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TPS65131: TPS65131 heats up and outputs go into thermal or current limit shutdown randomly

Brian Castro
Prodigy 30 points
Part Number: TPS65131

Hi,

I have a typical implementation as shown in the schematic. +5V in to +/-13V out.

Our application has a current demand of ~55 to ~90mA from the +13V output and a steady 50mA from the -13V output. This is well with the capability of the part w/ proper layout and thermal considerations (the negative output should be able to do about 270mA at -13V output).

We are finding that with some units the part will randomly get very hot and go into thermal shutdown, either both rails go into thermal shutdown or the negative rail goes into OVP first. It's definitely related to the negative output, if we don't use it there are no problems. The problem is it does this randomly. Normally the DC-DC is cruising and doesn't really get hot, you can touch it. This can be for two hours, ten hours or 48 hours. Then all of a sudden the temperature will rise drastically and the TPS gets super hot and goes into protection. However, the load never changed, and the current measurement over time is captured and is totally consistent.

 A few parameters I can detail are:

1) The layout is similar to the eval board.

2) We are not using power save mode, those pins are grounded.

3) The DC converter and related circuitry is on a relatively small module 43mm x 20mm. The thermal stitching and considerations are as good as possible, it should not be an issue with the low power requirement. The LDO regulators on the outputs are very close by on a main PCB assembly.

4) Vin under load has about +/-30mV p-p noise as shown in capture below

5) Vref under load remains about 1.21V with about +/-80mv p-p noise the noise as shown in capture below

6) FBN remains about ground with about +/-40mV noise as shown in capture below

7) +13V and -13V outputs have about +/-30mV noise as shown in capture below

Any idea on what might cause this? I there a problem with having too much capacitance on the raw outputs? The DC converter has 4x4.7uF MLCC's on each output but the post-regulators have an additional 47uF Elec on there inputs. Could this be a symptom of too much noise on the FBN?

Vin

 

  

Vref

 

 FBN

 

 

 +13V Out

 

 

 -13V Out

 

 

  • 0
    TI__Mastermind 18550 points

    Hello Brian,

    Thank you for the detailed description of the issue you are seeing. This one will be difficult to debug as it happens sporadically where the system works for many hours before the issue happens or it can happen within couple of hours of operation. Schematically I do not see anything remarkable that should cause such an issue. As far as the extra 47uF electrolytic at the LDO inputs, I think that they should only impact initial power-up ramp of the output rails and will make the ramp time longer but other than that, I do not think it should be an issue. If you suspect excessive noise on FBN pin, as an experiment, you could remove C88 to break that coupling path to see if it impacts this issue in any way. I am not sure what else to suggest and you will need to some how make it more reproduceable to be able to debug it.

    Kind Regards,

    Liaqat