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DRV8307: DRV8307

Sharath Kumar47
Prodigy 120 points
Part Number: DRV8307
Other Parts Discussed in Thread: DRV8308

Hello,

We designed a BLDC driver with DRV8307 for a 300W motor (18V, 15A). When I power-up the system fault pin is high for 60us and low for 5ms. This cycle is repeated continuously. From the datasheet it seems this is overcuurent fault but motor is taking only 290mA where it is supposed to take 3A, it is spinning with audible noise and having low torque. Voltage in ISENSE  pin is 100mV, I also tried by gorunding ISENSE pin directly to ground still the problem persists.  

Test conditions:

Vin - 18V

PWM duty cycle - Constant duty cycle (50% or 100%)

PWM always ON, motor is stopped/ started by pulling enable.  Motor is run in no-load condition.

I have attached the DRV8307 part of my schematics.  (Part number in the schematics will be DRV8308 please dont mind.) 

  • 0
    TI__Expert 4650 points
    Hi Sharath,

    Could you share the portion of your schematic containing the MOSFET bridges? Also, what is the purpose of the header block that all of the gate signals are tied to? Are the DRV8307 and MOSFET bridges on separate PCBs?
  • 0 in reply to Phil Beard
    Prodigy 120 points

    Hi Phil,

    Yes, DRV8307 and the MOSFETS  are in separate PCBs. Those headers are for connecting them. I have attached the HBridge schematics here.  

  • 0 in reply to Sharath Kumar47
    TI__Expert 4650 points

    Hey Sharath,

    If you reduce the value of the gate MOSFET gate resistors you have do these problems go away?  Also, are you sure the header pins from the DRV8307 to the MOSFET PCB are strongly connected with each other?

  • 0 in reply to Phil Beard
    Prodigy 120 points

    Hi Phil,

    We reduced the gate resistor value to 100E and added 10K between gate and source of all the mosfets. It has got better. Now the fault occurs only during the initial startup.

    Here probe 1 is midpoint of the Hbridge and probe 2 is fault signal. The time motor taking to return to normal state is depending on the input voltage, when Vin = 19V fault cycle repeats for 3secs, when Vin = 15V fault cycle repeats for 500msec.

  • 0 in reply to Sharath Kumar47
    Prodigy 120 points

    Hi Phil,

    Got any idea why this is happening?

  • 0 in reply to Sharath Kumar47
    TI__Expert 4650 points
    Hi Sharath,

    Have you tried decreasing your gate resistors to something closer to 50 Ohms? Also, we typically don't advise using pull down resistors on our Smart Gate Drive devices, so the 10k Ohm resistors in your system may actually be causing problems in your system.

    Because you're using a cable to connect the FET gates to the driver, you may need more source / sink current than what we used on our EVM. By decreasing the size of series resistor you're using in your system, you should be able to source / sink more current and effiectvely switch your MOSFET gates faster.
  • 0 in reply to Phil Beard
    Prodigy 120 points

    Hi Phil,

    I decreased gate resistance to 50ohm and removed pulldown resistors. No change. If switching time is the problem, does adding capacitors parallel to MOSFETs help?  

    Also, why is it working after some time, fault cycles is going off after some time (as explained in previous answer) .