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TPS2491: Calculation method of RθJC

Part Number: TPS2491
Other Parts Discussed in Thread: CSD19532KTT

Dear Specislists,

My customer has a question about equation(9) of datasheet P.21.

I would be grateful if you could advise. 


I'd like to know about calculation method of RθJC

RθCA is used in equation (9) of data sheet P.21.

In Equation (10), 30 ° C./W is used for RθCA.

I don't know if it's CSD19532KTT or CSD17552Q5B, (but I think either is a typo.)

RθCA is not described.

From each data sheet, subtract RJC from RθJA.

CSD19532KTT: 62 ℃ / W-0.6 ℃ / W = 61.4 ℃ / W

CSD17552Q5B: 50 ℃ / W-1.8 ℃ / W = 48.2 ℃ / W

In either case, it is not 30 ° C / W.

How was it calculated?

On the other hand, the Excel calculation tool uses θJA.

Here, TI EVM is listed as The EVM is 30 ° C / W number and a good starting point at 30 ° C / W.

In the data sheet, is the initial value of RθCA set to a typical value of 30 ° C / W for RθJA of EVM? 

(In this case, RθJA and RθJC are different, but are they ignored because RθJC is small?)


I appreciate your great help in advance.

Best regards,