This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS131M02-Q1: Accuracy and instruction confirmation

Part Number: ADS131M02-Q1

Hi Expert,

Thanks for your warm help!

Here are some question raised from me.

1. I use the excel of CS calculation sheet to calculate some parameter. Resolution(mA)=0.1/B3*1000. It seems that the resolution just has relationship with shunt resistor. From my perspective, the resolution do has some relationship with the bit of ADC.

2. Would you mind giving me some suggestions on the clock input of ADS131M02-Q1? Do we need another external clock? or the output of MCU is enough for our application?

Looking forward to your reply!

Kind Regards

Imelda

 

  • Hi Imelda,

    1. I use the excel of CS calculation sheet to calculate some parameter. Resolution(mA)=0.1/B3*1000. It seems that the resolution just has relationship with shunt resistor. From my perspective, the resolution do has some relationship with the bit of ADC.

    In short, with calibration, the shunt resistor should be the dominant source of error compared to the ADC. 

    That being said, thermal noise will limit the effective resolution of the ADC. The RMS noise is plugged into the equation below to obtain the effective resolution column determined by OSR (or data rate), and gain.

    Check out this TI Design to get an idea of the kind of error you can find for this device family: TI Design - High accuracy split-phase CT electricity meter reference design using standalone ADC: https://www.ti.com/tool/TIDA-010037  

    2. Would you mind giving me some suggestions on the clock input of ADS131M02-Q1? Do we need another external clock? or the output of MCU is enough for our application?

    Really the only issue with the clock is to make sure it falls within the specification according to the datasheet and scaling your frequency will affect your data-rate: 

    And then, acknowledge that jitter can your measurement, here's a FAQ: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/890938/faq-the-relationship-between-snr-and-adc-clock-jitter . I find that most MCUs can achieve pretty good performance so there's no real concern. It's even the best configuration because SCLK and f_CLKIN be derived from the same source. 

    We use a crystal on our EVM if you need a back up and we can get datasheet performance using that if the MCU has a limitation for some reason: https://www.ti.com/tool/ADS131M04EVM 

    Best,

    -Cole

  • Hi Cole,

    Thank you for the reply.

    Could you help me to confirm below current calculation is right or not? 

    Assumed condition: GAIN = 8, shunt = 100uΩ ,OSR = 16384 , 

    FSR = ±150mV(according to Table 8-1. Full - Scale Range) 

    Imax = U_FSR / R_shunt = ±1500A  ---> MAX Current can be detected.

    According to Table 7-2, Dynamic Range(Effective Resolution) 

    Effective Resolution = 2 ^ 18.3

    Umin = U_FSR / Effective Resolution = ±150mV / (2 ^ 18.3) = ±0.465uV

    Imin = Umin / R_shunt = ±4.54mA  ---> MIN Current can be detected.

    Looking forward to your reply!

    Kind Regards

    shen