• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 389 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.

TPS61202 only works when Vaux is floating

Adam McLeod
Prodigy 10 points
Other Parts Discussed in Thread: TPS61202, TPS61240, TPS61256

I'm debugging a simple power circuit involving a TPS61202.  It is boosting a 3.7v input from a battery to 5v.  For reasons I cannot explain, it only sporadically operates when a 0.1uF capacitor between Vaux and ground is present.  Vout is 0v most of the time, but (seemingly at random) about %10 of the time it will output 5v.  I am finding the success and failure conditions very hard to reliably reproduce.  However, if I remove the 0.1uF capacitor at Vaux, the device seems to work fine. 

I found mention of problems with UVLO triggering due to high inrush current, and a soft-start circuit was suggested to fix this, as described in this datasheet:

http://www.ti.com/lit/an/slva307a/slva307a.pdf

I installed this extra circuitry, and while it doesn't appear to hinder the operation of the circuit when missing the Vaux cap, it also doesn't fix the problem when the Vaux cap is present.  I had to substitute the following diode instead of a 1N4148, however:

http://www.comchiptech.com/cms/UserFiles/CGRM4001-G%20Thru.%20CGRM4007-G%20RevD.pdf

Any ideas about what might be going on?  I've done my best to rule out cold solder joints, bad discrete components, and mislabeled/incorrectly installed parts.  

  • 0
    TI__Guru**** 150820 points

    You would need to look at some waveforms of Vin, SW, Vaux, and Vout to see what is going on but it sounds like something in your soldering or board layout is amiss.  The D/S makes clear that a capacitor on Vaux is required.  I suggest ordering the EVM and testing its known good board.

    But for a li-battery to 5V rail, there may be other devices that give better performance and smaller size.  Such as TPS61256, TPS61240, etc.