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Original question:

UCC21540: Minimum pulse width system-level study

UCC21540: Dead time capacitor limits changed in November 2024 datasheet.

Nico Hugo
Prodigy 20 points
Part Number: UCC21540
Other Parts Discussed in Thread: UCC21550

Tool/software:

Hi,

The UCC21540 datasheet requirement for DT capacitor changed in the November 2024 release where the requirement was updated from >=2.2nF to <= 1nF, please see below.

This is a substantial application-level change in requirements and is a complete contradiction of the previous recommendations.

What is the reason for this change in recommendation? Are there changes on the die that require this adjustment? What are the risks of not adhering to this requirement?

Furthermore, the new revision of this IC, the UCC21550 also explicitly states that the deadtime resistors should not be greater than 100 kOhm where the UCC21540 seems to allow this, given that a capacitor is added to the dead time pin. Can you possibly provide details between the UCC21540 and UCC21550 that could explain the difference? We intend to upgrade our design to the UCC21550, but currently use a 150 kOhm DT resistor for 1.5 us dead time.

  • 0
    TI__Expert 8466 points

    Hi Nico,

    This is a very understandable concern and apologies for the confusion.

    The latest generation devices have a newly designed DT pin to have noise immunity built inside the device. This allows for customers to utilize the DT pin without the need for a DT capacitor for noise immunity. However, due to this new design we found that adding too much capacitance can have an effect on stability so we have the new generation device datasheets recommend <1nF.

    If 1.5us of deadtime is desired, I would recommend:

    • Add external deadtime through the controller and set a shorter internal deadtime on the device
    • Continue with UCC21540 for the wider range of deadtime

    Hope this is helpful.

    Regards,

    Hiroki