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Original question:

DRV8876: When VM = 0V - Current Draw and Pin Voltage Tolerances

DRV8876: Protection in fail mode

user5887279
Prodigy 30 points
Part Number: DRV8876

Hi,

I am considering using the DRC8876 CI in my new design and I am having problems with one of the failure modes that may occur to the circuit. 

In my circuit the driver will battery-powered and will control a DC motor with direction control (probably in PH / EN mode). In one of the failure modes analyzed, there is a risk of the DC motor(6V 2A) being driven by the user (torque applied to the mechanism connected to it).In that condition the motor can operate as a generator and may induce a voltage at the driver output (OUT1, OUT2) in this scenario VM=0.

The driver can be damaged in this condition?

Any indication of protection for this failure mode?

I considered implementing "Reverse Supply Protection" in the VM input pin to prevent  damage to the rest of my circuit. Would that be enough to protect the driver itself?

Note.: https://e2e.ti.com/support/motor-drivers/f/38/t/900354?tisearch=e2e-quicksearch&keymatch=reverse

  • 0
    TI__Mastermind 37683 points

    Hi,

    The driver can be damaged in this condition?


    - When the motor becomes a generator, the current generated will flow through the body diodes of the FETs which will cause VM to increase. In the case that VM increases past the recommended max voltage ratings of the device, then the driver could get damaged.

    Any indication of protection for this failure mode?

    - Since the current flows through the diodes and not through the FETs, protection features like over-current protection will not protect the driver. One way to protect against a high increase of the voltage at the outputs (OUTx) is to include schottky diodes between the outputs (OUTx) and GND and between output (OUTx) and VM. This will ensure that the current flows through the schottky diode, regardless of current direction, instead of flowing through the body diodes of the FETs which are inside the IC. Additionally, a zener diode can be placed either at the input or the output to clamp the voltage at VM to prevent exceeding abs max rating of the IC or other components in your design.  

  • 0 in reply to Pablo Armet
    Prodigy 30 points

    Thanks, I believe this will solve the problem. I will do some simulations, if any other problem arise I will add to this post.