IRDC3856W SupIRBuck TM USER GUIDE FOR IR3856W Dual Sided EVALUATION BOARD DESCRIPTION The IR3856W is a synchronous buck converter, providing a compact, high performance and flexible solution in a small 4mmx5mm Power QFN package. 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. 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. 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 Signal Name VIN+ Vin (+12V) VIN- Ground of Vin Vcc+ Vcc input Vcc- Ground for Vcc input VOUT- Ground of Vout VOUT+ Vout (+1.8V) Enable Enable Seq. Sequence Input P_Good 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 Vo Vin Seq AGND Enable PGood Top View Vo Vin GND GND Rear View Fig. 1: Connection diagram of IR3856W evaluation board Rev 0.0 08/10/2009 3 PGood 1 R17 10.0K VCC 1 C26 10nF 23.7K R9 2.05K R1 C11 220pF SS C13 1uF PGnd PVcc 4.02K R2 R4 130 R3 2.55k SW OCset IR3856W Vin 49.9K R18 B R6 20 2.8k R12 C19 1uF C8 2200pF VCC A 11 10 7 12 13 0.1uF C24 C2 10uF R? 0 C3 10uF C18 22uF 1 1 C17 22uF Vin- Vin+ Vin (+12V) C15 22uF 22uF C16 1 C14 0.1uF 1 Vout- Vout+ Vout (+1.8V) Ground and Signal ( “analog” ) Ground Single point of connection between Power L1 1.0uH C7 0.1uF Fig. 2: Schematic of the IR3856W evaluation board C10 0.1uF SS Rt PGood COMP FB seq NC VCC 2 6 5 8 3 1 16 U1 Enable 1 1 1 AGnd1 4 Vcc+ R19 7.50 17 Vcc- R16 0 AGnd2 Seq. 1 15 Vcc 9 14 Boot Enable 1 Rev 0.0 08/10/2009 1 VCC IRDC3856W 4 IRDC3856W Bill of Materials Item Quantity Part Reference 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 Rev 0.0 08/10/2009 Value Description Manufacturer Part Number 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 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 Efficiency (%) 91.5 91.0 90.5 90.0 89.5 89.0 20 30 40 50 60 70 80 90 100 90 100 Load Percentage (%) Fig.11: Efficiency versus load current 1.35 1.25 1.15 Power Loss (W) 1.05 0.95 0.85 0.75 0.65 0.55 0.45 0.35 0.25 20 30 40 50 60 70 80 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 10