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AMC1100: Vin and Vout relationship

Manmohan Vishwakarma
Prodigy 130 points
Part Number: AMC1100
Other Parts Discussed in Thread: ADS1115

Hi Team,

I am using AMC1100 for a current and voltage sensing application. I just hooked up a simple circuit on breadboard in which high voltage side of AMC is used for measuring voltage for 60mV to 130mV.

After Powering up(5V to VDD1 and another isolated 5V to VDD2) the circuit i am checking voltage on low voltage side of amplifier. When i apply 60mV on High Voltage side i am getting about 2.80V on low voltage side.

for 90mV Vin , output is 2.94V;  for 130mV Vin , output is 3.57V....

I am not able to find the relationship between the input and output. please help me... where I am doing things wrong.  ??

  • 0
    TI__Mastermind 31655 points

    Hello Manmohan,

    Can you please clarify how you're measuring your inputs and outputs? Since this is a fully differential amplifier, the input is measured between VINP and VINN, while the output is measured between VOUTP and VOUTN. The gain of the device is 8V/V, so it should be that (VOUTP-VOUTN) = (VINP - VINN) * 8.


    It seems like you may be measuring your output between VOUTP and GND2 instead. Are you also measuring the inputs between VINP and GND1? This may not be an issue if you have VINN connected to GND1.

    Assuming the VCM of the output is exactly the specified 2.55V, I can calculate your differential output by subtracting the VCM and multiplying by 2. This gives 0.5V differentially for your 60mV input, 0.78V for your 90mV input, and 2.04V for your 130mV input. The first two give gains of 8.33 V/V and 8.66V/V, which are on track, but the third measurement shows a gain of 15.7V/V, which suggests the VCM may have moved, or the measurement is somehow off.

    Can you describe how you are taking your measurements, and show a simple schematic of how you have the device hooked up?


    Thanks!

  • 0 in reply to Scott Cummins
    Prodigy 130 points

    Hi, thanks for your quick reply...

    I have grounded VINN and VOUTN. and measuring voltage between VOUTP & GND2, R1 and R2 are chosen such that i get desired voltage range.,

  • 0 in reply to Manmohan Vishwakarma
    TI__Mastermind 31655 points

    Hi Manmohan,

    It looks like the trouble here is related to the output configuration. The AMC1100 is a fully differential amplifier, so the VOUTN is always being driven, and it should not be shorted directly to ground. You can either leave it open, or pull it down to ground with a resistor on the order of 10kohm or similar.

    Keep in mind that your output will always be riding on the common mode of the AMC1100's output which is 2.55V with a 5V VDD2.

    If you are interfacing with a single-ended ADC you may also find this app note helpful: http://www.ti.com/lit/an/sbaa229/sbaa229.pdf

    Regards,

  • 0 in reply to Scott Cummins
    Prodigy 130 points

    Hi Scott,

    Thank you very much ..

    after disconnecting VOUTN from 0V ...it is working fine as expected..I want to use it in differential configuration.

  • 0 in reply to Manmohan Vishwakarma
    Prodigy 130 points

    please suggest any application note for differential design. I am using ADS1115 ADC.

  • 0 in reply to Manmohan Vishwakarma
    Guru 140200 points

    Hi Manmohan,

    you will find very useful material in the datasheet of ADS1115 itself. Go to section 10.2 "Typical Application".

    Kai