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DRV8818: PPAD GND connection

Greg Marshall68
Prodigy 110 points
Part Number: DRV8818

I have a hand-wired prototype for the DRV8818 to drive a small stepper motor.  Because the current required is very low I wondered if I could get away with not connecting the PPAD.  The data sheet makes no mention of electrical connection requirement (only thermal).  Reading some other posts on similar motor drivers suggests that there is a need for electrical connection to GND.  Can you confirm that?  It would be very difficult to modify at this point, so I want to be sure of the need before doing it.

Thanks,

Greg

  • 0
    TI__Guru** 114905 points
    Hi Greg,

    Leaving the thermal pad disconnected may work, but it is not recommended. The pad is not required for operation, and is used for thermal dissipation.

    What is a very low current? What is your system voltage? There could other devices that could be a better fit.
  • 0 in reply to Rick Duncan
    Prodigy 110 points
    Thanks, Rick. For the moment I am using a dummy load to confirm that the circuit is working, so I can set the current to whatever I want. Right now it is set to about 62mA. The real application will need 333mA (the app I'm now working on - there is another one coming up that will need more, but I don't yet have the specs).

    The VM is 12V and the motor is spec'ed for 5V, with 15 ohms per winding. I had initially hooked it up wrong and had almost 1 amp running through the dummy load for a few seconds, so I'm a little worried that the IC might be fried. I will proceed with testing after fixing my wiring error and if it doesn't work I'll go back and connect the PPAD, although there is no way to get any significant thermal connection.

    Greg
  • 0 in reply to Greg Marshall68
    Prodigy 110 points
    Rick, it seems to be working. After confirming current regulation with the dummy load I switched to the actual motor. Although the signals looked right, 62mA was not enough to get the motor to move. Not wanting to burn anything out before completing my tests, I increased the current to just 125mA (nominal is 333), which was enough to make the motor move reliably - with no load. I'll wait until I have a real PCB with thermal connections before trying it at full power.

    Greg
  • 0 in reply to Greg Marshall68
    Prodigy 10 points
    Hi friend, I want to know if your circuit works without the connection of the PowerPAD GND?
    Because I will use the DRV 8816 without the PowerPAD GND connection

    Arthur
  • 0 in reply to arthur mendes
    Prodigy 110 points

    Yes, it did, although I kept the current flow very low to avoid over-heating the chip.  The conclusion is that the internal connection between PPAD and GND pins is adequate for at least low-current applications.  Heat dissipation (and long-term reliability) are separate issues.  In this case the objective was simply to demonstrate that this chip could drive a particular model of stepper motor.  My client was satisfied and we are moving forward with a design.

  • 0 in reply to Greg Marshall68
    TI__Guru** 114905 points
    Hi Arthur,

    As I mentioned to Greg, using the device without the thermal pad connection is not recommended.