STM32H745 power up issue

[ABora.4]

Hello,

We are using the MCU STM32H745 in our current design.

We have faced the issue of working MCU properly and below are the problem,

Case 1 : At power ON, some time the MCU work properly and sometime does not work properly, when it is not work properly, after pressing the reset switch multiple time, it will start working properly but not every time. In the case of working properly, it takes current of around 300mA but sometime the current will reduce to 100mA, and the interfaces are going to stop.

Case 2 : After then, we remove the SDRAM and disable the other interfaces like I2C, SPI, ADC and keep only UART interface ON and check the log on dock light over UART. In this case, the situation is the same, at power ON, some time it works and some time it is not working and using the reset switch, some time it works. 

So now we have only MCU STM32H745 is mounted on board and we expect that it should be work properly at least at power ON.

Note: This board is working properly with full software and hardware for 30 Days and suddenly, it stops working and behave as mentioned above.

As of now, we are planning to check the voltage level, power on sequence with respect to reset signals.

Kindly provide the steps to debug the issue.

Regards,

Alpesh

[TDK]

Debug the chip during startup, see where it gets stuck during the boot process. Perhaps waiting for HSE or similar. Can you share a schematic? 300 mA is quite a lot, is that expected to take so much? Do you have any duplicate boards which are working or not working?

[ABora.4]

Hello,

We have assembled the 3 board out of them 1 board is working and 2 board has the issue. In working board, after programmed it take the 80mA current and it will take up to 300mA current as per the board interfaces up.(This current is the total current of the board)

Out of the 2 issue board,1st board has power up issue i.e sometime work and sometime not work (This board is also working up to 30D Days but after then this issue is generated, and it has the same current as mentioned above for the working board.)

Regards,

Alpesh

[AScha.3]

Hi,

just because i had similar "problem" : wich cpu /case you use ?

If > 100pin, then PDR on VDD ?

[TDK]

Ouch, 1 out of 3 isn't a good yield. Sounds like a hardware problem, possibly a design issue.

If you're using HSE, try changing it to HSI to see if the problem goes away.

[ABora.4]

Hello,

As of now, we are using 32.768KHz internal clock and 25MHz external crystal part#KC2016Z25.0000C1KX00.

Let me check by making 25MHz clock for internal setting and update you.

[ABora.4]

Hello, 

Our package is 265-TFBGA and on PDR_ON pin, we connect the 10K resistor to +3.3V. 

Is there any suggestion on this?

[AScha.3]

Hi,

so with pullup PDR_ON is ok.

Next...whats on BOOT0 pin ?

+

power : need 300mA - seem possible, at max speed -> 250...370 mA

But going to 100mA... maybe cpu now at 200M or lower... -> 80..100mA 

So set an MCO active, put out core clock pll  (/10) and check, when power dropped.

[ABora.4]

Hello,

Boot0 is kept GND through 10K.

Now we have done the task as mentioned below,

• Erase the programmed from the flash memory and check the current, it is 80mA.
• Check the 3.3V and RST signal rise time as per my understanding, it is OK. (Image attached).
• Programmed the STM32H745 in which we have use one GPIO and toggle is at every second and the LED is connected with this GPIO.
• At power ON,
  • sometime the LED will toggle. (it takes current around 120mA).
  • sometime the LED will not glow. After press the reset switch multiple time it will glow. (When not glow LED, it takes 110mA current).
• We have taken the reading with external 24MHz and internal 32.768KHz frequency.
• We have removed the SDRAM and other hardware from the Board and only keep the MCU and power supply components.
• This is the board which is working up to 1month and we have changed the SD card on this board during power ON condition and after than the issue is coming on this board.
• So, is this chip is partially damaged itself that's why it behaves like this?

Please provide the suggestion on it.

Regards,

Alpesh

 

[AScha.3]

Hi,

So everything seems ok, when CPU runs and LEDs blinking. 

But same CPU can be starting -- wrong.

Just this is a last test: there is the core supply with the 2 uF caps, Vcap. Try just soldering a 470 ohm SMD resistor on one cap, in parallel ( on top, is easy).

Then check starting behaviour again, with the simple test program.

Btw. I found, on some CPU the core voltage not going down fully, then the core gets no correct reset on external reset and behaves silly.

The additional resistor discharge the core voltage and helping the core correctly resets.

So you should check startup after short or longer time without power - might show different behaviour.

If this not giving good behaviour, replace the CPU.