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DRV8843 V3P3OUT usage (or not)

Phil Malone
Prodigy 20 points
Other Parts Discussed in Thread: DRV8843

Hi.

When I discovered the DRV8843 and saw that it has a 3.3 V VREF output I thought my dreams had been answered.  I had the brilliant idea to use the 3.3V output to power an ultra low power uProcessor to run my motor controller application.

I did the design, made a prototype and was a little surprized when the driver didn't seem to power up.

Then I re-read the spec. 

The Sleep and Reset are both active low, and with the sleep active, it doesn't generate a 3.3V outpu.

Unfortunately I was using that output as external VCC to drive the Sleep high.  D'oh.

Catch 22

So am I out of luck?  Is there no way to utilize the V3P3OUT line to power the external logic circuitry?

Not needing an external regulator that can match the DRV8843's input range would be so sweet.

Phil.

  • TI__Expert 7455 points

    Hi Phil,

    There is an easy way out of the catch 22, but before I go there let me state that the V3P3OUT was not designed with the intention of driving microcontrollers. It was intended to drive the Reference voltage dividers into the VREF inputs to configure the current regulation set point without needing extra circuitry. With all of that being said, if you can guarantee very little current draw from the V3P3OUT output, it can be used to power up your application's microcontroller. Thanks to very low power microcontrollers, such as the great majority of MSP430's, this is a viable option.

    So how do you "bootstrap" your device? What you need to do is use a simple voltage divider from VM so the nSLEEP pin is brought out of SLEEP mode when the system's power is applied. Once you know what your VM is, you can select the resistors to make sure nSLEEP is set. This will enable the device and bring V3P3OUT into an operational state.

    Hope the info helps. Best regards,

    Jose Quinones

  • in reply to Jose Quinones
    Prodigy 20 points

    Hi Jose

    Excellent.

    Now all I need to do is figure how to lift that teeny weeny pin on my proto PCB :)

    Thanks.

    Phil.