TOP412/414
Key Application Issues
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 VC power supply be
turned on before the DRAIN voltage is applied.
UseaKelvinconnectiontotheSOURCEpinfortheCONTROL
pin bypass capacitor. Use single point grounding techniques at
the SOURCE pin as shown in Figure 8. Use a ceramic high
frequencydecouplingcapacitortobypassnoisetransientswhich
mightappearontheCONTROLpin. TheTOP412andTOP414
have an over current latching shutdown feature. Failure to use
a high frequency decoupling capacitor may allow incidental
noise to accidentally trigger this feature.
CONTROLpincurrentsduringauto-restartoperationaremuch
lower at low input voltages (< 20 V) which increases the auto-
restart cycle period (see the IC vs. Drain Voltage Characteristic
curve).
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.
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.
DonotplugtheTOPSwitchdeviceintoa“hot”ICsocketduring
test. External CONTROL pin capacitance may deliver a surge
current sufficient to trigger the shutdown latch which turns the
TOPSwitch off.
ForadditionalapplicationsinformationregardingtheTOPSwitch
family, refer to Web site, www.powerint.com.
G PACKAGE
Bias/Feedback
Return
SOURCE
SOURCE
High Voltage
Return
Bias/Feedback
Input
CONTROL
DRAIN
CONTROL pin transient
decoupling capacitor
Kelvin-connected
auto-restart/bypass capacitor C5
and/or compensation network
TOP VIEW
PI-2210-102798
Figure 8. Recommended TOPSwitch Layout.
A
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