AN2344 datasheet(14/27 Pages) STMICROELECTRONICS

tên linh kiện	AN2344

Giải thích chi tiết về linh kiện	Power MOSFET avalanche characteristics and ratings

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14 / 27 page

Datasheet avalanche ratings

AN2344

14/27

Figure 9.

VDS/ID shapes with the Coil during the UIS

3.3.1

EAR (Energy during avalanche for repetitive pulse)

Often stated in the datasheet, this value is defined as the energy at IAR during repetitive

operation, and the value is usually calculated with a 10KHz power pulse train with a 50%

duty cycle and the nominal power rating of the device (see Equation 3).

Equation 3

For instance, if the available power of the MOSFET (PD in the datasheet) is 150W, the EAR

should be equal to 15mJ. However, this value is redundant and not very useful for the

design, as it gives very poor information about the maximum energy to be dissipated and

keep TJ below TJ(max). A quick way to evaluate the temperature during avalanche is to take

into account the extra power dissipation introduced by the repetitive avalanche, and to

calculate the heat sink size required to dissipate it. Because of a triangular pulse:

Equation 4

And the additional average power to be dissipated is expressed as:

Equation 5

where,

f= Frequency (see Equation 3),

tAV= Avalanche time,

V= Peak voltage, and

I= Peak current

EAR=power/f

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