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Original question:

PMP9766: Problems during the charging operation

PMP9766: Bidirectional energy transfer function and negative current limit

Wendy Wang1
Genius 11250 points
Part Number: PMP9766
Other Parts Discussed in Thread: TPS63020

Hi,

I read the document of PMP9766.http://www.ti.com/lit/ug/slva726/slva726.pdf 

It says that "The TPS63020 buck-boost converter operates bidirectionally and is able to transfer energy from its input
to its output as well as from its output to its input."  But in the datasheet of TPS63020, it doesn't say anything about the bidirectional energy transfer function. Does all the buck-boost have this function?

In the document, it says"The charge current is defined by the negative current limit of the TPS63020 buck-boost converter. Depending on the converters operating mode, either in buck mode or in boost mode, the negative current limit is typically between 0.6 A and 0.8 A."My second question: Does the TPS63020 charge the cap with constant volatge? Is the current between 0.6 A and 0.8 A enough to charge the cap?

Best Regards,

Wenxiu

  • 0
    TI__Expert 7925 points

    Hi Wenxiu,

    The first part I answered in your previous post:
    https://e2e.ti.com/support/power-management/f/196/t/833034

    When operating in reverse, the TPS63020 will charge the capacitor with a constant current, typically between 0.6 A and 0.8 A. Any current can charge the capacitor as long as it is sufficiently larger than the capacitor's leakage current, which for supercapacitors is typically below 1 µA. If the current is higher, the time needed to charge the capacitor is shorter, approximately:

    Δt=CΔV/I

    If you have a 1 F capacitor, to charge it to 5 V with the above current limit, it will take around 6-8 s.

    Best regards,
    Milos

  • 0
    TI__Expert 7925 points

    Hi Wenxiu,

    We haven’t heard back so we're assuming this answers your question. If not, just post a reply below, or create a new thread if the thread has locked due to time-out.

    Thanks and regards,
    Milos