LM74700-Q1： What's output voltage level for LM74700 gate control pin.

Hi Stan Chang,

When the motor breaks and due to inertia, voltage at cathode pin of LM74700-Q1 will rise from 24V to 60V. LM74700-Q1 will sense this (using reverse current comparator across anode to cathode) and turn off the MOSFET, where body diode protects the power supply from 50V.

Please note that LM747000 can support 65V at its cathode, beyond that requires additional TVS or other clamps. Evaluation module LM74700EVM has an option to mount a TVS at its cathode to GND, this can be used to evaluate.

Gate voltage is dependent on the load current. Please refer to waveform in datasheet page 19, Figure 24 and 25 showing Vgs voltage at 3A load and 5.8A load. 

This is due to 20mV regulation across anode to cathode, at light load Vgs will be above and close Vth of MOSFET and high current Vgs is close to 12V/13V.

Please refer to the application note http://www.ti.com/lit/an/slvae57/slvae57.pdf

Regards,

Kari.

Hi Kari:

            Thank you for your guidance . 

   If I have any questions, I will ask for support again.

Thanks!

Stan Chang