We found AMC1200 circuits' deviation is large, the gain range is big. Could you please help review the schematic to see if there is any improvement?
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I also would be interested to see the results with the diodes removed, they sometimes cause issues when interacting with the front end of the device. - Thanks Kai!
Their sensing resistance of 100ohm is not very high, but the differential input resistance of 28kohm is in parallel with the sensing resistance, resulting in an equivalent sensing resistance of 99.64ohm.
How many systems have they tested? Is this the first proto or have they tested several boards?
Are the values in the input/output columns calculated or measured? If measured, can you please indicate on the schematic exactly where?
I recommend measuring directly at the input and output pins with a digital multimeter to ensure correct device behavior.
Hi Kai, Alex,
Sorry for the mistake, 0.1202 is AMC1200 input and 0.9628 is AMC1200 output, so the gain is around 8.
The table below is the measure result, and they are measured at input and output of AMC1200, the voltage between VINP and VINN, and voltage between VOUTP and VOUTN.
Could you please analyze why gain deviation is big? From datasheet, 8 is normal value, there is no min or max value.
The device has a nominal gain of 8, with a specified gain error of +/-0.5% at ambient temperature. This means that the gain can vary from 7.96 to 8.04 and remain within spec. The device also has offset error, which I believe is why a larger "gain" value is seen at lower voltages - the offset error has a larger contribution to the overall error. As the common-voltage increases, the static offset error becomes smaller and smaller and you can see the gain moving closer and closer to spec.
Ask them to take an additional measurement at 0V Common Voltage. This should define their offset error. Subtract this offset error from the input/output values, (remember to multiply input offset by 8 for output) then re-calculate the gain of the device.
Thanks for this information. It is helpful.
To improve the system accuracy, we are convincing customer change single input to differential input.
If you have other devices for improving system accuracy, please tell us.
I do not understand the transition from single input to differential input. Can you please clarify what you are advising the customer?
What I was trying to point out in my previous post was that offset error may be included in the measurements that they are using to calculate gain error.