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DRV8848: The DRV8848 Vcc rail dips when I have sleep pins floating

Part Number: DRV8848

Hello there

I'm currently using 4 DRV8848 chips to each drive four motors for a personal project of mine. I received my PCB board, soldered the components for the motor section, and manually shorted out the control pins and SLEEP pins to drive my motors. I noticed if I have the SLEEP pin (I've connected all of the DRV8848 SLEEP pins together) floating, my power supply shows a voltage drop after a few seconds of powering up the board. To prevent this from happening, I have to solder a wire from the SLEEP pin to the 3V3 rail to prevent this.

The DRV8848 internally has a pull down resistor for the SLEEP pins, so I should be able to directly connect this pin to my MCU. Any help would be ace. Here's a screenshot of my schematic:

  • Phillip,

    DRV8848 doesn't have VCC pin. When nSLEEP is low, DRV8848 enters low-power sleep mode (only few uA quiescent curent) and VREF is turned off.
  • Because I'm running the chips in parallel mode, I know I need to configure the chip for this operation. Section 7.3.3 how to configure the chip for parallel operation. However, as I have four of the SLEEP pins connected together and connected to a single pin to my MCU, if I don't correctly initialize the DRV8848 chip for parallel operation, how would the chip perform (i.e. shutdown)? Just to note, I'm not currently in the stages of writing my firmware yet (due to the holidays) so the pin on my MCU used to control the SLEEP pins is left in its default state.

    Just to note, when I meant VCC rail, I meant the VINT rail (3V3 volts)

    Thanks

  • The DRV8848 internally has a pull down resistor for the SLEEP pins. When nSLEEP pin is low, VINT is low.
  • Oh I've just noticed that within the datasheet. 

    Just one more question before I investigate the voltage drop. If I have the DRV8848 paralleled and I don't correctly configure the chip for this operation, what state could the chip be in?  I think in my next revision, I will just simply tie the SLEEP pin to my 3V3 rail, as this fixes the issue which I'm facing (although I really would like to know why). I will have access to my board later on this week.

    Thanks

  • Phillip,

    "I don't correctly configure the chip for this operation, what state could the chip be in?"

    What do you mean "don't correctly configure the chip"? Do you mean nSLEEP pin low?
    If nSLEEP is low, DRV8848 is in sleep mode to get the lowest quiescent current.