IRDC3821 Infineon

IRDC3821 TM SupIRBuck USER GUIDE FOR IR3821 EVALUATION BOARD DESCRIPTION An output over-current protection function is The IR3821 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 IR3821 include This user guide contains the schematic and bill programmable soft-start ramp, precision of materials for the IR3821 evaluation board. 0.6V reference voltage, programmable The guide describes operation and use of the Power Good, thermal protection, fixed evaluation board itself. Detailed application 600kHz switching frequency requiring no information for IR3821 is available in the external component, input under-voltage IR3821 data sheet. lockout for proper start-up, and pre-bias start-up. BOARD FEATURES V = +12V (13.2V Max) in V = +1.8V 0- 7A out L=1.0uH C =3x10uF (ceramic 1206) + 330uF (electrolytic) in C =6x22uF (ceramic 0805) out Rev 0.1 1 01/07/2008IRDC3821 CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 7A 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. IR3821 has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). These inputs are connected on the board with a zero ohm resistor (R15). Separate supplies can be applied to these inputs. Vcc input cannot be connected unless R15 is removed. Vcc input should be a well regulated 5V-12V supply and it would be connected to Vcc+ and Vcc-. Table I. Connections Connection Signal Name VIN+ V (+12V) in VIN- Ground of V in Vcc+ Optional Vcc input Vcc- Ground for Optional Vcc input VOUT- Ground of V out VOUT+ V (+1.8V) out P Good Power Good Signal LAYOUT The PCB is a 4-layer board. All of layers are 2Oz. copper. The IR3821 SupIRBuck and all of the passive components are mounted on the top side of the board. Power supply decoupling capacitors, the charge-pump capacitor and feedback components are located close to IR3821. The feedback resistors are connected to the output voltage at the point of regulation and are located close to SupIRBuck. To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground current path. Rev 0.1 2 01/07/2008