IRDC3856 SupIRBuck TM USER GUIDE FOR IR3856 EVALUATION BOARD DESCRIPTION The IR3856 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 IR3856 include programmable soft-start ramp, precision 0.7V reference voltage, Power Good, thermal protection, over voltage protection, programmable switching frequency, synchronization to external clock, 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 IR3856 evaluation board. The guide describes operation and use of the evaluation board itself. Detailed application information for IR3856 is available in the IR3856 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= 3x10uF (ceramic 1206) + 330uF (electrolytic) • Cout= 4x22uF (ceramic 0805) 07/21/10 1 IRDC3856 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. IR3856 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-. If single 12V application is required connect R7 (zero Ohm resistor) which enables the on board bias regulator (see schematic). In this case there is no need of external Vcc supply. 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. The value of R14 and R28 can be selected to provide the desired ratio between the output voltage and the tracking input. For proper operation of IR3856, the voltage at Seq. pin should not exceed 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 PGood Power Good Signal SYNC External Synchronization Clock LAYOUT The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3856 SupIRBuck and all of the passive components are mounted on the top side of the board. Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located close to IR3856. 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. 07/21/10 2 IRDC3856 Connection Diagram Vin GND Enable GND Seq AGND Vout SS Vcc GND PGood Syc. Fig. 1: Connection diagram of IR385x evaluation boards 07/21/10 3 IRDC3856 Fig. 2: Board layout, top overlay Single point connection between AGND and PGND. Fig. 3: Board layout, bottom overlay (rear view) 07/21/10 4 IRDC3856 Fig. 4: Board layout, mid-layer I. Fig. 5: Board layout, mid-layer II. 07/21/10 5 1 PGood 1 1 R17 10K R9 23.7K R1 1.65k SS C12 0.01uF C10 0.1uF Sy nc 6 5 8 3 1 U1 SS Rt PGood COMP FB Vsns seq 2.55k R3 4.02k R7 4.02K 130 R2 PGnd Vcc OCset R4 IR3856 SW Vin 0.1uF C24 49.9K R18 11 10 7 SW PGND B 0 R50 C5 N/S L1 1.0uH C7 0.1uF C4 10uF R11 N/S N/S Vin C22 N/S Ground and Signal ( “analog” ) Ground D1 MM3Z5V6B Vcc N/S N/S N/S Q1 MMBT3904-TP + C36 + C35 C20 C14 0.1uF 1 1 1 1 Optional +5V supply for Vcc C32 0.1uF R8 3.30K N/S C21 C15 22uF C16 Vout 22uF Vin- Vin- Vin+ Vin+ C17 1 1 1 1 22uF 22uF 330uF C1 Vin C18 C2 + 10uF C23 C3 10uF Single point of connection between Power A C8 2200pF R6 20 2.74k C19 1uF VCC R12 12 N262216 13 0 R10 Fig. 6: Schematic of the IR3856 evaluation board R5 2.55k 10000pF 270pF C26 C11 2 16 R19 N/S 7.5k C37 1 15 Enable 1 1 Vcc+ VCC 1 Vcc- R28 N/S 1 AGnd1 4 Sync 9 14 Boot Enable 17 AGnd2 R16 0 1 R14 N/S 1 1 VCC 1 Seq. 2 07/21/10 1 AGND C34 10uF Vout- Vout+ Vout- Vout+ IRDC3856 6 IRDC3856 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 21 22 23 24 25 26 1 3 1 1 1 5 1 1 4 1 1 1 1 1 1 1 1 1 3 1 2 1 1 1 2 1 C1 C4 C3 C2 C34 C19 C12 C7 C10 C14 C24 C32 C8 C11 C15 C16 C17 C18 C26 D1 L1 Q1 R8 R18 R4 R6 R9 R16 R10 R50 R12 R3 R5 R17 R19 R1 R2 R7 U1 07/21/10 Value Description Manufacturer Part Number 330uF 10uF 10uF 1uF 0.01uF 0.1uF 2200pF 270pF 22uF 10000pF MM3Z5V6B 1.0uH MMBT3904/SOT 3.3k 49.9k 130 20 23.7k 0 2.74k 2.55k 10.0k 7.50k 1.65k 4.02k IR3856 SMD Elecrolytic, Fsize, 25V, 20% 1206, 25V, X5R, 20% 0805, 10V, X5R, 20% 0603, 16V, X7R, 10% 0603, 50V, X7R, 10% 0603, 25V, X7R, 10% 0603, 50V, NP0, 5% 0603, 50V, NP0, 5% 0805, 6.3V, X5R, 20% 0603, 25V, X7R, 10% MM3Z5V6B,Zener, 5.6V 6.9x6.5x5mm, 20%, 4.7mOhm NPN, 40V, 200mA, SOT-23 Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10 W,1% Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10 W,5% Thick Film, 0603,1/10 W,1% Thick Film, 0603,1/10 W,1% Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10W,1% Thick Film, 0603,1/10W,1% PQFN 4mmx5mm, 6A SupIRBuck Panasonic Murata TDK TDK TDK TDK Murata Murata TDK TDK Fairchild TDK Fairchild Rohm Rohm Panasonic - ECG Vishey/Dale Rohm Vishay/Dale Rohm Rohm Rohm Rohm Rohm Rohm International Rectifier EEV-FK1E331P GRM31CR61E106MA12L C2012X5R1A106KB C1608X7R1C105K C1608X7R1H103K C1608X7R1H104KB GRM1885C1H222JA01D GRM1885C1H271JA01D C2012X5R0J226M C1608X7R1E103K MM3Z5V6B SPM6550T-1R0M100A MMBT3904/SOT MCR03EZPFX3301 MCR03EZPFX4992 ERJ-3EKF1300V CRCW060320R0FKEA MCR03EZPFX2372 CRCW06030000Z0EA MCR03EZPFX2741 MCR03EZPFX2551 MCR03EZPFX1002 MCR03EZPFX7501 MCR03EZPFX1651 MCR03EZPFX4021 IR3856MPbF 7 IRDC3856 TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vcc=5V, Vo=1.8V, Io=0-6A, Room Temperature, No Air Flow Fig. 7. Start up at 6A Load Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:Enable Fig. 8. Start up at 6A Load, Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:VPGood Fig. 9. Start up with 1.62V Pre Bias, 0A Load, Ch2:Vo, Ch3:VSS Fig. 10. Output Voltage Ripple, 6A load Ch1: Vo Fig. 11. Inductor node at 6A load Ch1:LX Fig. 12. Short (Hiccup) Recovery Ch2:Vo , Ch3:VSS 07/21/10 8 IRDC3856 TYPICAL OPERATING WAVEFORMS Vin=12V, Vcc=5V, Vo=1.8V, Io=0-6A, Room Temperature, No Air Flow Fig. 13. Transient Response, 3A to 6A step 2.5A/μs Ch2:Vo, Ch4:Io 07/21/10 9 IRDC3856 TYPICAL OPERATING WAVEFORMS Vin=12V, Vcc=5V, Vo=1.8V, Io=6A, Room Temperature, No Air Flow Fig. 14. Bode Plot at 6A load shows a bandwidth of 106kHz and phase margin of 57 degrees and gain margin of 12db at 342kHz Fig. 15. Synchronization to External Clock Ch2: SW node Signal, Ch3: Sync. Pin 07/21/10 10 IRDC3856 TYPICAL OPERATING WAVEFORMS Vin=12V, Vo=1.8V, Io=0- 6A, Room Temperature, No Air Flow 93 92 Efficiency (%) 91 90 89 88 87 86 10 20 30 40 50 60 70 Load Percentage (%) 80 90 100 80 90 100 Fig.16: Efficiency versus load current 1.3 1.2 1.1 Power Loss (W) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 10 20 30 40 50 60 70 Load Percentage(%) Fig.17: Power loss versus load current 07/21/10 11 IRDC3856 THERMAL IMAGES Vin=12V, Vo=1.8V, Io=6A, Room Temperature, No Air Flow Fig. 18: Thermal Image at 6A load Test points 1 and 2 are IR3856 and inductor, respectively. 07/21/10 12 IRDC3856 Simultaneous Tracking at Power Up and Power Down Vin=12V, Vo=1.8V, Io=6A, Room Temperature, No Air Flow In order to run the IR3856 in the simultaneous tracking mode, the following steps should be taken: - Remove R16 from the board. - Set the value of R14 and R28 as R2 (4.02K) and R3 (2.55K), respectively. - Connect the controlling input across SEQ and AGND test points on the board. This voltage should be at least 1.15 time greater than Vo. For the following test results a 0-3.3V source is applied to SEQ input. - The controlling input should be applied after the SS pin is clamped to 3.0V. Fig. 19: Simultaneous Tracking a 3.3V input at power-up and shut-down Ch1: SS (1.8V) Ch2:Vout (1.8V) Ch3: SEQ (3.3V) 07/21/10 13 IRDC3856 PCB Metal and Components Placement 07/21/10 IRDC3856 Solder Resist 07/21/10 IRDC3856 Stencil Design 07/21/10 IRDC3856 IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 This product has been designed and qualified for the Consumer market Visit us at www.irf.com for sales contact information Data and specifications subject to change without notice. 06/10 07/21/10