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→Power Supply Unit (PSU) and recommended power-up sequence
The PSU is composed of two main blocks:
* power management integrated circuit (PMIC, NXP PF0100E0 - on request this part is available in automotive gradePF3000)
* additional generic power management circuitry that completes PMIC functionalities.
The PSU:
* generates the proper power-up sequence required by i.MX MX6UL 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:
# (optional) PMIC_LICELL is powered
# 3.3VIN VIN_SOM main power supply rail is powered
# CPU_PORn (active-low) is driven low
# PMIC activates PMIC_VSNVS power output
# PMIC transitions from OFF to ON state
# PMIC initiates power-up sequence needed by MX6 processor
# BOARD_PGOOD SOM_PGOOD signal is raised; this active-high signal indicates that SoM's I/O is powered. This signal can be used to manage carrier board power up sequence in order to prevent back powering (from SoM to carrier board or vice versa). For additional information, please refer to the [[Power_(AxelLite)#Note_on_BOARD_PGOOD_usage | Note]] below.
# CPU_PORn is released.
==== Note on BOARD_PGOOD SOM_PGOOD usage ==== BOARD_PGOOD SOM_PGOOD is generally used on carrier board to drive loads such as DC/DC enable inputs or switch onimplement proper power up sequencing. Generally speaking, all the circuitry that interfaces SOM's I/off control O signals. Depending should be powered on the kind of such loads, BOARD_PGOOD might not be able when SOM_PGOOD turns 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 AXEL LITE SoMlogic '1'.
[[File:Axel-lite-power-good.png]]
