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TPS62827: Negative current limit of Low Side FET

Yishan Chen
Intellectual 930 points
Part Number: TPS62827

Tool/software:

Hi Team,

How do we understand the negative current limit in the datasheet?

Thank you,

Yishan Chen

  • 0
    TI__Expert 3738 points

    Hello Yishan,

    this parameter is important for forced PWM applications, as described in 7.3.5

    In forced PWM devices, a negative current limit (ILIMN) is enabled to prevent excessive current flowing
    backwards to the input. When the inductor current reaches ILIMN, the low-side MOSFET turns off and the
    high-side MOSFET turns on and kept on until TON time expires.

    In case of low output currents, forced PWM causes negative current flow through the low side FET.

    I hope this answers your question.

    Regards, Werner

  • 0 in reply to Werner Lummer
    TI__Intellectual 930 points

    Hi Werner,

    Thank you for you support.

    Maybe go a little be deeper, So how do we calculate the negative current during in the operation? What is the relationship between the load current/Switching frequency and inductor and other specification?

    How customer know if they will not exceed the limit here?

    What is the switching frequency in FPWM mode?

    Thank you,

    Yishan Chen

  • 0 in reply to Yishan Chen
    TI__Guru*** 147250 points

    Hi Yishan,

    Equation 6 in the D/S calculates the ripple.  If you replace Iout,max with your minimum load current (usually 0A) and subtract 1/2 of the ripple, you get the minimum negative current in your application.

    Chris