TPS1211-Q1: The measured values of IMON do not match the calculations

Hi Wang,

Can you share the schematic and layout for review.

Is kelvin sensing approach followed for Rsense ? 

Have you measured IMON voltage with respect to device ground?

Best Regards

Rakesh

1. I measured another board, the results are shown below.The fourth column is VRSNS measured times GAIN calculated. 

IMON is still bigger than what is expected. 

2. Yes, I am sure that IMON is measured with respect to the device ground. 

Why VRSNS is 8.1mV at 15A ? It should be 0.5mOhm *15 A = 7.5mV. Where does that difference coming from ?

I don't know, maybe some noise. I have sent the SCH to you privately. 

You can add 10nF cap between CS+ and CS- close to IC pins and try once.

This much deviation in IMON measurement is not expected.

I re-measured the board with a high-precision multimeter and add 10nf Cap between CS+ & CS- as you told. Here are the results:

It looks similar to the original result. By the way, even though VRSNS is 8.1mA,  VIMON should be 398mV if 8.1mV times GAIN.  Have you measured ILOAD vs VIMON？Does it match the calculation?

We have not seen any such mismatch in our evaluation.

Your schematic looks fine. In layout, it is not clear on the Kelvin sensing for Rsense. It will have major impact on OCP and IMON results.

To confirm, you can increase Rsense to 1mOhm and see improvement in accuracy 

Best Regards,

Rakesh

What does Kelvin sensing in layout mean？From the datasheet，it seems like differential routing. Are they the same thing？