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Rise/Fall/Dead Times for the DRV8811 and DRV8812

Samual Baldwin
Prodigy 10 points
Other Parts Discussed in Thread: DRV8812, DRV8811

Hello Team,
I have a couple of questions regarding the Rise/Fall and Dead times as they relate to your two products, the DRV8811 and DRV8812.

I noticed that the DRV8812 specifies rise/fall times as well as dead time where the DRV8811 only specifies dead time.  Could you explain why?

Also, the dead time is specified for typical only (400nS) for the DRV8812 and min/typ/max for the DRV8811.  Doesn't the maximum fall time need to be less than the minimum dead time to prevent shoot through? (It appears that looking at the relationships of rise/fall/dead times between the two data sheets that this may not be the case).

Thank you,

Sam

  • 0
    TI__Guru 55605 points

    Sam,

     

    Your question somehow slipped through the cracks until I noticed it today.  I apologize for the delay.  The team is researching it now and will post a response within the week.

     

     

  • 0
    TI__Expert 7455 points

    Hi Sam,

    Thanks for posting this interesting question! First of I want to make sure we are not confusing both devices. It is very important to understand the DRV8811 and DRV8812 are two completely different designs based on two completely different H Bridges. Hence, the parameters on one device can not be used with the other.

    When it comers to shoot through, these devices are designed such that the occurrence of both FETs on the same half H Bridge leg to be enabled at the same time, is virtually impossible. These designs take into consideration all possible scenarios and the dead time is chosen so that the worst case scenario of device conditions does not induce the aforementioned condition. This is why you can see in the datasheet a note stating "Guaranteed by Design".

    It is very hard to answer this question conclusively other than by saying that we feel 100% confident our devices do not suffer from this malady. At least, from a personal point of view, on the thousands of hours worth of motion control that I have invested with these devices, I have not experienced evidence of shoot through not even once. We have also helped hundreds of different customers with different issues during their development cycles and shoot through has never been a problem. So I think it is safe to assume this is not a problem to worry about.

    Please let me know if there is anything else I can help you with. Best regards,

    Jose Quinones