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AURA SOM/AURA Hardware/Power and Reset/Power Supply Unit (PSU) and recommended power-up sequence

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== Power Supply Unit (PSU) and recommended power-up sequence ==
Implementing correct power-up sequence for ''TBD: i.MX93 SOC ''' processors is not a trivial task because several power rails are involved.
AURA SOM simplifies this task by embedding all the needed circuitry. The following picture shows a simplified block diagram of PSU/voltage monitoring circuitry:
The PSU:
* generates the proper power-up sequence required by the SOC processor and surrounding memories and peripherals
* synchronizes the powering up of carrier board in order to prevent back power
* provides some spare regulated voltages that can be used to power carrier board devices
=== Power-up sequence===
The typical power-up sequence is the following:
''TBD: descrizione dei segnali che intervengono nella PS''* 3.3VIN main power supply rail is powered* SNVS domain signals are pulled up (unless carrier board circuitry keeps this signal low for any reason)* CPU_PORn (active-low) is driven low by PMIC* RTC_RESET_B are internally released after 10ms* PMIC initiates power-up sequence needed by iMX93x processor* SOM_PGOOD goes up when all CPU I/O power rail is ready* CPU_PORn is de-asserted after the last regulator to bring the processor out of reset
==== Note on BOARD_PGOOD SOM_PGOOD usage ====
''TBD: verificare le note sul BOARD_PGOOD''SOM_PGOOD is generally used on carrier board to drive loads such as DC/DC enable inputs or switch on/off control signals.
BOARD_PGOOD is generally used on carrier board to drive loads such as DC/DC enable inputs or switch on/off control signals.  Depending on the kind of such loads, BOARD_PGOOD SOM_PGOOD might not be able to drive them properly. In these cases a simple 2-input AND port can be used to address this issue. The following picture depicts a principle schematic showing this solution.
VDD_SOM denotes the power rail used to power AURA SoM.
[[File:AURA-power-good.png]]
 
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