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PMP21455: Why using external current source

Lukas Kostorz
Prodigy 20 points
Part Number: PMP21455
Other Parts Discussed in Thread: UCC28881, , PMP20708

In your reference design PMP21455, UCC28881's Pin 4 (named as output in the datasheet) is fed from an external current source.

Is that correct? Why are you suggesting to use an external source?

Do you bypass the internal LDO when doing that?

Regards

Lukas

  • 0
    TI__Expert 4110 points

    Hi Lukas,

    The design that PMP21455 is derived from - PMP20708 need to take low DC input voltage (down to 24VDC). UCC28881 datasheet suggested minimum voltage on HV pin to startup the device is 30V. Therefore, I need to find a reliable way to startup the controller at 24VDC input. That is why I bypass the internal LDO and supply IC VDD with external current source.

    If you can make sure the minimum voltage at HV pin is higher than 30V, you don't need external bias for the IC.

    Regards,

    Sheng-Yang Yu