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Original question:

DRV8353: Fault condition swithcing from one to another state in "synchronous 1x PWM" mode

DRV8353: Protection to garantee safe operation

Emanuel Soares
Intellectual 530 points
Part Number: DRV8353

In (this thread)[https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1099670/drv8353-fault-condition-swithcing-from-one-to-another-state-in-synchronous-1x-pwm-mode/4110131?focus=true] we've discussed about some issues that can occur when ringing is present in the GHx and GLx lines.
I would like to know if the figure below represents a safe arrangement to garantee the secure operation (this was designed from the Absolute Maximum Ratings table):

Thus, is this schematic suficient to avoid the DRV8353 chip to burn?

  • 0
    TI__Mastermind 18981 points

    Hi Emanuel, 

    We'll aim to have Akshay or Anthony provide a follow-up response by middle of next week.

    Some comments from me in the meantime: 

    • the TVS diodes on HS Vgs (GHx-SHx) and LS Vgs (GLx-SLx) should help against over-voltage on those pins by clamping the voltage at/below 11V. 
      • you may want to check the breakdown voltage and tolerances of those diodes so ensure that they don't prematurely break down the gate-drive voltages which can exceed 11V depending on your VM operating values (see below table from E.C. table).
      • additionally, the TVS diodes also help reduce negative transients on those pins by becoming forward-biased when sufficient neg voltage is present. this is a common practice in our customers' various implementations. 
    • for the CSA's shunt resistor clamping diodes, I think these will help as well, but will note that the +/- 5V rating is a transient** abs max and not a DC one. 

    I think the implementation should be good for system protection, but you may want to experimentally verify the waveforms on the bench during normal motor operation. 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    Intellectual 530 points

    Hi, .
    In reference to your response, I have some questions:

    1. For what you said, to select the TVS should I look at the "Electrical Characteristics" instead of "Absolute Maximum Ratings" ?

    2. In "8.3.1.3 Gate Driver Voltage Supplies and Input Supply Configurations" it says:

    In addition to what you said, from "8.3.1.3" the GHx level refered to SHx is (theoretically) 10.5v for VM>12v.
    From the first table you showed, VM goes only as high as 15V, with no other information for higher VM values, for exemple, VM=24V.
    Thus, from "Electrical Characteristics", can we consider GHx to SHx voltage will be < 12v for any VM >12v ? In other words, would be a better solution to put a 12v TVS between GHx and SHx, instead of a 11v rated TVS?

    3.  Same for Vgls, in the "8.1 Overview": 

    But in the "7.5 Electrical Characteristics" it says:

    Both informations seems contraditory: the first says it will regulate to 11v and the second table presents a set of various values for Vgls.
    For exemple, for higher VM=24v, what TVS value is more apropriated, considering the tables above?

    4. The datasheet reccomends a 16v capacitor to the Vgls pin:

     

    According to question #3, is 11v considered the stable state of the regulator and a different voltage considered as a glitch? 



    Best Regards! 

  • 0 in reply to Emanuel Soares
    TI__Mastermind 23356 points

    Hey Emmanuel,

    I will consult the team and aim to provide feedback by Wednesday .

    Best Regards,

    Akshay

  • 0 in reply to Akshay Rajeev Menon
    Intellectual 530 points

    Hi, Akshay.
    Thanks for your attention.

  • 0 in reply to Emanuel Soares
    TI__Mastermind 23356 points

    No worries.

    Best,

    Akshay

  • 0 in reply to Emanuel Soares
    TI__Mastermind 23356 points

    Hey Emanuel,

     

    I have done a review of the schematic with the team and here are our findings:

     

    • You are correct, a 12 V TVS diode would be better between GHx and SHx.

     

    • For the low side MOSFET we recommend connecting the TVS diode between GLX and GND, to prevent current spike occurring on the CSA when the diode breaks down. We also recommend using a 16V TVS diode instead of 11V.

     

    • On the VGLS pin we recommend adding a 25V or 36V capacitor since VGLS can be 14.5V or even 16V so these higher voltage-rated capacitors should be better.

     

    • The CSA diodes should be helpful in protection, but please ensure that the Zener diode breaks down quick enough based on device specification (<200 ns) so that the voltage is not clamped at 5V for too long before being clamped to 1V.

     

    • Please note that CSA output is not valid if differential mode input range exceeds -0.3V to 0.3V.

     

    I would recommend checking out the following app note, which has some useful tips for mitigating ringing, such as RC snubbers.

    https://www.ti.com/lit/an/slvaf66/slvaf66.pdf

     

    Hope this offers some clarification.

     

    Best Regards,

    Akshay

  • 0 in reply to Emanuel Soares
    TI__Mastermind 18981 points

    Hi Emanuel, 

    Closing thread for now due to inactivity - can you let us know if the problem has been resolved? 

    Please let us know if further support is needed on this question. Thanks 

    Best Regards, 
    Andrew