge 12 14 16 cyclesOSCILLATORFSW ROSC = 73.2 kΩ 560 600 640 kHz

Switching frequencyFSW_range 250 2000 kHzTHERMAL PROTECTIONTTRIP_OTP Temperature rising 160 °C

Thermal protection trip pointTHYST_OTP Hysteresis 20 °C


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1.780

1.785

1.790

1.795

1.800

1.805

1.810

1.815

1.820

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Out

put

Vol

tage

(V

)

Output Load (A)

VIN=5V

VIN=12V

C006

VIN = 5 V

VIN = 12 V 1.190

1.194

1.198

1.202

1.206

1.210

4 6 8 10 12 14 16 18

Out

put

Vol

tage

(V

)

Input Voltage (V)

IOUT=0.1A

IOUT=1.5A

IOUT=3.0A

C007

IOUT = 0.1 A

IOUT = 1.5 A

IOUT = 3.0 A

1.180

1.185

1.190

1.195

1.200

1.205

1.210

1.215

1.220

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Out

put

Vol

tage

(V

)

Output Load (A)

VIN=5V

VIN=12V

C004

VIN = 5 V

VIN = 12 V 3.27

3.28

3.29

3.30

3.31

3.32

3.33

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Out

put

Vol

tage

(V

)

Output Load (A)

VIN=5V

VIN=12V

C005

VIN = 5 V

VIN = 12 V

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1

Effi

cien

cy (

%)

Output Load (A)

PSM Mode, Vout = 1.2V

PSM Mode, VO = 3.3V

PSM Mode, VO = 5.0V

FCC Mode, VO = 1.2V

FCC Mode, VO = 3.3V

FCC Mode, VO = 5.0V

C002

PSM Mode, VO = 1.2 V



FCC Mode, VO = 1.2 V


FCC Mode, VO = 5.0 V 0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1

Effi

cien

cy (

%)

Output Load (A)




FCC Mode, Vout = 1.8V



C003








7.6 Typical CharacteristicsTA = 25°C, VIN = 12 V, VOUT1 = 1.2 V, VOUT2 = 3.3 V, VOUT3 = 1.8 V, fSW = 600 kHz (unless otherwise noted)

Figure 1. BUCK 1 Efficiency Figure 2. BUCK 2 Efficiency

VOUT = 1.2 V VOUT = 3.3 V

Figure 3. BUCK1, PSM Mode, Load Regulation Figure 4. BUCK2, PSM Mode, Load Regulation


Figure 5. BUCK3, PSM Mode, Load Regulation Figure 6. BUCK1, PSM Mode, Line Regulation


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5

7

9

11

13

15

±50 ±25 0 25 50 75 100 125

Shu

tdow

n Q

uies

cent

Cur

rent

(

A)

Junction Temperature (C) C013

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

±50 ±25 0 25 50 75 100 125

En

Pin

On

Pul

lup

(A

)


0.594

0.596

0.598

0.600

0.602

0.604

0.606

±50 ±25 0 25 50 75 100 125

Vol

tage

Ref

eren

ce (

V)


560

580

600

620

640

-50 -25 0 25 50 75 100 125

Oscill

ato

r F

requency (

kH

z)

Junction Temperature (°C) C012

3.290

3.292

3.294

3.296

3.298

3.300

4 6 8 10 12 14 16 18

Out

put

Vol

tage

(V

)

Input Voltage (V)

IOUT=0.1A

IOUT=1A

IOUT=2A

C008

IOUT = 0.1 A

IOUT = 1.0 A

IOUT = 2.0 A 1.790

1.794

1.798

1.802

1.806

1.810

4 6 8 10 12 14 16 18

Out

put

Vol

tage

(V

)

Input Voltage (V)

IOUT=0.1A

IOUT=1A

IOUT=2A

C009

IOUT = 0.1 A

IOUT = 1.0 A

IOUT = 2.0 A


Typical Characteristics (continued)TA = 25°C, VIN = 12 V, VOUT1 = 1.2 V, VOUT2 = 3.3 V, VOUT3 = 1.8 V, fSW = 600 kHz (unless otherwise noted)


Figure 7. BUCK2, PSM MODE, LINE REGULATION Figure 8. BUCK3, PSM Mode, Line Regulation

ROSC = 73.2 kΩ

Figure 10. Oscillator Frequency vs TemperatureFigure 9. Voltage Reference vs Temperature

VIN = 12 V VIN = 12 V EN = 1 V

Figure 11. Shutdown Quiescent vs Temperature Figure 12. EN Pin Pull-Up Current vs Temperature, EN=1.0V


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4.7

4.9

5.1

5.3

5.5

±50 ±25 0 25 50 75 100 125

Hig

h S

ide

Cur

rent

Lim

it (A

)


2.7

2.9

3.1

3.3

3.5

±50 ±25 0 25 50 75 100 125

Hig

h S

ide

Cur

rent

Lim

it (A

)


1.07

1.11

1.15

1.19

1.23

±50 ±25 0 25 50 75 100 125

EN

Pin

Thr

esho

ld F

allin

g (V

)


4.6

4.8

5.0

5.2

5.4

±50 ±25 0 25 50 75 100 125

Sof

t Sta

rt C

urre

nt (

mA

)


6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

±50 ±25 0 25 50 75 100 125

En

Pin

On

Pul

lup

(A

)


1.12

1.16

1.20

1.24

1.28

±50 ±25 0 25 50 75 100 125

EN

Pin

Thr

esho

ld R

aisi

ng (

V)




VIN = 12 V EN = 1.5 V VIN = 12 V

Figure 13. EN Pin Pull-Up Current vs Temperature, EN=1.5V Figure 14. EN Pin Threshold Raising vs Temperature

VIN = 12 V VIN = 12 V

Figure 15. EN Pin Threshold Falling vs Temperature Figure 16. SS Pin Charge Current vs Temperature

VIN = 12 V VIN = 12 V

Figure 17. Buck1 High-Side Current Limit vs Temperature Figure 18. Buck2 High-Side Current Limit vs Temperature


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2.7

2.9

3.1

3.3

3.5

±50 ±25 0 25 50 75 100 125

Hig

h S

ide

Cur

rent

Lim

it (A

)


1.21

1.22

1.23

1.24

1.25

±50 ±25 0 25 50 75 100 125

VD

IV P

in T

hres

hold

(V

)




VIN = 12 V

Figure 19. Buck3 High-Side Current Limit vs Temperature Figure 20. VDIV Pin Threshold vs Temperature


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8 Detailed Description

8.1 OverviewThe TPS65261, TPS65261-1 is a monolithic triple synchronous step-down (buck) converter with 3A/2A/2A outputcurrents. A wide 4.5V to 18V input supply voltage range encompasses the most intermediate bus voltagesoperating off 5V, 9V, 12V or 15V power bus. The feedback voltage reference for each buck is 0.6V. Each buck isindependent with dedicated enable, soft-start and loop compensation pins.

The TPS65261, TPS65261-1 implements a constant frequency, peak current mode control that simplifiesexternal loop compensation. The wide switching frequency of 250kHz to 2MHz allows optimizing systemefficiency, filtering size and bandwidth. The switching frequency can be adjusted with an external resistorconnected between ROSC pin and ground. The switching clock of buck1 is 180° out-of-phase operation from theclocks of buck2 and buck3 channels to reduce input current ripple, input capacitor size and power supply inducednoise.

The TPS65261, TPS65261-1 has been designed for safe monotonic startup into pre-biased loads. The defaultstart up is when VIN is typically 4.5V. The ENx pin also can be used to adjust the input voltage under voltagelockout (UVLO) with an external resistor divider. In addition, the ENx pin has an internal 3.6uA current source, sothe EN pin can be floating to automatically power up the converters.

The TPS65261, TPS65261-1 reduces the external component count by integrating a bootstrap circuit. The biasvoltage for the integrated high-side MOSFET is supplied by a capacitor between the BST and LX pin. A UVLOcircuit monitors the bootstrap capacitor voltage VBST-VLX in each buck. When VBST-VLX voltage drops to thethreshold, LX pin is pulled low to recharge the bootstrap capacitor. The TPS65261, TPS65261-1 can operate at100% duty cycle as long as the bootstrap capacitor voltage is higher than the BOOT-LX UVLO threshold which istypically 2.1V.

The TPS65261, TPS65261-1 features a PGOOD pin to supervise each output voltage of the buck converters.The TPS65261, TPS65261-1 has power good comparators with hysteresis, which monitor the output voltagesthrough feedback voltages. When all bucks are in regulation range and power sequence is done, PGOOD isasserted to high.

The SS (soft start/tracking) pin is used to minimize inrush currents or provide power supply sequencing duringpower up. A small value capacitor or resistor divider is connected to the pin for soft start or voltage tracking.

At light loading, TPS65261 will automatically operate in pulse skipping mode (PSM) to save power.

The TPS65261, TPS65261-1 is protected from overload and over temperature fault conditions. The converterminimizes excessive output overvoltage transients by taking advantage of the power good comparator. When theoutput is overvoltage, the high-side MOSFET is turned off until the internal feedback voltage is lower than 105%of the 0.6V reference voltage. The TPS65261, TPS65261-1 implements both high-side MOSFET overloadprotection and bidirectional low-side MOSFET overload protection to avoid inductor current runaway. If the overcurrent condition has lasted for more than the OC wait time (256 clock cycles), the converter will shut down andre-start after the hiccup time (8192 clock cycles). The TPS65261, TPS65261-1 shuts down if the junctiontemperature is higher than the thermal shutdown trip point. When the junction temperature drops 20°C typicallybelow the thermal shutdown trip point, the TPS65261, TPS65261-1 will be restarted under control of the soft startcircuit automatically.


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2 1

out

0.6R R

V 0.6= ´

-

Vout

FB

R1

R20.6 V

COMP

PVIN3

BST3

LX3

PGND3

BUCK3

enable

clk V7V

VIN

BST

LX

PGND

OSC/Phase ShiftV7V LDO

BiasV7V

FB3

CLK

2

CLK

3

VINen_buck3PowerGood

AGND

FB1

FB2

OverTemp

EN1

EN2

SS

MODE

EN3

CLK

1

StateMachine

FB3

en_buck1

MODE

PGOOD

PVIN2

BST2

LX2

PGND2

BUCK2

enable

Comp

clkV7V

VIN

BST

LX

PGND

FB2

VINen_buck2

SS

MODE

PVIN1

BST1

LX1

PGND1

BUCK1

enable

clkV7V

VIN

BST

LX

PGND

FB1

VIN

SSSS1

V3V

en_buck1

en_buck2

en_buck3

OT

VIN

COMP1

COMP2

COMP3

1.23 V PowerFailuredeglitch

RESET

MODE

ROSC

1 µA

SS3

SS2

VDIV

1 µA

3 µA

1.2 V

3.6 µA

vfb

Comp

vfb

Comp

vfb

2 K 6.3 V

3 µA

1.2 V

3.6 µA

6.3 V

3 µA

1.2 V

3.6 µA

6.3 V

2 K

2 K

5 µA

5 µA

5 µA

3 µA

1.2 V

3.6 µA

2 K6.3 V

VIN

VIN


8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 Adjusting the Output VoltageThe output voltage of each buck is set with a resistor divider from the output of buck to the FB pin. It isrecommended to use 1% tolerance or better resistors.

Figure 21. Voltage Divider Circuit

(1)


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VIN

V7V

RESET

Threshold_r

Threshold_f

Power

FailureRESET

VIN V7V

R1

R2

VDIV

534 Cycles

Delay Time

1.23 V

1 µA

1 µA

i

ih

p


Feature Description (continued)To improve efficiency at light loads, consider using larger value resistors. If the values are too high, the regulatoris more sensitive to noise. The recommended resistor values are shown in Table 1.

Table 1. Output Resistor Divider SelectionOUTPUT VOLTAGE R1 R2

(V) (kΩ) (kΩ)1 10 15

1.2 10 101.5 15 101.8 20 102.5 31.6 103.3 45.3 103.3 22.6 4.995 73.2 105 36.5 4.99

8.3.2 Power Failure DetectorThe power failure detector monitors the voltage on VDIV, and sets open-drain output RESET low when VDIV isbelow 1.23V. There is deglitch on the rising edge, 534 frequency cycles. Figure 22 shows the power failuredetector timing diagram.

Figure 22. Power Failure Detector Timing Diagram


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VIN

R1

R2

EN

i

ih

p

PVIN

R1

R2

EN

ih

ip

( )

1 ENFALLING2

STOP ENFALLILNG 1 h p

R VR

V V R I I

´

=

- + +

ENFALLINGSTART STOP

ENRISING

1

ENFALLINGP h

ENRISING

VV V

VR

VI 1 I

V

æ ö

-ç ÷

è ø=

æ ö

- +ç ÷

è ø

_rh p

_ _r f

VrefR2

Threshold VrefI I

Threshold Threshold

=

-

´ +

-

_ _r f

h

Threshold ThresholdR1

I

-

=

( )_f P h

R1Threshold Vref 1 I I R1

R2

æ ö

= + - + ´ç ÷

è ø

_r p

R1Threshold Vref 1 I R1

R2

æ ö

= + - ´ç ÷

è ø


The thresholds can be calculated using Equation 2 and Equation 3.

(2)

(3)

The divider resisters can be calculated using Equation 4 and Equation 5.

(4)

(5)

Where Ih = 1µA, Ip = 1µA.

8.3.3 Enable and Adjusting Under-Voltage LockoutThe EN1/2/3 pin provides electrical on/off control of the device. Once the EN1/2/3 pin voltage exceeds thethreshold voltage, the device starts operation. If each ENx pin voltage is pulled below the threshold voltage, theregulator stops switching and enters low Iq state.

The EN pin has an internal pull-up current source, allowing the user to float the EN pin to enable the device. If anapplication requires controlling the EN pin, use open drain or open collector output logic to interface with the pin.

The device implements internal UVLO circuitry on the VIN pin. The device is disabled when the VIN pin voltagefalls below the internal VIN UVLO threshold. The internal VIN UVLO threshold has a hysteresis of 500mV. If anapplication requires either a higher UVLO threshold on the VIN pin or a secondary UVLO on the PVINx in splitrail applications, then the ENx pin can be configured as shown in Figure 23, Figure 24 and Figure 25. Whenusing the external UVLO function, it is recommended to set the hysteresis to be greater than 500mV.

The EN pin has a small pull-up current Ip which sets the default state of the pin to enable when no externalcomponents are connected. The pull-up current is also used to control the voltage hysteresis for the UVLOfunction since it increases by Ih once the EN pin crosses the enable threshold. The UVLO thresholds can becalculated using Equation 6 and Equation 7.

(6)

(7)

Where Ih = 3µA, IP = 3.6uA, VENSRISING = 1.2V, VENFALLING = 1.15V.

Figure 23. Adjustable VIN Figure 24. Adjustable PVIN Under-voltageUnder-voltage Lockout Lockout, VIN>4.5V


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EN1

EN2

EN3

SS1

SS2

SS3

Css

EN

Vout1 1.2 V

Vout2 1.8 V

Vout3 = 3.3 V

PGOOD

EN threshold=1.2 V

Tss = Css*0.6 V/15 µA

31

32

1

24

8

17

PGOOD Deglitch Time

( )Css(nF) Vref(V)

Tss msIss(µA)

´

=

VIN

R1

R2

EN

i

ih

p

PVIN


Figure 25. Adjustable VIN and PVIN Under-voltage Lockout

8.3.4 Soft-Start TimeThe voltage on the respective SS pin controls the start-up of the buck output. When the voltage on the SS pin isless than the internal 0.6V reference, the TPS65261, TPS65261-1 regulates the internal feedback voltage to thevoltage on the SS pin instead of 0.6V. The SS pin can be used to program an external soft-start function or toallow output of the buck to track another supply during start-up. The device has an internal pull-up current sourceof 5µA (typical) that charges an external soft-start capacitor to provide a linear ramping voltage at the SS pin.The TPS65261, TPS65261-1 regulates the internal feedback voltage to the voltage on the SS pin, allowingVOUT to rise smoothly from 0V to its regulated voltage without inrush current. The soft-start time can becalculated approximately by Equation 8.

(8)

Many of the common power supply sequencing methods can be implemented using the SSx and ENx pins.Figure 26 shows the method implementing ratio-metric sequencing by connecting the SSx pins of three buckchannels together. The regulator outputs ramp up and reach regulation at the same time. When calculating thesoft-start time, the pull-up current source must be tripled in Equation 8.

Figure 26. Ratio Metric Power Up Using SSx Pins


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EN1

EN2

EN3

SS1

SS2

SS3

Css1

Vout1 1.2 V

Vout2 1.8 V

Vout3 = 3.3 V

PGOOD

Tss = Css3*0.6 V/5 µA

31

32

1

24

8

17Css2

Css3

PGOOD Deglitch Time

EN

EN threshold = 1.2 V

Css1 Css2 Css3

Vout1 Vout2 Vout3= =


Simultaneous power supply sequencing can be implemented by connecting capacitor to SSx pin, shown inFigure 27. The capacitors can be calculated using Equation 8 and Equation 9.

(9)

Figure 27. Simultaneous Startup Sequence Using SSx Pins

8.3.5 Power Up SequencingTPS65261, TPS65261-1 features a comprehensive sequencing circuit for the 3 bucks. If the MODE pin ties highto V7V, three buck start up and shutdown is in sequence according to different buck enable pin setup. If theMODE pin ties low to ground, three buck on/off is separately controlled by three enable pins.

8.3.5.1 External Power SequencingThe TPS65261, TPS65261-1 has a dedicated enable pin and soft-start pin for each converter. The converterenable pins are biased by a current source that allows for easy sequencing with the addition of an externalcapacitor. Disabling the converter with an active pull-down transistor on the ENs pin allows for a predictablepower-down timing operation. Figure 28 shows the timing diagram of a typical buck power-up sequence byconnecting a capacitor at ENx pin.


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EN Threshold

ENx Rise Time

Dictated by CEN

Soft Start Rise Time

Dictated by CSS

ENx

VOUTx

EN Threshold

PGOOD

VIN

PGOOD Deglitch Time

T = CEN*(1.2-0.4) V/3.6 µA

V7V

T = CEN *0.4 V/1.4 µA

Charge CENwith 6.6 µA

Pre-Bias Startup

T = CSS*0.6 V/5 µA


Figure 28. Startup Power Sequence

8.3.5.2 Automatic Power SequencingThe TPS65261, TPS65261-1 starts with a pre-defined power-up and power-down sequence when the MODE pinties high to V7V. As shown in Table 2, the sequence is dictated by the different combinations of EN1 and EN2status. EN3 is used to start/stop the converters. Buck2 and buck3 are identical converters and can be swappedin the system operation to allow for additional sequencing stages. Figure 29 shows the power sequencing whenEN1 and EN2 are pulled up high.

Table 2. Power SequencingMODE EN1 EN2 EN3 Start Sequencing Shutdown SequencingHigh High High Buck1→Buck2→Buck3 Buck3→Buck2→Buck1

Used to start/stopHigh Low High Buck2→Buck1→Buck3 Buck3→Buck1→Buck2Automatic Power bucks in sequenceSequencing High High Low Buck2→Buck3→Buck1 Buck1→Buck3→Buck2

High Low Low Reserved Reserved ReservedExternally Used to start/stop Used to start/stop Used to start/stopcontrolled Low x xbuck1 buck2 buck3sequencing


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VIN

V7V

MODE

EN1

EN2

EN3

Buck1

Buck3

Buck2

PGOODt1 t2 t3 t4

T psdelay = t1 = t2 = t3 = t4 = 1024*(1/fsw)


Figure 29. Automatic Power Sequencing

8.3.6 V7V Low Dropout Regulator and BootstrapPower for the high-side and low-side MOSFET drivers and most other internal circuitry is derived from the V7Vpin. The internal built-in low dropout linear regulator (LDO) supplies 6.3V (typical) from VIN to V7V. A 1µFceramic capacitor should be connected from V7V pin to power ground.

If the input voltage, VIN, decreases to UVLO threshold voltage, the UVLO comparator detects the V7V pinvoltage and forces the converter off.

Each high-side MOSFET driver is biased from the floating bootstrap capacitor, CB, shown in Figure 30, which isnormally recharged during each cycle through an internal low-side MOSFET or the body diode of a low-sideMOSFET when the high-side MOSFET turns off. The boot capacitor is charged when the BST pin voltage is lessthan VIN and BST-LX voltage is below regulation. The recommended value of this ceramic capacitor is 47nF. Aceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10V or higher is recommendedbecause of the stable characteristics over temperature and voltage. Each low-side MOSFET driver is poweredfrom the V7V pin directly.

To improve drop out, the device is designed to operate at 100% duty cycle as long as the BST to LX pin voltageis greater than the BST-LX UVLO threshold, which is typically 2.1V. When the voltage between BST and LXdrops below the BST-LX UVLO threshold, the high-side MOSFET is turned off and the low-side MOSFET isturned on allowing the boot capacitor to be recharged.


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Figure 30. V7V Linear Dropout Regulator and Bootstrap Voltage Diagram

8.3.7 Out-of-Phase OperationIn order to reduce input ripple current, the switch clock of buck1 is 180° out-of-phase from the clock of buck2 andbuck3. This enables the system, having less input current ripple, to reduce the input capacitors’ size, cost andEMI.

8.3.8 Output Overvoltage Protection (OVP)The device incorporates an output overvoltage protection (OVP) circuit to minimize output voltage overshoot.When the output is overloaded, the error amplifier compares the actual output voltage to the internal referencevoltage. If the FB pin voltage is lower than the internal reference voltage for a considerable time, the output ofthe error amplifier demands maximum output current. Once the condition is removed, the regulator output risesand the error amplifier output transitions to the steady state voltage. In some applications with small outputcapacitance, the load can respond faster than the error amplifier. This leads to the possibility of an outputovershoot. Each buck compares the FB pin voltage to the OVP threshold. If the FB pin voltage is greater thanthe OVP threshold, the high-side MOSFET is turned off preventing current from flowing to the output andminimizing output overshoot. When the FB voltage drops lower than the OVP threshold, the high-side MOSFETturns on at the next clock cycle.

8.3.9 Slope CompensationIn order to prevent the sub-harmonic oscillations when the device operates at duty cycles greater than 50%, thedevice adds built-in slope compensation, which is a compensating ramp to the switch current signal.

8.3.10 Overcurrent ProtectionThe device is protected from over current conditions with cycle-by-cycle current limiting on both the high-sideMOSFET and the low-side MOSFET.


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OC limiting (waiting) time256 cycles

hiccup time8192 cycles

soft start time

T=Css*0.6V/5uA

iL

Inductor Current

SS

SS Pin Voltage

Vout

Output Voltage

Soft-start is reset after OC waiting time

OC fault removed, soft-start and output recovery 0.6V

~2.1V

Output over loading

OCP peak inductor current threshold

Output hard short circuit


8.3.10.1 High-side MOSFET Over Current ProtectionThe device implements current mode control which uses the COMP pin voltage to control the turn off of the high-side MOSFET and the turn on of the low-side MOSFET on a cycle-by-cycle basis. During each cycle, the switchcurrent and the current reference generated by the COMP pin voltage are compared, when the peak switchcurrent intersects the current reference, the high-side switch is turned off.

8.3.10.2 Low-side MOSFET Over Current ProtectionWhile the low-side MOSFET is turned on, its conduction current is monitored by the internal circuitry. Duringnormal operation, the low-side MOSFET sources current to the load. At the end of every clock cycle, the low-sideMOSFET sourcing current is compared to the internally set low-side sourcing current limit. If the low-sidesourcing current is exceeded, the high-side MOSFET is not turned on and the low-side MOSFET stays on for thenext cycle. The high-side MOSFET is turned on again when the low-side current is below the low-side sourcingcurrent limit at the start of a cycle.

The low-side MOSFET may also sink current from the load. If the low-side sinking current limit is exceeded, thelow-side MOSFET is turned off immediately for the rest of that clock cycle. In this scenario both MOSFETs areoff until the start of the next cycle.

Furthermore, if an output overload condition (as measured by the COMP pin voltage) has lasted for more thanthe hiccup wait time which is programmed for 256 switching cycles shown in Figure 31, the device will shut downitself and restart after the hiccup time of 8192 cycles. The hiccup mode helps reduce the device powerdissipation under severe overcurrent condition.

Figure 31. Over Current Protection

8.3.11 Power GoodThe PGOOD pin is an open drain output. Once feedback voltage of each buck is between 95% (rising) and 105%(falling) of the internal voltage reference, the PGOOD pin pull-down is de-asserted and the pin floats. It isrecommended to use a pull-up resistor between the values of 10kΩ and 100kΩ to a voltage source that is 5.5Vor less. The PGOOD is in a defined state once the VIN input voltage is greater than 1V, but with reduced currentsinking capability. The PGOOD achieves full current sinking capability once the VIN input voltage is above UVLOthreshold, which is 4.25V.


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PEAK

Vin VoutIL 230 mA tdly

L

-

= + ´

0

25

50

75

100

125

150

175

200

0 200 400 600 800 1000 1200 1400 1600 1800 2000

RO

SC

(k

Switching Frequency (kHz) C010

( )0.975

oscƒ kHz 39557 R(k )-

= ´ W


The PGOOD pin is pulled low when any feedback voltage of a buck is lower than 92.5% (falling) or greater than107.5% (rising) of the nominal internal reference voltage. Also, the PGOOD is pulled low if the input voltage isunder-voltage locked up, thermal shutdown is asserted, the EN pin is pulled low or the converter is in a soft-startperiod.

8.3.12 Adjustable Switching FrequencyThe ROSC pin can be used to set the switching frequency by connecting a resistor to GND. The switchingfrequency of the device is adjustable from 250KHz to 2MHz.

To determine the ROSC resistance for a given switching frequency, use Equation 10 or the curve in Figure 32.To reduce the solution size, set the switching frequency as high as possible, but tradeoffs of the supply efficiencyand minimum controllable on time should be considered.

(10)

Figure 32. ROSC versus Switching Frequency

8.3.13 Thermal ShutdownThe internal thermal shutdown circuitry forces the device to stop switching if the junction temperature exceeds160°C typically. The device reinitiates the power up sequence when the junction temperature drops below 140°Ctypically.

8.4 Device Functional Modes

8.4.1 Pulse Skipping MODE (PSM)The TPS65261 can enter high efficiency pulse skipping mode (PSM) operation at light load current.

When a controller is enabled for PSM operation, the peak inductor current is sensed and compared with 230mAcurrent typically. Since the integrated current comparator catches the peak inductor current only, the averageload current entering PSM varies with applications and external output filters. In PSM, the sensed peak inductorcurrent is clamped at 230mA.

When a controller operates in PSM, the inductor current is not allowed to reverse. The reverse currentcomparator turns off the low-side MOSFET when the inductor current reaches zero, preventing it from reversingand going negative.

Due to the delay in the circuit and current comparator tdly (typical 50ns at VIN = 12V), the real peak inductorcurrent threshold to turn off high-side power MOSFET, could shift higher depending on inductor inductance andinput/output voltages. The threshold of peak inductor current to turn off high-side power MOSFET can becalculated by Equation 11.

(11)


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IL_Peak

Inductor Peak Current

Inductor

Current Peak

Current

Sensing

x1

Current Comparator

Delay: tdly

Turn off

high-side Power MOSFET

230 mA


Device Functional Modes (continued)Once the charge accumulated on the Vout capacitor is more than loading need, COMP pin voltage drops to lowvoltage driven by the error amplifier. There is an internal comparator at the COMP pin. If COMP voltage is lowerthan 0.35V, the power stage stops switching to save power.

Figure 33. PSM Current Comparator


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BST1

PVIN1

LX1

MO

DE

SS

1

CO

MP

1

PGND1

EN

3

FB

1

EN1

EN2

Vout1

+1.2V

Max. 3A

Vin

AG

ND

PU

LL

PG

OO

D

RE

SE

TR

ES

ET

PG

OO

D

VIN

VDIV

Vin

4.7uH

10uF

47nF

10nF 3.3nF

20K

20K

100K

100K

146K

20K

20K

1 2 43

24

23

21

22

25

26

27

28

29

30

31

32

1uF

R2

R3

L1

C28

R29

R30

C231

C232 R23

C24

22uFC261 C262

22uF

R25

0

22pFC26

R262

R263

22pF

C29

C25

BST2

LX2

PVIN2

PGND2

PGND3

PVIN3

LX3

FB

2

BST3

CO

MP

3

V7V

SS

3

Vin

RO

SC

FB

3

Vout3

+1.8V

Max. 2A

Vout2

+3.3V

Max. 2A

CO

MP

2

SS

2

Vin

4.7uH

4.7uH

47nF

47nF

10uF

10uF

10nF

10nF

2.2nF

2.2nF

1uF

73.2K

39K

39K

19.5K

8.67K

30K

30K

5 6 87

20

19

17

18

16

15

14

13

12

11

10

9

C5C71

R7

C8

C9

L2

L3

C12

C13

C17

C182R18

C181

R20

22uF

22uF

C101 C102

C151 C152

R102

R103C1022pF

R9

0

R16

0

22pF

R152

R153 22pFC15

22pFC72

22uF

22uF

C16

TPS65261

TPS65261-1


9 Application and Implementation

9.1 Application InformationThe devices are triple synchronous step down dc/dc converters. They are typically used to convert a higher dcvoltage to lower dc voltages with continuous available output current of 3A/2A/2A. The following designprocedure can be used to select component values for the TPS65261 and TPS65261-1. This section presents asimplified discussion of the design process.

9.2 Typical Application

Figure 34. Typical Application Schematic


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rippleLpeak out

II I

2= +

( )out inmax out

inmax sw2

Lrms O

2V V V

V L ƒI I

12

æ ö´ -

ç ÷ç ÷´ ´è ø

= +

inmax out outripple

inmax sw

V V VI

L V ƒ

-

= ´

´

inmax out out

o in max sw

V V VL

I LIR V ƒ

-

= ´

´ ´


Typical Application (continued)9.2.1 Design RequirementsThis example details the design of triple synchronous step-down converter. A few parameters must be known inorder to start the design process. These parameters are typically determined at the system level. For thisexample, we start with the following known parameters:

Table 3. Design ParametersDESIGN PARAMETER EXAMPLE VALUE

Vout1 1.2 VIout1 3 AVout2 3.3 VIout2 2 AVout3 1.8 VIout3 2 A

Transient Response 1A Load Step ±5%Input Voltage 12 V normal, 4.5 V to 18 V

Output Voltage Ripple ±1%Switching Frequency 600 kHz

9.2.2 Detailed Design Procedure

9.2.2.1 Output Inductor SelectionTo calculate the value of the output inductor, use Equation 12. LIR is a coefficient that represents the amount ofinductor ripple current relative to the maximum output current. The inductor ripple current is filtered by the outputcapacitor. Therefore, choosing high inductor ripple currents impact the selection of the output capacitor since theoutput capacitor must have a ripple current rating equal to or greater than the inductor ripple current. In general,the inductor ripple value is at the discretion of the designer; however, LIR is normally from 0.1 to 0.3 for themajority of applications.

(12)

For the output filter inductor, it is important that the RMS current and saturation current ratings not be exceeded.The RMS and peak inductor current can be found from Equation 14 and Equation 15.

(13)

(14)

(15)

The current flowing through the inductor is the inductor ripple current plus the output current. During power up,faults or transient load conditions, the inductor current can increase above the calculated peak inductor currentlevel calculated above. In transient conditions, the inductor current can increase up to the switch current limit ofthe device. For this reason, the most conservative approach is to specify an inductor with a saturation currentrating equal to or greater than the switch current limit rather than the peak inductor current.

9.2.2.2 Output Capacitor SelectionThere are three primary considerations for selecting the value of the output capacitor. The output capacitordetermines the modulator pole, the output voltage ripple, and how the regulator responds to a large change inload current. The output capacitance needs to be selected based on the most stringent of these three criteria.


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( )inmin outoutinrms out

inmin inmin

V VVI I

V V

-

= ´ ´

( )out inmax out

corms

inmax sw

V V VI

12 V L ƒ

´ -

=

´ ´ ´

orippleesr

oripple

VR

I<

ooripplesw

oripple

1 1C

V8 ƒ

I

> ´

´

outo

sw out

2 IC

ƒ V

´ D

=

´ D


The desired response to a large change in the load current is the first criteria. The output capacitor needs tosupply the load with current when the regulator cannot. This situation would occur if there are desired hold-uptimes for the regulator where the output capacitor must hold the output voltage above a certain level for aspecified amount of time after the input power is removed. The regulator is also temporarily not able to supplysufficient output current if there is a large, fast increase in the current needs of the load such as a transition fromno load to full load. The regulator usually needs two or more clock cycles for the control loop to see the changein load current and output voltage and adjust the duty cycle to react to the change. The output capacitor must besized to supply the extra current to the load until the control loop responds to the load change. The outputcapacitance must be large enough to supply the difference in current for 2 clock cycles while only allowing atolerable amount of drop in the output voltage. Equation 16 shows the minimum output capacitance necessary toaccomplish this.

(16)

Where ΔIout is the change in output current, fsw is the regulators switching frequency and ΔVout is the allowablechange in the output voltage.

Equation 17 calculates the minimum output capacitance needed to meet the output voltage ripple specification.Where fsw is the switching frequency, Voripple is the maximum allowable output voltage ripple, and Ioripple is theinductor ripple current.

(17)

Equation 18 calculates the maximum ESR an output capacitor can have to meet the output voltage ripplespecification.

(18)

Additional capacitance de-ratings for aging, temperature and DC bias should be factored in, which increases thisminimum value. Capacitors generally have limits to the amount of ripple current they can handle without failing orproducing excess heat. An output capacitor that can support the inductor ripple current must be specified. Somecapacitor data sheets specify the root mean square (RMS) value of the maximum ripple current. Equation 19 canbe used to calculate the RMS ripple current the output capacitor needs to support.

(19)

9.2.2.3 Input Capacitor SelectionThe TPS65261, TPS65261-1 requires a high quality ceramic, type X5R or X7R, input decoupling capacitor of atleast 10 µF of effective capacitance on the PVIN input voltage pins. In some applications, additional bulkcapacitance may also be required for the PVIN input. The effective capacitance includes any DC bias effects.The voltage rating of the input capacitor must be greater than the maximum input voltage. The capacitor mustalso have a ripple current rating greater than the maximum input current ripple of The TPS65261, TPS65261-1.The input ripple current can be calculated using Equation 20.

(20)

The value of a ceramic capacitor varies significantly over temperature and the amount of DC bias applied to thecapacitor. The capacitance variations due to temperature can be minimized by selecting a dielectric material thatis stable over temperature. X5R and X7R ceramic dielectrics are usually selected for power regulator capacitorsbecause they have a high capacitance to volume ratio and are fairly stable over temperature. The outputcapacitor must also be selected with the DC bias taken into account. The capacitance value of a capacitordecreases as the DC bias across a capacitor increases. The input capacitance value determines the input ripplevoltage of the regulator. The input voltage ripple can be calculated using Equation 21.


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Current Sense

I/V Converter

LiESRR

1R

2R

cR

oC

cC

bC

LR

µSG EAm 300_ =

COMPVfb

EA

1C

G PSm _ = 7.4 A/V

LX

FB

VOUT

V ref = 0.6 V

ESRb

C

R CoC

R

´

=

LC

C

R CoC

R

´

=

o L

1ƒp .

C R 2

æ ö

=ç ÷

´ ´ pè ø

C_ _m EA m PS

2 ƒc Vo CoR

G Vref G

p ´ ´ ´

=

´ ´

outmaxin

in sw

I 0.25V

C ƒ

´

D =

´


(21)

9.2.2.4 Loop CompensationThe TPS65261, TPS65261-1 incorporates a peak current mode control scheme. The error amplifier is a trans-conductance amplifier with a gain of 300 µS. A typical type II compensation circuit adequately delivers a phasemargin between 60° and 90°. Cb adds a high frequency pole to attenuate high frequency noise when needed. Tocalculate the external compensation components, follow these steps.1. Select switching frequency fsw that is appropriate for application depending on L and C sizes, output ripple,

and EMI. Switching frequency between 500kHz to 1MHz gives best trade-off between performance and cost.To optimize efficiency, lower switching frequency is desired.

2. Set up cross over frequency, ƒc, which is typically between 1/5 and 1/20 of fsw.3. RC can be determined by

(22)

Where Gm_EA is the error amplifier gain (300µS), Gm_PS is the power stage voltage to current conversion gain(7.4A/V).

4. Calculate CC by placing a compensation zero at or before the dominant pole

(23)5. Optional Cb can be used to cancel the zero from the ESR associated with CO.

(24)

Figure 35. DC/DC Loop Compensation


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9.2.3 Application Curves

Figure 36. BUCK1, Soft-Start with No Load Figure 37. BUCK1, Soft-Start with Full Load




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Figure 42. BUCK1, PSM Mode, Figure 43. BUCK1, Steady StateSteady State Operation at Light Load Operation with Full Load

Figure 44. BUCK2, PSM Mode, Figure 45. BUCK2,Steady State Operation at Light Load Steady State Operation with Full Load

Figure 47. BUCK3,Figure 46. BUCK3, PSM Mode, Steady State Operation with Full LoadSteady State Operation with Light Load


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Figure 48. BUCK1, Load Transient, Figure 49. BUCK1, Load Transient,0.75A to 1.5A SR=0.25A/µs 1.5A to 2.25A SR=0.25A/µs

Figure 50. BUCK2, Load Transient, 0.5A to 1.0A Figure 51. BUCK2, Load Transient, 1.0A to 1.5ASR=0.25A/µs SR=0.25A/µs

Figure 52. BUCK3, Load Transient, 0.5A to 1.0A Figure 53. BUCK3, Load Transient, 1.0A to 1.5ASR=0.25A/µs SR=0.25A/µs


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Figure 54. BUCK1, Over Current Protection Figure 55. BUCK1, Hiccup and Recovery




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Figure 60. Automatic Power Sequencing, Figure 61. Automatic Power Sequencing,MODE=EN1=EN2=HIGH MODE=EN1=EN2=HIGH

Figure 62. Automatic Power Sequencing, Figure 63. Automatic Power Sequencing,MODE=EN1= HIGH, EN2=LOW MODE=EN1=HIGH, EN2=LOW

Figure 64. Automatic Power Sequencing, Figure 65. Automatic Power Sequencing,MODE=EN2=HIGH, EN1=LOW MODE=EN2=HIGH, EN1=LOW


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Figure 66. Trigger Voltage 1.23V, Reset vs VDIV Figure 67. Deglitch Time, Reset vs VDIV

VIN = 12 V VOUT1 = 1.2 V/1.5 A VOUT2 = 3.3 V/1 A VIN = 12 V VOUT1 = 1.2 V/3 A VOUT2 = 3.3 V/2 AVOUT3 = 1.8 V/1 A VOUT3 = 1.8 V/2 A

EVM Condition 4 Layers, 64mm x 69mm, TA = 27.2°C EVM Condition 4 Layers, 64mm x 69mm, TA = 27.2°C

Figure 68. Thermal Signature of TPS65261EVM Figure 69. Thermal Signature of TPS65261EVM


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10 Power Supply RecommendationsThe devices are designed to operate from an input voltage supply range between 4.5 V and 18 V. This inputpower supply should be well regulated. If the input supply is located more than a few inches from the TPS65261or TPS65261-1 converter additional bulk capacitance may be required in addition to the ceramic bypasscapacitors. An electrolytic capacitor with a value of 47 μF is a typical choice.

11 Layout

11.1 Layout GuidelinesThe TPS65261, TPS65261-1 can be laid out on 2-layer PCB, illustrated in Figure 70.

Layout is a critical portion of good power supply design. See Figure 70 for a PCB layout example. The topcontains the main power traces for PVIN, VOUT, and LX. Also on the top layer are connections for the remainingpins of the TPS65261, TPS65261-1 and a large top side area filled with ground. The top layer ground areashould be connected to the bottom layer ground using vias at the input bypass capacitor, the output filtercapacitor and directly under the TPS65261, TPS65261-1 device to provide a thermal path from the exposedthermal pad land to ground. The bottom layer acts as ground plane connecting analog ground and power ground.

For operation at full rated load, the top side ground area together with the bottom side ground plane must provideadequate heat dissipating area. There are several signals paths that conduct fast changing currents or voltagesthat can interact with stray inductance or parasitic capacitance to generate noise or degrade the power suppliesperformance. To help eliminate these problems, the PVIN pin should be bypassed to ground with a low ESRceramic bypass capacitor with X5R or X7R dielectric. Care should be taken to minimize the loop area formed bythe bypass capacitor connections, the PVIN pins and the ground connections. The VIN pin must also bebypassed to ground using a low ESR ceramic capacitor with X5R or X7R dielectric.

Since the LX connection is the switching node, the output inductor should be located close to the LX pins, andthe area of the PCB conductor minimized to prevent excessive capacitive coupling. The output filter capacitorground should use the same power ground trace as the PVIN input bypass capacitor. Try to minimize thisconductor length while maintaining adequate width. The small signal components should be grounded to theanalog ground path.

The FB and COMP pins are sensitive to noise so the resistors and capacitors should be located as close aspossible to the IC and routed with minimal lengths of trace. The additional external components can be placedapproximately as shown.


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PGOOD

RESET

EN3

MODE

FB2

COMP2

SS2

V7V

COMP1

FB1

SS1

AGND

FB3

COMP3

SS3

ROSC

LX1

PGND1

BST1

PVIN1

VDIV

EN1

EN2

VIN

LX3

PGND3

BST3

PVIN3

PGND2

LX2

BST2

PVIN2PVIN

VOUT2

VOUT3VOUT1

PVIN

VIN

TOPSIDE

GROUND

AREA

0.010 in. DiameterThermal VIA to Ground Plane

VIA to Ground Plane


11.2 Layout Example

Figure 70. PCB Layout


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12 Device and Documentation Support

12.1 Documentation Support

12.1.1 Related Parts

PART NUMBER DESCRIPTION COMMENTSTPS65262 4.5V to 18V, triple buck with dual adjustable Triple buck 3A/1A/1A output current, dual LDOs 100mA/200mA output

LDOs current, automatic power sequencingTPS65263 4.5V to 18V, triple buck with I2C interface Triple buck 3A/2A/2A output current, I2C controlled dynamic voltage

scaling (DVS)TPS65651-1/2/3 4.5V to 18V, triple buck with different Triple buck 3A/2A/2A output current, support 1s, 32ms, 256ms PGOOD

PGOOD deglitch time deglitch time, adjustable current limit setting by external resistorTPS65287 4.5V to 18V, triple buck with power switch Triple buck 3A/2A/2A output current, up to 2.1-A USB power with over

and push button control current setting by external resistor, push button control for intelligentsystem power-on/power-off operation

TPS65288 4.5V to 18V, triple buck with dual power Triple buck 3A/2A/2A output current, 2 USB power switches currentswitches limiting at typical 1.2A (0.8/1.0/1.4/1.6/1.8/2.0/2.2A available with

manufacture trim options)

12.2 Related LinksThe table below lists quick access links. Categories include technical documents, support and communityresources, tools and software, and quick access to sample or buy.

Table 4. Related LinksTECHNICAL TOOLS & SUPPORT &PARTS PRODUCT FOLDER SAMPLE & BUY DOCUMENTS SOFTWARE COMMUNITY

TPS65261 Click here Click here Click here Click here Click hereTPS65261-1 Click here Click here Click here Click here Click here

12.3 TrademarksAll trademarks are the property of their respective owners.

12.4 Electrostatic Discharge CautionThese devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foamduring storage or handling to prevent electrostatic damage to the MOS gates.

12.5 GlossarySLYZ022 — TI Glossary.

This glossary lists and explains terms, acronyms and definitions.

13 Mechanical, Packaging, and Orderable InformationThe following pages include mechanical, packaging, and orderable information. This information is the mostcurrent data available for the designated devices. This data is subject to change without notice and revision ofthis document. For browser-based versions of this data sheet, refer to the left-hand navigation.


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PACKAGE OPTION ADDENDUM

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Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status(1)

Package Type PackageDrawing

Pins PackageQty

Eco Plan(2)

Lead/Ball Finish(6)

MSL Peak Temp(3)

Op Temp (°C) Device Marking(4/5)

Samples

TPS65261-1RHBR ACTIVE VQFN RHB 32 3000 Green (RoHS& no Sb/Br)

CU NIPDAU Level-2-260C-1 YEAR -40 to 85 TPS65261-1

TPS65261-1RHBT ACTIVE VQFN RHB 32 250 Green (RoHS& no Sb/Br)

CU NIPDAU Level-2-260C-1 YEAR -40 to 85 TPS65261-1

TPS65261RHBR ACTIVE VQFN RHB 32 3000 Green (RoHS& no Sb/Br)

CU NIPDAU Level-2-260C-1 YEAR -40 to 85 TPS65261

TPS65261RHBT ACTIVE VQFN RHB 32 250 Green (RoHS& no Sb/Br)

CU NIPDAU Level-2-260C-1 YEAR -40 to 85 TPS65261

(1) The marketing status values are defined as follows:ACTIVE: Product device recommended for new designs.LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.PREVIEW: Device has been announced but is not in production. Samples may or may not be available.OBSOLETE: TI has discontinued the production of the device.

(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availabilityinformation and additional product content details.TBD: The Pb-Free/Green conversion plan has not been defined.Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement thatlead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used betweenthe die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weightin homogeneous material)

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuationof the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finishvalue exceeds the maximum column width.

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PACKAGE OPTION ADDENDUM

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Addendum-Page 2

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on informationprovided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken andcontinues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device PackageType

PackageDrawing

Pins SPQ ReelDiameter

(mm)

ReelWidth

W1 (mm)

A0(mm)

B0(mm)

K0(mm)

P1(mm)

W(mm)

Pin1Quadrant

TPS65261-1RHBR VQFN RHB 32 3000 330.0 12.4 5.3 5.3 1.1 8.0 12.0 Q2

TPS65261-1RHBR VQFN RHB 32 3000 330.0 12.4 5.25 5.25 1.1 8.0 12.0 Q2

TPS65261-1RHBT VQFN RHB 32 250 180.0 12.5 5.25 5.25 1.1 8.0 12.0 Q2

TPS65261-1RHBT VQFN RHB 32 250 180.0 12.4 5.3 5.3 1.1 8.0 12.0 Q2

TPS65261RHBR VQFN RHB 32 3000 330.0 12.4 5.3 5.3 1.1 8.0 12.0 Q2

TPS65261RHBT VQFN RHB 32 250 180.0 12.5 5.25 5.25 1.1 8.0 12.0 Q2

TPS65261RHBT VQFN RHB 32 250 180.0 12.4 5.3 5.3 1.1 8.0 12.0 Q2

PACKAGE MATERIALS INFORMATION

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Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

TPS65261-1RHBR VQFN RHB 32 3000 367.0 367.0 35.0

TPS65261-1RHBR VQFN RHB 32 3000 338.0 355.0 50.0

TPS65261-1RHBT VQFN RHB 32 250 205.0 200.0 33.0

TPS65261-1RHBT VQFN RHB 32 250 210.0 185.0 35.0

TPS65261RHBR VQFN RHB 32 3000 367.0 367.0 35.0

TPS65261RHBT VQFN RHB 32 250 338.0 355.0 50.0

TPS65261RHBT VQFN RHB 32 250 210.0 185.0 35.0

PACKAGE MATERIALS INFORMATION

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Pack Materials-Page 2

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