AN2344 datasheet(13/27 Pages) STMICROELECTRONICS

13 / 27 page

AN2344

Datasheet avalanche ratings

13/27

Figure 7.

Triangular pulse thermal response

Starting from this model, the experimental verification is made looking to the VDS shape

during the avalanche. In fact the breakdown voltage of the device is not constant when

varying the temperature and the current.

The variation of the blocking voltage with the current is nearly linear, and this resistance is

specific to the die size per a given set of design rules, the epitaxial layer, and the package.

Figure 8. shows the measured characteristic of BVDSS versus the ID for a 700V device. The

voltage variation with the temperature is positive as well, and the variation depends on the

structural characteristics of the silicon die. By taking these items into account, the TJ can be

extrapolated from the VDS curve.

Figure 8.

BVDSS vs ID

Figure 9. shows the actual VDS curve during an avalanche, where the increase of VDS

observed is due to the rise of the silicon temperature. Figure 9. also shows the waveforms

for the same device as it is subjected to different coils (i.e. different energy levels) at the

same peak current.

The different VDS shapes are due to different maximum temperatures reached by the

junction. The linear relationship of the VDS with the die temperature becomes clear when

comparing the VDS quasi-parabolic shape to the temperature profile for a triangular power

pulse (see Figure 7.).

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