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DRV8306: How to measure current feedback with Rsense

on off
Prodigy 20 points
Part Number: DRV8306
Other Parts Discussed in Thread: INA236

hello.

I used a translator.

I am driving a BLDC motor with the DRV8306 motor driver.

I am reading data with ADC by connecting a differential amplifier to both ends of Rsense.
I found something strange while implementing current control with ADC data.

  1. When there is no load on the motor.
    Power supply current value: 200mA
    ADC value: 2000

  2. When there is a load on the motor.
    Power supply current value: 300mA
    ADC value: 2000

If the ADC value read from Rsense is the same, the current value of the power supply should be the same, but it is not.

I wonder why the current value of the power supply and the ADC value are different.

Best Regards

On

  • 0
    TI__Mastermind 23536 points

    Hey On,

    Thank you for your question. 

    I have assigned this post to a team member who will provide feedback. 

    Best,
    Akshay

  • 0 in reply to Akshay Rajeev Menon
    TI__Genius 12231 points

    Hi On, 

    Thank you for using our forum, and I will be looking into your question. 

    What are the ADC values mapped to? It appears that the value range/resolution for current sensing is capped at 2000 when sensing a current up to 200mA and more (300mA). 

    Could you confirm this by doing a test measurement elsewhere on known smaller and larger currents to determine if the ADC is simply hitting a ceiling value, or if the issue is only occurring when measuring the Rsense resistor?

    Best Regards,

    -Joshua

  • 0 in reply to Joshua Maize
    Prodigy 20 points

    Hi,

    thanks for the answer

    The ADC value when the motor is stopped is 800.
    When the motor is at full torque, the ADC value goes up to 10000.

    Is this a unique phenomenon of BLDC motors?
    Could it be the ADC IC's problem?

    We purchased the INA236.
    Let's test with INA236 as well.

    Best Regards

    On

  • 0 in reply to on off
    TI__Genius 12231 points

    Hi On, 

    If you could confirm that this issue occurs when using that INA236 as well, we can narrow down the issue to potentially be BLDC/method related and go on from there. 

    Thank You and Best Regards,

    -Joshua