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DRV8770EVM: DRV8770 slow decay implementation

david lillaz
Prodigy 10 points
Part Number: DRV8770EVM
Other Parts Discussed in Thread: DRV8770, DRV8262, DRV8262EVM,

Tool/software:

Hello,

I am investigating a few TI solutions for a new design :

DRV8703 / DRV8262 / DRV8770

I want to drive a 24V BDC boosted to 36V motor (10A rms current with a peak current up to 18A).

DRV8262EVM is able to drive the motor without load, but with the load (70kg charge) the motor is not able to move it ...

DRV8703EVM is more powerful, but I broke 2 transistors on the EVM board (VDS max 60V). The motor generates voltage surges higher than 60V when I stop it.

Finally I will give a try to the DRV8770EVM rated for 100V (ordered this morning).

My question is : DRV8770 seems to be a simple driver, I want to implement 'slow decay' to stop my motor.

Do you know if I can manually drive the 2 low side transistors at the same time ?

It seems to be doable from the data sheet of the DRV8770.

Regards.

  • 0
    TI__Genius 9150 points

    Hi,

    Thanks for the question.

    I am assigning the thread to the device expert. He will review the request and get back to you.

    Thanks,

    Ibinu

  • +1
    TI__Genius 16320 points

    Hello,

    There should be no issues with implementing slow decay with the DRV8770. Yes, both low-side FETs should be turned on for slow decay. The inputs operate independently and have internal shoot-through protection with a deadtime insertion. On the QFN package, the deadtime pin (DT) can be used to adjust the deadtime between 200ns to 2000ns. 

    Please see the following app note for more information on current decay modes:

    Current Recirculation and Decay Modes (Rev. A) 

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 10 points

    Thank you for your answer.

    I will try to implement some external control signals such as 'enable, brake, DIR' using logical gates (and, or...).

    1. INHA = ENABLE AND DIR AND (NOT BRAKE)
    2. INLA = ENABLE AND PWM AND (NOT DIR) OR BRAKE
    3. INHB = ENABLE AND (NOT DIR) AND (NOT BRAKE)
    4. INLB = ENABLE AND (PWM AND DIR) OR BRAKE

    The idea is to simplify the microcontroller code and to have a basic PWM/DIR interface.

    Regards,

  • 0 in reply to david lillaz
    TI__Genius 16320 points

    Hi David,

    This sounds like a good idea and shouldn't be a problem due to the independent control of the half-bridges. However, this is why we encourage evaluation using our EVMs. Please let us know how the testing goes!

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 10 points

    Hi David,

    I noticed that on the DRV8770 eval board MODE=GVDD and INHx=INLx (R11, R49 and R50 are mounted). 

    If I understand correctly this configuration is used to connect one or two motors.

    If I want full control of my H bridge with only one motor I need to disconnect these resitors (and add R39 & R41).

    I not sure POT1 and POT2 will allow me to drive the H bridge with only one motor.

    Regards.

  • 0 in reply to david lillaz
    TI__Genius 16320 points

    Hi David,

    The EVM is designed to support different load configurations. Yes, removing R11 will disconnect GVDD from MODE pin and configure INLx to be in a non-inverting mode and removing R49 and R50 will disconnect INLx signals from INHx signals. This mode simply means the GLx output will follow INLx input. 

    The logic tables in the datasheet will be the best indicator of which mode to choose for your application based on input signals and desired output half-bridge states. Both modes offer the same half-bridge states but with different input logic required to achieve those states. 

    Best,

    David