Power sequencing inconsistency

[JensJorgen]

quote from hardware development application note -

"VDD3V3_USBHS must not be present unless VDDA1V8_REG is present, otherwise permanent
STM32MP15x lines damage can occur. It must be ensured by PMIC ranking order or with
external component in case of discrete component power-supply implementation."

this seems to contradict that (another quote) - 

"VDD3V3_USBFS is used to supply OTG_VBUS and OTG_ID (PA10) pins. Therefore,
VDD3V3_USBFS must be supplied as well when USB high-speed dual-role-port or USB
high-speed device is used. If not used, it must be connected to VDD."

along with quote - 

"VDD_DSI, VDD_PLL and VDD_ANA must be connected to VDD"

so essentially VDD= VDD_DSI = VDD3V3_USBFS = VDD3V3_USBHS 

Then VDD3V3_USBHS  WILL be 3.3V before VDDA1V8_REG is 1.8V will it not?

what i am essentially asking about is whether or not i can avoid having to use a whole other buck converter just to be able to supply VDD3V3_USBHS later after VDDA1V8_REG has reached 1.8V

[ThomasB · Accepted solution]

Hello,

I see no contradiction here:

Your first quote from application note 5031 says you must power on VDDA1V8_REG before VDD3V3_USBHS. You can do it either with PMIC ranking order (which you can find information about in AN5260) or with external component in case of using discrete power supply (you can find information about in AN5256)

In addition, Table 5. of AN5031 state that VDD3V3_USBHS should not be connected to VDD but to a dedicated 3.3V supply. So VDD ≠ VDD3V3_USBHS, you cannot connect directly VDD3V3_USBHS to VDD

Application note 5256 provide you different power supply options for VDD3V3_USBHS on part 3.1.2 section VDD_USB power domains, such as a dedicated LDO, integated power / load switch or a discrete power switch.

Please let me know if the subject is clearer now.

Regards,

Thomas

[JensJorgen]

Thank you for the quick reply. I still dont really get the statement that "If not used, it must be connected to VDD"

But i seem to have missed that table. Thanks a lot :))