AN2385 datasheet(11/14 Pages) STMICROELECTRONICS

11 / 14 page

AN2385

Pulsed drain current (IDM)

11/14

where RDSON(175°C@IDM) is the on resistance of the device at the guaranteed maximum

junction temperature and at the Pulsed Drain Current value, and that:

Equation 8

where ZTHJC is the junction to case thermal impedance at the specific operation conditions,

the maximum acceptable ZTHJC value can be achieved as:

Equation 9

Thus, considering a specific Power Pulse with a fixed duty cycle, the maximum Rectangular

Pulse Duration can be achieved.

As example, Figure 8. shows the determination of the maximum Rectangular Pulse Duration

considering a Pulsed Drain Current equal to 600A, TJMAX of 175°C, case temperature of

25°C, duty cycle of 0.02 and RDSON(175°C, IDM) equal to 20mOhm. ZTHJC can be calculated

as:

Equation 10

Figure 8.

Determination of the maximum rectangular pulse duration

In this example, the maximum Rectangular Pulse Duration equals 30usec. For power pulse

of higher duration the junction temperature overcomes 175°C and the device could fail.

It is important to highlight that the measured on resistance must be performed at the

maximum junction temperature and also at the specific Pulsed Drain Current. In fact,

increasing the drain current also RDSON increases and thus, of course, this effect must be

taken into account.

THJC

•

JMAX

° C

–

∆

THJC

JMAX

° C

–

DSON175

° CI

()

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

THJC

175

° C25° C

–

600

•

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

0.021

° C

-------

•

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