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DRV8320: transition from sleep to awake while driving the PWM in 6x mode

Lenio Cacula
Genius 16700 points
Part Number: DRV8320

My customer is using the DRV8320H motor driver chip and using it in 6X mode. The device is externally powered thus the chip’s sleep mode is not of interest. However it seems prudent to keep the chip disabled until needing to actually drive the motor.  The spec says that the ENABLE line must be pulled High and then must wait for 1ms before it is functional.  Question:  Is it acceptable for FW to both set the ENABLE line and also commutate immediate (setup the INHx/INLx) from the driver chip handling point of view. Of course our FW/application would need to be able to tolerate the possible 1ms delay before the motor driver becomes functional.  Or must the ENABLE line be done first, and then wait 1ms, and only then start commanding the INHx/INLx?

Thank you!

  • 0
    TI__Mastermind 18900 points

    Hello Lenio,

    Short answer:

    While we could experiment to see what the real value attributed to t_wake, which would be <1ms in most cases, we recommend to follow the datasheet spec.

    Longer answer:

    Unfortunately, the DRV8320's enable pin is synonymous with a "sleep" pin. Specifically datasheet says that "all gate drivers are disabled, ... all external MOSFETs are disabled, the charge pump is disabled, [and] the DVDD regulator is disabled." This means, the t_wake (1ms max) is the time for all of the rails and subcircuits to power up and be stable. 

    From a functionality perspective, DVDD is the responsible rail for logic rails inside the part, so if DVDD is not up, trying to commutate will not result in anything as the digital will not process the requests. In addition, the charge pump is necessary for any high side FETs, so if VCP is not up, the high side FETs cannot be driven successfully. So, the output to the motor will result in... a chopped or shortened first cycle (depending on how you've designed the start up algorithm).

    From a device safety perspective, we usually have ESD diodes on many of the input pins. Usually these ESD diode are connected to the various rails internal to part (or that are applicable for that circuit). So INHx or INLx would rely on DVDD or some rail derived from it. As such, the diode will conduct if the rail is less than the applied voltage. Normally, excessive current through the diode will cause it to burn up (as that is its function). However, I imagine the INHx or INLx come from a digital output that cannot supply much current so there's low risk it will damage the device.

    I know it sounds like we have to wait for 1ms, but from a design perspective, 1ms is usually some guard banded spec with some margin. Realistically, you probably don't have to wait the full 1ms. However, design usually designs these specs with process variation and temperature in mind to guarantee the spec. As such, if a robust system is required, we recommend to follow the spec

    Best,

    -Cole