CS5157GD16 datasheet(12/14 Pages) CHERRY

12 / 14 page

Applications Information: continued

A heatsink may be added to TO-220 components to reduce

their thermal impedance. A number of PC board layout

techniques such as thermal bias and additional copper foil

area can be used to improve the power handling capability

of surface mount components.

EMI Management

As a consequence of large currents being turned on and off

at high frequency, switching regulators generate noise as a

consequence of their normal operation. When designing for

compliance with EMI/EMC regulations, additional compo-

nents may be added to reduce noise emissions. These com-

ponents are not required for regulator operation and exper-

imental results may allow them to be eliminated. The input

filter inductor may not be required because bulk filter and

bypass capacitors, as well as other loads located on the

board will tend to reduce regulator di/dt effects on the cir-

cuit board and input power supply. Placement of the

power component to minimize routing distance will also

help to reduce emissions.

Figure 18: Filter components

Figure 19: Input Filter

Layout Guidelines

1. Place 12V filter capacitor next to the IC and connect

capacitor ground to pin 11 (PGnd).

2. Connect pin 11 (PGnd) with a separate trace to the

ground terminals of the 5V input capacitors.

3. Place fast feedback filter capacitor next to pin 8 (VFFB)

and connect it’s ground terminal with a separate, wide

trace directly to pin 14 (LGnd).

4. Connect the ground terminals of the Compensation

capacitor directly to the ground of the fast feedback filter

capacitor to prevent common mode noise from effecting

the PWM comparator.

5. Place the output filter capacitor(s) as close to the load as

possible and connect the ground terminal to pin 14 (LGnd).

6. Connect the VFB pin directly to the load with a separate

trace (remote sense).

7. Place 5V input capacitors close to the switching MOSFET

and synchronous MOSFET.

Route gate drive signals VGATE(H) (pin 10) and VGATE(L)

(pin 12 when used) with traces that are a minimum of 0.025

inches wide.

Figure 20: Layout Guidelines

To the negative terminal of the

input capacitors

100pF

VFFB

OFF TIME

SOFTSTART

VCC

0.1µF

To the negative terminal of the output capacitors

1.0µF

VCOMP

2µH

1200µF x 3/16V

33Ω

1000pF

2µH

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