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DRV8434: Commutating a stepper motor: xIN1 and xIN2 vs. chopper current control?

David Preiss1
Prodigy 80 points
Part Number: DRV8434

I am working on a project involving manually commutating a stepper using the DRV8434PRGER, while still driving VREFA and VREFB sinusoidally to microstep with Smart Tune Ripple Control enabled. My understanding would suggest that I should control current direction for each H-bridge with AIN1 and BIN1 (imagining that they're driving the left side of each H-bridge), and that if I wanted to manually chop for current control I would control AIN2 and BIN2 (imagining that they're driving the right side of the H-bridge). Given that I want to control current with VREFA and VREFB, it seems that either xIN1 or xIN2 should be left un-driven for my application, and that the IC would do this chopping for me. Do I need to configure the IC in any way for this? Is there a preference for controlling current direction with either xIN1 or xIN2?

The relevant header in the datasheet for Table 7-3. DRV8434P (PWM) Control Interface says "Note that this table does not take into account the current control built into the DRV8434P." From what I can tell the datasheet does not specify which pair of FETs are driven by the decay mode.

  • 0
    TI__Guru 56650 points

    David,

    The 1st paragraph statements are correct. DRV84xxPEVM GUI/Firmware supports a stepper motor control in full step mode (xVREF is fixed, instead of sinusoid waveform).

    BTW, if you select DRV8434PWPR device (step/dir interface), the internal indexer table can automatically set each winding step current and direction for you. You only need to give the step and dir signal.

    When the OUT1 and OUT2 are both high or both low, it is a slow decay. I really think you should use step/dir interface device, DRV8434PWPR, which can save you a lot of time to program the decay mode, microstepping mode, sinusoid waveform look-up table...

  • 0 in reply to Wang5577
    Prodigy 80 points

    Hi Wang, thank you for the fast response. For my application I need full control over the waveform, so using a step/dir interface is not an option.

    I believe what is missing from the datasheet is a schematic showing which inputs go to which FETs, and which FETs are controlled by VREFx. Is that something that can be provided?

  • 0 in reply to David Preiss1
    TI__Guru 56650 points

    David,

    You can make xOUT1 half bridge high and xOUT2 half bridge low to control the current flows from xOUT1 to xOUT2. Drive low is not undriven.

    When the output current reaches the Itrip which is set by the VREF, the high side FET of xOUT1 half bridge is turned off. The other FET's action is decided by the decay mode selection.

    Please let me know if you have further question.