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DRV8811EVM diodes

Gregory Dierksen
Prodigy 70 points
Other Parts Discussed in Thread: DRV8811EVM, DRV8811

I have recently received a DRV8811EVM board which has been very useful in understanding the operation of the DRV8811 chip.  However, I have two questions regarding the documentation and in particular this statement on page 7 of the DRV8811EVM User's Guide:

"Two pin jumpers (JP2 to JP5) connect the diodes to the motor outputs and are used under asynchronous rectification (SR = LO)."

The first problem is, I believe, simply a typo: SR = LO enables synchronous rectification, not asynchronous as stated above, correct?  This is according to the DRV8811 data sheet which specifies that SRn "When active low, synchronous rectification is enabled".

My second question is with regard to the diodes: if jumpers JP2 to JP5 are removed is asynchronous rectification possible, or must the diodes (D2 to D9) be connected to the motor for asynchronous rectification to be possible?

Thanks for the help.

  • 0
    TI__Mastermind 20985 points

    Gregory, sorry for the confusion.  You're right that the guide should say "SRn = High".  The extra diodes apply for asynchronous rectification, where the H-bridge FETs are all off and current travels into VM.

    Async rect should still be usable without the discrete diodes connected, because there are always parallel diodes inside the DRV8811 (the body diodes of the FETs).  I believe the discrete ones switch faster and reduce heat in the DRV8811.

    Best regards,
    RE