STPMIC1 with LPDDR2 and 3.3VDD

[PGE]

I am designing a board using STM32MP1, STPMIC1A and LPDDR2. I want to use 3.3V VDD not 1.8V as most of peripherals are 3.3V. I am following example in AN5031 Figure 32 LPDDR2 VDD1 is powered from LDO3 in bypass mode which is powered by VDD 1.8V.

I plan to change BUCK3 settings to output VDD 3.3V, use BUCK 4 to output 1.8V to power LDO3 in bypass mode which power LPDDR2 VDD1. I can't use BUCK directly to power LPDDR2 VDD1 as BUCK4 is rank 2 and turn on automatically with default 3.3V.

Is that the correct/recommended way to do it ?

Thanks in advance

[Olivier GALLIEN · Accepted solution]

Hi @PGE​ 

Actually you can generate the 1.8V from LDO3 using normal mode and any input between 2.8V to 5.5V. ( eg 3.3 from BUCK3)

You suggestion using BUCK4 as pre-regulation to 1.8V + LDO bypass is also possible and you will gain a bit on efficiency/power consumption. ( if this is important for you)

With STPMIC1A BUCK3 is already at 3.3V by default so you don't have to change anything.

Hope it help,

Olivier

[PGE]

Thanks for the reply. Yes power consumption/efficiency is important for me (hence the LPDDR2 choice). Will use BUCK3 in 1.8V mode.

Thanks again

[Olivier GALLIEN]

Hi @PGE​ 

BUCK3 ? Guess you mean BUCK4 in 1.8V right ? 😊

Olivier

[PGE]

Yes right BUCK4 sorry