How to reduce the zero current offset reading from one of the channel of STPM33?

[RMoha.18]

How to reduce the zero current offset reading from one of the channel of STPM33?

Hi, I am using STPM33 for energy monitering. I have 2 STPM33 in my design and hence there are 4 current sense channels where I use shunt resistors for sensing. The problem faced by me is that the fourth channel is showing an offset of 6 mA when zero current is flowing through the shunt. I was able to reduce it by reducing the low pass filter resistor between the stpm33 and shunt resistor from 1K to 220Ohm. Still the 4th channel has got 3mA offset where as all other ports show 1-2mA for zero current through their respective sense resistors. Anyway 3mA is acceptable for me but I want to know why this happens and if there is a better way to solve this problem. aAlso I want to know the significance of 1k resistor as low pass filter. Somebody please help.

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[Didier HERROUIN]

The RMS offset current when there is no current is due to SIgma-Delta ADC architecture itself. Moreover, the accuracy of RMS register is lower than Power/Energy registers: so even if you read a LSB bit in RMS registers, this value may not be considered for Power/Energy calculations.

1K resistors are part of the anti-aliasing filter with the 10nF capacitor, with a cut frequency around 15KHz (which could be higher).