RT8800B datasheet(21/26 Pages) RICHTEK

21 / 26 page

RT8800/B

DS8800/B-08 April 2011

www.richtek.com

Layout Considerations

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 and ICOMMON 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. R&C filter of choke

should place close to PWM and the R & C connect

directly to the pin of each output choke, use 10 mil

differencial pair, and 20 mil gap to other phase pair.

Less via as possible.

Figure 22. Power Stage Ripple Current Path

SW2

SW1

OUT

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 closed to MOSFET.

RT8800B Datasheet(PDF) 21 Page - Richtek Technology Corporation