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AMC1301: AMC1301 filter cap too large causing output error

Part Number: AMC1301

Hi support team,

My customer had a urgent issue while using AMC1301 for HV current sensing. They followed AMC1301EVM circuit for the input stage and found when they placed a 1uF cap for the differential mode filter cap, there will be huge output error. But if they reduced the differential mode cap to 220pF the output error will be gone.

Could you please help us to explain why? Here is the circuit they used: 

The table is the test result:

CID VINP-VINN VOUTP-VOUTN AMC1301 Gain
No Filter Cap 0.0021 0.0147 7.00
0.0084 0.0664 7.90
0.0147 0.117 7.96
0.0217 0.1742 8.03
0.027 0.2172 8.04
     
220pF 0.0022 0.014 6.36
0.0085 0.0659 7.75
0.0146 0.1153 7.90
0.0217 0.173 7.97
0.027 0.2152 7.97
     
1uF 0.002 0.0013 0.65
0.0085 0.048 5.65
0.0145 0.0944 6.51
0.0217 0.1497 6.90
0.027 0.1891 7.00

Is this due to the op-amp stability issue when the input capacitance is too large? What would be the maximum cap that can be used for AMC1301?

Thank you.

Best Regards,

Wei-Hao