• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 691 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS54140A: TPS54140A in 12V Batt Charger - light load start-up issue at low drop out

Mike Farley
Prodigy 735 points
Part Number: TPS54140A
Other Parts Discussed in Thread: TPS54341

Dear Forum,

My assigned customer has found some early field failures at minimum input voltage (10.8V), due to the device not starting up properly with their 60mA minimum load. As Vout is 9.5V (dropout of only 1.3V min) - I suspect the issue is related to this thread:

https://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/466590/1674306#1674306

Once Vin is increased, the issue goes away, which ties up with the above.

I passed along this http://www.ti.com/lit/an/slva547a/slva547a.pdf which may help, but they believe the easiest way might be to switch in an additional 100+mA load to increase frequency and hence ensure enough charge is available for the HS FET bootstrap.

Q: is it possible to get advice (or data / curve) on minimum load current vs. dropout voltage to ensure proper start up?

So far the parts are starting with load currents from 1-150mA, so is there a min current above which all parts can start? (if not which low Iq buck do we recommend without this issue).

Schematic and waveform attached.

Many thanks, Mike.TPS54140 12A charger_start up issue.docx

  • 0
    TI__Guru**** 191445 points

    Yes you are operating in low head room drop out due to BOOT UVLO.  Probably your best recourse is to use one of the work-arounds in the application note.  It is difficult to predict the eco-mode threshold, which is what you want to avoid.  See this application note:

    You could also consider a device like TPS54341 with an integrated pull down FET.

  • 0 in reply to JohnTucker
    TI__Prodigy 735 points
    Thanks John for the help.

    The customer has been considering TPS54341 due to your advice.
    "We would like to check with you that [TPS54341] will provide a steady output voltage under the following conditions:

    Vout (max) = 10.0V (with ripple <200mV)
    Vin = 10.8V
    Load = zero"

    - can you guarantee correction operation by design, or is Webench able to verify?
    - zero could be a couple of mA in case that makes a difference?

    Many Thanks!
    Mike
  • 0 in reply to Mike Farley
    TI__Guru**** 191445 points
    TPS54341 should work with no problem.