Motorola TVS/Zener Device Data

4-4

500 Watt Peak Power Data Sheet

1N6373, ICTE-5, MPTE-5,

through

1N6389, ICTE-45, C, MPTE-45, C

1N6267A/1.5KE6.8A

through

1N6303A/1.5KE200A

Figure 6. Dynamic Impedance

1000

500

200

100

50

20

10

5

2

1

1000

500

200

100

50

20

10

5

2

1

0.3

0.5 0.7

1

2

3

5

7

10

20

30

∆VZ, INSTANTANEOUS INCREASE IN VZ ABOVE VZ(NOM) (VOLTS)

0.3

0.5 0.7

1

2

3

5

7

10

20 30

∆VZ, INSTANTANEOUS INCREASE IN VZ ABOVE VZ(NOM) (VOLTS)

VZ(NOM) = 6.8 to 13 V

TL =25°C

tP =10 µs

VZ(NOM) = 6.8 to 13 V

TL =25°C

tP =10 µs

20 V

24 V

43 V

75 V

180 V

120 V

20 V

24 V

43 V

Figure 7. Typical Derating Factor for Duty Cycle

1 ms

10

µs

1

0.7

0.5

0.3

0.05

0.1

0.2

0.01

0.02

0.03

0.07

100

µs

0.1

0.2

0.5

2

5

10

50

1

20

100

D, DUTY CYCLE (%)

PULSE WIDTH

10 ms

APPLICATION NOTES

RESPONSE TIME

In most applications, the transient suppressor device is

placed in parallel with the equipment or component to be pro-

tected. In this situation, there is a time delay associated with

the capacitance of the device and an overshoot condition as-

sociated 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 volt-

age 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. These devices have excellent response time,

typically in the picosecond range and negligible inductance.

However, external inductive effects could produce unaccept-

able overshoot. 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 op-

eration.

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 7. 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 7 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 7 is multiplied by the peak power value of

Figure 1 for the same pulse, the results follow the expected

trend.