IRDC3831 TM SupIRBuck USER GUIDE FOR IR3831 EVALUATION BOARD DESCRIPTION An output over-current protection function is The IR3831 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 5mmx6mm Power QFN package. performance. Key features offered by the IR3831 include This user guide contains the schematic and bill programmable soft-start ramp, Power Good, of materials for the IR3831 evaluation board. thermal protection, programmable switching The guide describes operation and use of the frequency, tracking input, enable input, input evaluation board itself. Detailed application under-voltage lockout for proper start-up, information for IR3831 is available in the and pre-bias start-up. IR3831 data sheet. BOARD FEATURES V = +12V (13.2V Max) in V = +5V (5.5V Max) cc V = +0.75V 0- 8A out F = 400kHz s L = 0.68uH C = 3x10uF (ceramic 1206) + 330uF (electrolytic) in C = 8x22uF (ceramic 0805) out 02/10/09 1IRDC3831 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 8A 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. IR3831 has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). Separate supplies should be applied to these inputs. Vcc input should be a well regulated 4.5V-5.5V supply and it would be connected to Vcc+ and Vcc-. If single 12V application is required, connect R7 ( zero Ohm resistor) which enables the on board bias regulator (see schematic). In this case there is no need of external Vcc supply. The output tracks VDDQ input. The value of R14 and R28 can be selected to provide the desired ratio between the output voltage and the tracking input. For proper operation of IR3831, the voltage at Vp pin should not exceed Vcc. Table I. Connections Connection Signal Name VIN+ V (+12V) in VIN- Ground of V in Vcc+ Vcc input Vcc- Ground for Vcc input VOUT- Ground of V out VOUT+ V (+0.75V) out Enable Enable V Tracking Input DDQ PGood Power Good Signal LAYOUT The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3831 SupIRBuck and all of the passive components are mounted on the top side of the board. Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located close to IR3831. The feedback resistors are connected to the output voltage at the point of regulation and are located close to the SupIRBuck. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. 02/10/09 2