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TPS62000-HT: Voltage Drop at 185C

Part Number: TPS62000-HT
Other Parts Discussed in Thread: TPS62000,

Hello,

I am using twoTPS62000 to power a SM470R1B1 with 1.8V and 3.3V.

At 187C the 3.3V starts fluctuating between 2.9V and 3.0V - this is critical because it resets the microcontroller.

When cooling it down, it recovers at 175C.

The TPS62000 used for the 1.8V output, works well at 190C, just a small increase in voltage to 1.89V.

The two circuits are almost identical, the difference is the feedback resistors and the inductor 10uH for 1.8V and 22uH for the 3.3V. I tried with 10uH on the 3.3V and got the same result.

Now, my best guess is that one part (FLASH memory, EEPROM memory) that is powered by the 3.3V, increases its power consumption and make the voltage to drop. 

It is difficult to measure the circuit - it is in an oven and at 190C. To measure the DC/DC converters outputs, I am using external wires soldered on the PCB.

What can create this problem?

Thanks,

Marius Raducanu

  • Hi Marius,

    Let me repeat what you explained, both the devices have the same BOM and layout (except feedback resistors and inductor). The only difference is the load connected to it. Is that correct?

    Now, my best guess is that one part (FLASH memory, EEPROM memory) that is powered by the 3.3V, increases its power consumption and make the voltage to drop. 

    There are 3 possible reasons for this behavior; one due to a bad layout or a bad layout which is also not thermally stable or problems with the load circuit at high temperature.

    Most likely it is the increased power consumption of the load circuit at very high temperature causing an over-load condition for our TPS62000. The over-load can be easily triggered especially at high temperatures. The load the device can supply at high temp will be reduced and this causes the Vout to drop.

    I suggest to measure the load current (preferably) or monitor the input current at this high temperature. If possible, please install temperature sensors on different parts (like the IC, inductors, load, etc) to understand the part consuming increased power at 190C. We need to confirm if the load current is exceeding the maximum limits at 190C.

    Is it possible to share the complete schematic and layout?

    Could you share the part numbers of the inductor used?

    TPS62000-HT is an extremely old device. Do you have a new design you're working on?

    Regards,

    Febin

  • Febin,

    Thanks for your answer.

    The inductor for 3.3V is IHLP2525CZER220M8A. I tested it with the 10uH but got the same behavior.

    The 1.8V circuit uses IHLP2525CZER100M8A and it works at 190C.

    I am running a test with the loads disconnected and a thermocouple on the TPS62000.

    The design requirement is the board to be rated 175C: surviving at 190 (not required to work) and recover at 180C.

    My board is very close to the design requirement with a recover at 175C.

    This is a new design and TPS62000 is the best that I could find on the market. Can you recommend something else?

    Regards,

    Marius

       

  • Hi Marius,

    This is a new design and TPS62000 is the best that I could find on the market. Can you recommend something else?

    Our newer devices do not qualify for a temperature up to 180°C.

    Most likely it is the increased power consumption of the load circuit at very high temperature causing an over-load condition for our TPS62000 on the 3.3V rail. Please follow the above suggestions and let us know.

    Regards,

    Febin

  • Hi Febin,

    I ran a test with the TPS62000 DC/DC converter disconnected (no inductor) and using an external power supply for the 3.3V. The load was: SM470RR1B1MHKPC micro-controller rated 210C, two FLASH memories, one EEPROM. The memories power consumption in idle mode (no reading/writing) should consume less than 1mA.

    The current at room temperature up to 185C was ~20mA.

    At 185C the current jumped at ~35mA. This is the temperature where the circuit powered by the TPS62000 DC/DC converter became unstable.

    The micro-controller worked at 195C with a current of ~47mA - no reset. I stopped at this temperature.

    My conclusion is that the problem I have is a combination of micro-controller increase in power consumption and the TPS62000 output. From the datasheet, the TPS62000 DC/DC converter can provide up to 300mA but it looks that at 185C with only 47mA load it has a voltage drop that triggers the voltage supervisor in the circuit resetting the micro-controller.

    I am planning to run another test with the circuit powered by the TPS62000 DC/DC converter set for 3.5V. I hope that the drop in voltage will not affect the micro-controller if the voltage stay higher than 3.2V.

    Regards,
    Marius Raducanu

     

  • Hi Marius,

    Thanks for sharing the updates.

    At 185C the current jumped at ~35mA. This is the temperature where the circuit powered by the TPS62000 DC/DC converter became unstable.

    - Can you check the junction temperature of the TPS62000 at Ta-185C?

    My conclusion is that the problem I have is a combination of micro-controller increase in power consumption and the TPS62000 output. From the datasheet, the TPS62000 DC/DC converter can provide up to 300mA but it looks that at 185C with only 47mA load it has a voltage drop that triggers the voltage supervisor in the circuit resetting the micro-controller.

    - Can you share the layout as well?

    - Have you also tried to use ceramic capacitors instead of Electrolytics?

    - The converter should be able to deliver 300mA at 185C. 

    The inductor for 3.3V is IHLP2525CZER220M8A

    - I also see that these inductors are rated only upto 180C. Have you tried to change the inductors which can support higher temperatures? It could be that these inductors generate larger power loss at high temp causing the Vout to drop.

    I am planning to run another test with the circuit powered by the TPS62000 DC/DC converter set for 3.5V. I hope that the drop in voltage will not affect the micro-controller if the voltage stay higher than 3.2V.

    - Noted. Please post the results later.

    Regards,

    Febin

  • Hi Febin,

    Q: Can you check the junction temperature of the TPS62000 at Ta-185C?

    A: I measured the TPS62000 temperature with a RTD and it was only 1C over the oven temperature. This is not correct, I expected to be at least 5-10C over the oven temperature but I can say that the TPS62000 temperature wasn't much higher than the oven temperature.

    Q: Have you also tried to use ceramic capacitors instead of Electrolytics?

    A: I am using tantalum capacitors, 20uF total. In the test that I am running now, I doubled them to 40uF.

    Q: I also see that these inductors are rated only upto 180C. Have you tried to change the inductors which can support higher temperatures? It could be that these inductors generate larger power loss at high temp causing the Vout to drop.

    A: It is difficult/impossible to find/buy commercial (not custom) parts rated more than 175C. If the inductor is 180C rated, I expect it to work at higher temperatures with a slightly decrease in efficiency close to this temperature. I think the parameters of the inductor will drop linear (not a step) close to the rated temperature. I have tried with a 10uH inductor and got the same behavior. The 1.8V circuit using the TPS62000 and 10uH inductor, works w/o problems at 195C, indeed it might not have a big load.

    Q: Noted. Please post the results later.

    A: The test is running. I will post the results.

    Regards,

    Marius Raducanu

  • Hi Marius,

    It is difficult to make conclusions on the root cause.

    - The snippets of the layout does not help. What I wanted to understand is if there is any difference in layout for both the devices. Especially considering thermal dissipation on the PCB.

    - By installing temperature sensors on different parts (like the IC, inductors, load, etc) the part consuming increased power at 185C can be narrowed down. I think it is important to actually locate component with increased power loss at 185C.

    - Compensating for the Vout drop on the 3.3V by setting to 3.5V could be the easy way out. I hope it works...

    Regards,

    Febin

  • Hi Febin,

    There are no big differences between the 1.8V and 3.3V circuits.

    I installed temperature sensors on the microcontroller and TPS62000. The temperature (range 24-195C) is not much higher than the environment/oven temperature - measured is 1C higher but I suppose the real value is a little bit higher, error created by sensor offsets.

    I agree, the increase in current/power at 185C should increase the temperature of the part that creates this BUT we have a decrease in voltage too that can make the power consumption to be the same and not have an increase in temperature of the part - my best guess is that the microcontroller is the culprit.  

    Unfortunately, increasing the TPS62000 output voltage to 3.50V didn't work. At 185C there was a drop in voltage from 3.5V to 2.9-3.05V (fluctuating).

    In the last test, I removed the supervisor voltage from the circuit. The microcontroller worked at 195C with a voltage of only 2.55V. The microcontroller didn't reset although, from the datasheet, the minimum voltage is 3.0V. Before, in previous tests, the supervisor was keeping in reset the microcontroller because the voltage dropped under 3.0V. Removing the supervisor is not a solution because without it, the memory can get corrupted at power up.

    Cooling the board down, everything recovered at 180C. The voltage recovered from 2.55V to 3.05-3.20V (fluctuating) - this is an indicator that the system is not totally stable.

    I will ask help on the SM470R1B1 microcontroller forum with this problem.

     

    Regards,

    Marius Raducanu

  • Hi Marius,

    I will ask help on the SM470R1B1 microcontroller forum with this problem.

    Please post the updates here, Meanwhile, I will also discuss with my team to find any missing links if any.

    Regards,

    Febin

  • Hi Febin,

    I already asked help on SM470R1B1 microcontroller forum:

    https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1125530/sm470r1b1m-ht-increase-in-current-at-185c

    Based on our test results, the IRT temperature limitation is a combination of increasing current at 185C (25 to 35mA), caused by the microcontroller and a drop in voltage (3.55 to 2.95V) caused the TPS62000  DC/DC converter due to increase in current (although its maximum current is 300mA).

    To confirm that the microcontroller creates the drop in current at 185C, we are running a test with all other parts removed.

    I will update the results after the test.

    Regards,

    Marius Raducanu

  • Hi Marius,

    I will update the results after the test.

    Noted and thanks for the update.

    Regards,

    Febin

  • Hi Febin,

    Only with the microcontroller on the 3.5V, we still have a drop in voltage at 185C.

    The conclusion is that the microcontroller creates this drop.

    This drop wouldn’t be critical, if the TPS62000  DC/DC converter provided 50mA at 185C. It looks that TPS62000  DC/DC converter cannot provide this current keeping the voltage at 3.3V, it drops at 2.95-3.05V - in a previous test we powered the 3.3V with an external power supply that kept the voltage at 3.3V when the current increased from 20mA to 47mA.

    At this point, I am out of the options and accept the temperature ratings of the board: 185C survival with 180C working - desired was 195C with 180C.

    Regards,

    Marius Raducanu

  • Hi Marius,

    At this point, I am out of the options and accept the temperature ratings of the board: 185C survival with 180C working - desired was 195C with 180C.

    Unfortunately, this part is quite old and I could not find additional characterization data. 

    I will have to say, the quick solution would be to operate the board at a lower ambient temp as you just mentioned. 

    Please let me know if you require any other support from us.

    Regards,

    Febin

  • Hi Febin,

    At least, I know that I have done everything possible to find the rated temperature of my system.

    Regards,

    Marius Raducanu

  • Hi Marius,

    Do you need any further support on this issue? Or can I close this case?

    Regards,

    Febin

  • Hi Febin,

    Yes, you can close the case.

    I had planned to use this converter in another design but now I am looking for other options.

    Can you recommend one, Vin= 5V, Vout 2.5V, Iout=200mA?

    Regards,

    Marius

  • Hi Marius,

    I guess you are looking for a HT device. Our latest Extended Temperature device can handle only a max of 150C. Is this acceptable?

    If not, then we do not have other options in the HT portfolio.

    Regards,

    Febin

  • Hi Febin,

    Yes, I am looking for a HT converter that survives at 195C and works at 180C.

    Regards,

    Marius

  • FYI

    I have tested another 4 boards,185C survival and 180C working.

    At 182C one failed and recovered at 181C. The other three worked all the time. My initial requirement was 195C survival with 180C working.

    Regards,

    Marius

  • Thanks for sharing the update.

  • I know this thread is closed but I ran a few extra tests that solved this problem.

    The problem with the 3.3V converter was that it didn’t change correctly between the PFM and PWM modes at ~187C when the load increased to 50mA. I suppose, TI tested this converter, using a constant load (maybe ~300mA as in specs), starting from 24C to 210C and the converter worked. In my case, I increased the temperature and at 187C the microcontroller had a surge/jump in current/load destabilizing the converter (not changing correctly between the two modes: PFM and PWM). Forcing the converter to work only in PWM (SYNC connected high), I can avoid this problem, maybe with a lightly increase in power consumption (not significant).  

    NOTE: With the SYNC pin to GND, the converter changes between PFM and PWM function of the load. With the SYNC pin connected high, the converter works only in PWM mode, less efficient but more robust (no changes between PFM and PWM).

    Regards,

    Marius Raducanu

       

  • Hi Marius,

    Thank you for posting your findings here...

    Probably, the converter does not get enough time to react to this change in load and accordingly switch modes. Because the surge is too short to react at such a high temperature like this.

    Regards,

    Febin