IRDC3846-P1V2 TM SupIRBuck USER GUIDE FOR IRDC3846 EVALUATION BOARD DESCRIPTION The IR3846 is a synchronous buck A thermally compensated output over-current converter, providing a compact, high protection function is implemented by sensing performance and flexible solution in a small the voltage developed across the on-resistance 5mmx7mm QFN package. of the synchronous rectifier MOSFET for optimum cost and performance. Key features offered by the IR3846 include internal Digital Soft Start, precision 0.6V This user guide contains the schematic and bill reference voltage, Power Good, thermal of materials for the IRDC3846 evaluation board. 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 IR3846 is available in the load regulation with feed forward, external IR3846 data sheet. frequency synchronization with smooth clocking, internal LDO, true differential remote sensing and pre-bias start-up. BOARD FEATURES V = +12V, No Vcc required. in V = +1.2V 0-35A out F =600kHz s L= 0.250uH C = 7x22uF (ceramic 1206) + 1x330uF (electrolytic) in C = 6x100uF (ceramic 1206) out 9/11/2013 1 ALIRDC3846-P1V2 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 35A load should be connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I. IR3846 needs only one input supply and internal LDO generates Vcc from Vin. If operation with external Vcc is required, then R3 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 a 0 ohm resistor at R4. The board is configured for remote sensing. If local sense is desired, R18 should be uninstalled and R19 should be installed instead. External Enable signal can be applied to the board via exposed Enable pad and R100 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 IR3846 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 IR3846. The feedback resistors are connected to the output of the remote sense amplifier of the IR3846 and are located close to the IR3846. 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 R71. 9/11/2013 2 AL