November 2003

13

M9999-111803

MIC2168

Micrel

Design Example

Layout and Checklist:

1. Connect the current limiting (CS) resistor directly

to the drain of top MOSFET Q1.

2. Connect the VSW pin directly to the source of top

MOSFET Q1 thru a 4

Ω to 10Ω resistor. The pur-

pose of this resistor is to filter the switch node.

3. The feedback resistors R1 and R2 should be

placed close to the FB pin. The top side of R1

should connect directly to the output node. Run

this trace away from the switch node (junction of

Q1, Q2, and L1). The bottom side of R1 should

connect to the GND pin on the MIC2168.

4. The compensation resistor and capacitors should

be placed right next to the COMP/EN pin and the

other side should connect directly to the GND pin

on the MIC2168 rather than going to the plane.

5. The input bulk capacitors should be placed close to

the drain of the top MOSFET.

6. The 1

µF ceramic capacitor should be placed right

on the VIN pin of the MIC2168.

7. The 4.7

µF to 10µF ceramic capacitor should be

placed right on the VDD pin.

8. The source of the bottom MOSFET should connect

directly to the input capacitor GND with a thick

trace. The output capacitor and the input capacitor

should connect directly to the GND plane.

9. Place a 0.1

µF ceramic capacitor in parallel with the

CS resistor to filter any switching noise.