• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 48 subscribers
  • Views 669 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

INA240-Q1: Negative common mode input voltage

Tomoaki Yoshida91
Genius 5255 points

Part Number: INA240-Q1
Other Parts Discussed in Thread: INA240

Hi team,

We are examining the current detection using INA240-Q1 for the motor drive circuit .

The current is detected on the high side of the 12 V power supply, but input common voltage might be less than -6 V by the counter electromotive force.

We have taken measures, but it is difficult to keep -6V.

Are there any effective measures when the input common mode voltage isless than  -6 V?

We want to somehow use the INA240-Q1, for a balance of accuracy and gain.

If the reverse current flows when the voltage drops below -6 V, how about putting a diode in the path?

For example, insert a forward diode to the GND terminal.

Will the input filter relax this?

Best regards,

Tomoaki Yoshida

  • 0
    TI__Mastermind 27715 points
    Hello Yoshida-san,

    My apologies for the delay in response. Our INA240 expert was out of the office on Friday but will return on Monday. He'll evaluate your question and respond then. Have a great weekend!

    Best regards,

    Ian Williams
    Applications Manager
    Current & Magnetic Sensing
  • 0
    TI__Mastermind 33890 points
    Hello Yoshida-san,

    I am not the INA240 expert but I may have some inputs or questions that can help yourself or our expert.

    Do you need to make a measurement when the Common mode is below 6V or is this just a kick back from the inductance of the motor? You can place a diode from the inputs to GND if the voltage to limit the voltage to not go below GND + diode voltage but make sure it can handle the kick back current and the leakage during normal operation does not change your measurements.

    The input filter may help some but please be aware this also adds error to your measurement. Please see section 9.1.1 of the datasheet regarding input filtering.

    There are other devices that we have that can go below -6V but they do not have the same specification as the INA240. If you can add the diodes so that the voltage at the INA240 does not go below that will help.
  • 0 in reply to Javier Contreras4
    Genius 5255 points

    Hi Javier-san,

    Thank you for your support.

    It is not the kick back from the inductance of motor that a negative voltage occurs.

    Negative surge at battery connection.

    There is no need to make measurements, and we want the device not to break down.

    Is the input-to-GND diode that you commented in the figure below?

    I think that this method also reduces the accuracy due to the leakage current as with the input filter. Is this correct?

  • 0 in reply to Tomoaki Yoshida91
    TI__Mastermind 33890 points
    Hello Yoshida-san,

    Adding the diodes should work. The schematic you provided is how it can be added. I think this is all you need to do and below is further thoughts but I do not believe they are normally issues.

    If you do not add resistors from Rshunt to the diodes the leakage of the diodes will normally not be an issue but please be aware depending on the diode used the leakage will be different. Be aware that the INA240 also has input bias current and that is why we do not recommend the series resistors for filters to the inputs as I mentioned in section 9.1.1 of the datasheet.

    You also need to make sure the diodes can handle the power surge during the transient. Typically the larger (higher power) the diode the larger the reverse current. Be aware that the diode still will have a forward voltage and will be dependent on the current. I do not think this would be an issue unless the current is very large.
  • 0 in reply to Javier Contreras4
    Genius 5255 points

    Hi Javier-san,

    Thank you for your support.

    INA240's input bias is 90uA@typ.

    Since diode leakage is sufficiently small compared to the bias current of the IC, there is no problem with adding a diode.

    It is assumed that the diode leakage is even smaller than 1uA.

    Is it correct?

    Best regards,

    Tomoaki Yoshida

  • 0 in reply to Tomoaki Yoshida91
    TI__Mastermind 33890 points
    Hello Yoshida-san,

    That is correct. Be aware some diodes do have larger leakage but I think most will be below any concern.