AMC1200: AMC1200 Schematic Review

Chen Jiao

Part Number: AMC1200

Hi team,

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?

Thanks.

Schematic

Testing results

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi Chen,

what happens if you remove D5 and DV74 for a test? D5 and DV74 can show high leakage currents and by this decrease the precision of your circuit.

Kai

0 Alexander Smith over 3 years ago in reply to kai klaas69

TI__Mastermind 47595 points

Hi Chen,

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?

0 Chen Jiao over 3 years ago in reply to kai klaas69

TI__Intellectual 810 points

Hi Kai,

Thanks Kai, we will test it after removing D5 and DV74.

Best regards.

0 Chen Jiao over 3 years ago in reply to Alexander Smith

TI__Intellectual 810 points

Hi Alex,

Thanks Alex.

The testing results are from one board, but we have tested several boards with the similar situation.

I think customer concerns the deviation, from example Gain change from 8.0009 to 8.101.

Best regards.

0 Chen Jiao over 3 years ago in reply to Chen Jiao

TI__Intellectual 810 points

Hi Kai, Alex,

Customer remove diodes but no change of the results.

Could you please give other advice how to improve it?

Thanks a lot.

Best regards

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi Chen,

I don't understand the table :-)

22k + 22k +3k9 +100 gives a division factor of 480. So for an input voltage (between "BATV1+" and "BATV1-") of 60.02V the voltage at the input of AMC1200 should be 0.1250V, not 0.9628V. Can you please explain?

Kai

0 Alexander Smith over 3 years ago in reply to kai klaas69

TI__Mastermind 47595 points

Hi Chen,

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.

0 Chen Jiao over 3 years ago in reply to Alexander Smith

TI__Intellectual 810 points

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.

0 Alexander Smith over 3 years ago in reply to Chen Jiao

TI__Mastermind 47595 points

Hi Chen,

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.

0 Chen Jiao over 3 years ago in reply to Alexander Smith

TI__Intellectual 810 points

Hi Alex,

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.

Thanks.

0 kai klaas69 over 3 years ago in reply to Chen Jiao

Guru 140200 points

Hi Chen,

R90 and R? are a bit high. The datasheet recommends 12R.

Kai

0 Alexander Smith over 3 years ago in reply to Chen Jiao

TI__Mastermind 47595 points

Hi Chen,

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.

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AMC1200: AMC1200 Schematic Review