International Rectifier IR3847 User manual

IRDC3847-P1V2
4/11/2013 1
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
•Vin = +12V (+ 13.2V Max), No Vcc required.
•Vout = +1.2V @ 0-25A
•Fs=600kHz
•L= 0.215uH
•Cin= 7x22uF (ceramic 1206) + 1x330uF (electrolytic)
•Cout=10x47uF (ceramic 0805)
SupIRBuckTM

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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.
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.
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

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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 Vo
Gnd Gnd
Top View

IRDC3847-P1V2
Vref
C21 47uF
C22 47uF
C14
0.1uF
R40
N/S
Vref
M3
N/S
R41
N/S
BODE
JUMPER 2
L1
215nH PCDC1008-R215EMO
R44
0
Vp
Vout+
123456
R10
0
C50
N/S
Optional "1-bit VID" circuit
OCSelect
4pin jumper
1
2 3 4
Fb
Vref
1
Vout
PG_PU
Optional Pre-Bias test circuit
C38
N/S
C54
N/S
Sy nc
C40 N/S
C41 N/S
C25
0.1uF
C42 N/S
C43 N/S
Vp
R28
0
C26 8.2nF
VPB
1
R21
N/S
R19
7.5K
C44 N/S
C45 N/S
SWs
1
C66
10uF
C5 22uF
R1
1.91K
C3 22uF
R16
N/S
R4 127
PGD
R2
4.22K
C15 47uF
C4 22uF
R6
20
R31 0 ohm
C16 47uF
R8
0
C17 47uF
C18 47uF
+
C35
N/S
R30
0 ohm
C19 47uF
PGD
C20 47uF
C31 N/S
Vsns
C55 N/S
C32 N/S
C56 N/S
C39
1uF
C10 100pF
C6 22uF
7 x 22uF / 1206 / 25V Ceramic 25V 330uF
10 x 47uF / 0805 / 6.3V Ceramic
R35
N/S
R32 4.22K
+
C36
N/S
Vcc-
1
+
C34
N/S
D2
N/S
1 2
+
C51
N/S
D3 N/S
12
PVin
Vsns
R18 49.9K
+
C1 330uF
R29 10K
R33
0
C27
47uF
C8
2200pF
U3
IR3847
Vin 17
LGnd
11
Rt/Sync
4
SW 22
Vcc
18
Comp
8
Vsns 6
PGnd 26
OCSelec t
5
FB
7Boot 2
PGD
16
PVin 1
PGnd
10
RS-
12
RS+ 13
RSo
9
SW 21 SW 23 SW 20 SW 24 SW 32
Vref
14 Vp 15
Enable 3
PGnd
27
PGnd
29
SW 25
NC1
28
NC2
30
NC3
31
NC4
33
NC0
19
C24 0.1uF
Rt/Sy nc
R9
39.2K
C2
22uF
Rt/Sync
C9
N/S
R15
4.22K
Agnd
1
Vout
C28
47uF
R11
0
C29 N/S
R12
N/S
PG_PU
PG_Pullup
1
C30 N/S
Vo_R_P
R3
4.22K R43
N/S
VCC
Vout-
123456
Vcc+
1
Fb
PGood
1
Vout_Adj
1
C11 160pF
R26
N/S
Vo_R_N
R27
N/S
C52
N/S
C68
N/S
Vin
1
C7 22uF
R20
N/S
Vout
Sy nc
1
Enable
1
R17 10K
VCC
C37 0.1uF
Vp
Vin+
123456
Vin-
123456
Vp
1
C57
22uF
VDDQ
1
C33
0.1uF
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Fig. 1: Schematic of the IR3847 evaluation board
Single point of connection between Power
Ground and Signal ( “analog” ) Ground

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Schematic for Transient Load set up
Vout
N/S
R38
N/S
C65
N/S
C59
N/S
C58
N/S
C64
N/S
C46
N/S
R22
N/S
R23
N/S
R24
N/S
R25
N/S
ExtLoadCtrl
1
M1
IRF 6721 N/S
U2
MIC4452/SO8 N/S
VS
1
IN
2
GND
4GND 5
OUT1 6
OUT2 7
VS 8
N/A
3
R36
N/S
R37
N/S
S3
SW
2 1
3
C47
N/S
C49
N/S
R39
N/S
Vout
C48
N/S
C63
N/S
Vo_R_P
D6
ZHCS350
D7
ZH CS350
R53
100
R54
100
Vo_R_N
Optional transient load circuit
VCC
I-Monitor
1
C60
N/S
C61
N/S
C62
22uF

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Bill of Materials
Item Quantity Part Reference Value Description Manufacturer Part Number
17
C2 C3 C4 C5 C6 C7
C57 22uF 1206, 25V, X5R, 10% Murata GRM31CR61E226KE15L
2 1 C1 330uF SMD Elecrolytic, Fsize, 25V,
20% Panasonic EEV-FK1E331P
36
C9 C14 C24 C25
C37 C33 0.1uF 0603, 25V, X7R, 10% Murata GRM188R71E104KA01D
4 1 C8 2200pF 2200pF,0603,50V,X7R Murata GRM188R71H222KA01D
5 1 C11 160pF 50V, 0603, NP0, 5% Murata GRM1885C1H161JA01D
610
C16 C17 C18 C19
C20 C27 C28 C29
C30 C36
47uF 0805, 6.3V, X5R, 20% TDK C2012X5R0J476M
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 R8 R28 R10 R11
R44 R33 R34 0 0603,1/10 W,5% Vishay/Dale CRCW06030000Z0EA
16 1 C39 1uF 0603, X5R, 25V, 20% TDK C1608X5R1E105M
17 1 C66 10uF 0603, X5R, 10V, 20% TDK C1608X5R1A106M
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 PLUG 40 POS DBL ROW
STR Omron Electronics Inc. XG8W-4041-ND
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

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TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow
Fig. 6: Inductor node at 25A load
Ch2:LX
Fig. 3: Start up at 25A Load
Ch1:Vin, Ch2:Vo, Ch3:PGood,Ch4:Vcc
Fig. 2: Start up at 25A Load
Ch1:Vin, Ch2:Vo, Ch3:PGood, Ch4:Enable
Fig. 4: Start up with 1.08V Pre Bias, 0A Load
Ch1:Enable, Ch2:Vout, Ch3:PGood
Fig. 7: Short (Hiccup) Recovery
Ch2:Vout , Ch3:PGood, Ch4:Iout
Fig. 5: Output Voltage Ripple, 25A load
Ch1: Vout

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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)
Ch2:Vout, Ch4:Iout(10A/V)

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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)
Ch2:Vout, Ch4:Iout(10A/V)

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TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow
Fig. 10: Bode Plot at 25A load: Fo = 108.0kHz; Phase Margin = 50.2º

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Fig.12: Power loss versus load current
Fig.11: Efficiency versus load current
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V, Io=0A-25A, Fsw=600kHz, Room Temperature, No air flow
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
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
Power Loss [W]
Io [A]
70
72
74
76
78
80
82
84
86
88
90
92
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
Efficiency [%]
Io [A]

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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
Test point 1 is IR3847: 750C
Test point 2 is inductor: 61.50C

IRDC3847-P1V2
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IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: [phone]
TAC Fax: [phone]
Visit us at www.irf.com for sales contact information
Data and specifications subject to change without notice. 10/11