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
C
power supply be
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
C
vs. Drain Voltage Characteristic
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.
