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DRV8844: As Bipolar Stepper Motor Driver

Rav Kal
Prodigy 80 points
Part Number: DRV8844
Other Parts Discussed in Thread: DRV8825

Hi TI Motor Team:

I am using DRV8844 as a bipolar stepper driver to do a motor load test by combining the quad half bridges(IN 1-2 & IN 3-4) in two pairs.

Unfortunately my test so far with DRV8844 results in buzzing sound for half-steps and full steps, whining sound for micro-steps but no movement at all even with minimal motor load.  I have connected stepper to OUT1/OUT2 and the other pair to OUT3/OUT4. I have used the 8844  eval board schema for reference, connect the LGND to my MCU ground but GNDs on supply and MCU are isolated.

I am not sure if my connections are wrong since the fault line goes LOW right after it tries to step or it is some problem with charge pump. Kindly give me some suggestions and point me to a connection diagram/schema so I can get the motor moving,

Thanks,
Rav

  • 0
    TI__Expert 4435 points

    Hello Rav,

    The fault line going low means you have an overtemp, overcurrent, or UVLO condition.

    Figure 8 on datasheet shows stepper motor connections.

    Please refer to the hardware files under design files here. You will find schematics and layout recommended for proper operation. Thank you.

  • 0 in reply to Luis Riveros
    Prodigy 80 points
    Hi Luis:

    You are stating the obvious. I know what FAULT going LOW means and you pointed to schema I already referenced in my background summary.

    I gave background so I could get suggestions. Like check x, y and z to help trouble shoot the issue.

    I tried hard and stumbled in my effort, so I came to the forum. As a customer I deserve the basic courtesy of being pointed in the right direction ?

    Rav
  • 0 in reply to Rav Kal
    TI__Expert 4435 points

    Hi Rav,

    I pointed out to the layout files as well to make sure you have proper routing since you have seen a fault.

    Could you please provide the following:

    What voltage are you operating at? What are your load specs? How are you regulating current?

    You might have an overcurrent event. Are you using the sense resistors to monitor current? What voltage at those pins? Thank you.

  • 0 in reply to Luis Riveros
    Prodigy 80 points
    Hi Luis:

    It is operating at 24V. The stepper is rated at 3A and 24-48 V. I have run it with a DRV8825 before. I am using simple PWM - high, low and time delays to pulse from an Arduino board to do simple Full Step, Half-Steps and Micro-steps.

    Since fault occurs right at the outset I suspect an over-current(OC) too. If so can it be triggered by incompatible INx pulse combination(high/low side) or some other reasons ? I am currently rebuilding the circuit but got 24 V across VM and VNEG, 3-4 V and 330 mAmps across OUTx pins with prior circuit.

    Will get back on sense resistor current/voltage on the rebuilt circuit. Thank you for following up.

    Rav
  • 0 in reply to Rav Kal
    Prodigy 80 points
    Hi Luis:

    These are the various measurements I got on the new circuit:

    Sense Resistor
    SRC34 - 0.83 Amps; 5V (across 2 ohm resistor)
    SRC12 - 0.0 Amps; 0V (across 2 ohm resistor)

    Load
    OUT1 - OUT4 : 0.86 Amps and 5V (upto varies below based on type of stepping)
    OUT2 - OUT3 : 0.86 Amps and 5V (upto varies below based on type of stepping)

    The fault line input comes as HIGH while using a input pull-up resistor. But I still have no movement on the motor even though it continues to make noises and the chip also heats. Using 100uF charge pump and 10uF discharge capacitor as hinted in the data sheet.

    So please any suggestions to get the stepper moving.

    Rav
  • 0 in reply to Rav Kal
    TI__Guru** 114905 points
    Hi Rav,

    Does your circuit look like the functional block diagram shown in the datasheet (section 7.2) with the optional current sense resistors?

    The sense resistors should be less than 200mOhm to remain below the absolute maximum of 0.6V on SRC12 and SRC34. How are you measuring the voltage across the resistors to regulate the current?

    Also please note the datasheet recommends a 100nF charge pump cap and a 10nF cap across CP1 and CP2.
  • 0 in reply to Rick Duncan
    Prodigy 80 points
    Hi Rick:

    Yes, I mimic sec 7.2 block diagram with cap values from TI Ref board schema. But it seems for some reason my OUTx paring is off and only one pair shows regular volt/current variation while I am driving all INx with PWM and have enabled all ENx.

    I have ordered sense resistors so used the lowest value I had as a shunt resistor. Measured the drop across it with a meter. My final design will adjust PWM duty cycle based on the drop value.

    Today I was able to get a brief jerky sputter motion from the motor but it strains. In lieu of this behavior does it make sense to try a higher bulk cap value, say 300uF so it does not sputter ? Currently using 100uF/1uF bypass across both VM/VNEG pin pairs.

    Thanks,
    Rav
  • 0 in reply to Rav Kal
    TI__Guru** 114905 points
    Hi Rav,

    Sorry for the delay. Adding a larger bulk cap may help depending on the needs of the rest of the system.

    Have you been able to lower the sense resistor? Do you have any further updates?