RT9237 datasheet(12/15 Pages) ETC

12 / 15 page

RT9237

Preliminary

www.richtek-ic.com.tw

DS9237-00 January 2002

Layout Guide

Place the high-power switching components first, and

separate them from sensitive nodes.

1. Most critical path: the current sense circuit is

the most sensitive part of the converter. The

current sense resistors tied to ISP1,2,3,4 and

ISN1,2,3,4 should be located not more than 0.5

inch from the IC and away from the noise

switching nodes. The PCB trace of sense

nodes should be parallel and as short as

possible. Kelvin connection of the sense

component

(additional

sense

resistor

MOSFET RDS(ON)) ensures the accurate stable

current sensing.

No Kelvin sense, no guarantee

for stable operation!

2. Switching ripple current path:

a. Input capacitor to high side MOSFET

b. Low side MOSFET to output capacitor

c. The return path of input and output capacitor

d. Separate the power and signal GND

e. The switching nodes(the connection node of

high/low side MOSFET and inductor) is the

most noisy points. Keep them away from

sensitive small-signal node.

f. Reduce parasitic R, L by minimum length,

enough copper thickness and avoiding of via.

3. MOSFET driver should be close to MOSFET

4. The compensation, bypass and other function

setting components should be near the IC and

away from the noisy power path.

Fig.7 Power Stage Ripple Current Path

SW1

SW2

RIN

VIN

CIN

VOUT

COUT

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