Vbat pin drawn high currebt when power is off

[SJati.1]

I am using Nucleo 144 H745ZQi , connected vbat pin directly using coin cell, when power is off/unconnected, LD7 led ovcr indicator turned on and current consumption drawn from baterry was 50mA, also the LD5 led turned on. However when i reconnect the power, either using option jumper on stlink or ext 5V then the LD7 turn off and it seems normal again. I wonder why? Please help me, because it's will waste the battery when used power off.

[Peter BENSCH]

On this NUCLEO (MB1364), VBAT is connected to VDD-MCU via jumper SB52, so that you can also supply the MCU when the normal VDD is missing. So you have to unsolder SB52 first so that the 2032 only supplies VBAT.

Good luck!

If the problem is resolved, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster.

/Peter

[waclawek.jan]

Make sure that VBAT is not connected to VDD on the board, maybe through jumpers/solder bridges (review schematics and User Manual of the board).

JW

[Tesla DeLorean]

Placing the board on a metal surface is highly inadvisable. Similarly conductive foam..

[SJati.1]

Thanks for the replies , @Peter BENSCH​ @Community member​ @Community member​ 

I have just removed the SB83(from document MB1363: NUCLEO H745ZQ i) to unconnect VBAT and VDD_MCU then LD5 wont turn on when power is not present,then i got problem on LSE activation during the call function SystemConfig_Clock(), the LSE clock never in ready state :

   /* Wait till LSE is ready */

   while(__HAL_RCC_GET_FLAG(RCC_FLAG_LSERDY) == 0U)

   {

    if((HAL_GetTick() - tickstart ) > RCC_LSE_TIMEOUT_VALUE)

    {

     return HAL_TIMEOUT;

    }

   }

it never go out from this while loop, but sometimes it works in the middle of debugging then it wont work again. Do I break the connection near SB86 , but I think I cleanly remove the jumper SB86 or the soldering or, if VBAT unconnected to VCC_MCU , are there any SBx connection should I unsolder or solder? Thanks for the reply

[SJati.1]

Update:

when I disable RTC in STM32CubeMX then it run as usual

[Peter BENSCH]

On the MB1363, SB83 is the right one to disconnect the connection from VDD_MCU to VBAT.

Please double check that you just misspelled it here?

/Peter

[SJati.1]

Yes , the default is ON (connected), then I remove it so VBAT pin disconnect from VDD-MCU

[Peter BENSCH]

OK, you previously wrote that you removed SB86, not SB83. Incidentally, LD5 has nothing to do with SB83, since LD5 is supplied by 5V, which in turn comes via JP2, usually from 5V_USB_STLK.

However, the RTC is part of the VBAT domain. Without SB83, VBAT must of course have a sufficient voltage so that the VBAT domain can work.

[SJati.1]

Sorry for my misunderstanding, I have edited the earlier reply, I removed SB83 not SB86. The problem now is LSE initialization fail when I use LSE as clock source on RTC, then my Board won't run the program , it will run forever on while loop:

stm32h7xx_hal.rcc.c

...

 if((RCC_OscInitStruct->LSEState) != RCC_LSE_OFF)

  {

   /* Get Start Tick*/

   tickstart = HAL_GetTick();

   /* Wait till LSE is ready */

   while(__HAL_RCC_GET_FLAG(RCC_FLAG_LSERDY) == 0U)

   {

    if((HAL_GetTick() - tickstart ) > RCC_LSE_TIMEOUT_VALUE)

    {

     return HAL_TIMEOUT;

    }

   }

  }

when I use other clock for RTC, LSI for example the MCU running. The RTC also running but when it turned off, the RTC also did.