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INA225 The error factor of the load of the PWM drive

Tomoaki Yoshida
Expert 2200 points


Hi,

 

I want to estimate the total error at monitoring solenoid current drived PWM.

 

The maximum PWM frequency is 18kHz and Vcm will swing from 0V to 16V.

The ambient temperature is between -40 and 125 degree.

I would like to know the influence of the CMRR against vout error.

I can easily estimate the offset voltage and drift.

I have no idea the output voltage level when Vcm swings by square wave.

Let me know the how to estimate.

 

Best regards.

  • 0
    TI__Expert 4595 points
    Hi Tomoaki,
    CMRR specification is 95 db (17.78 uV/V). So you can estimate error due to CMRR Refered to input @ 0V to be about 213.36 uV (17.78 * (12-0))and @ 16 V (17.78 * (16-12)) to be about 71.12 uV (12 V Common mode is the datasheet test condition). Multiply this by the gain for output referred error. Please let me know if you have questions.
  • 0 in reply to Rabab Itarsiwala
    Expert 2200 points

    Hi Rabab,

     

    Thank you for your reply.

    Dose CMRR depend on frequency?

    I think that 95dB is specified at DC or low frequency.

    The Vcm will swing square between 16V and 0V, and at 18kHz .

     Can I use this formula to estimate peak voltage in this case?

     

     

    Best regards,

    Tomoaki Yoshida 

  • 0 in reply to Tomoaki Yoshida
    TI__Expert 4595 points

    Hi Tomoaki,

    Yes CMRR depends on frequency.

    In this case there will be a transient response when the common mode switches from 0V to 16 V and 16 V to 0V which might take few micro second to settle. Once the output settles the DC error estimation can be used. The numbers I mentioned in the earlier post are only CMRR error estimation; offset voltage, offset drift, gain error, gain error drift, shunt resistor errors also need to be accounted for total error estimation. Please let me know if you have questions.

    Also what will be the rise time of the PWM wave?