AN2738 datasheet(32/54 Pages) STMICROELECTRONICS

32 / 54 page

Application example

AN2738

32/54

Doc ID 14589 Rev 2

As discussed above, the equivalent gate driver output circuit can be represented as in

Figure 29:

Figure 29.

Total equivalent circuit for the turn-off

Given the equivalent circuits in Figure 29 and the approximations of the power IGBT

(MOSFET) switching behavior, the timing equations are as follows:

Equation 11

Equation 12

As above, CISS_max is used because when the VCE (or VDS) of the power IGBT (or

MOSFET) is minimum (equal to VCE_sat) the CISS (which depends on the VCE) shows its

maximum value. Even if they are just approximations, the Tfall and Trise are very important

values to be estimated because they provide an indication of the power dissipation during

the switching of the power IGBT (or MOSFET), which can be approximated as indicated in

Figure 30.

RGATE

RDSon_sink

Cge = Ciss_max

Vge

Isink

Toff

RGATE

RDSon_sink

Vge_p

Isink

Trise

OFF

DS on

()

GATE

() C

ISSmax

⊥MAX

GEP

-------------------------

⎝⎠

⎛⎞

⋅⋅

⋅

RISE

SINK

-------------

DS on

()SINK

GATE

()

GEP

---------------------------------------------------------------

⋅

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