CS5159

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13

A heatsink may be added to TO−220 components to

reduce their thermal impedance. A number of PC board

layout techniques such as thermal vias 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

components may be added to reduce noise emissions. These

components are not required for regulator operation and

experimental 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 circuit

board and input power supply. Placement of the power

component to minimize routing distance will also help to

reduce emissions.

Figure 20. Filter Components

1000 pF

33 Ω

2.0 μH

Figure 21. Input Filter

1200 pF × 3.0/16 V

2.0 μH

+

Layout Guidelines

1. Place 12 V 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 5.0 V input capacitors.

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).

trace (remote sense).

7. Place 5.0 V input capacitors close to the switching

MOSFET and synchronous MOSFET.

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

inches wide.

Figure 22. Layout Guidelines

To the negative terminal of the output capacitors

100 pF

0.1 μF

SOFT START

OFF TIME

To the negative terminal

of the input capacitors

15

11

5

8

1.0 μF