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AMC1200: AMC1200

Hironari Ishiguro
Prodigy 90 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 

  • 0
    TI__Guru 52722 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 in reply to Alexander Smith
    Prodigy 90 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 in reply to Hironari Ishiguro
    TI__Guru 52722 points

    Hi Hironari-san,

    Yes - thank you! 

  • 0 in reply to Alexander Smith
    Prodigy 90 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

    Book2.xlsx

  • 0 in reply to Hironari Ishiguro
    TI__Expert 4900 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 in reply to Saleh Ahmad
    Prodigy 90 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 in reply to Hironari Ishiguro
    TI__Guru 52722 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 in reply to Alexander Smith
    Prodigy 90 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 in reply to Hironari Ishiguro
    TI__Guru 52722 points

    Hi Hironari-san,

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