This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8705-Q1: difference between PH/EN control and H-bridge control mode

Part Number: DRV8705-Q1

Hi Expert,

I have a question about the DRV8705-q1 PH/EN control and H-bridge PWM control mode. What is the major difference about these two control mode?
From my understanding, during drive SH1 to SH2, the major difference is the way to motor winding freewheeling control? The diagram Shows as below
The major difference is the way for motor winding freewheeling control? Shows as below
Is it correct? 
And the other difference is that H-bridge have the diode freewheel, but this method will have more dissipation, my customer said this method is not used much. What else?
Thanks!
Ethan Wen
  • Hi Ethan,

    Today is a holiday in the US so we'll reach out to you tomorrow.

  • Hi Ethan,

    We have written an FAQ on this topic. The FAQ explains the basic differences between the two control modes. Please read it to better understand the two control modes.

    And the other difference is that H-bridge have the diode freewheel, but this method will have more dissipation, my customer said this method is not used much. What else?

    As shown in the DRV8705-Q1 datasheet. You can set the H-bridge to Diode freewheel (High-Z) during the current decay phase or to low-side/high-side active freewheel (current recirculate between two low-side or high-side FETs. The diode freewheel will cause more power consumption but the active freewheel will not. diode freewheel will cause the current to decay faster but at the expense of higher current ripple. active freewheel will make the current decay slower but create lower current ripple.

  • Hi Pablo,

    Thanks for your detailed description. 

    For the H-bridge PWM control mode, you mentioned it also can set the H-bridge to low-side/high-side active freewheel. But still not really understand how to set this active freewheel. Could you please give a example for IN1 and IN2 PWM signal to set the forward direction active freewheel mode?

    And if I send below two opposite PWM signal into IN1/IN2 like below. Does it will enter fast Synchronous Decay? 

    Ethan Wen

  • Hi Ethan,

    The DRV8705 does not have synchronous fast decay by default. It only supports HS/LS re-circulation and asynchronous fast decay. In the IN1 and IN2 example above, both signals are complementary of each other. So the H-bridge is never really going to H-bridge decay mode. Instead, it is changing current direction with a brief moment in coast decay during the dead time duration. This is technically "asynchronous fast decay" but note that if the device goes into current regulation, the decay mode will not be synchronous fast decay but rather a mix of asynchronous fast decay(coast) and slow decay (braking).

    I hope this answers your question.