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DRV8870: driver Chip blow up

steve de coen
Prodigy 140 points
Part Number: DRV8870

We use the DRV8870 as motor driver at 24V 15kHz to drive a DC 24V motor. Vref = 5V ISEN = GND , VM  is connected trough a LC 15µH and 220uF to 24V

For some reason the driver blow up when we block the motor.

The firmware has a stall detection and put the motor in break (both Motor pins at 0V) after 1 second stalling.

Even while the chip have an aditional current and termal protection the chip blow up every time we stall the motor.

What can cause a failure of internal protection circuits in this chip? We already lowered input protection resitors to 10 Ohm.

Thank you

  • 0
    TI__Genius 14485 points
    Hi Steve,

    Can you tell what seems to be the failure? Is the device hot when it fails? Does it pop, crack, or otherwise let out smoke?

    Does it fail before detecting stall, or does it fail after detecting stall when it is in brake mode?

    Are you able to repeat the failure and take scope shots of the VM and VREF voltage at the pins and the current through the motor?
  • 0 in reply to James Lockridge19
    Prodigy 140 points
    Hi James ,
    It start getting hot and eventualy smoke up after i detect stall and immediatly put iT at break.
    I have the impression this does not happen when I ramp down to zero and Then break.
    So iT seems to happen when I break too fast .

    I use a pi filter for the drivers supply voltage.
    And wondering if immediat break from a 2-3A load situation can cause a large voltage Spike on VM which kills the driver ? On the other side, should the cap after the inductor prevent any spikes in VM.

    Thx
  • 0 in reply to steve de coen
    Prodigy 140 points
    So iT seems to happen Just after break mode
  • 0 in reply to steve de coen
    TI__Genius 14485 points
    Steve,

    I am also wondering if there is somehow a voltage spike on VM. The current through the inductor cannot change instantly, so it will try to continue pushing the stall current even though you are in brake mode and do not require that current. This is what causes the voltage spikes (V = L di/dt).

    Here are two things you can try:
    1) Remove the inductor and short the connections with a piece of wire. This should eliminate inductance spikes on the VM rail.
    2) Take scope shots of the VM and VREF voltages at the device pins and the current through the motor to see what transients occur during your stall condition.
  • 0 in reply to James Lockridge19
    Prodigy 140 points

    That was my first thought too, but the CAP after the coil cannot change voltage instantly so this counters the coil .

    Meanwhile we figured out what caused the meltdown, it seems that the internal current protection is not sufficient when we put  ISEN pin 7 to GND.

    So we put a 0.25R resistor and 2.2µF cap on this pin to lower max allowed current, and now it withstand stalling’s just fine.

  • 0 in reply to steve de coen
    TI__Genius 14485 points
    Steve,

    I'm glad you found a workaround!

    I'll make a note of your feedback regarding the issues you found by putting ISEN pin to ground.