NX2116A datasheet(14/14 Pages) MICROSEMI

14 / 14 page

NX2116/2116A/2116B/2117/2117A

Rev. 3.0

03/14/06

Layout Considerations

The layout is very important when designing high

frequency switching converters. Layout will affect noise

pickup and can cause a good design to perform with

less than expected results.

Start to place the power components, make all the

connection in the top layer with wide, copper filled ar-

eas. The inductor, output capacitor and the MOSFET

should be close to each other as possible. This helps to

reduce the EMI radiated by the power traces due to the

high switching currents through them. Place input ca-

pacitor directly to the drain of the high-side MOSFET, to

reduce the ESR replace the single input capacitor with

two parallel units. The feedback part of the system should

be kept away from the inductor and other noise sources,

and be placed close to the IC. In multilayer PCB use

one layer as power ground plane and have a control cir-

cuit ground (analog ground), to which all signals are ref-

erenced.

The goal is to localize the high current path to a

separate loop that does not interfere with the more sen-

sitive analog control function. These two grounds must

be connected together on the PC board layout at a single

point.

OCP

comparator

OCP

40uA

OCP

Figure 10 - Over current protection

vbus

The over current limit can be set by the following

equation

OCP

SET

DSON

If MOSFET R

DSON=6.5mΩ, the worst case thermal

consideration K=1.5 and the current limit is set at 15A,

then

××

×Ω

=Ω

SET

DSON

OCP

15A 1.5 6.5m

3.656k

40uA

Choose R

OCP=3.7kΩ

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