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IRDC3856W
SupIRBuck
DESCRIPTION
TM
USER GUIDE FOR IR3856W Dual Sided EVALUATION BOARD
The IR3856W is a synchronous buck converter, providing a compact, high performance and flexible solution in a small 4mmx5mm Power QFN package. Key features offered by the IR3856W include programmable soft-start ramp, precision 0.7V reference voltage, Power Good, thermal protection, programmable switching frequency, Sequence input, Enable input, input under-voltage lockout for proper start-up, and pre-bias start-up.
An 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 IR3856W evaluation board. The guide describes operation and use of the evaluation board itself. Detailed application information for IR3856W is available in the IR3856W data sheet.
BOARD FEATURES * Vin = +12V (+ 13.2V Max) * Vcc=+5V (5.5V Max) * Vout = +1.8V @ 0- 6A * Fs=600kHz * L= 1.0uH * Cin= 2x10uF (ceramic 1206) * Cout= 4x22uF (ceramic 0805) * Small footprint of design (16mmx8mm)
Rev 0.0 08/10/2009
1
IRDC3856W
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 6A load should be connected to VOUT+ and VOUT-. The connection diagram is shown in Fig. 1 and inputs and outputs of the board are listed in Table I. IR3856W has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). Separate supplies should be applied to these inputs. Vcc input should be a well regulated 4.5V-5.5V supply and it would be connected to Vcc+ and Vcc-. The output can track a sequencing input at the start-up. For sequencing application, R16 should be removed and the external sequencing source should be applied between Seq. and Agnd.. External Enable signal can be applied to the board via exposed Enable pad and R18 should be removed for this purpose, For proper operation of IR3856W, the voltage at Seq. and Enable should always be kept below Vcc. Table I. Connections
Connection VIN+ VINVcc+ VccVOUTVOUT+ Enable Seq. P_Good Signal Name Vin (+12V) Ground of Vin Vcc input Ground for Vcc input Ground of Vout Vout (+1.8V) Enable Sequence Input Power Good Signal
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3856W SupIRBuck and input capacitors and some of the passive components are mounted on the top side of the board. The output caps, inductor, and the rest of passive components are located on the bottom side of the board. The total footprint of the design is 16mmx8mm, which is very compact. Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located close to IR3856W. The feedback resistors are connected to the output voltage at the point of regulation and are located close to the SupIRBuck. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. Rev 0.0 08/10/2009
2
IRDC3856W
Connection Diagram
GND
Vcc
SS
GND
GND
Vin
Vo
Seq AGND Enable Top View
PGood
Vin
Vo
GND
GND
Rear View
Fig. 1: Connection diagram of IR3856W evaluation board Rev 0.0 08/10/2009
3
Enable 1 R18 1 R19 7.50 1 Vin49.9K C2 10uF C7 0.1uF C3 10uF Vin+
Vin (+12V)
1
1
1
R1 16 Boot seq Vin SW 12 7 10 11 C19 1uF VCC 2.8k L1 1.0uH R12 13 FB COMP PGood OCset Rt PVcc SS Vcc PGnd AGnd1 AGnd2 Enable 1 3 8 5 SS 2 9 4 17 1 6 2.05K
C26 10nF U1 15 14
1
1
R3 2.55k
A
1
Rev 0.0 08/10/2009
C11 220pF 0.1uF C24 Vout (+1.8V)
VCC
Seq.
R16 0
Vcc-
Vcc+
VCC
PGood
R17 10.0K
IR3856W
1 C18 22uF C17 22uF C16 C15 22uF 22uF C14 0.1uF 1
Vout+
Vout-
R9 23.7K C10 0.1uF C13 1uF
NC VCC
R4 130 R2 4.02K
C8 2200pF
R6 20
B
R? 0
Single point of connection between Power Ground and Signal ( "analog" ) Ground
IRDC3856W
Fig. 2: Schematic of the IR3856W evaluation board
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IRDC3856W
Bill of Materials
Item Quantity Part Reference Value Description Manufacturer Part Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
2 4 1 1 4 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1
C2, C3 C7 C14 C24 C10 C8 C11 C15 C16 C17 C18 C26 C13 C19 L1 R2 R3 R4 R6 R9 R16 R17 R18 R19 U1 R1 R12
10uF 0.1uF 2200pF 220pF 22uF 10000pF 1uF 1.0uH 4.02K 2.55K 130 20 23.7k 0 10.0k 49.9k 7.50k IR3856W 2.05k 2.8k
1206, 16V, X5R, 20% 0603, 25V, X7R, 10% 0603, 50V, X7R, 10% 50V, 0603, NP0, 5% 0805, 6.3V, X5R, 20% 0603, 50V, X7R, 10% 0603, 10V, X5R, 10% 7.0mmx6.6mmx4.8mm, 5.6mOhm, 20% 0603,1/10W,1% 0603,1/10W,1% 0603,1/10W,1% 0603,1/10 W,1% 0603,1/10W,1% 0603,1/10 W,5% 0603,1/10 W,1% 0603,1/10 W,1% 0603,1/10W,1% PQFN 4x5mm, 6A, SupIRBuck 0603,1/10W,1% 0603,1/10W,1%
Panasonic - ECG Panasonic - ECG Panasonic - ECG Murata Panasonic - ECG Panasonic - ECG Panasonic - ECG Cyntec Rohm Rohm Panasonic - ECG Vishey/Dale Rohm Vishay/Dale Rohm Rohm Rohm International Rectifier Rohm Rohm
ECJ-3YB1C106M ECJ-1VB1E104K ECJ-2VB2D222K GRM1885C1H221JA01D ECJ-2FB0J226M ECJ-1VB1H103K ECJ-BVB1A105K PCMB065T-1R0MS MCR03EZPFX4021 MCR03EZPFX2551 ERJ-3EKF1300V CRCW060320R0FKEA MCR03EZPFX2372 CRCW06030000Z0EA MCR03EZPFX1002 MCR03EZPFX4992 MCR03EZPFX7501 IR3856WMPbF MCR03EZPFX2051 MCR03EZPFX2801
Rev 0.0 08/10/2009
5
IRDC3856W
TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vcc=5V, Vo=1.8V, Io=0-6A, Room Temperature, No Air Flow
Fig. 3: Start up at 6A Load Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:Enable
Fig. 4: Start up at 6A Load, Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:VPGood
Fig. 5: Start up with Pre Bias, 0A Load, Ch2:Vo, Ch3:VSS
Fig. 6: Output Voltage Ripple, 6A load Ch3: Vout ,
Fig. 7: Inductor node at 6A load Ch3:LX
Fig. 8: Short (Hiccup) Recovery Ch2:Vout , Ch3:Vss
Rev 0.0 08/10/2009
6
IRDC3856W
TYPICAL OPERATING WAVEFORMS Vin=12V, Vcc=5V, Vo=1.8V, Io=0-6A, Room Temperature, No Air Flow
Fig. 9: Transient Response, 3A to 6A step (2.5A/us) Ch3:Vout, Ch4:Iout
Rev 0.0 08/10/2009
7
IRDC3856W
TYPICAL OPERATING WAVEFORMS Vin=12V, Vcc=5V, Vo=1.8V, Io=6A, Room Temperature, No Air Flow
Fig. 10: Bode Plot at 6A load shows a bandwidth of 104kHz and phase margin of 54 degrees
Rev 0.0 08/10/2009
8
IRDC3856W
TYPICAL OPERATING WAVEFORMS Vin=12V, Vo=1.8V, Io=0- 6A, Room Temperature, No Air Flow
92.0
91.5
Efficiency (%)
91.0
90.5
90.0
89.5
89.0 20 30 40 50 60 70 80 90 100 Load Percentage (%)
Fig.11: Efficiency versus load current
1.35 1.25 1.15 1.05 Power Loss (W) 0.95 0.85 0.75 0.65 0.55 0.45 0.35 0.25 20 30 40 50 60 70 80 90 100 Load Percentage(%)
Fig.12: Power loss versus load current
Rev 0.0 08/10/2009
9
IRDC3856W
THERMAL IMAGES Vin=12V, Vo=1.8V, Io=6A, Room Temperature, No Air Flow
Fig. 13: Thermal Image of Top side of the board at 6A load Test points 1 is IR3856W
Fig. 14: Thermal Image of Rear side of the board at 6A load Test points 1 is Inductor Rev 0.0 08/10/2009
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