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MCT8316Z: Active Demagnetization

Stefan Lintner
Expert 4255 points
Part Number: MCT8316Z

Hi Team,

Customer is currently testing the AR und ASR mode which can be activated during synchronous modulation and they have following question:

What does the “Active Demagnetization” do different/better compared to the synchronous modulation (which already shortens the body diode – Active Free wheeling)?

BR,
Stefan

  • 0
    TI__Mastermind 24405 points

    Hi Stefan,

    I will get back to you shortly!

    Regards,

    Vishnu

  • 0 in reply to Vishnu Balaraj
    TI__Mastermind 24405 points

    Hi Stefan,

    Synchronous modulation and Active demagnetization are two different concepts. Synchronous and asynchronous modulation decides the switching pattern of the FETs. In Synchronous modulation, HS and LS FETs are switched in complimentary pattern. During the commutation change over, in synchronous modulation, current will still flow through the diode and not through the FETs. In active demagnetization, body diode conduction is reduced during the commutation changeover and the floating phase current is allowed to decay through FETs to minimize power losses.

    Regards,

    Vishnu.

  • 0 in reply to Vishnu Balaraj
    TI__Expert 4255 points

    Hi Vishnu,

    There seems to be a misunderstanding.

    According to customer «Synchronous Rectification» and «Active Freewheeling» are both terms for the same thing: Shortcutting the voltage drop over the body diode, caused by the freewheel current.

    This thread talks about this as well:

    DRV8703-Q1: active freewheeling - Motor drivers forum - Motor drivers - TI E2E support forums

    What is the difference between AAR and ASR mode then?

  • 0 in reply to Stefan Lintner
    TI__Mastermind 24405 points

    Stefan,

    Yes, Synchronous Rectification and Active Freewheeling are both same terms. In your question, you mentioned "Synchronous modulation" which is different from Active demagnetization. 

    In ASR, when PWM is applied to the high-side and low-side FETs, the current can decay to zero and becomes negative in low inductance motors since low side FET is in on-state. This creates a negative torque on the BLDC motor operation. When AAR mode is enabled, the current during the decay is monitored and the low-side FET is turned off as soon as the current reaches near to zero. Hope this clarifies the difference between ASR and AAR. 

    Regards,

    Vishnu.