IRDC3895-P1V2 TM SupIRBuck USER GUIDE FOR IR3895 EVALUATION BOARD 1.2Vout DESCRIPTION Output over-current protection function is The IR3895 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 rectifier MOSFET for optimum cost and 5mm X 6 mm Power QFN package. performance and the current limit is thermally compensated. Key features offered by the IR3895 include internal Digital Soft Start/Soft Stop, precision This user guide contains the schematic and bill 0.5Vreference voltage, Power Good, of materials for the IR3895 evaluation board. thermal protection, programmable switching The guide describes operation and use of the frequency, Enable input, input under-voltage evaluation board itself. Detailed application lockout for proper start-up, enhanced line/ information for IR3895 is available in the load regulation with feed forward, external IR3895 data sheet. frequency synchronization with smooth clocking, smart internal LDO and pre-bias start-up. BOARD FEATURES V = +12V (+ 13.2V Max) in V = +1.2V 0- 16A out F =600kHz s L= 0.4uH C = 5x10uF (ceramic 1206) + 1X330uF (electrolytic) in C =6x47uF (ceramic 0805) out 12/5/2012 1IRDC3895-P1V2 CONNECTIONS AND OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 16A load should be connected to VOUT+ and VOUT-. The input and output connections of the board are listed in Table I. IR3895 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/LDOout pins should be shorted together for external Vcc operation (use zero ohm resistor for R29). 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 R28 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 Gnd 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 IR3895 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 IR3895. 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