user guide for ir3891 evaluation board · located close to the supirbuck ic. to improve efficiency,...

IRDC3891-P1V2

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

04-08-2013 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 15mmx11mmevaluation 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 = 450kHz

• Vout1 = +1.2V @ 3A Vout2 = +1.2V @ 3A

• L1 = 2.2uH L2 = 2.2uH

• Cout1=1x22uF (ceramic 1206) Cout2=1x22uF (ceramic 1206)

• Cin= 2x10uF (ceramic 1206)

SupIRBuckTM

mchen4

Text Box

MC

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

CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUT

The PCB is a compact 15mmx11mm, 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)

Vo1+ Vout1(+1.2V)

Vo2+ Vout2(+1.2V)

Gnd Power Ground

En1 Enable 1

En2 Enable 2

Trim1Vout adjustment for channel 1

Trim2Vout adjustment for channel 2

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Connection Diagram

Vo1 Gnd Vin Vin Gnd Vo2

Top View

Bottom View

Fig. 1: Connection Diagram of IR3891 Evaluation Boards

Trim2 En2 En1 Trim1

15mm

11mm

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Fig. 2: Board Layout-Top Layer

Fig. 3: Board Layout-Bottom Layer

Single point connection between AGnd and PGnd

11mm

15mm

Trim En TrimEn

Vin Vin GndGndVo Vo

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Fig. 5: Board Layout-Mid Layer 2

Fig. 4: Board Layout-Mid Layer 1

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Fig

.6:

Sch

emat

ico

fth

eIR

3891

eval

uat

ion

bo

ard

Vin

=12

V,V

o=

1.2V

,fsw

=45

0kH

z,Io

max

=3A

J1 CO

N6

123456

R5

49.9

K

R6

7.5

k

VIN

R13

4.0

2k

Vin

R14

210

R12

5.6

2k

R15

10

C13

220

0pF

C1

0

0.1u

F

C1

1

10n

F

R16

N/S

Trim

1

1

Trim

2

1

R26

N/S

R9

53.6

K

GN

DV

OU

T1R

11

1.5

k

U1

IR3

89

1 PVin215

PVin214

EN

28

PGood212

Rt/

Sy

nc7

Vin

3

Se

q6

Comp211

PGND216

Vs

ns1

1

Vc

c/LD

O4

FB210

Boot213

GN

D5

Vs

ns2

9

EN

12

PGND217

PGND218

SW

219

SW

220

SW

121

SW

122

PGND123

PGND124

PGND125

PVin126

Boot128

PGood129

PVin127

Comp130

FB131

C12

2

22u

F

C2

0

0.1u

F

C8

2.2u

F

Single Point Connection between AGND and PGND

L2

2.2

uH

, IH

LP

-2020-C

Z-A

1

R23

4.0

2k

R24

210

R22

5.6

2k

R25

10

C23

2200

pF

GN

D

L1

2.2

uH

, IH

LP

-2020-C

Z-0

1

C11

2

10u

F

C6

1.0

uF

Vin

C11

1

10uF

C12

470p

F

C21

10n

F

R21

1.5

k

C22

470

pF

EN

2

1

R3

49.9

K

R4

7.5

k

EN

11

VO

UT

2

Vin

C22

2

22u

F

IRDC3891-P1V2

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Bill of Materials

Item Qty Part Reference Value Description Manufacturer Part Number

1 2 C112, C111 10uF 1206, 25V, X5R, 20% TDK C3216X5R1E106M

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

3 2 C10, C20 0.1uF 0402, 50V, X5R, 10% TDK C1005X5R1H104K050BB

4 2 C11, C21 10nF 0402, 25V, X5R, 10% TDK C1005X5R1E103K050BA

5 2 C12, C22 470pF 0402, 50V, X5R, 10% TDK C1005X5R1H471K050BA

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

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

8 2 C122, C222 22uF 1206, 10V, X5R, 20% TDK C3216X5R1A226M160AC

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

10 2 R14, R24 210Ω Thick film, 0402, 1/10W, 1% PanasonicERJ-2RKF2100X

11 2 R12, R22 5.62kΩ Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF5621X





16 1 R9 53.6kΩ Thick film, 0402, 1/10W, 1% Panasonic ERJ-2RKF5362X

17 1 L1, L2 2.2uH 5.49mm x 5.18mm, DCR=27.8mΩ Vishay IHLP-2020CZ-A1 2.2uH

18 1 U1 IR3891 5mm x 6 mm QFN IR IR3891MTR1PBF

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-4A, Room Temperature, no airflow

Fig. 10: Output Voltage Ripple, 3A load Ch3: Vout ,

Fig. 11: Inductor node at 3A load, Ch2:LX, Due to the limit of board size, the reference of the probe is connected to GND terminal of Cout. Thus, the negative spike is high.

Fig. 8: Start up with 1V Pre Bias, 0A Load, Ch2:VoFig. 7: Start up at 3A Load, Ch2:Vo

Fig. 9: Transient Response, 1.5A to 3A stepCh2:Vout Ch4-Iout

Fig. 12: Short circuit (Hiccup) Recovery, Ch2:Vout , Ch4:Iout

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-3A, Room Temperature, no air flow

Fig. 14: Bode Plot at 3A load shows a bandwidth of 87kHz and phase margin of 50 degrees and gain margin of -10dB

Fig. 14: Bode Plot at 3A load with one additional 47uF/10V/1210 output capacitors. Bandwidth is 35.6kHz and phase margin of 47.8 degrees and gain margin of -24dB.

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Fig.17: Power loss versus load current

Fig.16 : Efficiency versus load current

TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-3A, Room Temperature, no air flow

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THERMAL IMAGESVin=12.0V, Vo=1.2V, Io=3A, Room Temperature, No Air flow

Fig. 19: Thermal Image of the board at 3A load of both phases. Test point is IR3891 Temperature = 82ºC. For easy test, Vin, GND and Vout1 and Vout2 of IR3891 demo board are connected to another PCB

through the copper leads. There copper leads help remove the heat from the IR3891demo board. Using large copper area on the other PCB will further help reduce the temperature of IR3891 demo board.

user guide for ir3891 evaluation board · located close to the supirbuck ic. to improve efficiency,...

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