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DRV8353R: Calibration Questions, Offset

Ue
Genius 16565 points
Part Number: DRV8353R

Hi all

My customer has below question, please review and comment.

Best regards

Ueli

-------------------------------

Our motor controller can drive up to 4 BLDC motors. Therefore 4 DRV8353RTA are being used. In total we use 8 of the 12 differential amplifiers to monitor the motor currents.

Now I could see a special effect. Some of the current sense values have sometimes an extra offset. The offset value changes only when the power gets switched off and on again. It doesn’t matter if only VDRAIN or VM&VREF or VDRAIN&VM&VREF gets repowered, the offset changes sometimes. Typically 1 to 3 current monitor paths are showing the described behavior. All others do not have offset jumps at any time. Until now, the value of the offset jumps was always about 15mV or 30mV (@Gain = 40 and without a load I=0A) and never in between. 15mV offsets are more often seen then 30mV offsets.

 In the data sheet I found some information about  calibration during the power up of VREF. Please, could you tell me more about the calibration.

  • How are the differential amplifier supplied? Only from Vref?
  • When does the calibration start?
  • What impact have supplies such as VREF, VM and VDrain on the calibration.

What steps have to be taken to get to a perfect calibration ?

  • 0
    TI__Guru 63350 points

    Ueli,

    The CSA are powered by VREF, the datasheet explains the autocalibration:

    Auto calibration occurs automatically on device power up for both the hardware and SPI device options. The
    power up auto calibration starts immediately after the VREF pin crosses the minimum operational VREF voltage.
    50 us should be allowed for the power up auto calibration routine to complete after the VREF pin voltage crosses
    the minimum VREF operational voltage. The auto calibration functions by doing a trim routine of the amplifier to
    minimize the amplifier input offset. After this the amplifiers are ready for normal operation.

    I assume the hardware device is being used? If so the customer could measure the offset themselves post calibration and store that value for subtraction from the read back value within the MCU.

    Regards.

    -Adam

  • 0 in reply to Adam Sidelsky
    TI__Genius 16565 points

    Adam

    Thank you for the quick reply.

    Best regards

    Ueli