• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 64 subscribers
  • Views 328 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC21542: Is it ok driving MOSFETs as DC switches?

Charalampos Stavros
Prodigy 10 points
Part Number: UCC21542

Hello,

I need to drive several MOSFETs on lines ranging from 270-530VDC. As these are used for heaters, due to the application, they're expected to operate at 100% duty cycle for minutes.
The connectivity is shown below.

In the image, the MOSFETs are actually driven by, UCC12051 isolated modules, so it's not technically accurate.
This was more practical, but as the number of heaters increased, using a single PSU and dual isolated gate drivers, results in smaller footprint and should only have nanosecond scale delay for activation.

Does UCC21542 have any issue operating MOSFETs as DC switches? As in 100% duty cycle for minutes.
Given the low switching frequency of the system, it should be practically drawing current, equal to the quiescent value of UCC21542 on the isolated side.

Due to availability, it's more practical for me to use 2 UCC12051 in series, to power the UCC21542, or even better 21542A (5V UVLO variant).
Would connecting 3 or 4 UCC21542 be a problem for the PSU, as it's only rated ~100mA at 5V.

  • 0
    TI__Expert 4065 points

    Hi,

    The UCC21542 is capable of being used in 100% duty cycle so long as it has its own bias supply. Can you illustrate how you intend to power multiple UCC21542 drivers? 

    Regards,

    Krystian

  • 0 in reply to Krystian Plaskota
    Prodigy 10 points

    The concept is this.

    2 MOSFETs, which operate in DC. DT pin is tied to VCCI. The heater is illustrated as a resistor.
    This does not look like it's going to work though. At least, not without a dedicated bias supply on the high side, unless I misunderstood.

    After revisiting the datasheet, I noticed that page 36 in the datasheet states:
    "The high side VDDA-VSSA must maintain enough voltage to stay in the recommended power supply range, which means the low side switch must turn-on or have free-wheeling current on the body (or anti-parallel) diode for a certain period during each switching cycle to refresh the bootstrap capacitor. Therefore, a 100% duty cycle for the high side is not possible unless there is a dedicated power supply for the high side, like in the other two example circuits."

    edit: Highlight on heater.

  • +1 in reply to Charalampos Stavros
    TI__Expert 4065 points

    That is correct, with a bootstrap circuit you wont be able to keep the high side active for that long and in the VDD range at 100% duty cycle. But if each channel had its own dedicated power supply, you can use this driver for your application.