DRV11873: Use of Schottky diodes

Hi Sanmesh,

Many thanks for your explanation. The diodes are simply fly-back diodes in this case.

My answers:

a) The failure seems to be a complete and permanent shutdown of the chip. In some case the chip can be restarted but fails to start the motor, which suggests that the half-bridge switches may be damaged. In other cases, the chip over heats and emits smoke.

b) Failure seems to occur most commonly if the connection to the motor is broken during steady-state operation while running at the target speed and then trying to re-establish a connection while the motor is coasting down.

c) I’ve made this assumption as failure usually occurs when I re-connect the motor while it’s coasting down. If I reconnect the motor while it’s stationary, the chip doesn’t seem to have a problem starting and running the motor in that case.

Hope this clarifies the problem. I look forward to your response

so you are basically disconnecting the motor while the motor driver is spinning the motor, and then reconnecting the motor phases while the motor is coasting.

1) The connecting and disconnecting of the motor can cause the inductor kickback in the motor and a high negative voltage, so the Schottkey diodes might protect against the kickback. Let me confirm with my coworkers.

2) I know there is failure when reconnecting the motor while it is spinning, but is there failure when disconnecting the motor while it is driving? Any spark phenomena from driving current? Or does the motor go into lock?

2) To circumvent this issue, is there a possibility to just stop driving the motor and waiting for it to stop before disconnecting?

1) The causes of damage could be one of the following:

a) Inductor kickback. Use the schottkey diodes to protect against this,

b) Charge being pumped into the supply from the BEMF. Usually the device has AVS (Antivoltage surge) to stop this, but the driver may be in a confused state when the motor is suddenly disconnected. To protect against this, I would wait till the motor is stopped before reconnecting the driver.

2) I know there is failure when reconnecting the motor while it is spinning, but is there failure when disconnecting the motor while it is driving? Any spark phenomena from driving current? Or does the motor go into lock? 

3) When you disconnect the motor, make sure you put 0% duty cycle on the speed cmd before you reconnect the motor

4) To circumvent this issue, is there a possibility to just stop driving the motor and waiting for it to stop before disconnecting?

Any follow up?

Many thanks Sanmesh for your support.

a) I have not had a chance to try using the Schottky diodes yet. I will attempt this shortly and I will follow up with my results.

b) I’m currently using a diode in series with Vdd between the power supply and the driver to prevent voltage surging. This has worked well before with other drivers to prevent surging and damage to the power supply.

2) generally no failure or sparks can be seen when disconnecting the motor while it’s being driven. The driver goes into lock on the RD pin when then motor disconnects and remains there.

3) This is achieved as I am able to independently detect when the motor connector is unplugged. The micro-controller on board detects this events and sends a 0% duty on the PWM pin.

4) Unfortunately it is not possible to prevent motor disconnection in this application as the device is hand held and therefore it is very likely that the motor can be unplugged by the user or accidentally at any time.

I will get back to you after I’ve tested with the Schottky diodes.

Regards,

Youssef

Thanks Youssef.

Like you said, the diode between Vcc and ground might help Vcc from not surging and thus help stop the issue.

Im glad that the device correctly goes into lock and stays in lock when the motor is disconnected.

Does the problem go away completely when using this diode between Vcc and ground? If not, how much does it help?

Let me know when you try the  Schottky diodes on the motor phase pins