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# CSD17570Q5B: To know the thermal rise within current go through the CSD17570Q5B body diode

Part Number: CSD17570Q5B

Hi Expert,

The application is from the redundant power supply.

The continue current will go through the body diode for a certain period.

Conditions:

Vo=12V

Io (into body diode) =31A

Duration=1.87mS

Pls advice how to know the temperature rise for this condition.

Best regards,

Eric Lai

Field Application Engineer

Texas Instruments Taiwan Limited

O: +886-2-2175-2582

M: +886-909-262-582

E-Mail:Eric.Lai @ti.com

• Eric,
It is impossible to predict this accurately without knowing all the details of your thermal environment. While the junction to case thermal impedance can be estimated from the transient thermal impedance curve (Figure 1), the case to ambient is still completely unknown.

At 31A, the voltage drop about the diode is going to be 0.75V and 0.6V, depending on the junction temperature at this time. Lets take the worst case of 0.75V and say the FET will be dissipating 31A*.75V = 23W.

For this short of a duration, we can assume the bulk of the thermal impedance will be junction to case, as case to ambient is much slower (more
capacitance). So if you take 0.3 (from 1ms on thermal impedance curve), 0.3*0.8degC/W*23W = 5degC/W.

I'm not sure how precise this is given your thermal layout can have a big impact, but this is more so the case for longer pulse durations. All that to say, for this single event, the temperature increase should not be very severe.