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ADS131M08: ADS131M08

Part Number: ADS131M08
Other Parts Discussed in Thread: LMP2022,


I've designed a PCB using ADS131m08 and LMP2022 amplifiers to read 4 load cell outputs.

I've tested it and there is no problem.

But, I want to remove the external amplifier and only use the internal amplifier.

I tested the ADS131m08  eval board and everything is ok and I could read the load cell outputs using the internal amplifier.

Then, I removed the external amplifier from my custom board and tried to read the values. With Gain=1 and Gain=2, everything is ok. But, when I change the gain to 3, values go negative but still change when I change the load.

The offset voltage for the eval board is about 1.2V, and for the custom board is about 500mV.


I wonder if you guide me regarding this issue and solve the problem.


  • Hello Hamed,

    If I understand correctly, You have both the EVM and your custom board with the same kind of sensor or equipment for the input. Everything works as expected, even when removing the LMPx amplifier. But when PGAGAINx[2:0] = 0b10 = 3 = 4V/V your output flips polarity for the custom board only and not the EVM. Also the offset seems to be different between the EVM and your custom board. Is this correct?

    In general, swapping the gains shouldn't swap the polarity. The V_IN signal (V_IN = V_AINxP - V_AINxN) is the only reason for the output flip polarity. As a result, I suggest you directly measure VAINxP and VAINxN and see if there's any difference. 

    If some of my assumptions are wrong, I could see the differential to single ended conversion of the LMP2022 could be a different transfer function compared to the load cell.