DRV8834 Applying digital input while VM is 0V

Pascal BAIJOT

Other Parts Discussed in Thread: DRV8834

Hello,

I plan to use DRV8834 to drive a stepper motor. VM = 5V and digital input voltage is 3.3V.

In case of emergency button being pushed, the +VM will be shut down (0V) to release the motor
while the digital input signals (DIR, STEP, M0, M1, nENBL) will still be applied to input pins.

Is it safe to apply digital signals while VM is 0V ?

Thanks in advance,

Pascal BAIJOT

over 10 years ago

0 Wilson Zuo over 10 years ago

TI__Mastermind 26065 points

Hi Pascal

When VM is shutdown, how about the internal impedance of the supply? I mean it's disconnected or shorted.
Normally when we switched off a supply, it is 0V and opened. Similar to disconnected. In this case, it will be safe to have the input signals (The DRV device maybe partly powered by the signals, but no risk of the device and the MCU).
In another case, the VM is 0V and shorted. First, the BEMF of the motor will cause big braking current through the shorted VM. Also the inputs from the MCU will be loaded down in this case, similar as all the inputs are short to GND. It may cause risk to the MCU.

Best regard,

0 Pascal BAIJOT over 10 years ago in reply to Wilson Zuo

Prodigy 20 points

Hi Wilson,

In my case the VM will be disconnected from the supply by the emergency dry switch.
Only the input capacitors (10 µF+0.01µF) will stay connected, this will help limiting voltage spike on VM.

Do you advise to add a 9V zener diode between VM and GND pins to limit voltage trip on VM pin due to braking current returning to VM ?

Many thanks for this helpfull answer.

Best regards,
Pascal Baijot

Motor drivers

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DRV8834 Applying digital input while VM is 0V