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TPS61099: Questions with Down mode

Hedy Hung1
Intellectual 325 points

Part Number: TPS61099
Other Parts Discussed in Thread: TPS61029, TPS61022

Hi sir,

If TPS61099 operates ‘Down mode’ for long time, will that causing side effect? E.g. shorten chip life cycle

Do the inductor current calculation still follow Equation 4 in Down mode? (refer datasheet, SLVSD88K –JULY 2016–REVISED MAY 2018)?

If TPS61099 output current is limit, the Vout is near Vin, that means it enters ‘Pass Through’ mode, right?

Thanks.

 

B.R., Hedy

  • 0
    TI__Mastermind 21565 points
    Hi Hedy
    You need to check the thermal if the converter work in "Down Mode" for a long time. The efficiency in this mode is much lower than normal mode.

    The calculation is not suitable in down mode. As the operate function of the FET is change. It will bring a larger voltage drop.

    For the current limit related question, please check the "8.3.5 Current Limit Operation" as:
    The TPS61099x employs cycle-by-cycle over-current protection (OCP) function. If the inductor peak current reaches the current limit threshold ILIM, the main switch turns off so as to stop further increase of the input current. In this case the output voltage will decrease until the power balance between input and output is achieved. If the output drops below the input voltage, the TPS61099x enters into Down Mode. The peak current is still limited by ILIM cycle-by-cycle in Down Mode. If the output drops below 1.6 V, the TPS61099 enters into startup process again. In Pass-Through operation, current limit function is not enabled.
  • 0 in reply to Minqiu Xie
    TI__Mastermind 21565 points
    Besides, you could share your requirements and target for us. How about the Vin, Vout range and load condition?
  • 0 in reply to Minqiu Xie
    Intellectual 325 points

    Hi Mingiu,

    Thanks your quick response.

    I have dual source to input, one is Li-MnO2 (3V to 2V), another is adaptor power (3.4V).

    And I design Vout is 3.1V, loading current is 3uA to 650mA.

     

    I knew the TPS61099 would enter Down mode or reach current limit at some condition, but those operate in “short time” but many cycles.

     

    That is why I need to know the potential risk and the defective phenomenon.

     

    B.R., Hedy

  • 0 in reply to Hedy Hung1
    TI__Mastermind 21565 points
    Hi Hedy:
    If you could deal with the thermal problem, the converter could continued operate in down mode or full current load.

    I afraid TPS61099 may not to support boost from 2V to 3.1V/650mA. The minimal Isw_limit 0.8A. We have TPS61029, TPS61022 for larger current capability.
  • 0 in reply to Minqiu Xie
    Intellectual 325 points
    Hi Mingiu,
    Thank you, I'll study that.