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TPS62122: TPS62122 behaviour when VIN below threshold

Sanika Joshi
Prodigy 70 points
Part Number: TPS62122
Other Parts Discussed in Thread: TPS63050
Hello,
I am trying to understand behaviour of TPS62122 below 2V. 
I am planning to use TPS62122 to convert 3.7V LiPo battery voltage to my circuit voltage 2.8V. I would like to use a LiPo battery without Protection Circuit Module to reduce total cost of the design. Which means the battery won't shut down when it reaches under voltage limit. Due to this the battery voltage may go below 2V which is the min voltage limit for TPS62122. 
What happens when Vin is below 2V? Will TPS62122 shutdown or will it keep on generating Vout wrt the Vin?
Thanks,
Sanika

  • 0
    TI__Guru*** 140510 points
    Hi Sanika,

    Most DC/DCs, including the TPS62122, have a UVLO circuit. This turns off the IC when Vin gets too low.

    Using a higher Vin device for a single cell application is not typical, as the DC/DC is not optimized for the lower voltage. But they do have a higher UVLO level. At what Vin would you like the DC/DC to turn off in your application?
  • 0 in reply to Chris Glaser
    Prodigy 70 points

    Hi Chris,

    Thanks for the input.

    In my circuit prefered operating voltage range is 2.5V to 3.0V.

    I am planning to set the Feedback such that Vout is 2.8V. Since this is a Step-down converter I am guessing Vin should not go below 2.8V. Is that correct?

    What will happen if the Vin goes below 2.8V? Will the device shut down automatically or will it generate some Vout till Vin goes below 2V?

    Thanks,

    Sanika

  • 0 in reply to Sanika Joshi
    TI__Guru*** 140510 points
    Hi Sanika,

    Is the low end of your battery voltage 2.5V or 3V or is this undecided? I expect a single cell, rechargeable lithium battery voltage to be above 4V when fully charged. A voltage range of 2.5V to 3V seems very narrow.

    Do you need the 2.8V to stay at 2.8V when Vin is below this?

    If so, then you need a buck-boost converter like TPS63050.

    A buck converter will enter 100% mode, as described in the D/S, when Vin is too low.