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DRV8432EVM Motor Driver Problem - Mode 4 - Dual PWM with Single PWM input per bridge

Vaughan Harvey
Prodigy 70 points


Hi,

I am using the DRV8432EVM in Mode 4 to switch 12v across an actuator from a PWM signal generated by an arduino. This will eventually be used in a force control PID loop.
I am currently applying a 0%, 25%, 50%, 75% and 100% pwm duty cycle into PWM A and C inputs to view the outputs. With this in mode 4, i would expect to see the voltage across the OUT A and B average 0v when 50% pwm is put through PWM A. Unfortunately, i do not see this, instead getting the same PWM signal as the output across OUTA and B, only amplified to 12v.

Can you offer any advice to ensure when i apply a PWM signal (eg. 25%, the motors go foward, 50% they stop and 75% they reverse.) to perform the switching. I assumed the complimentary pwm input across the PWM B when in mode 4 would do what i described above.

Thanks,
Vaughan

  • 0
    TI__Mastermind 21320 points

    Hi Vaughan,

    Can you check that the half-bridges are generating the correct waveforms with a scope under no load. A scope shot posted here with the input and two outputs for one full bridge posted here would be helpful. Can you check with a meter that the Mode Pins are at the correct voltage levels.

  • 0 in reply to Nicholas Oborny
    Prodigy 70 points

    Hi Nic,

    Thanks for the reply! Unfortunately I can't seem to find the scope shots or output shots mentioned in your reply. Would it be possible to repost the shots?

    Thanks,
    Vaughan 

  • 0 in reply to Vaughan Harvey
    TI__Guru** 114905 points

    Hi Vaughan,

    I believe Nick was asking you to post any scope shots. Providing scope shots will allow Nick to determine if the outputs are driving the motor properly.

    Thank you.

  • 0 in reply to Rick Duncan
    Prodigy 70 points

    Hi Duncan,

    Thanks for clearing that up! I must have misread Nick's comment. I will post up screenshots in a few hours.

    Thanks,
    Vaughan

  • 0 in reply to Vaughan Harvey
    Prodigy 70 points

    Hi Nick,

    I have tested the two half bridge outputs of the power driver to a 3V DC PVDD voltage. Unfortunately, the scope im using only has two inputs, so i have included the photos in two seperate lots. I used a 25% duty cycle PWM wave with a maximum of 3.3V at 100% duty cycle. I also tested the voltage of the mode pins, and they are at the correct voltage levels for M1 and M2 to be high and M3 low.
    It was my understanding that the output voltage would switch across the OUTA and OUTB ports. I have also included a shot of the output across A and B to the PWM input.

    For all images below, the PWM input is Scope 1, and the output is Scope 2.

    Image 1: Half Bridge 1 (Output A to GND)

    Image 2: Half Bridge 2 (Output B to GND)

    Image 3: Full Bridge Output (OutA to OutB)

    Any help you could give would be fantastic!

    Thanks,
    Vaughan

  • 0 in reply to Vaughan Harvey
    Prodigy 70 points

    Also for comparison, here are the same shots at 75% pwm duty cycle with a 3V DC PVDD input.

    Image 1: Half Bridge 1

    Image 2: Half Bridge 2

    Image 3: Full Bridge Output

  • 0 in reply to Vaughan Harvey
    Prodigy 70 points

    Hi Nick,

    It appears the Power Driver works to switch the output across A and B. I just wasnt seeing that on the scope, but it does seem to be working.

    Thanks for the help.
    Vaughan

  • 0 in reply to Vaughan Harvey
    TI__Mastermind 21320 points

    Hi Vaughan,

    From your scope shots, it appears the device is functioning correctly. Has your question been answered? Please elaborate if you have additional questions.

  • 0 in reply to Nicholas Oborny
    Prodigy 70 points

    Hi Nick,

    Thanks for all your help. One last quick question.
    In mode 4, if i apply a 0 PWM duty cycle input to the power driver, will i recieve a full negative output across the load, or will i receive no output across the load.

    Thanks,
    Vaughan

  • 0 in reply to Vaughan Harvey
    TI__Mastermind 21320 points

    Hi Vaughan,

    From the datasheet.

    "In mode 4, one PWM signal controls one full bridge to relieve some I/O resource from MCU, i.e., PWM_A controls half bridges A and B and PWM_C controls half bridges C and D.In this mode, the operation of half bridge B is complementary to half bridge A, and half bridge D is complementary to operation: half bridge C."

    So if you are applying a 0% PWM to PWM_A you will see Half-Bridge A Off (High-Side Off, Low-Side on) and Half-Bridge B On (High-Side On, Low-Side Off).

    So if you have a load across OUTA and OUTB you will see "full negative output" or full reverse current.