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DRV8432: PWM Signals relations to H-Bridge Hi/Low side mosfet gate

Marco Virgulti
Prodigy 40 points

Part Number: DRV8432

Hello,

i have to develop an application to drive two brushed dc motor with mid power requirements, so i choose this powerful driver. I read the datasheet but i have, perhaps, some silly questions about it.

I didn't understand exacty how the four signals (PWM_A to PWM_D) are related to mosfet gate of the bridges; i would dimmer the motors with two signals in order to reach 0% to 90% (to be sure to not overload the driver) and to use both directions of rotation (clockwise and counter clockwise). For example, if i use the MODE 1 (or 2) i have two PWM signals (A and B) for bridge A and B (on datasheet); i'm not sure if it means that:

-PWM A controls both Hi-side and Low-side of A bridge?

-PWM B controls both Hi-side and Low side of B bridge?

So in this configuration how i can control direction and speed of motor? Or PWM A controls Hiside of A and low Side of B?

For MODE 4, using one single signal for each bridge, very useful configuration, but how to achieve both rotations? it is related to duty cicle (less than 50% and above 50%)? where i can read this in datasheet?

Thanks in advance and sorry for my english

  • 0
    TI__Guru** 114905 points

    Hi Marco,

    For example, if i use the MODE 1 (or 2) i have two PWM signals (A and B) for bridge A and B (on datasheet); i'm not sure if it means that:

    -PWM A controls both Hi-side and Low-side of A bridge?

    PWM A controls both Hi-side and Low-side of A bridge?

    -PWM B controls both Hi-side and Low side of B bridge?

    PWM_A controls the hi-side and low-side of OUT_A
    PWM_B controls the hi-side and low-side of OUT_B

    So in this configuration how i can control direction and speed of motor? Or PWM A controls Hiside of A and low Side of B?

    Set PWM_B low and drive PWM_A with a duty cycle for one direction.
    Set PWM_A low and drive PWM_B with a duty cycle for the opposite direction.
    NOTE: at the end of the duty cycle it is recommended to provide a small pulse on the PWM_x that is set low. Information about this can be found in section 7.4 of the datasheet. 

    "However, in order for the output to be recovered, the PWM input
    corresponding to that driver in CBC must be toggled. Because of this, CBC mode does not support operation
    when one half-bridge PWM input is tied to dc logic level."

    For MODE 4, using one single signal for each bridge, very useful configuration, but how to achieve both rotations? it is related to duty cicle (less than 50% and above 50%)? where i can read this in datasheet?

    There are two methods to achieve rotations in both directions:
    1) less than 50% and above 50% as you suggested. This is typically preferred.
    2) PWM the RESET_AB while keeping the PWM_A high or low for direction. This also works but can create more heat in the device as the current flows through the body diodes.

    Would you mind providing your requirements?
    Desired motor voltage?
    Desired current?
    Desired PWM frequency?

    We may have other devices that are a better fit.

  • 0 in reply to Rick Duncan
    Prodigy 40 points

    Thanks for your suggestion!! 

    Rick Duncan said:
    Set PWM_B low and drive PWM_A with a duty cycle for one direction.
    Set PWM_A low and drive PWM_B with a duty cycle for the opposite direction.

    Perfect, that's what i need to know Rick, i wasn't sure about that reading the datasheet...I will use MODE 1 with four appropriate signals...in the past i print a circuit for a similar application but i used discrete mosfet and a gate driver, not a complex driver like DRV8432 and it wasn't clear for me how to configure it.

    Rick Duncan said:
    Would you mind providing your requirements?
    Desired motor voltage?
    Desired current?
    Desired PWM frequency?

    I searched a lot on the TI database to find a good performance and easy to use driver like this. I need to drive two brushed dc motors with 28V and about 4A each; i choose DRV8432 for that. I still don't have motors to measure windings inductance, but i think to use a PWM frequency from 50 to 100KHz. I think i will get an DRV8432EVM (a little expensive unfortunately :( ) in order to test the system.