Is the backup domain operates directly out of Vdd or Vbat ?

[bivin mato]

Microcontroller used : STM32F779NI

Question:

[1] My understanding is that the backup domain is directly supplied from Vdd or Vbat (When Vdd is removed) without any regulation (1.8V to 3.6V).

Does this means below blocks can operate directly using Vdd or Vbat ?

[1] RTC

[2] RTC backup registers

[3] LSE oscillator

[2] Regarding backup SRAM, when Vdd is the supply, backup SRAM is directly powered from Vdd without any further regulation. Am i right ?

[2] Regarding backup SRAM, when Vbat is the supply, backup SRAM is powered through the low-power regulator which steps downs Vbat to 1.2 V. LP regulator is just required only during Vbat supply. Am i right ?

Regards,

Vinoth

[Mohamed Aymen HZAMI]

Hello,

Regarding the first and third questions are correct your thought is right, but the second question which is :

[2] Regarding backup SRAM, when Vdd is the supply, backup SRAM is directly powered from Vdd without any further regulation => incorrect

When the Vdd is the supply the backup SRAM powred by the voltage regulator.

You can refer to the reference manual RM0410 section 4.1.6 and figure 8.

Best Regards,

Mohamed Aymen.

[bivin mato]

Hi Mohamed,

Thanks for your response.

You had mentioned that my understanding for point 1 is right. But in the above diagram it shows that RTC & LSE is also powered through 1.2 V domain.

Does it mean all the backup domain blocks operate in 1.2 V domain ?

Different question:

My understanding is that there are two 1.2 V internal regulator.

[1] The regulator that gets enabled by holding BYPASS_REG pin as low

[2] The backup regulator that gets enabled through PWR_CSR1.BRE

Am i right ?

Regards,

Vinoth

[Mohamed Aymen HZAMI]

Hello,

In section 4.1.6 :

"An embedded linear voltage regulator supplies all the digital circuitries except for the backup domain and the Standby circuitry". This means that only backup SRAM is powered by the 1.2V domain.

Best Regards,

Mohamed Aymen.

[bivin mato]

Thanks for the response, Mohamed !.