• State
  • Locked Locked
  • Replies 4 replies
  • 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.

TPS62133 stops starting

Rodrigo Daniel Trevizan
Prodigy 30 points
Other Parts Discussed in Thread: TPS62133, LM25011

Hello everyone

I'm having an issue in an application where I'm using TPS62133. I'm currently working on a switched mode power supply with 12V and 5V outputs. 12V output is provided by an isolated flyback converter connected to mains and TPS62133 steps down 12V to 5V. The 5V power supply is backed up by a Li-ion cell when power from mains is cut off (e.g. fault in electrical grid, mains plug disconnected by user).  A battery management IC steps up battery voltage to 5V when in backup mode, and it recharges battery when in normal mode.

For this application I have used L=2.2uH  and Cout=150uF. Maybe it is not the best, but output is correctly regulated.

It works fine for some hours. But then TPS62133 stops operating. And I can mesure a short circuit between 12V and 5V when the whole circuit is unpowered.

I am pretty sure that the IC is being mishandled, but I have no idea of what is going on. TPS62133 has a short circuit protection and I have never measured any significant overvoltage in the 5V rail, so I really don't know what is the issue. Input voltage (12V rail) peak is about 15V.

In fig. 1 the circuit is working correctly. Ch1 is 12V and Ch3 is 5V. fig 2 shows the "damaged circuit" operation. Ch1 is 12V and Ch2 is 5V.

Has anyone ever seen something like this?
FIG1


FIG2
 

  • 0
    TI__Guru**** 150820 points

    Based on those waveforms, your 12V supply is overshooting past and above 12V.  This is a typical failure of a DC/DC converter powered from an AC adapter typically.  Once the adapter is plugged in, its voltage overshoots due to the inductance in the input cable.  It would be good to see if this ever happens.

    Also, it is worth removing the TPS62133 from the board and seeing if the short still exists on the output.  It could be a downstream circuit that is broken.

  • 0 in reply to Chris Glaser
    Prodigy 30 points

    Chris,

    First, thank you for answering.

    Yes, indeed. It is overshooting above 12V. I may take a closer look at that later. Now I'm concerned about finding the event that causes the TPS62133 failure.
    As it is clearly written in the datasheet, the IC input voltage absolute maximum is 20V... so a 14V overshoot shouldn't be a concern.

    When I remove the TPS62133 the short circuit no longer exists. But when the circuit is powered on, there is no short circuit.

    I have a question about thermal shut down. In the D/S it says that if Tj exceeds 160ºC, the IC goes into thermal shut down. But the absolute maximum operating temperature is 125ºC when operating and 150ºC when stored. Couldn't the IC be damaged before it goes into thermal shut down?

  • 0 in reply to Rodrigo Daniel Trevizan
    TI__Guru**** 150820 points

    14V overshoot is fine but if it overshoots at all, it likely overshoots more under some conditions.  It is worth looking for.

    Yes, the abs max temperature would be exceeded before the thermal shutdown is reached.  The reason thermal shutdown is set so high is so that the maximum operating temperature can be reached without shutting down.  Good board layout should prevent you from reaching it under almost all application conditions.

  • 0 in reply to Chris Glaser
    Prodigy 30 points

    Solved the overshoot problem "slowing down" the compensation loop response.
    However, I have no spare parts to replace TPS62133 and it is unavaible in the market until March, so I can't verify if the problem was solved.

    I guess it could be a thermal issue with my board. Even though the ground plane close to the IC has about 5 cm² of copper, soldering was hand made. I have tested it with less than 700mA  load. It is not close from 3A, but as the buck converter is fully functional for some period of time, I suspect that it may overheat and then gets damaged. 

    The project needs to be concluded before March, so Iam replacing the TPS62133 another buck converter. I think a more robust one would be a better choice, like LM25011.