STM32U585 BACKU RAM VBAT RETENTION ISSUE

[VAIKUNDAMGURUSAMY]

We are using the part STM32U585 controller in our board and we have designed it with battery backup support of 3.0v

We are evaluating the backup ram (address 0x50036400)performance and found that it is not able to retain the information on power down

Initialization routine

1)MX_RAMCFG_Init();

2)__HAL_RCC_PWR_CLK_ENABLE();

3)HAL_PWR_EnableBkUpAccess();

4)RCC->AHB1ENR |= RCC_AHB1ENR_BKPSRAMEN; // Enable backup RAM retention

5)PWR->BDCR1 |= PWR_BDCR1_BREN; // Enable backup RAM retention

6) PWR->BDCR1 |= 1; // Enable backup RAM retention

test procedure

1) write the test  value at address 0x50036400

2)power down the board

3)power up the board

4)read the content at address 0x50036400

5)check for the test value

but, it returns garbage value though we attempted this trials few times

Kindly support us in solving this issue

[ELABI.1]

Hi @VAIKUNDAMGURUSAMY,

What is the VBAT voltage while your board is in power down mode? You need to maintain a voltage on VBAT higher than 1.65V when it no longer supplies VDD.

You can also refer to the Application Note AN5373, specifically the section "2 Power Supply Management" which can help you.

Thank you.

ELABI.1

[VAIKUNDAMGURUSAMY]

Hi ELAB1

Thanks for your reply

It is 3.2V battery 

Thanks 

G.Vaikundam