Olimex Support Forum

OLinuXino Android / Linux boards and System On Modules => AM3352 => Topic started by: BrianBrianBrian on July 28, 2015, 12:32:58 pm

Title: AM3352-SOM 3.3V output
Post by: BrianBrianBrian on July 28, 2015, 12:32:58 pm
How much current is available for our custom board to draw from the SOM's 3.3V output?

According to the datasheet for the SY8009AAC, this regulator can output up to 1.5A.  On the SOM schematic there is the following text next to the 3.3V regulator:

VDDSHV1-6__PWR(max): 3.3V/4%/350mA
VDDA3P3V_USB0 and 1_PWR(max): 3.3V/4%/ 80mA
PERIPHERAL_PWR(max) approx: 3.3V/4%/500mA

How am I suppose to interpret this?  Is the PERIPHERAL_PWR what is allocated for the custom board?
Title: Re: AM3352-SOM 3.3V output
Post by: dave-at-axon on July 28, 2015, 02:35:43 pm
It will depend on the final parts chosen around the SY8009AAC that dictates the final max current. Olimex may have chosen an inductor for instance that only allows a max 500mA.

One of the issues I have with this device is that it is a BUCK regulator only so the input has to be higher than the output for it to give out 3.3V. It works great when you have a 5V input from an external supply, be it from the USB or DC supply. The issue is when on battery power and the battery voltage gets down close to 3.3V and your current draw on the 3.3V rail includes the board, an LCD and it's backlight. If often drops low enough to reset the processor.

Ideally this regulator should be a BUCK/BOOST type that even if the battery level drops to 3.3V or lower, it will still output 3.3V
Title: Re: AM3352-SOM 3.3V output
Post by: BrianBrianBrian on July 29, 2015, 08:51:01 am
In terms of the inductor on the SY8009 output, we are in luck.  According to the schematic:

2.2uH/1.5A/DCR<0.1R/CD32

As for the BUCK/BOOST vs BUCK issue:  Since the 3.3V BUCK is fed from the user's +5V, you can put a +5V BUCK/BOOST on your battery and be OK?
Title: Re: AM3352-SOM 3.3V output
Post by: dave-at-axon on July 29, 2015, 12:31:05 pm
You could but then you need to change the charging system to account for this. :)