IRDC3897-P1V2 TM SupIRBuck USER GUIDE FOR IR3897 EVALUATION BOARD 1.2Vout DESCRIPTION Output over-current protection function is The IR3897 is a synchronous buck implemented by sensing the voltage developed converter, providing a compact, high across the on-resistance of the synchronous performance and flexible solution in a small Mosfet for optimum cost and performance and 4mm X 5 mm Power QFN package. the current limit is thermally compensated. Key features offered by the IR3897 include This user guide contains the schematic and bill internal Digital Soft Start/Soft Stop, precision of materials for the IR3897 evaluation board. 0.5Vreference voltage, Power Good, The guide describes operation and use of the thermal protection, programmable switching evaluation board itself. Detailed application frequency, Enable input, input under-voltage information for IR3897 is available in the lockout for proper start-up, enhanced line/ IR3897 data sheet. load regulation with feed forward, external frequency synchronization with smooth clocking, internal LDO and pre-bias start- up. BOARD FEATURES V = +12V (+ 13.2V Max) in V = +1.2V 0- 4A out F =600kHz s L= 1.5uH C = 2x10uF (ceramic 1206) + 1X330uF (electrolytic) in C =4x22uF (ceramic 0805) out 12/5/2012 1IRDC3897-P1V2 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 4A load should be connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I. IR3897 has only one input supply and internal LDO generates Vcc from Vin. If operation with external Vcc is required, then R15 can be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vin pin and Vcc/LDO Out pins should be shorted together for external Vcc operation. The output can track voltage at the Vp pin. For this purpose, Vref pin is to be connected to ground (use zero ohm resistor for R21). The value of R14 and R20 can be selected to provide the desired tracking ratio between output voltage and the tracking input. Table I. Connections Connection Signal Name VIN+ Vin (+12V) VIN- Ground of Vin Vout+ Vout(+1.2V) Vout- Ground for Vout Vcc+ Vcc/ LDO Out Pin Vcc- Ground for Vcc input Enable Enable PGood Power Good Signal AGnd Analog ground LAYOUT The PCB is a 4-layer board (2.23x2) using FR4 material. All layers use 2 Oz. copper. The PCB thickness is 0.062. The IR3897 and other major power components are mounted on the top side of the board. Power supply decoupling capacitors, the bootstrap capacitor and feedback components are located close to IR3897. The feedback resistors are connected to the output at the point of regulation and are located close to the SupIRBuck IC. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. 12/5/2012 2