SP6120EYSLASHTR datasheet(20/22 Pages) SIPEX

20 / 22 page

Date: 5/25/04

SP6120 Low Voltage, AnyFETTM, Synchronous, Buck Controller

Layout Guideline

PCB layout plays a critical role in proper func-

tion of the converters and EMI control. In switch

mode power supplies, loops carrying high di/dt

give rise to EMI and ground bounces. The goal

of layout optimization is to identify these loops

and minimize them. It is also crucial on how to

connect the controller ground such that its op-

eration is not affected by noise. The following

guideline should be followed to ensure proper

operation.

1. A ground plane is recommended for mini-

mizing noises, copper losses and maximizing

heat dissipation.

2. Connect the ground of feedback divider, com-

pensation components, oscillator resistor and

soft-start capacitor to the GND pin of the IC.

Then connect this pin as close as possible to

the ground of the output capacitor.

3. The VCC bypass capacitor should be right

next to the Vcc and GND pin.

4. The traces connecting to feedback resistor

and current sense components should be short

and far away from the switch node, and switch-

ing components.

5. Connect the PGND pin close to the source of

the bottom MOSFET, and the SWN pin to the

source of the top MOSFET. Minimize the

trace between GH/GL and the gates of the

MOSFETs. All of these requirements reduce

the impedance driving the MOSFETs. This is

especially important for the bottom MOSFET

that tends to turn on through its miller capaci-

tor when the switch node swings high.

6. Minimize the loop composed of input capaci-

tors, top/bottom MOSFETs and Schottky di-

ode, This loop carries high di/dt current. Also

increase the trace width to reduce copper

losses.

7. Maximize the trace width of the loop con-

necting the inductor, output capacitors,

Schottky diode and bottom MOSFET.

APPLICATIONS INFORMATION: Continued

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