SM470R1B1M-HT: Increase in Current at 185C

Hi,

Marius Raducanu said:

1 - Can I use the microcontroller for a short period of time powerd by 2.55V?

2 - Can I use the microcontroller with a 2.5V supervisory circuit? I know that the answers of 1 and 2 are "NO" but I am trying find what could happen if I push the microcontroller limits.

No, 2.55V will be out of the recommended operating conditions which is between 3V and 3.6V for VCCIO. It may seem to work briefly but there is no guarantee that it will always work. 

Marius Raducanu said:

3 - What can create this behavior of the microcontroller and what can I do to avoid these problems?

What is the VCC voltage? Does it drop too? 

Is the problem only happening on one unit? Can you replicate the issue on other units?

Can you do a ABA swap? Swap a good known device to the problem board? Will the good unit continue to work as expected? Also swap the problem device to a good known board. Can you observe the same issue on the good board?

Hi Charles,

VCCAO is 3.5V, VCC1-VCC6 is 1.8V with an increase to 1.9V at 185C.

I have tested only one board but I am planning to test another four this week.

Regards,

Marius Raducanu

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

Hi Marius,

  Thanks for the info. At this moment I don't really have a good explanation why three works but not all. There seems to be some marginality issue for one of the four. Do you have proper decoupling cap on the power supplies to the MCU? 

Hi Charles,

The microcontroller has a surge in power consumption/current at ~185C.

The problem is created by the DC/DC converter that cannot provide 50mA at 185C - it is rated 300mA. The 3.3V drops under 3.0V and the supervisory circuit triggers a reset. I have tried with the converter set at 3.5V but at 185C the voltage still drops under 3.0V. With an external power supply on 3.3V the microcontroller works and the current measured is ~47mA.

Yes, I have decoupling capacitors.

Regards,

Marius Raducanu

Hi Marius,

Marius Raducanu said:

The problem is created by the DC/DC converter that cannot provide 50mA at 185C - it is rated 300mA.

  I don't have much knowledge on the DC/DC converter you use. Can the DC/DC converter support high temp at 185C and above? If it is rated for 300mA then why would it stop at 50mA? Is it temperature dependent, I'm really not the expert to answer it. Have you raised the question to the power management forum that supports TPS62000?

Marius Raducanu said:

The 3.3V drops under 3.0V and the supervisory circuit triggers a reset.

I think your supervisory circuit is doing what it is supposed to do.

Marius Raducanu said:

I have tried with the converter set at 3.5V but at 185C the voltage still drops under 3.0V.

Again, I'm not the expert on this DC/DC converter. Reading the datasheet of it, it says it is rated for 85C.

Marius Raducanu said:

With an external power supply on 3.3V the microcontroller works and the current measured is ~47mA.

Although I can't say for sure it is a not a MCU problem but it seems that it is working at 185C if you use the external supply. 

What I will suggest you try is to do an ABA swap test. You say 3 out 4 boards are working. Can you swap the MCU in the failing board to one of the three good boards? Also swap the MCU from one of the three good boards to the failing board? What results do you have? This is the way to determine if it is a MCU problem or board level problem.

Hi Charles,

I asked/presented this question in the power management forum:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1123998/tps62000-ht-voltage-drop-at-185c/4181018#4181018'

The DC/DC converter used is TPS62000SHKK (TPS62000-HT), rated 210C, 300mA - in my board, based on my tests, it cannot provide 47mA at 185C. The voltage drops under 2.92V triggering the microcontroller reset, the voltage recovers, the microcontroller starts again and reset again - being unstable, until the temperature drops under 180C when recovers.

The three out of four boards work up to 185C but if I go higher, they have the same problem at ~187C. Maybe the board that fails at 182C has an external pull-up resistor (used for a RS232 communication) that makes the board to consume more power and trigger the failure earlier.  

Based on my tests, the main problem is the TPS62000SHKK DC/DC converter.

Regards,

Marius

Hi Marius,

  At this moment, I will wait for your update with the power management forum team if you believe the problem is more on the DC/DC converter. 

Hi Marius,

  In that case, I will close this thread for now. If you have update, you can simply write back and the thread will automatically reopen.