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DRV8343-Q1: Jitter on gate drive output in independent MOSFET mode

Cameron Wutzke
Expert 3612 points
Part Number: DRV8343-Q1
Other Parts Discussed in Thread: DRV832X, DRV8328

Hi Experts! 

When I trigger an oscilloscope on one of the PWM inputs to the DRV8343, I see approximately 45 nanoseconds of jitter on the corresponding gate drive output. 

Section 8.3.1.4.3 Propagation Delay of the data sheet mentions several small delays which makes sense to me but I am wondering what "small" means and if it is possible for these delays to produce this amount of jitter.  The jitter seen when the gate turns on and when it turns off appear to be uncorrelated.  I may have been wrong in thinking that independent mosfet mode put the chip into a fairly direct drive mode.  That is, the smart gate drive features were mostly bypassed such that there would be a relatively fixed timing between the PWM input and the gate drive outputs.

 

So, several questions arise:

What internal logic remains in the signal path in independent mosfet mode that we would need to consider?

Is it possible for this logic to produce a 45 nanosecond jitter or variation?

Since we have set a deadtime close to this variation, does the chip design guarantee that the variation cannot produce a shoot-through condition?

Thank you,

Cameron

  • +1
    TI__Mastermind 26046 points

    Hi Cameron,

    Jitter can occur in DRV832x, DRV834x, and DRV835x due to synchronous PWM input in logic to toggle predrivers in Smart Gate Drive devices. The system clock is 20MHz (50ns period), so jitter from 1 to 50ns occurs depending on input timing of the input PWM. 

    Bootstrap devices like DRV8328 do not have any jitter since PWM inputs are asynchronous in logic to toggle predrivers. 

    Despite the jitter, the device uses a state machine to ensure dead time is set internally in the driver depending on the dead time setting. So even if MCU dead time is 0ns, the driver dead time will be one of these settings to ensure both FETs are not on simulataneously. However, if independent mode is used, dead time is bypassed, so if a motor is being controlled in independent mode, I would ensure to add at least 50ns dead time to protect against shoot-through caused by jitter. 


    Thanks,
    Aaron