TPS62000-HT not regulating at high temperature

Shawn,

        1. Can you share your schematic and external components that you are using. 

         2. Are the external components used rated for the higher temperature.

          3.  How about the inductor being used make sure that it is not saturating at high temperature.  You can monitor the the current waveform in the output inductor to make sure it is not saturating.   If it is saturanting you will see a high peaks in the inductor waveforms.

 

 

Ramesh,

The schematic is shown below.  All of the capacitors have at least a 200C rating, and the inductors I have tried are rated anywhere from 200C to 300C.  I was thinking along the same lines as you, so I tried several different inductors of different values and current ratings.  However, they all had similar results. One of the inductors rated for 200C has a saturation current of 5.6A.  Even at very light loads (~50mA), the output drops off.  I have not watched the inductor waveforms, but even if I derate the allowed current down to 10% of its maximum value to accommodate the extreme temperatures,  I would not expect that light of a load to saturate it. 

Apparently, the schematic did not make it through.  Let's try again...

Shawn,

      Can you specify the core material for the output inductor used?  Is it rated for high temperature so it does not saturate when operating at 200C.   Note micrometal has some powerder iron type matreials that are rated for 200C.

I want to make sure that you are not using ferrite material for your output inductor.

Ramesh,

I tried two different inductors.  One is from the Coilcraft AT524PYA series.  They use a composite material for the core, and they are rated for 200C operation.  The other part I tried was from NASCENTechnology.  They use some type of co-fired ceramic ferrite that is supposed to be good to 300C.  The results were the same for both parts.        

Ramesh,

When TI qualified the TPS62000-HT at temperature, what inductor was used during the test? 

Thanks,

Shawn

Dear Mr. Shawn Wallace,

I believe I see exactly the issue described by you on our PCB as well. The TPS62000 seems to stop regulating at high temperatures (even for static load currents). I get the same problem with a TPS62000 device in the plastic package, and also with a proper TPS62000SHKK device in a 210 deg-C rated ceramic package for 58$ per piece.

I already posted on the TI high reliability forum about my issue, and also pointed to your older forum post, but unfortunately until now I did not receive any response at all.

Were you able to solve your high-temp issue with the TPS62000 after the last forum post? If so, what was the root cause?

Thank you very much in advance for your help,

with best regards,

Alexander Wolf

Hi Alexander,

Unfortunately, I was never able to resolve the issue. I am not convinced that TI has ever tested these parts in a circuit at the higher temperatures. I notice they do not include it on their H.E.A.T. board. It would be nice if their Applications Engineers would look into the issue.

Good luck,
Shawn Wallace

Shawn / Alexander,

 

          TPS62000  is rated for 150C Tj  as highlighted in the datasheet.  However TPS62000-HT is is rated up to 210C.   On ATE tests on the TPS62000-HT device is subjected to the higher temperature per the datasheet parameters where as the external components are not subected to higher temperature.

Shawn,

   Can you send me your test board so I can validate the results under our test conditons as well as verify the device datecode etc being used..  Will send you my shipping details in seperate mail.

Also note as highlighted in the datasheet on pg 10 at 210C  load regulation has wide variation/ tolerance.

Dear Mr. Shawn Wallace,

Thank you very much for your quick answer, it helped a lot. I hope there is a way to fix our circuitry, because otherwise I really liked the performance of the TPS62000.

But after changing major external things in our circuit (like using a very big high current high temp rated inductor, or only using half of our multiple output capacitors) during  my experiments in the oven, but still getting basically the same behavior and problems at high temp I am also not so convinced anymore that the problem maybe is outside the package. Because if there is a problem with my inductor selection or with the output capacitors I would have expected completely different behavior after the changes are done, but this did not happen.

 And the second thing I have observed during my measurements is that almost exactly around 166 deg-C the load step response of the circuit changes very suddenly.
 (independent of another inductor and so on). This is also something which makes me to believe that maybe whatever I change in the circuitry around the TPS62000
 the problem will stay. But of course it could also still be a bad external part selection on our side.

 May I ask you what your solution was for the TPS62000 problem? Did you switch to another device for your power supply? Is there maybe another useful device if
 we fail to solve the issue?

 Thank you again for your feedback,

   Alexander Wolf

Dear Mr. Ramesh Khanna,

thank you very much for your response and help. We are aware that the TPS62000 is only rated up to 150C Tj,
and therefore this part delivers its performance without any problems at all.

But also using a proper TPS62000-HT in the ceramic package has the same behavior/problem (at least
in our power supply), and this is something I would not expect. But maybe the problem can soon be found.

I am also well aware of the load regulation data sheet specification at 210 deg-C. The datasheet specifies
typical 23% load regulation for load currents from 10mA up to 300 mA at 210deg-C (in comparision to 0.6% up to 125deg-C).

Therefore I also expected a less good regulation at very high temperatures. But If I draw 120mA from
our 3.3V power supply at 210deg-C I end up with an output voltage of only 1.42V, and I almost think that
this is worse than 23% load regulation. At least from an application point of view this voltage drop
is unacceptable.

Thank you very much for your help on the subject,

Alexander Wolf

Alexander,

I ended up going back to a proprietary hybrid power supply that one of my colleagues developed several years ago. It's rather large, but it does seem to work. My main goal with the TPS62000 was to find a smaller, more discrete solution.

Good luck with your design,
Shawn

Hello Shawn,

 thank you very much for your answer. I appreciate it. 

   Have a nice day,

        Alexander