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LT3513
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TYPICAL APPLICATION
DESCRIPTIONFEATURES
APPLICATIONS
2MHz High Current5-Output Regulator
for TFT-LCD Panels
The LT3513 5-output adjustable switching regulatprovides power for large TFT-LCD panels. The 385mm 7mm QFN device can generate a 3.3V or 5V lsupply along with the triple output supply required forTFT-LCD panel. A lower voltage secondary logic sumay also be generated with the addition of an exterNPN driven by the internal linear regulator. A step-dregulator provides a low voltage output, VLOGIC, with upto 1.2A of current while capable of operating from a w
input range of 4.5V to 30V. A high power step-up cverter, a lower power step-up converter and an invertconverter provide the three independent output voltagAVDD, VON and VOFF required by the LCD panel. A high-sPNP provides delayed turn-on of the VON signal and canhandle up to 30mA. Protection circuitry ensures that VON is disabled if any of the four outputs are more than 1below the programmed voltage.
n Automotive TFT-LCD Displaysn Large TFT-LCD Desktop Monitorsn Flat Panel Televisions
n 4.5V to 30V Input Voltage Rangen Four Integrated Switches: 2.2A Buck, 1.5A Boost,
0.25A Boost, 0.25A Inverter (Guaranteed MinimumCurrent Limit)
n External NPN LDO Drivern Fixed Frequency, Low Noise Outputsn Inductor Current Sense for Buckn Soft-Start for All Outputsn Externally Programmable VON Delayn Three Integrated Schottky Diodesn PGOOD Pin for AVDD Output Disconnectn PanelProtect Circuitry Disables VON Upon Faultn Thermally Enhanced 38-Lead 5mm 7mm QFN
Package
Start-Up Waveforms
AVDD10V/DIV
RUN/SS 2V/DIVVLOGIC5V/DIV
IIN(AVG)1A/DIV
VOFF10V/DIV
VE3 20V/DIV
VON20V/DIV
5ms/DIV 3513 TA01b
L , LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks andPanelProtect, True Color PWM and ThinSOT are trademarks of Linear Technology CorporAll other trademarks are the property of their respective owners.
VC1
7.5k 4.7k
2.7nF 4.7nF
10F
VLDO3.3V0.5A
VLOGIC5V
0.5A
VOFF10V
20mA
VIN8V TO 16V
22F
4.7H 0.22F47nF 15nF 15nF 15nF
VON22V20mA
2.2F
VC3
30k
165k
232k
10k
1.5nF
VC2VC1 GND
13k
2.2nF
VC4
VIN
VLOGIC5V
LDOPWR
LT3513
UVLO SW2
2.2F
FB5 FB3BD
FB1SENSESENSE+SW1
BOOSTBIAS
SW36.8H
42.2k
10k
30.1k
10k
69.8k
10H
0.47F
10k
60.4k
178k 53.6k 100k
10k
10F
10H
AVDD8V
80mA
10F
0.47F
NFB4
D4
SW4
RUN-SS3/4CT
RUN-SS2
RUN-SS1
VONSINK
E3
VON
VON_CLK VON_CLK
PGOOD
FB2
VLOGIC5V
3513 TA01a
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(Note 1)VIN, LDOPWR Voltage ...............................................32VUVLO Voltage ............................................................32V
SW2, SW3, SW4 Voltage ..........................................40VE3 Pin Voltage ...........................................................40VVON, VONSINK Voltage ................................................40VPGOOD Voltage .........................................................40VD4 Voltage ........................................................1V, 40VBOOST Voltage .........................................................37VBOOST Over SW1 .......................................................8VSENSE+, SENSE Voltage ..........................................10VVON_CLK Voltage ........................................................10VBIAS, BD Voltage ......................................................10VCT Pin Voltage .............................................................5V
RUN-SS1, RUN-SS2, RUN-SS3/4 Voltage ...................5VFB1, FB2, FB3, FB5 Voltage .........................................5VNFB4 Voltage ......................................................5V, 5VVC1, VC2, VC3, VC4 Voltage ..........................................5VJunction Temperature (Note 8) ............................. 125COperating Temperature Range (Note 2).. 40C to 125CStorage Temperature Range .................. 65C to 125C
The l denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at T A = 25C. VIN = 12V, BIAS = 3V, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAXMinimum Input Voltage l 4.5 VQuiescent Current Not Switching
VRUNSS1 = 0V7.530
1265
mAA
RUN-SS1, RUN-SS2, RUN-SS3/4 Pin Current RUN-SS1= RUN-SS2 = RUN-SS3= RUN-SS4 = 0.4V
2 A
RUN-SS1, RUN-SS2, RUN-SS3/4 Threshold 0.8BIAS Pin Voltage to Begin RUN-SS2, RUN-SS3/4 l 2.25 2.7 VBIAS Pin Current BIAS = 3.1V, All Switches Off 16.5 20
PIN CONFIGURATION
13 14 15 16
TOP VIEW
39
UHF PACKAGE38-LEAD (5mm 7mm) PLASTIC QFN
17 18 19
38 37 36 35 34 33 32
24
25
26
27
28
29
30
31
8
7
6
5
4
3
2
1FB5
VC1RUN-SS3/4
FB3
RUN-SS2
SW3
E3
VONVONSINKVON_CLKPGOOD
VC3
SENSE+
SENSE
BIAS
BOOST
LDOPWR
BD
SW4
D4
NFB4
RUN-SS1
VC4VC2
U V L O
V I N
V I N
S W 1
S W 1
G N D
F B 1
C T
G N D
S W 2
S W 2
G N D
B I A S
F B 2
23
22
21
20
9
10
11
12
TJMAX = 125C, JA = 34C/W, JC = 1C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATLT3513EUHF#PBF LT3513EUHF#TRPBF 3513 38-Lead (5mm 7mm) Plastic QFN 40C to 125C
LT3513IUHF#PBF LT3513IUHF#TRPBF 3513 38-Lead (5mm 7mm) Plastic QFN 40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shippinFor more information on lead free part marking, go to:http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to:http://www.linear.com/tapeandreel/
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
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ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX U
FB Threshold Offset to Begin CT Charge (Note 3) 90 125 160 mV
CT Pin Current Source All FB Pins = 1.5V, CT = 0.35V 16 20 25 ACT Threshold to Power VON All FB Pins = 1.5V 1 1.1 1.2VON Switch Drop VON Current = 30mA 200 400 mVMaximum VON Current VE3 = 30V l 30 50 mAVON_CLK Input Voltage High 1.5 VVON_CLK Input Voltage Low 0.3 VVONSINK Voltage On VONSINK Current = 1A l 1.2 VMaster Oscillator Frequency
l1.901.80
2 2.122.22
MHzMHz
Foldback Switching Frequency FB2 = 0V, FB3 = 0V, NFB4 = 0V 200UVLO Pin Threshold UVLO Pin Voltage Rising 1.25
UVLO Pin Hysteresis Current VUVLO = 1V 3.4 3.9 4.5 APGOOD Threshold Offset 90 125 160 mVPGOOD Sink Current PGOOD Connected to 40V Through 100k 4 mPGOOD Pin Leakage VPGOOD = 40V 1 ASwitch 1 (2.2A Buck)
FB1 Voltagel
1.2151.205
1.235 1.2551.265
VV
FB1 Voltage Line Regulation 4.5V < VIN < 30V 0.01 0.03 %/VFB1 Pin Bias Current (Note 4) l 30 200 nAError Amplifier 1 Voltage Gain 250 VError Amplifier 1 Transconductance I = 10A 220 mhos
Maximum Duty Cycle l 75 85 %Switch 1 Current Limit Duty Cycle = 35% (Note 6) 2.2 3 3.5Switch 1 VCESAT ISW = 1.5A 430 mVSwitch 1 Leakage Current FB1 = 1.5V, RUN-SS1 = 0V 0.1 10Minimum BOOST Voltage Above SW1 Pin ISW = 1.5A (Note 7) 1.8 2.5 VBOOST Pin Current ISW = 1.5A 30 50 mABOOST Schottky Diode Drop I = 170mA 700Switch 2 (1.5A BOOST)
FB2 Voltagel
1.201.19
1.22 1.241.25
VV
FB2 Voltage Line Regulation 4.5V < VIN < 30V 0.01 0.03 %/VFB2 Pin Bias Current (Note 5) l 30 200 nAError Amplifier 2 Voltage Gain 250 VError Amplifier 2 Transconductance I = 10A 220 mhosSwitch 2 Current Limit (Note 6) 1.5 1.85 2.4
Switch 2 VCESAT ISW2 = 1.2A 360 mVSwitch 2 Leakage Current FB2 = 1.5V, RUN-SS1 = 0V 0.1 1BIAS Pin Current Due to SW2 ISW2 = 1.2A 45 mAMaximum Duty Cycle (SW2) l 75 90 %
The l denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at T A = 25C. VIN = 12V, BIAS = 3V, unless otherwise noted.
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PARAMETER CONDITIONS MIN TYP MAX
Switch 3 (250mA BOOST)
FB3 Voltage l 1.201.19 1.22 1.241.25 VVFB3 Voltage Line Regulation 4.5V < VIN < 30V 0.01 0.03 %/VFB3 Pin Bias Current (Note 4) l 30 200 nAError Amplifier 3 Voltage Gain 250 VError Amplifier 3 Transconductance I = 10A 220 mhosSwitch 3 Current Limit (Note 6) 0.25 0.3 0.38Switch 3 VCESAT ISW3 = 0.2A 200 mVSwitch 3 Leakage Current FB3 = 1.5V, RUN-SS1 = 0V 0.1 1BIAS Pin Current Due to SW3 ISW3 = 0.2A 18 mAMaximum Duty Cycle (SW3) l 84 88 %
Schottky Diode Drop I = 170mA 900 mSwitch 4 (250mA Inverter)
NFB4 Voltagel
1.2051.215
1.180 1.1551.145
VV
NFB4 Voltage Line Regulation 4.5V < VIN < 30V 0.01 0.03 %/VNFB4 Pin Bias Current (Note 4) l 5 16 AError Amplifier 4 Voltage Gain 200 VError Amplifier 4 Transconductance I = 10A 220 mhosSwitch 4 Current Limit (Note 6) 0.25 0.3 0.40Switch 4 VCESAT ISW4 = 0.2A 200 mVSwitch 4 Leakage Current NFB4 = 1.5V, RUN-SS1 = 0V 0.1 1
BIAS Pin Current Due to SW4 ISW4 = 0.2A 18 mAMaximum Duty Cycle (SW4) 84 88
Schottky Diode Drop (D4) I = 170mA 700 mNPN LDO
FB5 Voltagel
0.610.6
0.625 0.630.65
VV
FB5 Pin Bias Current (Note 4) l 30 200 nABase Drive Current FB5 = 0.5V 6 8 10 mLDOPWR Minimum Voltage BD = 3.5V 4.5
Note 1: Stresses beyond those listed under Absolute Maximum Ratingsmay cause permanent damage to the device. Exposure to any AbsoluteMaximum Rating condition for extended periods may affect devicereliability and lifetime.Note 2: The LT3513E is guaranteed to meet specified performance from0C to 125C junction temperature. Specifications over the 40C to125C operating junction temperature range are assured by design,characterization and correlation with statistical process controls. TheLT3513I is guarenteed over the full 40C to 125C operating junctiontemperature range.Note 3: The CT pin is held low until FB1, FB2, FB3 and NFB4 all rampabove the FB threshold offset.Note 4: Current flows out of FB1, FB3, NFB4 and FB5.
Note 5: Current may flow in or out of FB2. The absolute value of this teis used.Note 6: Current limit is guaranteed by design and/or correlation to statictest. Slope compensation reduces current limit at higher duty cycles.Note 7: This is the minimum voltage across the boost capacitor needed guarantee full saturation of the internal power switch.Note 8: This IC includes overtemperature protection that is intendedto protect the device during momentary overload conditions. Junctiontemperature will exceed the maximum operating junction temperaturerange when overtemperature protection is active. Continuous operationabove the specified maximum operating junction temperature may impdevice reliability.
The l denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at T A = 25C. VIN = 12V, BIAS = 3V, unless otherwise noted.ELECTRICAL CHARACTERISTICS
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TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Output Current forVLOGIC = 3.3V SW1 Current Limit vs Duty Cycle Start and Run VLOGIC = 3.3V
BOOST Pin Current SW2 Current Limit SW3 Current Limit
SW4 Current Limit SW1 VCESAT SW2 VCESAT
VIN (V)0
2.0
2.2
2.6
15
3513 G01
1.8
1.6
5 10 20
1.4
1.2
2.4
I O U T ( M A X )
( A ) L = 2.4H
L = 4.3H
DUTY CYCLE (%)25
0
S W 1 C U R R E N T L I M I T ( A )
0.5
1.0
1.5
2.0
2.5
3.0
35 45 55 65
3513 G02
75
SW1 CURRENT LIMITvs DUTY CYCLE
MINIMUM
LOAD CURRENT (A)0.001
4 V
I N (
V )
6
8
0.01 0.1 1
3513 G03
2
3
5
7
1
0
VIN(MIN) START
VIN(MIN) RUN
SWITCH CURRENT (mA)0
70
60
50
40
30
20
10
01500 2500
3513 G04
500 1000 2000 3000
B O O S T C U R R E N T ( m A )
AMBIENT TEMPERATURE (C)40
1.5
S W
C U R R E N T L I M I T ( A )
1.6
1.8
1.9
2.0
2.5
2.2
10 60 85
3513 G05
1.7
2.3
2.4
2.1
15 35 110AMBIENT TEMPERATURE (C)
50
S W
C U R R E N T L I M I T ( m A )
300
350
400
110
3513 G06
250
200
10010 30 7030 10 50 90
150
500
450
AMBIENT TEMPERATURE (C)50
S W
C U R R E N T L I M I T ( m A )
300
350
400
110
3513 G07
250
200
10010 30 7030 10 50 90
150
500
450
SW1 CURRENT (mA)0
0
V C E S A T
( m V )
200
400
600
500 1000 1500 2000
3513 G08
2500
800
1000
100
300
500
700
900
3000ISW2 (mA)
0
V C E 2 S A T
( m V )
200
400
600
100
300
500
400 800 1200 1600
3513 G09
20000
TA = 25C, unless otherwise noted.
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TYPICAL PERFORMANCE CHARACTERISTICS
SW3 VCESAT SW4 VCESAT VON Current Limit
Oscillator Frequency Frequency Foldback Reference Voltage
ISW3 (mA)0
V C E 3 S A T
( m V ) 200
250
300
150 250
3513 G10
150
100
50 100 200 300 350
50
0
ISW (mA)0
200
250
350
150 250
3513 G11
150
100
50 100 200 300 350
50
0
300
V C E S A T
( m V )
VE3 (V)0
0
I O N
L I M I T ( m A )
5
15
20
25
20
45
3513 G12
10
105 25 3015 35
30
35
40
AMBIENT TEMPERATURE (C)50
F R E Q U E N C Y ( M H z )
2.1
2.2
2.3
3513 G13
2.0
1.9
1.70 50 100
1.8
2.5
2.4
VFB (mV)0
S W I T C H I N G F R E Q U E N C Y ( k H z )
1500
2000
2500
450 750 1200
3513 G14
1000
500
0150 300 600 900 1050
TEMPERATURE (C)40 15
1.20
R E F E R E N C E V O L T A G E ( V )
1.22
1.25
10 60 85
3513 G15
1.21
1.24
1.23
35 110
TA = 25C, unless otherwise noted.
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BIAS Pin Current Efficiency, AVDD = 13V Efficiency, VLOGIC = 5V
TEMPERATURE (C)50
0
B I A S C U R R E N T ( m A )
10
20
30
40
50
60
0 50 100 150
3513 G16
L2 = 10HL3 = 10HL4 = 10H
ISW2 = 0AISW3 = 0AISW4 = 0A
LOAD CURRENT (mA)1
40
E F F I C I E N C Y ( % )
50
60
70
80
90
100
100 200 300 400
3513 G17
500IOUT (mA)
100
E F F I C I E N C Y ( % )
70
80
90
100
700 1100
3513 G18
60
50
300 500 900 1300 150040
TYPICAL PERFORMANCE CHARACTERISTICS
LDO Current Limit vs Temperature VUVLO vs Temperature Reference Voltage for FB5, LDO
AMBIENT TEMPERATURE (C)50
0 B A S E C U R R E N T L I M I T O F I N T E R N A L P N P ( m A )
1
3
4
5
50
9
3513 G19
2
025 75 10025 125
6
7
8
AMBIENT TEMPERATURE ( C)50
1.30
1.31
1.33
100
3513 G20
1.29
1.28
0 50
1.27
1.26
1.32
U V L O
( V )
UVLO FORSTART
UVLO MINIMUMFOR RUN
TEMPERATURE (C)40
640
650
670
35 85
3513 G21
630
620
15 10 60 110
610
600
660
R E F E R E N C E V O L T A G E ( m V )
TA = 25C, unless otherwise noted.
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FB5 (Pin 1): Feedback Pin. Tie the resistor tap to this pinand set the output of the LDO according to VLDO = 0.625 (1 + R14/R15). Reference designators refer to Figure 1.
VC1 (Pin 2): Control Voltage and Compensation Pin forInternal Error Amplifier. Connect a series RC from this pinto ground to compensate switching regulator 1.
RUN-SS3/4 (Pin 3): Run/Soft-Start Pin. This is the soft-start pin for switching regulators 3 and 4. Place a soft-startcapacitor here to limit start-up inrush current and outputvoltage ramp rate. When the BIAS pin reaches 2.25V, a 2Acurrent source charges the capacitor. When the voltage atthis pin reaches 0.8V, switches 3 and 4 turn on and beginswitching. For slower start-up use a larger capacitor. Forcomplete shutdown tie RUN-SS3/4 to ground.FB3 (Pin 4): Feedback Pin. Tie the resistor tap to this pinand set VON according to VON = 1.22V (1 + R8/R9) 150mV. Reference designators refer to Figure 1.
RUN-SS2 (Pin 5): Run/Soft-Start Pin. This is the soft-startpin for switching regulator 2. Place a soft-start capacitorhere to limit start-up inrush current and output voltageramp rate. When the BIAS pin reaches 2.25V, a 2A cur-rent source charges the capacitor. When the voltage at thispin reaches 0.8V, switch 2 turns on and begins switching.For slower start-up use a larger capacitor. For completeshutdown tie RUN-SS2 to ground.
SW3 (Pin 6): Switch Node. The SW3 pin is the collector ofthe internal NPN bipolar transistor for switching regulator 3.Minimize trace area at this pin to keep EMI down.
E3 (Pin 7): This is switching regulator 3s output andthe emitter of the output disconnect PNP. Tie the outputcapacitor and resistor divider here.
VON (Pin 8): This is the delayed output for switchingregulator 3. V
ON reaches its programmed voltage after the
internal CT timer times out. Protection circuitry ensuresVON is disabled if any of the four outputs are more than10% below normal voltage. This output is also disabledwhen VON_CLK is high.
VONSINK (Pin 9): This is an open-collector output controlledby the VON_CLK pin. When VON_CLK is low, this pin draws nocurrent and when VON_CLK is high, this pin draws current.
VON_CLK (Pin 10): This pin controls the output disconnedevice and the open collector of VONSINK. When this pin islow, the VON pin is enabled and the VONSINK pin is a highimpedance. When this pin is high, the VON pin is disabledand the VONSINK pin sinks current to ground.PGOOD (Pin 11): Power Good Comparator Output. Thisthe open collector output of the power good comparaand can be used in conjunction with an external P-chanMOSFET to provide output disconnect for AVDD as shown inFigure 2. When switcher 2s output reaches approxima90% of its programmed voltage,PGOOD will be pulled toground. This will pull down on the gate of the MOSconnecting AVDD. A 100k pull-up resistor between th
source and the gate of the P-channel MOSFET keepoff when switcher 2s output is low.
VC3 (Pin 12): Control Voltage and Compensation Pin Internal Error Amplifier. Connect a series RC from thito ground to compensate switching regulator 3.
CT (Pin 13): Timing Capacitor Pin. This is the inputthe VON timer and programs the time delay from all fofeedback pins reaching 1.125V to VON turning on. The CT capacitor value can be set using the equation C = (20 tDELAY)/1.1V.
GND (Pins 14, 17, 33): Ground.SW2 (Pins 15, 16): Switch Node. The SW2 pin is the clector of the internal NPN bipolar transistor for switchregulator 2. Minimize trace area at this pin to keep down.
BIAS (Pins 18, 29): The BIAS pin is used to improve efciency when operating at higher input voltages. Connecthis pin to the output of switching regulator 1 forces mof the internal circuitry to draw its operating current fVLOGIC rather than VIN. The drivers of switches 2, 3 an4 and the LDO are supplied by BIAS. Switches 2, 3 aand the LDO will not function until the BIAS pin reaapproximately 2.7V. Both BIAS pins must be tied to VLOGIC.
FB2 (Pin 19): Feedback Pin. Tie the resistor divider tto this pin and set AVDD according to AVDD = 1.22V (1 + R5/R6). Reference designators refer to Figure 2.
PIN FUNCTIONS
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VC2 (Pin 20): Control Voltage and Compensation Pin forInternal Error Amplifier. Connect a series RC from this pinto ground to compensate switching regulator 2.
VC4 (Pin 21): Control Voltage and Compensation Pin forInternal Error Amplifier. Connect a series RC from this pinto ground to compensate switching regulator 4.
RUN-SS1 (Pin 22): Run/Soft-Start Pin. This is the soft-startpin for switching regulator 1. Place a soft-start capacitorhere to limit start-up inrush current and output voltageramp rate. When power is applied to the VIN pin, a 2Acurrent source charges the capacitor. When the voltageat this pin reaches 0.8V, switch 1 turns on and beginsswitching. For slower start-up use a larger capacitor. Forcomplete shutdown tie RUN-SS1 to ground.NFB4 (Pin 23): Negative Feedback Pin. Tie the resistor di-vider tap to this pin and set VOFF according to VOFF = 1.18 (1 + R3/R4). Reference designators refer to Figure 2.
D4 (Pin 24): Internal Schottky Diode Pin. This pin is theanode of an internal Schottky diode with the other endconnected to ground. This Schottky diode is used ingenerating the VOFF output.
SW4 (Pin 25): Switch Node. The SW4 pin is the collector of
the internal NPN bipolar transistor for switching regulator 4.Minimize trace area at this pin to keep EMI down.
BD (Note 26): NPN LDO Base Drive. This pin controls thebase of the external NPN LDO transistor.
LDOPWR (Pin 27): Input Voltage for LDO Driver. This pinsupplies the current for the NPN LDO base. This pin canbe connected to VIN. To save power at high VIN voltages,the pin can alternatively be connected to the AVDD supply.
BOOST (Pin 28): The BOOST pin is used to provide adrive voltage higher than VIN to the switch 1 drive circuit.
An internal Schottky diode is connected between BIASand BOOST. A capacitor needs to be connected betweenBOOST and SW1.
SENSE (Pin 30) Negative Current Sense Input. This p(along with the SENSE+ pin) is used to sense the inductocurrent for the buck switching regulator.
SENSE+ (Pin 31) Positive Current Sense Input. This p(along with the SENSE pin) is used to sense the inductocurrent for the buck switching regulator.
FB1 (Pin 32): Feedback Pin. Tie the resistor divider tto this pin and set VLOGIC according to VLOGIC = 1.235V (1 + R1/R2). Reference designators refer to Figure 2.
SW1 (Pins 34, 35): Switch Node. The SW1 pins are temitter of the internal NPN bipolar power transistorswitching regulator 1. These points must be tied toget
for proper operation. Connect these pins to the induccatch diode and boost capacitor.
VIN (Pins 36, 37): Input Voltage. This pin supplies curreto the internal circuitry of the LT3513. This pin muslocally bypassed with a capacitor.
UVLO (Pin 38): Undervoltage Lockout. A resistor diviconnected to VIN is tied to this pin to program the minimuinput voltage at which the LT3513 will operate. This pcompared to the internal 1.25V reference. When UVLless than 1.25V, the switching regulators are not allowto operate (the RUN/SS pins are still used to turn on eswitching regulator). When this pin falls below 1.23.9A will be pulled from the pin to provide programmhysteresis for UVLO.
Exposed Pad (Pin 39): Ground. The Exposed Pad of thpackage provides both electrical contact to ground agood thermal contact to the printed circuit board. TExposed Pad must be soldered to the circuit board proper operation.
PIN FUNCTIONS
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6
12
+
+
+
S Q
1.22V
gm
1.18V
1.22V
1.1V
1.235V
R
DRIVER
BIAS
VC3
SW3
9VONSINK
10VON_CLK
VON_CLK
7E3
3513 F01
FOLDBACKOSCILLATOR
25
21
+
+
+
+
+
+
S QR
DRIVER
BIAS
VC4
23NFB4100k100k
SW4
24D4
FOLDBACKOSCILLATOR
20
+
+
+
1.1V
FB2
+
+
S QR
DRIVER
VC2
30SENSE
31
28
SENSE+
SW2
15, 16
BIAS
18, 29
FOLDBACKOSCILLATOR
gm
gm
2
+
+
+
S QR
DRIVER
BIAS
CURRENTSENSE AMP
VC1
SW134, 35
BOOST
VINSLOPE COMP/ ONE-SHOT
gm
gm
+
13CT
22RUN-SS1
3RUN-SS3/4
BIAS
38 UVLO
11 PGOOD
UVLO1.25V
3.9A
2A
2A
20A
19 FB2
32FB1
BD
1FB5
LDOPWR
GND
14,17,33
VIN36,37
2.7V +
1.1V
VON_CLK
+
SW3LOCKOUT
INTERNALREGULATOR
AND REFERENCE
MASTEROSCILLATOR
2MHz
5RUN-SS2
4 FB3
8VON
SW2LOCKOUT
+0.625V
26
27
+
Figure 1
BLOCK DIAGRAM
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The LT3513 is a highly integrated power supply IC contain-ing four separate switching regulators and a low dropoutlinear regulator (LDO). Switching regulator 1 is a step-down 2.2A regulator with inductor current sense and anintegrated boost Schottky diode. Switching regulator 2 canbe configured as a step-up or SEPIC converter and has a1.5A switch. Switching regulator 3 consists of a step-upregulator with a 0.25A switch as well as an integratedSchottky diode. Switching regulator 4 is a negative regula-tor with a switch current limit of 0.25A and an integratedSchottky diode. Linear regulator 5 is capable of providing8mA of current to the base of an external NPN transistor.The regulators share common circuitry including inputsource, voltage reference and master oscillator. Operationcan be best understood by referring to the Block Diagramas shown in Figure 1.
If the RUN-SS1 pin is pulled to ground, the LT3513 is shutdown and draws 30A from the input source tied to VIN.An internal 2A current source charges the external soft-start capacitor, generating a voltage ramp at this pin. If theRUN-SS1 pin exceeds 0.8V, the internal bias circuits turnon, including the internal regulator, reference and 2MHzmaster oscillator. The master oscillator generates fourclock signals, one for each of the switching regulators.
Switching regulator 1 will only begin to operate when theRUN-SS1 pin reaches 0.8V. Switcher 1 generates VLOGIC,which must be tied to the BIAS pin. When BIAS reaches 2.8V,the NPNs pulling down on the RUN-SS2 and RUN-SS3/4pins turns off, allowing an internal 2A current sourceto charge the external capacitors tied to RUN-SS2 andRUN-SS3/4 pins. When the voltage on RUN-SS2 reaches0.8V, switcher 2 is enabled. Correspondingly, when thevoltage on RUN-SS3/4 reaches 0.8V, switchers 3 and 4are enabled. AVDD, E3 and VOFF will then begin rising at arate determined by the capacitors tied to the RUN-SS2 and
RUN-SS3/4 pins. When all four switching outputs reach90% of their programmed voltages, the NPN pulling down
on the CT pin will turn off, and an internal 20A currsource will charge the external capacitor tied to the CT pin.When the CT pin reaches 1.1V, the output disconnect PNturns on, connecting VON to E3. In the event of any of thfour outputs dropping below 90% of their programmvoltage, PanelProtect circuitry pulls the CT pin to GNDdisabling VON.
(2a)
(2b)
Figure 2. LT3513 Power-Up Sequence. (Traces from Both Photosare Synchnonized to the Same Trigger)
RUN-SS 2V/DIVVLOGIC5V/DIV
IL1 1A/DIV
IL2 500A/DIV
SS-234 2V/DIV
AVDD10V/DIV
PGOOD 20V/DIV
5ms/DIV 3513 F02a
VOFF 10V/DIVVSS3/4 2V/DIV
VCT 2V/DIV
IL4 500mA/DIV
IL3 500mA/DIV
VE3 20V/DIV
VON 20V/DIV
5ms/DIV 3513 F02b
OPERATION
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OPERATION
A power good comparator monitors AVDD and turns onwhen FB2 is at or above 90% of its regulated value. Theoutput is an open-collector transistor that is off when theoutput is out of regulation, allowing an external resistorto pull the pin high. This pin can be used with a P-channelMOSFET that functions as an output disconnect for AVDD.
The four switchers are current mode regulators. Insteadof directly modulating the duty cycle of the power switch,the feedback loop controls the peak current in the switchduring each cycle. Compared to voltage mode control, cur-rent mode control improves loop dynamics and providescycle-by-cycle current limit.
All four switchers employ a constant-frequency currentmode control scheme. Switcher 1, the step-down regula-tor, differs slightly from the others with inductor currentsense. Instead of monitoring the current at the switch,current nodes are used to measure the current throughthe inductor. Inductor current sense does not suffer fromminimum on-time problems, therefore always keep-ing the switch current limited with any input-to-outputvoltage ratio. Switcher 1 is always synchronized to themaster oscillator. The other three switchers each havetheir own slave oscillator. The slave oscillator reduces thefrequency when the feedback voltage dips below 0.75Vand decreases linearly below the threshold as shown inthe Performance Characteristics Frequency Foldback plot.Other than these two differences, the control loop is similarin all four switchers. A pulse from the master oscillatorfor switcher 1 or a pulse from the slave oscillator for theother three switchers sets the RS latch and turns on theinternal NPN bipolar power switch. Current in the switchand the external inductor begins to increase. When thiscurrent exceeds a level determined by the voltage at VC, thecurrent comparator resets the latch, turning off the switch.The current in the inductor flows through the Schottky
diode and begins to decrease. The cycle begins againthe next pulse from the oscillator. In this way, the volton the VC pin controls the current through the inductor the output. The internal error amplifier regulates the outby continually adjusting the VC pin voltage. The thresholfor switching on the VC pin is 0.8V, and an active clamof 1.8V limits the VC voltage. Switchers 2, 3 and 4 alscontain an independent current limit not dependent onC or duty cycle. Switcher 1s current limit is controlledthe VC voltage and varies with duty cycle. All four swiers also use slope compensation to ensure stability wthe current mode scheme at duty cycles above 50%. TRUN-SS1, RUN-SS2 and RUN-SS3/4 pins control theof rise of the feedback pins.
The switch driver for SW1 operates either from VIN or fromthe BOOST pin. An external capacitor and an integrSchottky diode are used to generate a voltage at the BOOpin that is higher than the input supply. This allows driver to saturate the internal bipolar NPN power swfor efficient operation.
INPUT VOLTAGE RANGE STEP-DOWN CONSIDER
The minimum operating voltage of switcher 1 is determieither by the LT3513s undervoltage lockout of ~4V oits maximum duty cycle. A user defined undervoltlockout may be set with the UVLO pin at a voltage hithan the internal undervoltage lockout. The duty cyclthe fraction of time that the internal switch is on anddetermined by the input and output voltages:
DC= VOUT +VF
VIN VSW +VFwhere VF is the forward voltage drop of the catch dio(~0.4V) and VSW is the voltage drop of the internal swit
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(~0.3V at maximum load). This leads to a minimum inputvoltage of:
VIN(MIN) = VOUT +VFDCMAX VF +VSW
with DCMAX = 0.75.
The user defined undervoltage is set by a resistor dividerconnected to the UVLO pin. The comparator pulls 3Afrom the pin when the UVLO pin is higher than 1.25V.The hysteresis and minimum input voltage equations areas follows:
VHYS = R2+2k( ) 3.9A
VIN(MIN) =1.25VR1+R2
R1
current should be at least 30% higher. For highest efficiethe series resistance (DCR) should be less than 0.1 .Table 1 lists several vendors and types that are suitab
Table 1. Inductor VendorsVENDOR URL PART SERIES TYPECoilcraft www.coilcraft.com MSS7341 ShieldeMurata www.murata.com LQH55D Open
TDK www.component.tdk.com SLF7045SLF10145
ShieldedShielded
Toko www.toko.com DC62CBD63CBD75CD75F
ShieldedShieldedShielded
OpenSumida www.sumida.com CR54
CDRH74CDRH6D38
CR75
OpenShieldedShielded
Open
The optimum inductor for a given application may difrom the one indicated by this simple design guide. A larvalue inductor provides a higher maximum load curreand reduces the output voltage ripple. If your load is lowthan the maximum load current, then you can relax tvalue of the inductor and operate with higher ripple crent. This allows you to use a physically smaller inducor one with a lower DCR resulting in higher efficiencyaware that the maximum load current depends on inpvoltage. A graph in the Typical Performance Charactetics section of this data sheet shows the maximum locurrent as a function of input voltage and inductor vafor VOUT = 3.3V. In addition, low inductance may resin discontinuous mode operation, which further reducmaximum load current. For details of maximum outcurrent and discontinuous mode operation, see LineTechnologys Application Note 44. Finally, for duty cygreater than 50% (VOUT /VIN > 0.5), a minimum inductance is required to avoid subharmonic oscillations, sApplication Note 19.
OPERATION
R2
R1
UVLO
3513 A1
VIN
38
INDUCTOR SELECTION AND MAXIMUM OUTPUTCURRENT
A good first choice for the inductor value is:
L= VOUT +VF
1.8
where VF is the voltage drop of the catch diode (~0.4V)and L is in H. The inductors RMS current rating must begreater than the maximum load current and its saturation
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The current in the inductor is a triangle wave with an averagevalue equal to the load current. The peak switch currentis equal to the output current plus half the peak-to-peakinductor ripple current. The LT3513 limits its switch cur-rent in order to protect itself and the system from overloadfaults. Therefore, the maximum output current that theLT3513 will deliver depends on the switch current limit, theinductor value, and the input and output voltages. Whenthe switch is off, the potential across the inductor is theoutput voltage plus the catch diode drop. This gives thepeak-to-peak ripple current in the inductor:
IL =
1DC( ) VOUT +VF( )L f
where f is the switching frequency of the LT3513 and Lis the value of the inductor. The peak inductor and switchcurrent is:
ISW(PK) =ILPK =IOUT +
IL2
To maintain output regulation, this peak current must beless than the LT3513s switch current limit of ILIM. For SW1,ILIM is at least 2A at DC = 0.35, and decreases linearly to1.5A at DC = 0.75 as shown in the Typical PerformanceCharacteristics section. The maximum output current isa function of the chosen inductor value:
IOUT(MAX) =ILIM IL
2 =2.5A 1 0.57 DC( ) IL
2
Choosing an inductor value so that the ripple current issmall will allow a maximum output current near the switchcurrent limit. One approach to choosing the inductor is tostart with the simple rule given above, look at the availableinductors and choose one to meet cost or space goals.Then use these equations to check that the LT3513 willbe able to deliver the required output current. Note againthat these equations assume that the inductor current iscontinuous. Discontinuous operation occurs when IOUT is less than IL /2.
OUTPUT CAPACITOR SELECTION
For 5V and 3.3V outputs, a 10F 6.3V ceramic capa
(X5R or X7R) at the output results in very low output age ripple and good transient response. Other types avalues will also work; the following discussion expltradeoffs in output ripple and transient performance.
The output capacitor filters the inductor current to gerate an output with low voltage ripple. It also stoenergy in order satisfy transient loads and stabilizes LT3513s control loop. Because the LT3513 operates high frequency, minimal output capacitance is necessaIn addition, the control loop operates well with or withthe presence of output capacitor series resistance (ESRCeramic capacitors, which achieve very low output riand small circuit size, are therefore an option.
You can estimate output ripple with the followiequations:
VRIPPLE =
IL8 f COUT
for ceramic capacitors, and
VRIPPLE = IL ESR for electrolytic capacitors (tantalumand aluminum)
where
IL is the peak-to-peak ripple current in the inducThe RMS content of this ripple is very low so the Rcurrent rating of the output capacitor is usually notconcern. It can be estimated with the formula:
IC(RMS) =
IL12
Another constraint on the output capacitor is that it mhave greater energy storage than the inductor; if the stoenergy in the inductor transfers to the output, the resultvoltage step should be small compared to the regulatvoltage. For a 5% overshoot, this requirement indicat
COUT >10 L
ILIMVOUT
2
OPERATION
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The low ESR and small size of ceramic capacitors makethem the preferred type for LT3513 applications. However,not all ceramic capacitors are the same. Many of the highervalue capacitors use poor dielectrics with high temperatureand voltage coefficients. In particular, Y5V and Z5U typeslose a large fraction of their capacitance with applied volt-age and at temperature extremes.
Because loop stability and transient response depend onthe value of COUT, this loss may be unacceptable. UseX7R and X5R types. Electrolytic capacitors are also anoption. The ESRs of most aluminum electrolytic capacitorsare too large to deliver low output ripple. Tantalum andnewer, lower ESR organic electrolytic capacitors intended
for power supply use are suitable, and the manufacturerswill specify the ESR. Chose a capacitor with a low enoughESR for the required output ripple. Because the volumeof the capacitor determines its ESR, both the size and thevalue will be larger than a ceramic capacitor that wouldgive similar ripple performance. One benefit is that thelarger capacitance may give better transient responsefor large changes in load current. Table 2 lists severalcapacitor vendors.
Table 2. Low ESR Surface Mount CapacitorsVENDOR TYPE SERIES
Taiyo Yuden Ceramic X5R, X7RAVX Ceramic
TantalumX5R, X7R
TPSKemet Tantalum
Ta OrganicAl Organic
T491, T494, T495T520A700
Sanyo Ta or Al Organic POSCAPPanasonic Al Organic SP CAP
TDK Ceramic X5R, X7R
DIODE SELECTION
The catch diode (D1 from Figure 1) conducts current onlyduring switch-off time. Average forward current in normaloperation can be calculated from:
ID(AVG) =IOUT
VIN VOUTVIN
The only reason to consider a diode with a larger currrating than necessary for nominal operation is for worst-case condition of shorted output. The diode currwill then increase to the typical peak switch current. Preverse voltage is equal to the regulator input voltaUse a diode with a reverse voltage rating greater thaninput voltage. Table 3 lists several Schottky diodes their manufacturers.
Table 3. Schottky DiodesPART NUMBER VR (V) IAVE (A) VFAT 1A (mV) VF at 2A (mV)
On SemiconductorMBRM120E 20 1 530MBRM140 40 1 550MBRS240 40 2MBRA340 40 3 450Diodes Inc.
B120 20 1 500B240 40 2 500B340A 40 3 450
BOOST PIN CONSIDERATIONSThe minimum operating voltage of an LT3513 appltion is limited by the undervoltage lockout ~4V andthe maximum duty cycle. The boost circuit also limthe minimum input voltage for proper start-up. If input voltage ramps slowly or the LT3513 turns on wthe output is already in regulation, the boost capacimay not be fully charged. Because the boost capacicharges with the energy stored in the inductor, the circwill rely on some minimum load current to get the bocircuit running properly. This minimum load will depon input and output voltages. The Typical PerformaCharacteristics section shows a plot of the minimum lcurrent to start as a function of input voltage for a 3
OPERATION
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output. The minimum load current generally goes to zeroonce the circuit has started. Even without an output loadcurrent, in many cases the discharged output capacitorwill present a load to the switcher that will allow it to start.
INVERTER/STEP-UP CONSIDERATIONS
Regulating Positive Output Voltages
The output voltage is programmed with a resistor dividerbetween the output and the FB pin. Choose the resistorsaccording to:
R3=R4 VOUT
1.25
1
R4 should be 10k or less to avoid bias current errors.
Regulating Negative Output Voltages
The LT3513 contains an inverting op amp with a gain of 1.The NFB4 pin works just as the other FB pins. Choose theresistors according to:
R6= VOUT
R51.25
R5
R5 should be 2.5k or less to avoid bias current errors.
The duty cycle for a given application using the stepor charge pump topology is:
DC= VOUT VINVOUT
The duty cycle for a given application using the inveor SEPIC is:
DC=
VOUTVIN + VOUT
The LT3513 can still be used in applications where the cycle, as calculated above, is greater than the maximu
However, the part must be operated in discontinuous moso that the actual duty cycle is reduced.
Inductor Selection
Table 1 lists several inductor vendors and types that suitable to use with the LT3513. Consult each manufactfor detailed information and for their entire selectiorelated parts. Use ferrite core inductors to obtain the befficiency, as core losses at frequencies above 1MHzmuch lower for ferrite cores than for powdered-iron unA 10H to 22H inductor will be the best choice for
LT3513 step-up and charge pump designs. Choose inductor that can carry the entire switch current withsaturating. For inverting and SEPIC regulators, a coupinductor, or two separate inductors is an option. Whusing coupled inductors, choose one that can handat least the switch current without saturating. If usuncoupled inductors, each inductor need only handle proximately one-half of the total switch current. A 4.to 15H coupled inductor or two 10H to 22H uncouinductors will usually be the best choice for most LT3inverting and SEPIC designs.
R6
R5
NFB4
3513 A2
VOUT
22
OPERATION
Duty Cycle Range
The maximum duty cycle (DC) of the LT3513 switchingregulator is 75% for SW2, and 84% for SW3 and SW4.
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Output Capacitor Selection
Use low ESR (equivalent series resistance) capacitors at
the output to minimize the output ripple voltage. Multilayerceramic capacitors are an excellent choice, as they havean extremely low ESR and are available in very small pack-ages. X7R dielectrics are preferred, followed by X5R, asthese materials retain their capacitance over wide voltageand temperature ranges. A 10F to 22F output capaci-tor is sufficient for most LT3513 applications. Even lesscapacitance is required for outputs with |VOUT| > 20V or|IOUT| < 100mA. Solid tantalum or OS-CON capacitors willalso work, but they will occupy more board area and willhave a higher ESR than a ceramic capacitor. Always use
a capacitor with a sufficient voltage rating.Diode Selection
A Schottky diode is recommended for use with theLT3513 switcher 2 and switcher 4. The Schottky diode forswitcher 3 is integrated inside the LT3513. Choose diodesfor switcher 2 and switcher 4 rated to handle an averagecurrent greater than the load current and rated to handlethe maximum diode voltage. The average diode current inthe step-up and SEPIC is equal to the load current. Each ofthe two diodes in the charge pump configurations carriesan average diode current equal to the load current. Theground connected diode in the charge pump is integratedinto the LT3513. The maximum diode voltage in the step-up and charge pump configurations is equal to |VOUT|.The maximum diode voltage in the SEPIC and invertingconfigurations is VIN + |VOUT|.
Input Capacitor Selection
Bypass the input of the LT3513 circuit with a 4.7F or higherceramic capacitor of X7R or X5R type. A lower value ora less expensive Y5V type will work if there is additionalbypassing provided by bulk electrolytic capacitors or if the
input source impedance is low. The following paragradescribe the input capacitor considerations in more detStep-down regulators draw current from the input suply in pulses with very fast rise and fall times. The icapacitor is required to reduce the resulting voltage ripat the LT3513 input and to force this switching currinto a tight local loop, minimizing EMI. The input cator must have low impedance at the switching frequeto do this effectively and it must have an adequate ripcurrent rating. The input capacitor RMS current cancalculated from the step-down output voltage and curreand the input voltage:
CIN(RMS) =IOUTVOUT VIN VOUT( )
VIN
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