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ADS1260: Current Sense using ADS123x or ADS126x

Sanket Patadiya
Prodigy 20 points
Part Number: ADS1260


Hi,

I am Sanket Patadiya from Volansys Technologies.

We are trying to design an current sense circuitry to measure 1uA to 15A.

For that Can we use ADS123x or ADS126x series ADC?

Note: We do not want to use the current Sense Monitor IC or Amplifier.

If yes then please provide the application note for the same or any reference design.

Thanks  

  • 0
    TI__Guru 53766 points

    Hi Sanket Patadiya,

    The ADS126x can be used for high resolution current sensing measurements

    How are you intending to architect the circuit? There are many ways this can be done

    Also, what is the voltage across the shunt resistor? Or at least the size of the shunt?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 20 points

    Hi

    I want to implement something like below. 

    Where R is the Sense Resistor.

    I have done some calculations based on reference voltage, Resolution and Offset Voltage. Please see the below table.

    Please review and let us know if you find this feasible.

    Thanks

  • 0 in reply to Sanket Patadiya
    TI__Guru 53766 points

    Hi Sanket Patadiya,

    Are you going to use different shunts for different ranges? Can you provide the target accuracy for each range?

    I am not sure what "step size = 0.584nV" means. You are going to be limited by the ADC noise, which is much greater than 0.584nV i.e. the lowest possible noise with the ADS1260 is 6nVRMS at G = 128 and data rate = 2.5 SPS

    How fast do you intend to sample?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 20 points

    HI Brayan,

    Here are the responses to your questions.

    Q: Are you going to use different shunts for different ranges? Can you provide the target accuracy for each range?

    Response: We will use only one shunt which can sense 1uA to 15A , in the previous table it was 100mohm. 

    Q: I am not sure what "step size = 0.584nV" means. You are going to be limited by the ADC noise, which is much greater than 0.584nV i.e. the lowest possible noise with the ADS1260 is 6nVRMS at G = 128 and data rate = 2.5 SPS

    Response: The step size is the voltage difference between one digital level and the next one. That is calculated with Step size = Vref/2^n where n is bits of ADC and Vref is reference voltage of ADC

    Q: How fast do you intend to sample?

    Response: We would like to sample at highest rate possible.

    As per your comments i think, For the Highest sampling rate 38400 and Gain=32, The noise is 3.276nVrms in ADC126x.

    So Imin = 3.276nV/100mohm = 32.76nA and Imax = 2.5V/100mohm = 25A where2.5V is the full scale reference voltage

    Do you find above calculation correct?

  • 0 in reply to Sanket Patadiya
    TI__Guru 53766 points

    Hi Sanket Patadiya,

    How are you going to determine when to switch the gain then? At 15A * 100mohm = 1.5V, which means you could only use a gain of 1 (with the internal VREF) or a gain of 2 with an external 5V VREF. Are you just going to measure back the voltage across the shunt and then when it drops by a factor of 2 you will increase the gain, then retake data?

    Sanket Patadiya said:
    The step size is the voltage difference between one digital level and the next one. That is calculated with Step size = Vref/2^n where n is bits of ADC and Vref is reference voltage of ADC

    As mentioned, the inherent ADC noise is much larger than the LSB size, so the LSB size is not really meaningful for your purposes. You can only measure to the level of the noise

    Sanket Patadiya said:
    We would like to sample at highest rate possible.

    The faster you sample, the worse the noise performance gets because then fewer samples are averaged within the filter.

    Sanket Patadiya said:

    As per your comments i think, For the Highest sampling rate 38400 and Gain=32, The noise is 3.276nVrms in ADC126x.

    The noise in Table 8-1 is expressed in uVRMS, not nVRMS. So the noise is 3.7266 uVRMS

    You can refer to our ADC Precision Labs training content for more information about ADC operation, behaviors, and parametrics (including noise): https://www.ti.com/video/series/precision-labs/ti-precision-labs-analog-to-digital-converters-adcs.html

    -Bryan