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<section begin="History" />
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<section end="History" /><section begin="Body" />
== Power Supply Unit (PSU) and recommended power-up sequence ==
Implementing correct power-up sequence for ''TBD: SOC 'STM32MP1'' processors is not a trivial task because several power rails are involved.
ETRA SOM simplifies this task by embedding includes a PMIC that manage all the needed circuitry. power on and poweroff timings to ensure the correct sequence The following picture shows a simplified block diagram of PSU/voltage monitoring circuitry:
[[File:ETRA-power-sequence.png | 800px]]
The PSU:
''TBD: descrizione dei segnali che intervengono nella PS''
==== Note on BOARD_PGOOD SOM_PGOOD usage ==== ''TBD: verificare le note sul BOARD_PGOOD'' 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 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 ETRA SoM. [[File:ETRA-power-good.png]]
SOM_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, SOM_PGOOD might not be able to drive them properly. On ETRA SOM this signal is driven by the VDD rail so, if many loads has to be driven, connect them to the VDD output pins through a resistor.
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[[Category:ETRA]]