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DRV8412 operating waveforms for mode 4

John Stevens
Expert 7395 points

Hey all,

For mode 4 where1 input controls 1 full bridge and the another input controls the other full bridge.

So, in this mode, PWMA will control A and B bridge, and PWMC will control C and D bridge.

 

Page 14 states the following:

“For example, when PWM_A is high, high side FET in half bridge A and low side FET in half bridge B will be on and low side FET in half bridge A and high side FET in half bridge B will be off.”

 

Questions:

If PWMA goes low, how does the switch turn off and on?

I'm assuming that if PWMA goes low,  high side FET in half bridge A and low side FET in half bridge B will be turn off, there will be some dead time, and then  high side FET in half bridge A and low side FET in half bridge B will turn on. This would be a "hard switching" type configuration correct.

I just want to be sure there isn't some other "soft-switching" type algorithm where maybe at first both the high side FET A and High side FET B turn off similar to maybe what a phase-shifted full-bridge waveforms would look like. 

This information will help determine whether to use this device or not. I hope to get a response today.

Thanks,

John Stevens

Field Applications Team Lead  

 

  • 0
    TI__Guru** 114905 points

    Hi John,

    Your assumption is correct, with the exception that the high side FET in half bridge B and low side FET in half bridge A will turn on after the dead time. This mode allows the current to quickly decay.

    Mode 1 (000) provides additional control of the bridges, but increases the complexity. Additional control signals from the microcontroller are required to use Mode 1.