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INA301: Current shunt monitor solution using INA301 + ADC122S101 questions

Vlad Blanshey
Intellectual 770 points
Part Number: INA301
Other Parts Discussed in Thread: ADC122S101,

Tool/software:

Hello, I want to ask your thought regarding this solution for the current shunt monitoring. Our goal is - a fast conversion of the shunt voltage with subsequent ADC via SPI reporting to MCU and also fast alarm trigger in case of programmed over-current event. This solution I want to apply in two different scenarios. One is a shunt in series with a ground side of power input from the main battery. The battery is up to 150V. The other place is the low side of H-Bridges powering a motor. Any scenario current expected under 100A , a single polarity. Shunt value we use so far is from 0.7m Ohm to 1 mOhm.

Both placements of a shunt make it's differential voltage reading from 0V to 100 mV .  Also I want to measure the battery voltage using a voltage divider from 150V to whatever common mode voltage limit is in ADC122S101 converter (30V ?). I'll use 0.1% precision resistors.

Am I correct assuming that these ways CMV will not accede the limits of ADC122S101 chip ? Also can I use  both channels of ADC122S101 chip (in reference to common ground) as one for current shunt measurement and another channel for battery voltage measurement via dividers? I think that using a single channel to measure a shunt voltage on a low side (at the common ground point) would not be any different than using both channels for a differential input from this shunt (if it is indeed no different then one channel would simply be wasted). Am I right or am I missing something?

The SPI lines from ADC122S101  to MCU bus are galvanically isolated with fast isolator .

Please comment on this usage of INA301 + ADC122S101  for both cases. Is this a good solution? Do you think the INA301 precision is acceptable for these scenarios (after all this is the only chip I found to do both fast shunt voltage amplification and built-in comparator).

  • 0
    TI__Genius 17280 points

    Hello, 

    Thank you for your post. 

    I will take a look at this and provide feedback tomorrow on the INA301 side. 

    Unfortunately this is the only product I support. 

    Thank you for your patience, 

    Joe

  • 0 in reply to Joe Vanacore
    TI__Genius 17280 points

    Hello, 

    I do believe the INA301 is the correct choice for this application. 

    Best Regards, 

    Joe

  • 0 in reply to Joe Vanacore
    Intellectual 770 points

    Thank you Joe, I also need a confirmation on mating output of INA301 with ADC122S converter. Especially usage of ADC single channel in reference to the ground as oppose to a differential input using both channels. Can somebody give advice ?

  • 0 in reply to Vlad Blanshey
    TI__Expert 5560 points

    Vlad,

    Thanks for the question and using the E2E forum.

    Due to the U.S. holiday on July 4, we are currently out of the office. Someone will reply when we return on Monday, July 7.

    Thank you for your patience.

  • +1 in reply to Louis L
    TI__Genius 17280 points

    Hello Vlad, 

    I am providing you with a document that will go through the design considerations that you need to take into account. 

    https://www.ti.com/lit/an/sboa443/sboa443.pdf 

    Please go through this and let me know if you have any questions.

    Best Regards,

    Joe

  • 0 in reply to Joe Vanacore
    Intellectual 770 points

    Thank you Joe, I did my best to learn the science from that doc and have a question. It well explains the need for a so called a "charge bucket filter" (that is in between the output of shunt amplifier and ADC chip) , which is not currently in my schematic. I have directly connected output of INA301 to the input of ADC122S. But I do have the input filter on INA301 inputs (Rfilter=10 Ohm in series  and 0.1uF Cfilter) and this filter in essence is a low pass filter thus reducing the bandwidth and shortens the transients at the INA301 outputs. This , in turn, should help to slow down changes to the input tracking capacitor of ADC converter. In other way to look at this is to compare the input capacitors: the ADC input tracking capacitor is 33pF while my shunt amplifier input Cfilter is 0.1uF - it seems to significantly slow down any transient changes to the input signal whence to the output of INA301 and then, down the stream, to the input of ADC . Please let me know whether my analysis is correct or, otherwise I am just justifying my omission of the charge bucket filter to ADC chip.

  • 0 in reply to Vlad Blanshey
    TI__Genius 17280 points

    Hi Vlad, 

    I do apologize but I will not be able to provide you with an update until tomorrow. 

    I have an emergency to address today. 

    Thank you for your patience, 

    Joe

  • +1 in reply to Vlad Blanshey
    TI__Expert 5590 points

    Hi Vlad,

    The need for the charge bucket filter is less about speed and more about being able to supply the necessary inrush current to the ADC at each sample. The filter on the input will not help with this therefore the charge bucket filter is needed.

    Best,

    Holly