TVS Diodes
Surface Mount > 600W > 1SMB10CAT3G Series
Application Notes
Figure 5.
ResponseTime
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 capacitive
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 5.
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 6. Minimizing this overshoot is very important in the
application, since the main purpose for adding a transient
suppressor is to clamp voltage spikes. The SMB series
have a very good response time, typically < 1 ns and
negligible inductance. However, external inductive effects
could produce unacceptable overshoot. Proper circuit
layout minimum lead lengths and placing the suppressor
device as close as possible to the equipment or
Figure 6.
components to be protected will minimize this overshoot.
Some input impedance represented by Zin 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 25ºC. If the duty cycle
increases, the peak power must be reduced as indicated
by the curves of Figure 7. Average power must be derated
as the lead or ambient temperature rises above 25ºC. The
average power derating curve normally given on data
sheets may be normalized and used for this purpose.
Figure 7. Typical Derating Factor for Duty Cycle
At first glance the derating curves of Figure 7 appear to be
in error as the 10 ms pulse has a higher derating factor
than the 10 s pulse. However, when the derating factor for
a given pulse of Figure 7 is multiplied by the peak power
value of Figure 1 for the same pulse, the results follow the
expected trend.
© 2017 Littelfuse, Inc.
Specifications are subject to change without notice.
Revised: 11/17/17
