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TPS61085's off-time is fixed?How to realize?

LI MINGYU
Prodigy 30 points
Other Parts Discussed in Thread: TPS61085

TPS61085's  off-time is fixed?How to realize?And , DOesTPS61085 work  in PFM mode?

  • 0
    TI__Guru 65300 points

    Hello Li,

    TPS61085 is a regulator that operates with fixed off-time instead of fixed frequency. You just need to connect the input voltage and the necessary external parts as given in the datasheet and the part will regulate to the required output voltage as long as it is above the input voltage.

    For more details you might have a look at the datasheet or order an evaluation module and check it out.

    The part will stop switching if the output voltage will be above a certain threshold. This is some type of PFM.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 30 points

    hi Brigitte,

    TPS61085's  datesheet  is  too  rough.So even  I have no ideal about how to fix the off-time .Currently I'm using the TPS61085  in an  isolated flyback topology.

    In my design ,I need the duty cycle and frequency  to calculate   suitable  transformer.But I can't  find it in the datasheet.

    Does the TPS61085 works like  the D-CAP chips?

  • 0 in reply to LI MINGYU
    TI__Guru 65300 points

    Hello Li,

    The frequency is given in the typical characteristics Figure 9 and Figure 10 on page 7 of the datasheet.

    The duty cycle depends on the ratio of the output voltage to the input voltage. The IC measures the output voltage on the SW pin and the input voltage on the IN pin and sets the off-time the way that the frequency is either close to 650kHz or 1.2MHz dependent on the setting of the FREQ pin.

    So you can calculate the duty cycle dependent on the FREQ setting, the input voltage and the reflected output voltage on the transformer.

    Best regards,
    Brigitte