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TLV62080: behavior at soft start (Urgent Help/)

Part Number: TLV62080
Other Parts Discussed in Thread: TLV62084, TPS62080

TLV62080(A), TLV62084(A), TLV62082

In any cases, the soft start time is described as 40us.
Due to the large capacity of the output line capacitor and the large load current from startup,
If the target voltage could not be reached within the soft start time,
I think it will shift to normal operation and continue to power on.

Switching operation starts 40us after EN is set,
It is described that it starts with a slope of 10 mV/us.


I hope to know if it does not move out of the set voltage at startup, or continue the soft start behavior until the target voltage is reached.

Any advice will be appreciated.

Jin

  • Hi Jin,

    The output voltage is not able to reach to set up the voltage in soft start-up time due to the high load and output capacitor. It will reach to nominal output voltage with the standard start-up of the pre-bias voltage capacitor. If you take look in Figures 16 and 17 in the datasheet, it shows the device start-up behavior with and without load. The device will archive the target value.

    Best regards,

    Tanvee

  • Hello Tanvee,

    Thanks for your reply. I still have inquiries about soft start. Could you advise me ?


    (1) Soft start period
    There is no description in the data sheet. How much is its period ?

    (2) Slope at soft start
    There is a description of about 10 mV/usec. Is its value regardless of the set voltage etc.


    (3) If the soft start cannot be started within the soft start period

    There is a description in the E2E response and data sheet,
    However if it could not start within the soft start period, The normal operation mode is entered and the startup continues, and the inductor current at that time works according to the conditions of inductor current limit.

    In Fig-16 and Fig-17 of the data sheet,
    The power supply has started up appropriately  with or without load,
    I think it's because it started up within the soft start period.

    The startup could not be completed within the soft start period,
    Also, marginal starting up condition (with or without inductor current limit works)
    Engineer worries about voltage overshoot.

    ≪In particular, our usage conditions are compounded as follows.
    ・Start up the input VIN and EN at the same time
    ・Input voltage VIN: 5V
    ・Output voltage VOUT: 3.3V
    ・VIN voltage rises from 0V to 5V in about 2ms,
    During the startup of VIN, the output of this IC will start up first
    ・The total capacitance of the output line capacitors is 100uF to 150uF
    ・I think that it consumes almost no current at startup, but it consumes about 300 to 500 mA after startup.

    From the data of Load Transient and Line Transient of the data sheet,
    Is it considered that its overshoot will be within a fluctuation of less than about 100 mV?


    (4) If it is difficult to answer (3) above
    If it is difficult to answer the above (3), on the evaluation board of the target device,
    Can you test the conditions described above on our EVM ?

    (5) External soft start circuit
    Please refer to the application note "slva307b"
    There is a description of the external soft start circuit,
    Is this method applicable to the TLV62080 series and TPS62080 series?

    Any advice will be appreciated.

    Jin

  • Hi Jin,

    Sorry for the delayed responses. 

    • The expected start-up timing is 1ms
    • The soft start-up Slope is 10mV/us with output rise regardless of voltage set. 
    • The BOM used in the application if its inside datasheet recommendation it will not create a critical issue and you can double-check it through PSPICE and webench simulation model. However, the device can support 100uF output capactoiior value above 100uF should be evaluated as it is outside datasheet recommendation. Please use the simulation model for evaluation.

    For further discussion, I would suggest connecting through the mail.

    Best regards,

    Tanvee