RT9205APS datasheet(14/15 Pages) RICHTEK

14 / 15 page

RT9205/A

Preliminary

DS9205/A-08 March 2007

www.richtek.com

The power components and the PWM controller should

be placed firstly. Place the input capacitors, especially the

high-frequency ceramic decoupling capacitors, close to

the power switches. Place the output inductor and output

capacitors between the MOSFETs and the load. Also

locate the PWM controller near by MOSFETs.

A multi-layer printed circuit board is recommended. Figure

13 shows the connections of the critical components in

the converter. Note that the capacitors CIN and COUT

represent numerous physical capacitors. Use a dedicated

grounding plane and use vias to ground all critical

components to this layer. Apply another solid layer as a

power plane and cut this plane into smaller islands of

common voltage levels. The power plane should support

the input power and output power nodes. Use copper filled

polygons on the top and bottom circuit layers for the

PHASE node, but it is not necessary to oversize this

particular island. Since the PHASE node is subjected to

very high dV/dt voltages, the stray capacitance formed

between these islands and the surrounding circuitry will

tend to couple switching noise. Use the remaining printed

circuit layers for small signal routing. The PCB traces

between the PWM controller and the gate of MOSFET

and also the traces connecting source of MOSFETs

should be sized to carry 2A peak currents.

Figure 13

LOAD

VCC

GND

RT9205/A

LGATE

UGATE

IQ1

OUT

IQ2

GND

RT9205APS 데이터시트(PDF) 14 Page - Richtek Technology Corporation