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TLVM23625: LDO output Vcc < Vcc possible?

Hans
Genius 12865 points
Part Number: TLVM23625

Hello Team,

once operating Vcc could be higher than Vin? Can you clarify, please? 

Is this module ok for a Vin =3.55V +/-1% (Vin, min=3.51V and Vin,max=3.59V) and Vout=3.3V? Why is Tss specified for Vin =4.2V?

Thank you and Best Regards,

Hans

  • 0
    TI__Mastermind 35210 points

    Hi Hans,

    I believe VCC will drop below VIN in that case by its Vdrop. I can double check.

    Additionally for Tss, without having access to the original engineer who worked on that, it will be hard to tell you for certain, but, often test conditions are setup so the measurement can be done accurately and efficienctly, while still being able to gauge if the device is exhibiting, normal performance.

    Is this just a curiosity question, or does the customer want to know what the soft start time is at ~4V?

  • 0 in reply to Marshall_Beck
    TI__Genius 12865 points

    Hi Marshall,

    1. LDO Vcc: thank you for double checking; do you agree that the data sheet is a bit unclear?

    2. basically we need to know if the part works and starts operating if Vin=3.55V+/-1% at Vout = 3.3V

       If you could provide the Tss for Vin =3.55V would be appreciated.

    according to table 8-5, DS it is not possible to use this module:

    But according to Webench it works:

    Thank you, Hans

  • 0 in reply to Hans
    TI__Mastermind 35210 points
    Hans said:

    1. LDO Vcc: thank you for double checking; do you agree that the data sheet is a bit unclear?

    It would be more troubling if we advised powering things off the the LDO (besides I/O of DCDC). Being that this is a buck with an internal LDO, I dont think it should be too much of a surprise the I/O will be less than Vin, but if you can advise on what you would like to see, I can provide that feedback to the datasheet authors.

    Hans said:

    2. basically we need to know if the part works and starts operating if Vin=3.55V+/-1% at Vout = 3.3V

       If you could provide the Tss for Vin =3.55V would be appreciated.

    according to table 8-5, DS it is not possible to use this module:

    Those rules are not hard and fast. I am happy you came here to ask, as the device can operate at 3.55Vin with VOUT being approximately equal to VIN, minus vdrop due to I*DCR, DCR being that of the inductor and HSFET. I attached some dropout curves and also soft start time across temp in the attached word doc.

    TPSM33625 Startup Time Dropout.docx

  • 0 in reply to Marshall_Beck
    TI__Genius 12865 points

    Hi Marshall, thank you for the additional measurements! Is my understanding correct: Measurements show startup Vin = 3.4V at lower currents and then you increase Vin up to the regulated Vout and then you decrease VIn down to Vout <3V?

    It would be good to see these measurements in the data sheet :-)

    Thank you and Best Regards, Hans

  • 0 in reply to Hans
    TI__Mastermind 35210 points

    You are welcome.

    Yes in the dropout plots, included are rising Vin and falling Vin ramp.