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

[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.

[AScha.3]

Hi,

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

If > 100pin, then PDR on VDD ?

 

[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.

[BarryWhit]

> After replacing new MCU, we observe that, it takes around 1A peak current  

> we remove the MCU again and give power to board (without MCU) at this time it takes 70mA 

> we check the resistance on BGA pin of VCC and GND which is OPEN.

 

Every sign suggests that whomever is doing the soldering is doing a bad job.

 

[TDK]

Edit:

• FB1 should definitely not be there.
• VFBSMPS should not be tied to VDD.
• Ground planes should be tied directly, but it seems like R1 does that.
• I don't see why FB12 is present, although I don't think it is hurting anything (provided R1 is placed)

See reference figure in datasheet:

@ABora.4 I updated this reply. My original reply had some issues.

[AScha.3]

@TDK  , 

i think he using direct smps connection, VCAP connected to vfbsmps :

But i wouldnt do this - seems to dangerous to me. If anything wrong with smps hardware or setting - kill cpu.