TOP209 datasheet(8/16 Pages) POWERINT

8 / 16 page

8/97

TOP209/210

Figure 9. Recommended PC Layout for the TOP209/210.

CONTROL

SOURCE

DRAIN

TOP VIEW

PI-1744-011796

High Voltage

Return

Bias/Feedback

Return

Bypass

Capacitor

Bias/Feedback

Input

TOP210 PFI

Use a Kelvin connection to the SOURCE pin for the CONTROL

pin bypass capacitor as shown in Figure 9.

Minimize peak voltage and ringing on the DRAIN voltage at

turn-off. Use a Zener or TVS Zener diode to clamp the DRAIN

voltage.

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

C power supply be

turned on before the DRAIN voltage is applied.

Key Application Considerations

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

C vs. Drain Voltage Characteristic

curve).

Short interruptions of AC power may cause TOPSwitch to enter

the 8-count auto-restart cycle before starting again. This is

because the input energy storage capacitors are not completely

discharged and the CONTROL pin capacitance has not

discharged below the internal power-up reset voltage (V

C(RESET)).

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 AN-14 in the 1996-97 Data Book and Design

Guide or on our Web site.

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