GENERAL DATA — 600 WATT PEAK POWER
100
10
PULSE WIDTH (t ) IS DEFINED
AS THAT POINT WHERE THE PEAK
CURRENT DECAYS TO 50%
P
NONREPETITIVE
PULSE WAVEFORM
SHOWN IN FIGURE 2
t
r
OF I
.
RSM
10
100
50
0
PEAK VALUE – I
t
≤
µs
RSM
r
I
RSM
2
HALF VALUE –
1
t
P
0.1
0.1
µs
1
µs
10
µs
100 µs
1 ms
10 ms
0
1
2
3
4
t , PULSE WIDTH
t, TIME (ms)
P
Figure 1. Pulse Rating
Curve
Figure 2. Pulse Waveform
160
140
120
TYPICAL PROTECTION CIRCUIT
Z
in
100
80
LOAD
V
V
L
in
60
40
20
0
0
25
50
75
100
125
150
T , AMBIENT TEMPERATURE (
°C)
A
Figure 3. Pulse Derating Curve
APPLICATION NOTES
RESPONSE TIME
the suppressor device as close as possible to the equipment
or components to be protected will minimize this overshoot.
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
ofminorimportanceintheparallelprotectionschemebecause
it only produces a time delay in the transition from the
operating voltage to the clamp voltage as shown in Figure 4.
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 5. 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 over-
shoot. Propercircuitlayout, minimumleadlengthsandplacing
Some input impedance represented by Z is essential to
in
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.
Motorola TVS/Zener Device Data
600 Watt Peak Power Data Sheet
5-69
