IRDC3843W TM SupIRBuck USER GUIDE FOR IR3843W EVALUATION BOARD DESCRIPTION An output over-current protection function is The IR3843W 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 IR3843W This user guide contains the schematic and bill include programmable soft-start ramp, of materials for the IR3843W evaluation board. precision 0.7V reference voltage, Power The guide describes operation and use of the Good, thermal protection, programmable evaluation board itself. Detailed application switching frequency, Sequence input, information for IR3843W is available in the Enable input, input under-voltage lockout for IR3843W data sheet. proper start-up, and pre-bias start-up. BOARD FEATURES V = +12V (13.2V Max) in V =+5V (5.5V Max) cc V = +1.8V 0- 2A out F =600kHz s L= 3.3uH C = 1x10uF (ceramic 1206) + 330uF (electrolytic) in C = 2x22uF (ceramic 0805) out 10/27/2009 1IRDC3843W CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 2A 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. IR3843W 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 can track a sequencing input at the start-up. For sequencing application, R16 should be removed and the external sequencing source should be applied between Seq. and Agnd. 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 IR3843W, the voltage at Seq. 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 (+1.8V) out Enable Enable Seq. Sequence Input P Good Power Good Signal LAYOUT The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3843W 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 IR3843W. 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. 10/27/2009 2