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ADC102S021: Suitable ADC for low BW and low latency

Nick
Intellectual 672 points
Part Number: ADC102S021
Other Parts Discussed in Thread: ADC101S021, TL061, TINA-TI, TPS65130

Tool/software:

Hello,

I am searching ADC for Analog Accelerometer.  Sample rate is 100HZ.   Measurement error of less than 10% up to 10HZ with low latency  (< 50 ms) is required. 

I am afraid about latency and signal attenuation in passband due to digital filter in delta sigma ADC.  I don't see flat response in passband in Sinc1 filter. so I have decided to use SAR architecture. I have opted for ADC102S021 as it meets my requirements. 

System requirement:

Minimum Resolution : 10mV. 

Sensor O/p : 0.5V to 4.5 V

Sampling Frequency: 100 sps

I concluded that 10 bit SAR ADC should be fine for my requirement  (LSB : 4.88mV with Ref:5V) .

Please let know if you see any issue in ADC102S021.  Any better option available in Delta Sigma.

Thanks

Nick

  • 0
    TI__Genius 17760 points

    Hi Nick,

    The ADC102S021 is definitely a good choice that would meet your requirements. Are there any other needs or wants for the ADC in your design? Are 2 input channels necessary? The single channel version of this device would be the ADC101S021 if that interests you more.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 672 points

    Dear Joel,

    Thanks for reply. There are two accelerometer so using two channel ADC.

    Another question I want to ask. I am also thinking to add Bessel filter with cutoff fc  25 HZ before ADC, as I am interested in Accelerometer data with up to only 10HZ.   I have selected TL061 op-amp for that purpose. PDF from design filter application also attached.

    With this filter design TINA-TI shows 6 % attenuation at 10HZ which meets my requirement of max 10 %.  Any comments/feedback6735.design.pdf

  • 0 in reply to Nick
    TI__Genius 17760 points

    Hi Nick,

    Can't see anything that would be off here. Looks great! 

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 672 points

    Thanks Joel,

  • 0 in reply to Nick
    TI__Genius 17760 points

    Hi Nick,

    Let me know if you were able to resolve the issue with your simulation. It looks like you have edited the post, but it seemed to me to be an issue with the common-mode voltage of the amplifier. 

    The datasheet gives a Vcc+ -4V figure, which is likely conservative, since it doesn't clip until over that. The solution would be to do as you did, and increase the positive voltage rail.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 672 points

    Yes, I increased the supply voltage to +-10V.  Now there is no more voltage clipping.  I have shortlisted TPS65130 for make dual supply from  lithium cell. And the same +10V rail will be using for excitation voltage for my Analog Accelerometer sensor. 

    Does this plan sounds good ?

    Regards 

  • 0 in reply to Nick
    TI__Genius 17760 points

    Hi Nick,

    Theoretically that should be fine, but I am not really familiar with the TPS65130, and don't know if it would be optimal for your application. Feel free to repost this question on the power management E2E forum and someone should be able to give you some more insight into this. Alternatively, there could be an amplifier that allows you to get away with only one supply. 

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 672 points

    I just realized my sensor o/p voltage range is from  -0.5V to 4.5 V.  AIN_M will also be at ground(zero). 

     One option I see is Level shifting.  Shifting up by 0.5V so  0 - 5 V i/p range.  Any suggestion on Level Shifting.. I see few app notes.. Am I on right track ?

    If I am on right track, I plan to use REF35120QDBVR   to make 1.2V . Will use 1% resistance with voltage divider to make 0.5V.   If this is ok, then what is the best way for level shift.

  • 0 in reply to Nick
    TI__Genius 17760 points

    Hi Nick,

    Apologies for the very late reply, as I was out on business travel for the past week. I believe you are definitely onto the right path, but it might be helpful to get some more insight onto the sensor that you are using, since it's output seems so particular. Are you able to provide more information on this part?

    Otherwise, let me know if you were able to make any more progress on this front beyond that, since it has been a little while.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 672 points

    Sensor output is from 0.5v to 4.5 v during normal operation.  There is self test option when one the lead is shorted to ground, the sensor reads -0.5v. 

    So I have considered a range from -.5 to 4.5 v    and after shifting it will be 0 to 5V.  I have shifted using inverting sum amplifier and again inverting with unity gain to get positive polarity. TINA simulation shows ok. Output goes to ADC. Please have a quick look at schematic. 

  • +1 in reply to Nick
    TI__Genius 17760 points

    Hi Nick,

    I was able to verify this configuration on TINA as well. Let me know if you have any more questions on configuring the ADC102S021 in the future.

    Regards,
    Joel