IRDC3847-P1V2 TM SupIRBuck USER GUIDE FOR IR3847 EVALUATION BOARD DESCRIPTION A thermally compensated output over-current The IR3847 is a synchronous buck protection function is implemented by sensing converter, providing a compact, high the voltage developed across the on-resistance performance and flexible solution in a small of the synchronous rectifier MOSFET for 5mmx6mm QFN package. optimum cost and performance. Key features offered by the IR3847 include This user guide contains the schematic and bill internal Digital Soft Start, precision 0.6V of materials for the IR3847 evaluation board. reference voltage, Power Good, thermal The guide describes operation and use of the protection, programmable switching evaluation board itself. Detailed application frequency, Enable input, input under-voltage information for IR3847 is available in the lockout for proper start-up, enhanced line/ IR3847 data sheet. load regulation with feed forward, external frequency synchronization with smooth clocking, internal LDO, true differential remote sensing and pre-bias start-up. BOARD FEATURES V = +12V (+ 13.2V Max), No Vcc required. in V = +1.2V 0-25A out F =600kHz s L= 0.215uH C = 7x22uF (ceramic 1206) + 1x330uF (electrolytic) in C =10x47uF (ceramic 0805) out 4/11/2013 1IRDC3847-P1V2 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 25A load should be connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I. IR3847 needs only one input supply and internal LDO generates Vcc from Vin. If operation with external Vcc is required, then R33 should be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vin pin and Vcc pins should be shorted together for external Vcc operation by installing R35. The board is configured for remote sensing. If local sense is desired, R8 should be uninstalled and R16 should be installed instead. External Enable signal can be applied to the board via exposed Enable pad and R18 should be removed for this purpose. Table I. Connections Connection Signal Name VIN+ Vin (+12V) VIN- Ground of Vin Vout+ Vout(+1.2V) Vout- Ground for Vout Vcc+ Vcc Pin Vcc- Ground for Vcc input Enable Enable PGood Power Good Signal AGnd Analog ground LAYOUT The PCB is a 6-layer board. All of layers are 2 Oz. copper. The IR3847 and most of the passive components are mounted on the top side of the board. Power supply decoupling capacitors and feedback components are located close to IR3847. The feedback resistors are connected to the output of the remote sense amplifier of the IR3847 and are located close to the IR3847. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. Separate power ground and analog ground are used and may be connected together using a 0 ohm resistor at one of three possible locations. It is preferred to use one of R43 or R44. 4/11/2013 2