SAMA5D27_SOM1_EK RGB Led Circuit

Moderator: nferre

oyildirim
Posts: 1
Joined: Thu Nov 14, 2019 10:31 am

SAMA5D27_SOM1_EK RGB Led Circuit

Wed Nov 27, 2019 3:26 pm

Hello,

First of all, I searched forum about this weird situation (Maybe forgotten may it has a meaining).


I am designing my custom board and I want to use same circuit for RGB boot leds.
I have the document 03-10759-RD2.PDF which is in the SAMA5D27-SOM1-EK1_REVD2 Design and Manufacturing Files\REVD2\Project_Outputs\DevTools folder.

But here is the thing I want to be sure on page 8 (LED circuit):

1) There is a 10K resistor (R133) connected to ground between PA31 and 100R (R136) connection
2) There is a 10K resistor (R137) connected to ground between PB1 and 100R (R135) connection
3) There is NO resistor connected to ground between PA10 and 100R (R134) connection


(I wanted to upload circuit image here but I couldnt, sorry)


Why is there NO 10k resistor right before PA10?

Best regards,

Onur
blue_z
Location: USA
Posts: 2005
Joined: Thu Apr 19, 2007 10:15 pm

Re: SAMA5D27_SOM1_EK RGB Led Circuit

Sat Nov 30, 2019 2:32 am

I'm not a board designer, but those look like resisters to limit the current, i.e. current dividers versus a dropping resister.
Apply Kirchhoff's current law.

Study the datasheet of the RGB LEDs. The green and blue LEDs are probably more efficient (i.e. need less current) than the red.

Regards

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