Posted on February 28, 2017 at 12:09Are VCAP_1 and
VCAP_2 used in Vbat-mode?
I have an issue with the content of the Backup SRAM is lost when i power down the device, even though the Vbat is active.
If i do a reset the content of backup SRAM and RTC-registers remain. But if i remove Vdd for a few ms the content of the backup SRAM becomes garbage but the
RTC
-registers are not affected.
I have checked with an oscilloscope that the voltage at Vbat never drops below 3.1 Volts.
I have enabled the backup regulator with a call to 'HAL_PWREx_EnableBkUpReg()'. I have also checked that the BRE and BRR flags gets set in the PWR->CSR register.
My theory that i hope someone can confirm or discard:
Backup SRAM does not work in 'BYPASS_REG'-mode.
I use my own 1.2Volt regulators connected to VCAP_1 and
VCAP_2
and have pin 'BYPASS_REG' hardwired to 3.3 Volts in normal mode.
When i power down Vdd,
VCAP_1,
VCAP_2
and BYPASS_REG are pulled low.
After a power cycle the 'Backup regulator enable' in register 'PWR power control/status register' is still set, but the 'Backup regulator ready' takes some time before it becomes set. I believe this indicates that there is some issue with the power...
I use a STM32F429
#stm32f429 #sram-backup-rtc #bypass_reg
