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INA241A: PWM rejection

Ohad Bonneh
Intellectual 2650 points

Part Number: INA241A
Other Parts Discussed in Thread: INA296A,

I am checking the possibility of integrating the INA241A or INA296A components into my power board, which performs phases voltage switching for a PWM motor.

In the INA241A datasheet, it states that it has a PWM rejection mechanism:
"When INA241x senses the large common-mode V/t transients, the device holds the output for 1 us, thereby preventing the common-mode disturbance from propagating to the output."

In contrast, the INA296A does not have such a mechanism.

My questions is:

  1. Does the device indeed hold the output for 1usec when it detects large common-mode transients? Did I understand this correctly?
  2. Why does the INA296A not include such a mechanism?
  3. What is the advantage of having this type of mechanism?
  4. If I want to integrate a current-sensing device (up to 70A) on a phase that is being switched in a three-phase motor drive, is the INA241A a good choice?
  • 0
    TI__Mastermind 20060 points

    Hello Ohad, 

    Thank you for your post.

    Please see my responses to my questions:

    1. Yes your understanding is correct. The output will be held for 1us.
    2. We wanted to offer multiple flavors of this device. Some customers prefer low distortion from PWM voltage edges for downstream ADCs/MCUs and some prefer the response to track the input for that 1us hold time. 
    3. The advantage is less output distortion from the common mode voltage input edges. So for control loops where this will create error, this is where the advantage comes in. 
    4. My follow-up question would be what is your switching frequency? The faster the switching frequency, the more impactful that this 1us hold time will be. I would say that there are filtering techniques to address this distortion of the INA296 so it depends on your system requirements. 

    I look forward to your response, 

    Joe

  • 0 in reply to Joe Vanacore
    TI__Intellectual 2650 points

    I work with switching frequency of 20Khz-40Khz

  • 0 in reply to Ohad Bonneh
    TI__Mastermind 20060 points

    Hello Ohad, 

    Thank you for this additional information. 

    At your highest frequency, the period of your switching waveform is 25µs. So with the 1µs hold time, you may have as much as 4% phase error in that 1µs window. 

    So I would recommend using the IN241 if this phase error is not an issue and you need to prioritize minimal peak to peak coupling from input to output of the INA. 

    Hopefully that helps, 

    Joe

  • 0 in reply to Joe Vanacore
    TI__Intellectual 2650 points

    Can you show me the graph where the output is held for 1 µs when there is a large change in common-mode voltage?

  • 0 in reply to Ohad Bonneh
    TI__Mastermind 20060 points

    Hello Ohad,

    I will provide you with data tomorrow. Unfortunately we do not have a plot in the datasheet.

    Thank you for your patience,

    Joe

  • 0 in reply to Joe Vanacore
    TI__Mastermind 20060 points

    Hello Ohad, 

    I apologize for not hitting reply yesterday. 

    Here is a scope capture of the typical output behavior where the INA241 output (CH4) is held for 1us.

    I hope this helps, 

    Joe