IRDC3891 TM SupIRBuck USER GUIDE FOR IRDC3891 EVALUATION BOARD DESCRIPTION The IR3891 is a dual synchronous buck output over voltage protection as well as open feedback line protection. converter, providing a compact, high performance and flexible solution in a small Output over-current protection function is 5mm X 6mm Power QFN package. implemented by sensing the voltage developed across the on-resistance of the synchronous rectifier MOSFET for optimum cost and Key features offered by the IR3891 include performance and the current limit is thermally internal Digital Soft Start, precision 0.5V compensated. reference voltage, Power Good, thermal protection, programmable switching This user guide contains the schematic and bill frequency, Enable input, input under-voltage of materials for the IRDC3891 evaluation board. The guide describes operation and use of the lockout for proper start-up, enhanced line/ evaluation board itself. Detailed application load regulation with feed forward, external information for IR3891 is available in the frequency synchronization with smooth IR3891 data sheet. clocking, internal LDO, pre-bias start-up, BOARD FEATURES V = +12.0V in Fs = 600kHz V = +1.8V 4A V = +1.2V 4A out1 out2 L = 2.2uH L = 1.5uH 1 2 C =4x22uF (ceramic 0805) C =4x22uF (ceramic 0805) out1 out2 C = 4x10uF (ceramic 1206) + 1x330uF (electrolytic) in 04-30-2013 1 ALIRDC3891 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12.0V input supply should be connected to VIN+ and VIN-. A maximum 4A 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. IR3891 has 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 should be applied between Vcc+ and Vcc- pins. Vin pin (input of the LDO) and Vcc/LDO pins should be shorted together (populate R4) for external Vcc operation. The output of channel2 (Vout ) can follow the voltage at the Seq pin. For this purpose, The value of R5 and 2 R6 can be selected to provide the desired sequencing ratio between Seq input and Vout . For normal 2 operation (non-sequencing) Seq pin should be left floating. Seq pin is internally pulled up to 3.3V. Table I. Connections Connection Signal Name VIN+ PV (+12V) in VIN- Ground of PV in VOUT1+ V (+1.8V) out1 VOUT1- Ground of Vout 1 VOUT2+ V (+1.2V) out2 VOUT2- Ground of Vout 2 VCC+ VCC/LDO pin VCC- Connected to PGND VSEQ Sequence input EN1, EN2 Enable input of each channel Sync Synchronous input LAYOUT The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3891 and other components are mounted on the top and bottom side of the board. Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located close to IR3891. The feedback resistors are connected to the output voltage at the point of regulation and are located close to IR3891. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. 04-30-2013 2 AL