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STM32L152 getting really hot

Bharath Kumar
Associate II

‎2017-08-23 11:12 PM

Posted on August 24, 2017 at 08:12

Hello I'm new to STM32L152 MCU,

I had a custom board made after working on STM32L152-DISCO. My board was working well, was able to work on stlinkv/2 and IAR. After couple of days of working my STM32L152 , then all of a sudden few days later MCU got really hot and eventually my STLINKv/2 could not recognize the MCU (IAR throws this error) . MCU does not smoke nor leave black residue on the pcb just really hot.

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Now I started to investigate as per the following.

  1. Put the boot0 pin to high and connected it to STLINK utillity , its able to detect the MCU.
  2. Tried erasing the chip thinking that some faulty line of code could be a problem. I use the STlink utillity to erase but it throws me a error stating Readout Protection enabled. 
  3. Checking Option byte thing to disable the Readout Protection.
  4. So as to troubleshoot I checked the 3.3V on my switching regulator it was fine.
  5. Regulator was not getting that hot that was ok.
  6. So to speak that something wrong from the pcb or bridge is ruled out. I reconnected the power source thinking that there must be temporary glitch. Again the MCU gets really hot. So now I'm thinking may be MCU is bricked and I have a spare STM32L152VCT6 with me and removed the bricked MCU and re soldered the new one. Now the new one also gets really hot. 
  7. Again repeated steps 1 to 5 with the new IC just get the same things.

Now I'm really freaking out, coz I could have bricked my replacement IC as well.(Not really sure though)

I had another spare pcb with me , so wanted to investigate if there is any pcb side issues.

  1. Checked the 3.3V and GND continuity. No beep sound that was good.
  2. Quickly resoldered all the required essential components.
  3. Before transferring the IC from PCB old to new, I again checked continuity 3.3V to GND , NO short.
  4. Transferred the IC from PCB Old to new. Now I get Beep sound between 3.3V to GND.
  5. Now 95% I'm convinced the replacement IC is also smoked. 
  6. There are some peripherals connected to MCU like PCF8574 which should not draw lot of current. However could not verify it since I don't know how much current its drawing.
  7. Replacing a new IC on the new PCB will also yield failure and double blow.

If there is some one who can tell me what the problem is please let me know.

Thank you

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AvaTar
Lead

‎2017-08-23 11:21 PM

Posted on August 24, 2017 at 08:21

I would suspect an ESD.

Did you, and everybody else who touched the board, always observe the necessary precautions ?

There are some peripherals connected to MCU like PCF8574 which should not draw lot of current.

The PCF85xx chips I knew were 5V based.

But I guess you considered that.

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