Motor acts as generator and damages VNHD7008AY

[Marc1]

We use the VNHD7008AY to control the motor of a cargo lift. The lift has an emergency switch, which disconnects the battery from the circuit.

In case of an emergency cutout, the lift runs down while its motor generates a high voltage, which finally kills the VNHD7008AY.

To solve that problem I want to analyse the generator voltage (Pin VCC) and shortcut the H-bridge in case the generated voltage exceeds a limit.

This provides that the motor generated voltage passes the reverse battery protection transistor, so that it can supply the other parts of the circuit (microcontroller, etc).

My question:

If supply voltage comes from the motor side (Pin VCC) instead of battery side (Pin Vbatt), will the reverse battery protection transistor conduct so that voltage can pass from VCC pin to Vbatt pin?

[Alessio Corsaro]

Hi Marc1,

Thank you for your inquiry. We appreciate your interest in our products and your active participation in the ST forum.

Regarding your question, if you have connected the external MOSFET for reverse battery protection as suggested in our datasheet, in the event of a battery disconnection, the MOSFET will turn off and prevent the current from Vcc from passing through and reaching Vbatt.

If you need further assistance or have any additional questions, please do not hesitate to reach out. We are here to help.

[Marc1]

Hi Alessio, Thank you for your reply.

Can we just omit the reverse voltage protection and leave pin CP floating?

We want to use the motor generated voltage to supply our microcontroller, in order to brake the motor (pulling output A and B to ground) in case the voltage exceeds 30 V. This is the only way I know to prevent damage by motor generated high voltage.