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INA230 or what?

Thomas Forster
Prodigy 180 points

Other Parts Discussed in Thread: INA230

Hi
I hope someone can help me with the following design problem:
I have to measure the current for the following pulse width coded signal:

 

Pulse width either 58 or 95 us. Voltage between +/-15V up to +/- 18V.
The loads are PWM-decoders with a standby current as low as 15mA and maximum load current of about 3 to 4 amps.
Now I need to:

  1. Detect overcurrent (4 or 5 Amps)
  2. Detect the presence of decoders even when they are in standby. That means reliably differentiate between 0 mA and 10 mA as well as between 10 mA and 20 mA.

The overcurrent should generate y interrupt to the connect processor.
The measurement result will be polled every 5 or 10 ms.

Can this be done with an INA320?

Thank you.

Best regards

Thomas

  • 0
    TI__Genius 15770 points
    Hi Thomas,

    I will review the requirements and get back to you with a suggestion.
  • 0 in reply to Mayrim Verdejo
    Prodigy 180 points
    looking forward...
    Thomas
    PS: All Decoders use some Kind of bridge rectifier. So measuring the current for the positive half wave would be enough....
  • 0 in reply to Thomas Forster
    TI__Prodigy 380 points
    Hi Thomas,

    To measure current from 10mA to 5A it should be feasible using a 16mOhm shunt resistor.

    My concern is more regarding the fact you want to measure small signals. Indeed the ADC acquisition time is minimum 140µs. Means you need to hold the signal for at least this time. But you application has signals that last only 58 or 98µs.
    In addition you say that the microcontroller is going to poll every 5 or 10ms.

    Can you clarify what you really want to measure on the decoder signal?

    Best regards,
    Aymeric Nicolas
  • 0 in reply to Aymeric NICOLAS50
    Prodigy 180 points

    Hi Aymeric

    Basically I have 2 concerns:
    -          The +18 -18V signal rather than just positive values
    -          The short acquisition time requires a sample and hold mechanism or a very low conversion time
    The microcontroller should supervise the current and it will also decode the digital content of the signal.
    In case of overcurrent it will switch off a solid state relay and cut off the load. In case of a small current (10mA and above) it will report the presence of a Decoder.
    The signal itself is generated on a booster (max. 8A) that will supply the signal to several branches. Each microcontroller will control 2 branches.
    Since the controller is interpreting the digital content of the signal it could trigger a measurement at the beginning of the 100us period.
    With the 5 to 10ms I meant that current supervising does not need to be continuous. A sample every 5 to 10 ms would be enough.

     Thank you and best regards

     Thomas

  • 0 in reply to Thomas Forster
    TI__Prodigy 380 points

    Hi Thomas,

    1) Regarding your first concern it's ok. As you can see bellow the INA230 can sense positive and negative voltage. You just need to adjust the resistor to fit with your range.

    2) For your second concern if I correctly understood you will have difficulties to use the INA230 to measure current on high speed signals. Indeed since the minimal conversion time required is 140µs and your signal can move during the conversion you will not have a relevant result.

    You also say that you need current measurement every 5 to 10ms. Here again, if you're signal is to fast the information you will get will not be relevant.

    Hope those information will be helpful for you.

    Best regards,

    Aymeric Nicolas

  • 0 in reply to Aymeric NICOLAS50
    Prodigy 180 points

    HI Aymeric

    thank you for your inputs. It looks as if TI does not have an out of the box solution for this.
    Start looking at isolated amplifiers now.....

    Thanks and best regards

    Thomas