USER GUIDE FOR IR3891 EVALUATION BOARD

IRDC3891-P1V5/P3V3

Preliminary

This evaluation board is a preliminary version meant for the engineering evaluation of the IR3891. Based on the results of the continuing evaluation, this board can evolve and change without notice

06-18-2013 1

USER GUIDE FOR IR3891 EVALUATION BOARD

DESCRIPTION

The IR3891 is a dual synchronous buck

converter, providing a compact, high

performance and flexible solution in a small

5mm X 6mm Power QFN package.

Key features offered by the IR3891 include

internal Digital Soft Start, precision 0.5V

reference voltage, Power Good, thermal

protection, programmable switching

frequency, Enable input, input under-voltage

lockout for proper start-up, enhanced line/

load regulation with feed forward, external

frequency synchronization with smooth

clocking, internal LDO, pre-bias start-up,

output over voltage protection as well as openfeedback line protection.

Output over-current protection function isimplemented by sensing the voltage developedacross the on-resistance of the synchronousrectifier MOSFET for optimum cost andperformance and the current limit is thermallycompensated.

This user guide contains the schematic and billof materials for the IR3891 22.6mmx11.6mmevaluation board. The guide describesoperation and use of the evaluation board itself.Detailed application information for IR3891 isavailable in the IR3891 data sheet.

BOARD FEATURES

• Vin = +12.0V

• Fs = 600kHz

• Vout1 = +1.5V @ 3A (100LFM)

• Vout2 = +3.3V @ 3A (100LFM)

• L1 = 2.2uH

• L2 = 4.7uH

• Cin= 2x10uF (ceramic 1206)

• Cout1 = Cout2 = 2x47uF (ceramic 0805)

SupIRBuckTM

IRDC3891-P1V5/P3V3

Preliminary


06-18-20132

A well regulated +12V input supply should be connected to VIN+ and GND. A maximum of 3A load shouldbe connected to Vout1+/GND and Vout2+/GND . The inputs and output connections of the board are listedin Table I.

CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUT

The PCB is a compact 22.6mmx11.6mm, 4-layer board using FR4 material. All layers use 2 Oz. copper.The PCB thickness is 0.062”.

Power supply decoupling capacitors, the bootstrap capacitor and feedback components are locatedclose to IR3891. The feedback resistors are connected to the output at the point of regulation and are

located close to the SupIRBuck IC. To improve efficiency, the circuit board is designed to minimize the

length of the on-board power ground current path.

Table I. Connections

Connection Signal Name

VIN+ Vin (+12V)

Vout1+ Vout1(+1.5V)

Vout2+ Vout2(+3.3V)

Gnd Power Ground

En1 Enable 1

En2 Enable 2

Trim1Vout adjustment for channel 1

Trim2Vout adjustment for channel 2

IRDC3891-P1V5/P3V3

Preliminary


3

Fig. 2: Board Bottom Layer Picture

11.6mm

Fig. 1: Board Top Layer Picture

22.6mm

Trim2 En2 Trim1En1Vin GndGndVout2 Vout1

IRDC3891-P1V5/P3V3

Preliminary


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Fig. 3: Board Layout-Top Layer

Fig. 4: Board Layout-Bottom LayerSingle point connection

between AGnd and PGnd

11.6mm

22.6mm

Trim2 En2 Trim1En1Vin GndGndVout2 Vout1

3.3mm

IRDC3891-P1V5/P3V3

Preliminary


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Fig. 6: Board Layout-Mid Layer 2

Fig. 5: Board Layout-Mid Layer 1

IRDC3891-P1V5/P3V3

Preliminary


06-18-20136

Fig

.7:

Sch

emat

ico

fth

eIR

3891

eval

uat

ion

bo

ard

R5

49.9

k

R6

7.5

k

J1

CO

N9

123456789

VIN

Vou

t2Tr

im2

R13

2.8

7k

Vin

R14

143

R12

5.7

6k

R15

10

C13

2200

pF

C10

0.1u

F

C11

4.7n

F

R16

N/S

R26

N/S

R9

39.2

k

GN

D

GN

D

R11

5.4

9k

U1

IR3

89

1 PVin215

PVin214

EN

28

PGood212R

t/S

ync

7

Vin

3

Seq

6Comp2

11

PGND216

Vsn

s11

Vcc

/LD

O4

FB210

Boot213

GN

D5

Vsn

s29

EN

12

PGND217

PGND218

SW

219

SW

220

SW

121

SW

122

PGND123

PGND124

PGND125

PVin126

Boot128

PGood129

PVin127

Comp130

FB131

C12

2

47uF

C20

0.1u

F

C8

2.2u

F

Trim

1

Single Point Connection between AGND and PGND

L2

4.7

uH

C24

0.1u

F

C14

0.1u

F

C21

1

10uF

C21

2

N/S

EN

2

EN

1

R23

1.2

1k

R24

143

R22

6.8

1k

R25

10

C23

2200

pF

L1

2.2

uH

C11

2

N/S

C6

1.0u

F

Vin

Vou

t1

C11

1

10uF

C12

68pF

C21

4.7n

F

R21

6.0

4k

C22

68pF

R3

49.9

k

R4

7.5

k

C12

3

47uF

C22

3

47uF

Vin

C22

2

47uF

IRDC3891-P1V5/P3V3

Preliminary


06-18-20137

Bill of Materials

Item Qty Part Reference Value Description Manufacturer Part Number

1 2 C111 C211 10uF 1206, 25V, X5R, 20% TDK C3216X5R1E106M

2 2 C13 C23 2200pF 0402, 50V, X5R, 10% TDK C1005X5R1H222K050BA

3 4C10 C20C14 C24

0.1uF 0402, 50V, X5R, 10% TDK C1005X5R1H104K050BB

4 2 C11 C21 4.7nF 0402, 25V, X7R, 10% Murata GRM155R71E472KA01D

5 2 C12 C22 68pF 0402, 50V, NP0, 5% Murata GRM1555C1H680JA01D

6 1 C6 1.0uF 0402, 16V, X5R, 10% TDK C1005X5R1C105K050BC

7 1 C8 2.2uF 0402, 10V, X5R, 10% TDK C1005X5R1A225K050BC

8 4C122 C123 C222

C22347uF 0805, 6.3V, X5R, 20% Murata GRM21BR60J476ME15

9 2 R15 R25 10Ω Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF10R0X

10 2 R14 R24 143Ω Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF1430X

11 1 R12 5.76kΩ Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF5761X






17 2 R3 R5 49.9kΩ Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF4992X

18 2 R4 R6 7.5kΩ Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF7501X


20 1 L1 2.2uH7.1mm x 6.5mmx3.0mm,

DCR=17.3mΩTDK SPM6530T-2R2M

21 1 L2 4.7uH7.1mm x 6.5mmx3.0mm,

DCR=35.8mΩTDK SPM6530T-4R7M

22 1 U1 IR3891 5mm x 6 mm QFNInternational

RectifierIR3891MTRPBF

IRDC3891-P1V5/P3V3

Preliminary


10/16/20138

Fig. 11: Vout1 voltage ripple, 3A loadCh2: Vout1

Fig. 12: Vout2 voltage ripple, 3A loadCh2: Vout2

Fig. 9: Vout1 start up with 0.4V pre bias , 0A Ch2:Vout1

Fig. 8: Start up with Iout1=Iout2=3ACh1:Vin, Ch2:Vout1, Ch4:Vout2

Fig. 10: Vout2 start up with 2.2V pre bias , 0A Ch2:Vout2

Fig. 13: Inductor node of Vout1Ch3: SW node 1

TYPICAL OPERATING WAVEFORMSVin=12.0V, Vout1=1.5V, Vout2=3.3V, Iout1=Iout2=0-3A, Room temperature, 100LFM

IRDC3891-P1V5/P3V3

Preliminary


10/16/20139

Fig. 17: Vout1 transient response to a load step from 1.5A to 3.0ACh2: Vout1, Ch4: Iout1

Fig. 18: Vout2 transient response to a load step from 1.5A to 3.0A

Ch2: Vout2, Ch4: Iout2

Fig. 15: Vout1 short circuit (hiccup) recoveryCh2:Vout1

Fig. 14: Inductor node of Vout2Ch3: SW node 2

Fig. 16: Vout2 short circuit (hiccup) recoveryCh2:Vout2


IRDC3891-P1V5/P3V3

Preliminary


06-18-201310

Fig. 19: Bode plot of Vout1 at 3A load shows a bandwidth of 120.54kHz and phase margin of 55.48 degrees


-60

-40

-20

0

20

40

60

-200

-150

-100

-50

0

50

100

150

200

103 104 105

TR

1/d

B TR

2/°

f/HzTR1: Mag(Gain) TR2: Unwrapped Phase(Gain)

Fig. 20: Bode plot of Vout2 at 3A load shows a bandwidth of 111.89kHz and phase margin of 53.34 degrees

-60

-40

-20

0

20

40

60

-200

-150

-100

-50

0

50

100

150

200

103 104 105

TR

1/d

B TR

2/°

f/HzTR1: Mag(Gain) TR2: Unwrapped Phase(Gain)

IRDC3891-P1V5/P3V3

Preliminary


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Fig. 22: Power loss versus load current

Fig. 21 : Efficiency versus load current


IRDC3891-P1V5/P3V3

Preliminary


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Fig. 23: Thermal Image of the board with Iout1=Iout2=3A IR3891: 76.08oC Ambient: 26.04oC


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USER GUIDE FOR IR3891 EVALUATION BOARD