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DRV8714-Q1: Charge Pump to Drive back-to-back FETs?

PY (Pengyu) Song
Expert 5860 points
Part Number: DRV8714-Q1
Other Parts Discussed in Thread: DRV8106-Q1

Hi team,

Can we use DRV8714-Q1's VCP to drive back-to-back FETs such that it can be used as reverse polarity protection as well as high side enable? Currently only reverse protection design is supported per datasheet & EVM. 

  • +1
    TI__Mastermind 24615 points

    Hi,

    Thank you for your question. Yes,  it is possible to drive back-to-back FET.

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Expert 5860 points

    Hi Shinya,

    Is there any app note or any design guide for it to drive back-to-back FETs? What is the recommended FET gate charge/capacitance for VCP to drive it?

    I know there is an app note "Protecting Automotive Motor Drive Systems from Reverse Polarity Conditions" which has only discussed reverse polarity protection. Can I just re-use the circuit to drive one additional FET such as below? 

  • 0 in reply to PY (Pengyu) Song
    TI__Mastermind 24615 points

    Hi PY,

    It is strange for me to put back to back diode as you described. With original configuration, VBAT/12V goes though diode of FET to PI_IN even FET is OFF. Then DRV wakes up then turn on VCP. VCP will be ~22V generated by charge pump. Finally VCP turn on FET.  

    With your schematic, Both FETs are OFF no diode path from VBAT to PI_IN. VBAT voltage cannot be delivered to PI_IN. So DRV cannot wake up.

    Is customer looking for this type of solution?

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Expert 5860 points

    Hi Shinya,

    It is strange for me to put back to back diode as you described. With original configuration, VBAT/12V goes though diode of FET to PI_IN even FET is OFF. Then DRV wakes up then turn on VCP. VCP will be ~22V generated by charge pump. Finally VCP turn on FET.  With your schematic, Both FETs are OFF no diode path from VBAT to PI_IN. VBAT voltage cannot be delivered to PI_IN. So DRV cannot wake up.

    • Got it - DRV8714-Q1 will not be able to wake up as PVDD is also blocked. 

    Is customer looking for this type of solution?

    • Yes. Is there any way to drive the back-to-back FETs by DRV8714-Q1 (using VCP pin?)? 
  • +1 in reply to PY (Pengyu) Song
    TI__Mastermind 24615 points

    Hi PY,

    Thank you for your feedback. VCP is not designed to drive external FET such a way. VCP can be used to drive small FET for reverse current protection.

    Here is example to drive back to back NMOS driving. Schematic is for DRV8106-Q1, but can be referred for DRV8714-Q1 as well. Please e-mal me if you have further question for this schematic.

    regards

    Shinya Morita