Testing avalanche ruggedness

AN2344

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The device is essentially an open circuit up to its own blocking voltage, therefore the extra

current flows through the DUT, dissipating the accumulated energy that was stored in the

coil during the charging operation. Table 1.: UIS circuit equations on page 8 explains several

commonly defined rugged, or avalanche-rated, if during some stated coil and conducted

current conditions, the device survives this test.

In the past, circuits like the one in Figure 4. were recommended to test for this capability.

The current is maintained constant for a set time, eliminating the requirement for the coil.

However, the only recognized method is to use the circuit described in Figure 2. (per JEDEC

standard No. 24-5, MIL-STD750D method 3040.2).

A circuit commonly used to test the avalanche ruggedness of the MOSFET is shown in

source to the circuit only during the coil charging, disconnecting it a few microseconds

before the switch-off and the avalanche operation. This technique allows the user to

coil during turn-on, and consequently decreases the turn-on state time. Also, the energy

dissipated is different (see Table 1.).

Figure 4.

Constant current avalanche fixture

Figure 5.

Disconnected supply UIS fixture