A

4/99

TOP412/414

7

Figure 8. Recommended TOPSwitch Layout.

PI-2210-102798

CONTROL

SOURCE

SOURCE

DRAIN

TOP VIEW

High Voltage

Return

Bias/Feedback

Return

Bias/Feedback

Input

G PACKAGE

Kelvin-connected

auto-restart/bypass capacitor C5

and/or compensation network

CONTROL pin transient

decoupling capacitor

Key Application Issues

Use a Kelvin connection to the SOURCE pin for the CONTROL

pin bypass capacitor. Use single point grounding techniques at

the SOURCE pin as shown in Figure 8. Use a ceramic high

frequency decoupling capacitor to bypass noise transients which

might appear on the CONTROL pin. The TOP412 and TOP414

have an over current latching shutdown feature. Failure to use

a high frequency decoupling capacitor may allow incidental

noise to accidentally trigger this feature.

Limit peak voltage and ringing on the DRAIN voltage at turn-

off to a safe value. Use a Zener or TVS Zener diode to clamp

the DRAIN voltage.

Do not plug the TOPSwitch device into a “hot” IC socket during

test. External CONTROL pin capacitance may deliver a surge

current sufficient to trigger the shutdown latch which turns the

TOPSwitch off.

Under some conditions, externally provided bias or supply

current driven into the CONTROL pin can hold the TOPSwitch

in one of the 8 auto-restart cycles indefinitely and prevent

starting. Shorting the CONTROL pin to the SOURCE pin will

reset the TOPSwitch. To avoid this problem when doing bench

evaluations, it is recommended that the V

turned on before the DRAIN voltage is applied.

CONTROL pin currents during auto-restart operation are much

lower at low input voltages (< 20 V) which increases the auto-

restart cycle period (see the I

curve).

In some cases, minimum loading may be necessary to keep a

lightly loaded or unloaded output voltage within the desired

range due to the minimum ON-time.

For additional applications information regarding the TOPSwitch

family, refer to Web site, www.powerint.com.