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 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 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

Vin

VL

V

Vin

Vin (TRANSIENT)

VL

td

V

VL

Vin (TRANSIENT)

Zin

LOAD

OVERSHOOT DUE TO

INDUCTIVE EFFECTS

tD = TIME DELAY DUE TO CAPACITIVE EFFECT

t

t

Figure 7.

Figure 8.