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DRV8308EVM: Motor will not drive without USB 5V power

Part Number: DRV8308EVM
Other Parts Discussed in Thread: DRV8308

I am using the DRV8308EVM to test out the DRV8308 IC for a BLDC motor driving application. I have burned my desired register values in to the OTP memory using the GUI and am now controlling the IC directly with with my Arduino Mega using the exposed SPI pins. I am able to read out the values of each register and they match what I have burned into the OTP memory, confirming my SPI connection to the IC.

My issue is that when I toggle the enable pin ACTIVE from my Arduino, my motor only briefly turns before stopping. However, when the USB is plugged in or I apply 5V directly to the USB5V test point the motor behaves exactly how I expect it to.

I have had no luck looking through the DRV8308EVM user guide for a schematic of what this USB5V is supplying, is there some setting or jumper I am missing that will supply this 5V internally? 

  • Hi Matthew, 

    I've assigned this thread to my colleague Vishnu from our team,

    But chiming in quickly with a suggestion: if removing USB 5V rail impacts the device performance, you may want to look at the various logic-level signals in the functional block diagram and probe test points on the EVM to see what's "different" with/without 5V rail present.

    Best Regards, 

  • Hi Andrew,

    Thanks for the quick response. I have done as you've suggested and probed the available test points with and without my external 5V supply.

    Vreg appears unaffected by the external 5V, as probing the hall sensor supply showed no change when the USB5V was removed.

    I was able to determine that the inactive "high" voltage of the FAULTn line was around 1.8V when the USB5V was disconnected, but around 3.25V when the USB5V was connected. The block diagram shows that the FAULTn line comes directly from a pin of the DRV8308 IC, does this mean that the IC is using the USB5V supply for internal power? The block diagram indicates that the power is stepped down from the VM, but I am unsure if something different is happening on the evaluation board.

    Supplying voltage through the EEPROM DIP connector is working for now, but any help towards a cleaner solution would be appreciated. 

    Matt B

  • Hi Matt,

    In the DRV8308EVM schematic, the 5VCC is coming from the USB and this powers the FTDI chip. The FTDI chip outputs 3.3V which is used to powerup the MSP430. Pin 10 in MSP430 toggles the ENABLE pin ACTIVE. Can you remove Jumper JP12 which connects the ENABLE pin to MSP430 and try toggling using Arduino?



  • Hi Vishnu,

    I have am using my Arduino to toggle the enable pin and am seeing the same results. I have also grounded the enable pin and flipped the ENPOL bit in register 0x00 in order to toggle the motor on. Again this works when providing the board with USB5V, but as soon as the USB5V supply is removed the toggling no longer works.

    Additionally, I have set the VREGEN bit to 1 so the VREG supply should stay on regardless of the enable pin. The reset pin has also been grounded.

    Matt B

  • Hi Matt,

    The 5VCC coming from the USB is used to power the Hall sensors. When the USB is removed, Hall doesn't receive the power so the motor doesn't spin. 

  • Hi Vishnu,

    Thanks for digging into this, looks like there is no way around supplying that USB5V. I'm surprised that the U7 chip isn't being powered off the VREG rail, but glad to have an answer all the same.

    Matt B