RT8801

Preliminary

21

DS8801-04

August 2007

www.richtek.com

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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 CSP1,2,3,4 and CSN 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 or Inductor DCR) ensures the accurate

stable current sensing.

Keep well Kelvin sense to ensure the 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 closed to MOSFET.

4. The compensation, bypass and other function setting components should be near the IC and away from the noisy

power path.

Figure 26. Power Stage Ripple Current Path

SW2

L2

SW1

L1

C

OUT

R

L

V

OUT

V

IN

R

IN

C

IN

V