OLIMEX© 2015
A20-SOM user's manual
CHAPTER 5: CONTROL CIRCUITY
5. Introduction to the chapter
Here you can find information about reset circuit and quartz crystals locations, the power supply
circuit is also briefly discussed.
5.1 Reset
The board has hardware reset controlled by the AXP209 power system management IC.
It is a good practice to perform software reset of the board. Performing reset by disconnecting the
power supply might lead to software corruption of the operating system of choice.
5.2 Clocks
32 768 Hz (RTC) quartz crystal Q1 is found at pins F1 and F2 of the A20 microcontroller.
24 MHz quartz crystal Q2 is found at pins N22 and N23 of the A20 microcontroller.
5.3 Power supply circuit
The power supply is handled mainly by AXP209 power management system, an Allwinner chip that
goes together with the A20 processor. It is mounted on the board but since it is relatively hard to
find we also sell it separately (if you have provided over voltage and want to repair the board
yourself).
A20-SOM typically consumes between 0.20A and 0.25A when connected to a 5V voltage source
(provided at pins GND and 5VEXT).
During heavy load of the processor the consumption might raise up to 0.35A (tested with 'top d0').
The current consumed might have peaks as high as 0.50A during start-up when different modules
are initialized.
Make sure your supply is capable of providing at least half an ampere of current at 5V of voltage.
For more info on how to power the board refer to chapter “2.3 Powering the board”.
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