International Rectifier IR3847 User Manual

IRDC3847-P1V2

SupIRBuck

TM

USER GUIDE FOR IR3847 EVALUATION BOARD

DESCRIPTION

The IR3847 is a synchronous buck converter, providing a compact, high performance and flexible solution in a small 5mmx6mm QFN package.

Key features offered by the IR3847 include internal Digital Soft Start, precision 0.6V 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, true differential remote sensing and pre-bias start-up.

A thermally compensated output over-current protection function is implemented by sensing the voltage developed across the on-resistance of the synchronous rectifier MOSFET for optimum cost and performance.

This user guide contains the schematic and bill of materials for the IR3847 evaluation board. The guide describes operation and use of the evaluation board itself. Detailed application information for IR3847 is available in the IR3847 data sheet.

BOARD FEATURES

• V

= +12V (+ 13.2V Max), No Vcc required.

in

= +1.2V @ 0-25A

• V

out

• F

=600kHz

s

• L= 0.215uH

• C

= 7x22uF (ceramic 1206) + 1x330uF (electrolytic)

in

• C

=10x47uF (ceramic 0805)

out

4/11/2013

1

IRDC3847-P1V2

CONNECTIONS and OPERATING INSTRUCTIONS

A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 25A load should be connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I.

IR3847 needs only one input supply and internal LDO generates Vcc from Vin. If operation with external Vcc is required, then R33 should be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vin pin and Vcc pins should be shorted together for external Vcc operation by installing R35.

The board is configured for remote sensing. If local sense is desired, R8 should be uninstalled and R16 should be installed instead.

External Enable signal can be applied to the board via exposed Enable pad and R18 should be removed for

this purpose.

Table I. Connections

Connection Signal Name

VIN+ Vin (+12V)

VIN- Ground of Vin

Vout+ Vout(+1.2V)

Vout- Ground for Vout

Vcc+ Vcc Pin

Vcc- Ground for Vcc input

Enable Enable

PGood Power Good Signal

AGnd Analog ground

LAYOUT

The PCB is a 6-layer board. All of layers are 2 Oz. copper. The IR3847 and most of the passive components are mounted on the top side of the board.

Power supply decoupling capacitors and feedback components are located close to IR3847. The feedback resistors are connected to the output of the remote sense amplifier of the IR3847 and are located close to the IR3847. To improve efficiency, the circuit board is designed to minimize the length

of the on-board power ground current path. Separate power ground and analog ground are used and may be connected together using a 0 ohm resistor at one of three possible locations. It is preferred to use one of R43 or R44.

4/11/2013

2

IRDC3847-P1V2

CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUT

The PCB is a 6-layer board. All of layers are 2 Oz. copper. The IR3847 and most of the passive components are mounted on the top side of the board.

Power supply decoupling capacitors and feedback components are located close to IR3847. The feedback resistors are connected to the output of the remote sense amplifier of the IR3847 and are located close to the IR3847. To improve efficiency, the circuit board is designed to minimize the length

of the on-board power ground current path. Separate power ground and analog ground are used and may be connected together using a 0 ohm resistor at one of three possible locations. It is preferred to use one of R43 or R44.

Vin

Gnd

Vo

Top View

4/11/2013

3

IRDC3847-P1V2

Vout+

Vout-

123456

C51

N/S

C14

N/S

Boot

FB

SWs

0

0.1uF

8

Vcc+

VCC

Vout

C15

C16

C17

C18

C19

C20

C27

C28

C29

C30

C33

L1

1

22

SW21SW23SW20SW24SW

Vcc18Comp

1

0.1uF

47uF

N/S

10 x 47uF / 0805 / 6.3V Ceramic

N/S

0.1uF

R15

4.22K

Vsns

215nH PCDC1008-R215EMO

R32

4.22K

32

25

6

SW

IR3847

Rt/Sync

OCSelec t

PGD

4

5

16

19

Rt/Sync

PGD

10K

R29

R17 10K

2 3

PG_PU

OCSelect

Vin-

Vin+

123456

R30

R31

0 ohm

PVin

C1

330uF

+

C2

22uF

C3

22uF

C4

22uF

C5

22uF

C6

22uF

C7

22uF

C24

0.1uF

C31

N/S

7 x 22uF / 1206 / 25V Ceramic 25V 330uF

C32

N/S

C56

N/S

C55

N/S

0

R33

R35

N/S

VCC

R18 49.9K

1

Enable

7.5K

R19

R8

R20

N/S

C38

C39

1uF

R28

C25

0.1uF

C37

26

2

C57

22uF

PGnd PVin

Vin

1

Vin

17

Enable

3

Vp

15

Vp

RSo

U3

7

9

C26

8.2nF

0

160pF

C11

R1

1.91K

+

C34

N/S

+

C36

N/S

+

C35

N/S

+

C22

47uF

C21

47uF

C41

N/S

C40

N/S

C43

N/S

C42

N/S

C44

N/S

C45

N/S

Vo_R_N

Vo_R_P

Vout

0

R10

N/S

R11

R12

C50

N/S

13

RS-

RS+

Vsns

12

PGnd

29

PGnd

27

PGnd

10

LGnd

11

Vref

14

NC128NC230NC331NC433NC0

R9

39.2K

1

N/S

C68

4pin jumper

4

C66

10uF

1

R16

20

R6

0

C8

2200pF

R2

R4

127

Fb

R3

Vref

1

Agnd

Vcc-

0

N/S

R43

R44

N/S

BODE

JUMPER 2

C54

N/S

Vsns

4.22K N/S

R21

4.22K

Single point of connection between Power

Ground and Signal ( “analog” ) Ground

Fig. 1: Schematic of the IR3847 evaluation board

1

VDDQ

N/S

R40

Vref

1

Vref

C10

100pF

4/11/2013

Fb

N/S

PGD

1

Vp

N/S

R41

N/S

C9

PGood

Vp

1

Vp

PG_PU

1

PG_Pullup

D3

N/S

Sync

Rt/Sync

12

1

Sync

Vout

D2

N/S

1 2 1

VPB

R27

N/S

Optional "1-bit VID" circuit

N/S

M3

C52

R26

N/S

1

Optional Pre-Bias test circuit

Vout_Adj

4

Schematic for Transient Load set up

Vout

VCC

IRDC3847-P1V2

ExtLoadC trl

1

R39 N/S

R36 N/S

C49 N/S

3

S3 SW

2 1

N/S

C46

R53

N/S

R37 N/S

100

R54

U2

1

VS

2

IN

OUT2

3

OUT1

N/A GND4GND

MIC4452/SO8 N /S

8

VS

7 6 5

Optional transient load circuit

D7

ZHC S350

D6

ZHCS350

M1

IRF 6721 N/S

C48 N/S

1

R38 N/S

R22

N/S

R23

N/S

R24

N/S

R25

N/S

I-Monitor

C47 N/S

C58 N/S

C59 N/S

Vo_R_N

Vo_R_P

Vout

C60 N/S

C61 N/S

C62 22uF

C65 N/S

C64 N/S

C63 N/S

4/11/2013

5

IRDC3847-P1V2

Bill of Materials

Item Quantity Part Reference Value Description Manufacturer Part Number

17

2 1 C1 330uF

36

4 1 C8 2200pF 2200pF,0603,50V,X7R Murata GRM188R71H222KA01D 5 1 C11 160pF 50V, 0603, NP0, 5% Murata GRM1885C1H161JA01D

6

7 1 C26 8.2nF 0603, 50V, X7R, 10% Murata GRM188R71H822KA01D 8 1 L1 0.215uH 0.215uH, DCR=0.29mohm Cyntec PCDC1008-R215EMO

9 1 R1 1.91K 0603,1/10W,1% Panasonic ERJ-3EKF1911V 10 1 R2 4.22K 0603,1/10W,1% Panasonic ERJ-3EKF4221V 11 1 R3 4.22K 0603,1/10W,1% Panasonic ERJ-3EKF4221V 12 1 R4 127 0603,1/10W,1% Panasonic ERJ-3EKF1270V 13 1 R6 20 0603,1/10 W,1% Vishay/Dale CRCW060320R0FKEA 14 1 R9 39.2K 0603,1/10 W,1% Panasonic ERJ-3EKF3922V

15 7

16 1 17 1 18 2 R15 R32 4.22K 0603,1/10 W,1% Panasonic ERJ-3EKF4221V 19 2 R30 R31 0 1206,1/4 W, 5% Yageo RC1206JR-070RL 20 1 R18 49.9K 0603,1/10 W,1% Panasonic ERJ-3EKF4992V 21 1 R19 7.5K 0603,1/10 W,1% Panasonic ERJ-3EKF7501V 22 2 R17 R29 10K 0603,1/10 W,1% Panasonic ERJ-3EKF1002V

23 1 Jumper

24 2 Vin+ Vout+ RED SCREW TERMINAL Keystone Electronics 8199-2 25 2 Vin- Vout- BLACK SCREW TERMINAL Keystone Electronics 8199-3 26 1 U1 IR3847 IR3847 5mm X6mm International Rectifier IR3847MPBF

C2 C3 C4 C5 C6 C7

C9 C14 C24 C25

C37 C33

C16 C17 C18 C19

10

C20 C27 C28 C29

C30 C36

R8 R28 R10 R11

R44 R33 R34

C57

C39 1uF 0603, X5R, 25V, 20% TDK C66 10uF 0603, X5R, 10V, 20% TDK

22uF 1206, 25V, X5R, 10% Murata GRM31CR61E226KE15L

SMD Elecrolytic, Fsize, 25V,

20%

0.1uF 0603, 25V, X7R, 10% Murata GRM188R71E104KA01D

47uF 0805, 6.3V, X5R, 20% TDK

0 0603,1/10 W,5% Vishay/Dale CRCW06030000Z0EA

PLUG 40 POS DBL ROW

STR

Panasonic EEV-FK1E331P

Omron Electronics Inc. XG8W-4041-ND

C2012X5R0J476M

C1608X5R1E105M C1608X5R1A106M

4/11/2013

6

IRDC3847-P1V2

TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow

Fig. 2: Start up at 25A Load

Ch

, Ch2:Vo, Ch3:PGood, Ch4:Enable

1:Vin

Fig. 4: Start up with 1.08V Pre Bias, 0A Load

Ch

:Enable, Ch2:Vout, Ch3:PGood

1

Fig. 3: Start up at 25A Load

Ch

, Ch2:Vo, Ch3:PGood,Ch4:V

1:Vin

cc

Fig. 5: Output Voltage Ripple, 25A load

Ch

: Vout

1

Fig. 6: Inductor node at 25A load

Ch

:LX

2

4/11/2013

Fig. 7: Short (Hiccup) Recovery

Ch

:Vout , Ch3:PGood, Ch4:Iout

2

7

IRDC3847-P1V2

TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=2.5A-12.5A, Fsw=600kHz, Room Temperature, No air flow

Fig. 8: Transient Response, 2.5A to 12.5A step (2.5A/us)

4/11/2013

:Vout, Ch4:Iout(10A/V)

Ch

2

8

IRDC3847-P1V2

TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=15A-25A, Fsw=600kHz, Room Temperature, No air flow

Fig. 9: Transient Response, 15A to 25A step (2.5A/us)

4/11/2013

:Vout, Ch4:Iout(10A/V)

Ch

2

9

IRDC3847-P1V2

TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow

4/11/2013

Fig. 10: Bode Plot at 25A load: Fo = 108.0kHz; Phase Margin = 50.2º

10

IRDC3847-P1V2

TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow

92 90 88 86 84 82 80 78

Efficiency [%]

76 74 72 70

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Io [A]

Fig.11: Efficiency versus load current

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

Power Loss [W]

1.0

0.5

0.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Io [A]

Fig.12: Power loss versus load current

4/11/2013

11

IRDC3847-P1V2

THERMAL IMAGES Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow

Fig. 13: Thermal Image of the board at 25A load

4/11/2013

Test point 1 is IR3847: 75

Test point 2 is inductor: 61.5

0

C

0

C

12

IRDC3847-P1V2

IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105

4/11/2013

TAC Fax: (310) 252-7903

Visit us at www.irf.com for sales contact information

Data and specifications subject to change without notice. 10/11

13