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

History
Issue Date	Notes
2025/08/06	First documentation release

Power Supply Unit (PSU) and recommended power-up sequence

Implementing correct power-up sequence for AM62x SoC processors is not a trivial task because several power rails are involved.

DADA 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 is composed of two main blocks:

• power management integrated circuit (PMIC)
• additional generic power management circuitry that completes PMIC functionalities

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's circuitry to prevent back powering

See the pinout section for more details on the signals.

Power-up sequence

The typical power-up sequence is the following:

1. VIN_SOM (+3.3V) main power supply rail is powered.
2. POR_OUT (active-low) is driven low; PMIC initiates power-up sequence needed by AM62x processor.
3. SOM_PGOOD goes up when all SoC, memories, and I/O power rails are ready.
4. Finally, the processor is brought out of reset and the POR_OUT signal is released.

For a detailed description of the reset circuit and its signals see the page Reset_scheme_and_control_signals.

Control signals and their purpose

SOM_PGOOD

SOM_PGOOD is generally used on carrier board to drive loads such as DC/DC enable inputs or switch on/off control signals in order to prevent back power.

Depending on the kind of such loads, SOM_PGOOD might not be able to drive them properly. On DADA SoM this signal is driven by a push-pull output at VIN_SOM (3.3 V) rail, with max 10 mA output current (recommended 1 mA).

On Unica Industrial Dave standard pinout it is a always-present type signal i.e. the pin only covers this functionality on any other Industrial SoM.

ONOFF

Long ONOFF signal retention causes the SoM to turn OFF or ON, with a complete power off/on sequence. This is not intended as a low-power mode, since completely turning off the SoM causes the loss of volatile content such as data in RAM.

When the SoM is first powered it turns on without acting on ONOFF signal.

On SoM the signal is pulled-up with 10 kOhm to VIN_SOM (3.3 V).

On Unica Industrial Dave standard pinout it is a variable type signal i.e. the pin can assume different functions on other Industrial SoMs.

COLD_RESET

COLD_RESET is an input signal that cause a SoC cold reset. On SoM the signal is pulled-up with 10 kOhm to VDD_3V3 (3.3 V).

A cold reset of the SoC does not result in a complete power sequence of the SoM.

On Unica Industrial Dave standard pinout it is a always-present type signal i.e. the pin only covers this functionality on any other Industrial SoM.

POR_OUT

POR_OUT is an open-drain output (a pull-up on a carrier is required) to be used to reset peripherals on carriers. The signal is released by the SoC when it exits reset (either cold or warm reset).

On Unica Industrial Dave standard pinout it is a variable type signal i.e. the pin can assume different functions on other Industrial SoMs.

Note on reset signals usage and carrier board PSU

In Unica Industrial Dave standard, only SOM_PGOOD and COLD_RESET signals were foreseen as always-present. With only the SOM_PGOOD output signal you need to:

• ensure the carrier PSU activates before the SoM exits reset (for DADA SoM POR_OUT is released about 17 ms after SOM_PGOOD)
• generate a peripheral reset signal on the carrier

It is possible if variable signals are also available:

• with POR_OUT output: reset the peripherals on carrier synchronously with the SoM
• with WARM_RESET input: keep SoM in reset until the carrier PSU is active