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TPS61021A: TPS61021A

Part Number: TPS61021A

 Hi Sir

According TI document, “Figure 14. Startup Waveform” mention that

After EN high about 1.5ms, Vout output 3.3v stably(When R=12, so current load is I=V/R=3.3/12=0.275A)

So in this condition, the typical startup time is about 1.5ms

 

May I know the typical start time of boost ic(TPS61021) when output condition is 3.4V/0.5A or 3.4V/0.4A?

And capacitance value of output will effect start time also?

Thanks a lot

  • Hi Kuo,

    Please see TPS61021A datasheet page 9 section 7.3.2 Enable and Soft start.

    When the input voltage is above the under-voltage lockout (UVLO) rising threshold and the EN pin is pulled to logic high voltage, the TPS61021A is enabled and starts up. At the beginning, the switching frequency and current limit are internally controlled. The load capability is limited. After the output voltage is above 1.6 V, the peak current limit is determined by the output of an internal error amplifier which compares the feedback of the output voltage and the internal reference voltage. Because the output voltage is below the setting target, the peak current limit rises and thus the output voltage ramps quickly. The soft startup time varies with the different output capacitance and load condition. The typical startup time is around 200 μs for a 44-μF output capacitor with no load.

  • Hi Zack

    Our test condition is:

    Setting Vout=3.4v, loading is R=10 Ohm, after enable is high, TPS61021A can output 3.4V/0.34A immediately

    Setting Vout=3.4v, loading is R=5 Ohm, after enable is high, TPS61021A can not output 3.4V/0.68A, it seems protection mechanism is activated

    Setting Vout=3.4v, No loading, after enable is high, TPS61021A can output 3.4V/0A, then we add loading R=5 Ohm, TPS61021A can output 3.4V/0.68A

    We want to know what mechanism inside the TPS61021A to causes this phenomenon, thank you

     

  • Hi Kuo,

    As datasheet section 7.3.2 Enable and Soft start explains, during startup, TPS61021A current limit is controlled and modified lower when Vout is low. The reason is usually TPS61021A input source is a battery, such as li-ion battery or AA battery. With this mechanism the input inrush current is reduced and input voltage won't crash down.

    Normally we would suggest customer apply to loading after Vout reaching to setting voltage because device will set the current limit to its rated current limit spec in EC table.

  • Hi Zack

    thanks for your information, appreciate