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DRV8836: DRV8836 vs DRV8834 lower phase current / RDSon

Genius 16385 points
Part Number: DRV8836
Other Parts Discussed in Thread: DRV8834, , DRV8834EVM

Hi all

Referring to this former post:

https://e2e.ti.com/support/motor-drivers/f/motor-drivers-forum/977132/drv8836-parameters-affecting-rdson

my customer has provided these additional comments:

For their stepper-motor: Initially they worked with the DRV8834EVM, later on they worked with the DRV8836 on their own PCB and found 24% lower torque compared to the DRV8834. This came as a surprise as the two devices have comparable RDSon values.

As to measuring the RDSon: The VCC is a stable 3.3V in their design. The voltage drop was calculated as the maximum available voltage (2*3.3V=6.6V pk-pk) minus the measured phase voltage. From this value they calculated the RDSon.

Please also find a comparison for the DRV8834 vs. DRV8836 current where the DRV8836 draws less current.

Please comment as to the possible root-cause for the lower torque of the DRV8836 vs DRV8834.

Best regards

Ueli

  • Hi Ueli,

    On first glance, i would say curves for DRV8834 and DRV8836 were taken at two different voltages or for different motors or for

    the same motor but at different temperatures (winding resistance depends on temperature).

    For Rds to have such a big influence it would have to be at least a few Ohms, so I do not think it is a problem.

    The problem may be caused by differences in both drivers or their control.

    DRV8834 is primarily designed for stepper motors while DRV8836 is not.

    I think to find out what is going on it would be helpful to measure with an oscilloscope output voltage and phase current for one phase (at the same time)

    for both drivers with the same motor. Motor in both cases should have similar temperature and have the same load.

    It would be good to take these measurements at two different speeds, let's say 600 and 6000 rpm.

    Best Regards,

    Grzegorz

  • All good points Grzegorz!

    Ueli,

    Will wait for your response to the above suggestions.

    Regards,

    Ryan

  • Grzegorz,

    Thanks, agree with you. We need to compare output voltage and current to understand their setting difference between DRV8834 and DRV8836.

    Regards,

    Wang

  • Hi Gregorz

    Thank you for the quick reply. I will let the customer comment on these questions.

    Best regards

    Ueli