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TPS25982: TPS259823LNRGER IMON Current Calculations

Part Number: TPS25982
Other Parts Discussed in Thread: TPS25944L

Hello everyone,

I have used this eFuse on a board with a max load of 5V/6A.  In general, it seems to be working well.  But there seems to be some differences between the datasheet and the spreadsheet calculator on the value of R(IMON) and how to calculate the load current from the voltage on the IMON pin.

Using the TPS25982x Design Calculator spreadsheet on the product page, I get a R(IMON) value of 2K.  I've attached my version of this document with all my design parameters entered.

However, when I use the datasheet equation (7) I come up with a value for R(IMON) of ~5.2K:

  - I(lim) = 7.2A (6A typical load)

  - VIN-2.2 = 5.29-2.2 = 3.09V

  - gain = 52E-6

I measured V(IMON) ~0.481V with 1A load.  But I'm not sure how to correlate that.  Full range (3.32V) divided by full load (7.2A) gives 0.461V/A.  that is close.  But using equation (7) from the datasheet I get a voltage of 0.1056V if I use R(IMON) = 2K (from spreadsheet) or 0.275V if I use R(IMON) = 5.2K.  Neither is close to measured value.

Can someone explain what is going on here?

James