IRDC3847-P1V2
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This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 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=1000kHz
•L= 0. 15uH
•Cin= 5x22uF (ceramic 1206) + 1x330uF (electrolytic)
•Cout=7x22uF (ceramic 0805)
SupIRBuckTM
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 2
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.
This version of the demoboard was built with a previous revision of the IR3847 for which Vp was pin 14 and
Vref was pin 15. However, in the new revision, these pins have been interchanged in order to allow easier
bypass of the Vref pin. The consequence of this is that the Vp input on the board should be considered Vref
and the Vref input on the board should be considered Vp.
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
Table I. Connections
Connection Signal Name
VIN+ Vin (+12V)
VIN- Ground of Vin
Vout+ Vout(+1.2V)
Vout- Ground for Vout
Vcc+ Vcc Pi n
Vcc- Ground for Vcc input
Enable Enable
PGood Power Good Signal
AGnd Analog ground
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 3
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
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This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 4
Fig. 1: Schematic of the IR3847 evaluation board
Single point of connection between Power
Ground and Signal ( “analog” ) Ground
Vp C21
N/S
C22
N/S
C14
0.1uF
Vref
R40
N/S
PGD Vo
Vo
M3
N/S
R41
N/S
BODE
J U MPER 2
L1
150nH PCDC1008-R15EMO
R14 N/S
R44 0
Vout+
1
Vref
C50
N/S
R10
0
Optional "1-bit VID" circuit
OCSelect
4pin jumper
1
2 3
4
Fb
Vref
1
Vout
PGDPU
Optional Pre-Bias test circuit
C38
N/S
Sctrl
1
C54
N/S
Sync
C40
N/S
C41
N/S
C25
0.1uF
C42
N/S
C43
N/S
Vp
R28
0
C26
10nF
VPB
1
R21
N/S
R19
39.2K
C44
N/S
C45
N/S
SWs
1
C66
10uF
C5
22uF
R1
1K
C3
22uF
R16
N/S
R4
84.5
R2
2.67K
C4
22uF
C15
22uF
R6
20
C16
22uF
R31
0 ohm
R8
0
C17
22uF
+
C35
N/S
C18
22uF
R30
0 ohm
C19
22uF
PGD
U1
IR3847
Vin 17
LGnd
11
Rt/Sync
4
SW 22
Vcc
18 Comp
8
Vsns 6
PGnd 26
OCSelect
5
FB
7
Boot 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
C20
22uF
Sctrl
C31
N/S
C55
N/S
Vsns
C32
N/S
C56
N/S
C39
1uF
C10
N/S
C6
N/S
Ceramic cap 16V 5X22uF 1206
6X22uF/805/6.3V+1X22uF/805/6.3V (transient schematic)
25V 330uF
PGD
JU MPER 2
R35
N/S
R32
23.2K
Vcc-
1
+
C36
N/S
R29 N/S
+
C34
N/S
N/S
Vo
D2
N/S
1 2
+
C51
N/S
Vref
D3
N/S
12
PVin
Vsns
R18
49.9K
+
C1
330uF
R33
0
C27
N/S
C8
2200pF
R34
0
C24
0.1uF
C53
N/S
Rt/Sync
R9
23.2K
C2
22uF
C9
100n
R15
23.2K
Agnd
1
C28
N/S
Vout
R11
0
C29
N/S
PGDPU
PGDPU
1
C30
N/S
Rt/Sync Vo_R_P
R3
2.61K
R43
N/S
VCC
Vout-
1
Vcc+
1
Fb
SW
PGood
1
Vout_Adj
1
C11
150pF
R26
N/S
R27
N/S
Vo_R_N
C52
N/S
C68
N/S
Vin
1
C7
N/S
R20
N/S
Vout
Sync
1
Enable
1
R17
10K
VCC
C37 0.1uF
Vp
PVin+
1
PVin-
1
Vp
1
VDDQ
1
C57
22uF
C33
0.1uF
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 5
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
R45
N/S
ExtLoadCtrl
1
M1
IR F6721 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
Vo_R_N
Optional transient load circuit
VCC
I-Monitor
1
C60
N/S C61
N/S C62
22uF
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 6
Bill of Materials
Item Quantity Part Reference Value Description Manufacturer Part Number
1 5C2 C3 C4 C5 C57 22uF 22uF,1206,16V, X5R, 20% Panasonic ECJ3YB1C226M
2 1C1 330uF SMD Elecrolytic, Fsize, 25V,
20% Panasonic EEV-FK1E331P
36
C9 C14 C24 C25
C37 C33 0.1uF 0603, 25V, X7R, 10% Panasonic ECJ-1VB1E104K
4 1C8 2200pF 2200pF,0603,50V,X7R Panasonic ECJ-1VB1H222K
5 1C11 150pF 50V, 0603, NP0, 5% Murata GRM1885C1H151JA01
D
6
7C15 C16 C17 C18
C19 C20 C62 22uF 0805, 6.3V, X5R, 20% TDK
C2012X5R0J226M
7 1 Vo Tektronix test connector Tektronix 131-5031-00
8 1C26 10nF 0603, 50V, X7R, 10% Panasonic ECJ-1VB1H103K
9 1L1 0.150uH 0.150uH, DCR=0.29mohm Cyntec PCDC1008-R150EMO
10 1R1 1K 0603,1/10W,1% Rohm MCR03EZPFX1001
11 1R2 2.67K 0603,1/10W,1% Rohm MCR03EZPFX2671
12 1R3 2.61K 0603,1/10W,1% Rohm MCR03EZPFX2611
13 1R4 84.5 0603,1/10W,1% Panasonic ERJ-3EKF84R5V
14 1R6 20 20,0603,1/10 W,1% Vishay/Dale CRCW060320R0FKEA
15 7R8 R28 R10 R11
R44 R33 R34 0 0,0603,1/10 W,5% Vishay/Dale CRCW06030000Z0EA
16 1C39 1uF 0603, X5R, 16V TDK C1608X5R1C105M
17 C66 10uF 0603, X5R, 10V TDK C1608X5R1A106M
18 2 R15 R32 23.2K 0603,1/10 W,1% Rohm MCR03EZPFX2322
19 2R30 R31 0 1206,1/4 W,5% Panasonic ERJ-8GEY0R00V
20 1R18 49.9K 49.9K,0603,1/10 W,1% Rohm MCR03EZPFX4992
21 1R19 39.2K 39.2K,0603,1/10W,1% Rohm MCR03EZPFX3922
22 1R9 23.2K 23.2K,0603,1/10W,1% Rohm MCR03EZPFX2322
23 1 R17 10K 0603,1/10 W,1% Rohm MCR03EZPFX1002
24 1U1 IR3847 IR3847 5mm X6mm International Rectifier IR3847
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 7
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V , Io=0A-25A, 1MHz, Room Temperature, no airflow
Fig. 5: Output Voltage Ripple, 25A load Ch1: Vout
Fig. 6: Inductor node at 25A load
Ch2:LX Fig. 7: Short (Hiccup) Recove ry
Ch2:Vout; Ch4=Io
Fig. 3: Start up at 25A Load,
Ch1:Vin, Ch2:Vo, Ch3:VPGood,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, Ch2:Vo,
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 8
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V , Io=2.5A-10 A, 1MHz, Room Temperature, no air flow
Fig. 8: Transient Response, 2.5A to 10A step (2.5A/us)
Ch2:Vout
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 9
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V , Io=17.5A-2 5A, 1MHz, Room Temperature, no air flow
Fig. 9: Transient Response, 17.5A to 25A step (2.5A/us)
Ch2:Vout
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 10
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vo=1.2V , Io=0A-25A, 1MHz, Room Temperature, No air flow
Fig. 10: Bode Plot at 25A load shows a bandwidth of 170kHz and phase margin of 51degrees
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 11
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, Room Temperature, no air flow
IRDC3847-P1V2
Confidential
This evaluation board is a preliminary version meant for the engineering evaluation of the IR3847. B ased on t he results of the
continuing evaluation, this board can evolve and change without notice
2/13/2012 12
THERMAL IMAGES
Vin=12.0V, Vo=1.2V , Io=0A-25A, 1MHz, Room Temperature, No airflow
Fig. 13: Thermal Image of the board at 25A load
Test point 1 is IR3847: 1030C
Test point 2 is inductor: 700C
