RT9202GS datasheet(13/14 Pages) RICHTEK

13 / 14 page

RT9202

DS9202-09

March 2007

www.richtek.com

There are two sets of critical components in a DC-DC

converter using the RT9202. The switching power

components are most critical because they switch large

amounts of energy, and as such, they tend to generate

equally large amounts of noise. The critical small signal

components are those connected to sensitive nodes or

those supplying critical bypass current.

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 10 shows the connections of the critical

components in the converter. Note that the capacitors

CIN and COUT each of them represents 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 island 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 10

LOAD

VCC

GND

RT9202

LGATE

UGATE

IQ1

OUT

IQ2

GND

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