AMC1200: AMC1200

Hironari Ishiguro

Prodigy 130 points

Part Number: AMC1200
Other Parts Discussed in Thread: ISO224, AMC1300

Tool/software:

Please advise about AMC1200. For detail please look at atached circuit.

There are 3 AMC1200 to change 3 output voltage from one 4 to 20mA through 3 10 ohm.

Based on your data sheet, Diferential input voltage is +/-250mV. Can my circuit work properly?

If any problem, please advise.

Also, I am looking for other isolation amp. having better Nonlinearity than 1200.

I would like to get output as equal as changing input current.

Any advise or suggestions I highly appreciated.

BEST REGARDS,

Hironari

Book1.xlsx

over 1 year ago

0 Alexander Smith over 1 year ago

TI__Guru 56592 points

Hi Hironari-san,

I think this circuit looks fine. For better linearity, I would consider the AMC1300B or ISO224.

I am curious why all three devices are measuring the same current? For reliability?

0 Hironari Ishiguro over 1 year ago in reply to Alexander Smith

Prodigy 130 points

Alex,

Thank you very much your prompt reply. I was concerned 3 staright 10ohm that would cause DC voltage up specialy first 10ohm. But it seemed OK. Thank you again. I will consider using your devices. BTW, I actually didn't draw volt to current conversion circuit which convert volt to 4 to 20mA. The current use for controller at several plases. Does this answere for you? If I had any question to use your devices, I will ask.

BEST REGARDS,

Hironari

+1 Alexander Smith over 1 year ago in reply to Hironari Ishiguro

TI__Guru 56592 points

Hi Hironari-san,

Yes - thank you!

0 Hironari Ishiguro over 1 year ago in reply to Alexander Smith

Prodigy 130 points

Alex

I have changed AMC1300 from AMC1200. The result was good but I got another problem. Please take a look at attached excel file.

When I applied 4mA for Iin, the current increased about 40uA after 1st 10ohm. (4.056mA t IB compaired to 4.000mA at Iin)

Is this because of bias current? This delta cause the error at output.

AMC1200 doesn't have such delta current.

I would like to minimise the delta or nothing.

I apprciate if you could provide me any idea or suggestion.

BEST REGARDS,

Hironari

Book2.xlsx

0 Saleh Ahmad over 1 year ago in reply to Hironari Ishiguro

TI__Expert 6750 points

Hi Hironari-san,

Did you do a 1 to 1 swap of the AMC1200 with the AMC1300?

How did you measure the output? Was there any oscillation on the output?

Thanks.

0 Hironari Ishiguro over 1 year ago in reply to Saleh Ahmad

Prodigy 130 points

I dropped in replacement from 1200 to 1300. And measured the current directly to compaire. I didn't see any oscillation. Does this kind of delta current things never happen?

0 Alexander Smith over 1 year ago in reply to Hironari Ishiguro

TI__Guru 56592 points

Hi Hironari-san,

Apologies for the delay in response, I was out on leave.

The AMC1300 and AMC1200 input structures are different. You are correct this difference is due to the input bias current. Please see this application note for additional details. https://www.ti.com/lit/an/sbaa350a/sbaa350a.pdf?ts=1723729863459

This offset can be corrected by increasing the negative different RC filter resistor from 15ohms to 25ohms.

0 Hironari Ishiguro over 1 year ago in reply to Alexander Smith

Prodigy 130 points

Alex,

Thank you very much your suggestions. Actually I put a buffer before 15ohm. The result seemed OK. Please take a look at excel file. Any problem, pleae let me know. In addion to this, I will try your suggetion to change 15ohm. But what is the maximum value to allow?Book3.xlsx

0 Alexander Smith over 1 year ago in reply to Hironari Ishiguro

TI__Guru 56592 points

Hi Hironari-san,

It would be dependent on the value of the sensing resistor. There is not necessarily a maximum value to observe.

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AMC1200: AMC1200