P6KE6.8A through P6KE200A
Motorola TVS/Zener Device Data
4-10
600 Watt Peak Power Data Sheet
APPLICATION NOTES
RESPONSE TIME
In most applications, the transient suppressor device is
placed in parallel with the equipment or component to be
protected. In this situation, there is a time delay associated
with the capacitance of the device and an overshoot condition
associated with the inductance of the device and the
inductance of the connection method. The capacitance effect
is of minor importance in the parallel protection scheme
because it only produces a time delay in the transition from the
operating voltage to the clamp voltage as shown in Figure A.
The inductive effects in the device are due to actual turn-on
time (time required for the device to go from zero current to full
current) and lead inductance. This inductive effect produces
an overshoot in the voltage across the equipment or
component being protected as shown in Figure B. Minimizing
this overshoot is very important in the application, since the
main purpose for adding a transient suppressor is to clamp
voltage spikes. The P6KE6.8A series has very good response
time, typically < 1 ns and negligible inductance. However,
external inductive effects could produce unacceptable over-
shoot. Proper circuit layout, minimum lead lengths and placing
the suppressor device as close as possible to the equipment
or components to be protected will minimize this overshoot.
Some input impedance represented by Z
in
is essential to
prevent overstress of the protection device. This impedance
should be as high as possible, without restricting the circuit
operation.
DUTY CYCLE DERATING
The data of Figure 1 applies for non-repetitive conditions
and at a lead temperature of 25°C. If the duty cycle increases,
the peak power must be reduced as indicated by the curves of
Figure 6. Average power must be derated as the lead or
ambient temperature rises above 25°C. The average power
derating curve normally given on data sheets may be
normalized and used for this purpose.
At first glance the derating curves of Figure 6 appear to be in
error as the 10 ms pulse has a higher derating factor than the
10 µs pulse. However, when the derating factor for a given
pulse of Figure 6 is multiplied by the peak power value of
Figure 1 for the same pulse, the results follow the expected
trend.
TYPICAL PROTECTION CIRCUIT
V
in
V
L
V
V
in
V
in
(TRANSIENT)
V
L
t
d
V
V
L
V
in
(TRANSIENT)
Z
in
LOAD
OVERSHOOT DUE TO
INDUCTIVE EFFECTS
t
D
= TIME DELAY DUE TO CAPACITIVE EFFECT
t t
Figure 7. Figure 8.
