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Circuit for CFAL25664C0-021M-W

justine.haupt

New member
I just ordered a couple samples of OLED display CFAL25664C0-021M-W, with the intention of using this display in this product: https://skysedge.com/unsmartphones/RUSP/index.html

I'm working on the schematic for driving the display now, but I'm a bit confused about the V_LOGIC (V_DD) pin. Both the datasheet for the display and for the SSD1362 driver seem to suggest that this pin can either be left unconnected or driven externally, although there are some contradictions with the absolute maximum ratings (i.e. the max voltage appears to be 2.6V, but in other places the logic voltage is listed as 3V).

Questions:

-Can/should I drive V_LOGIC externally from a 3V source? If so would 3.3V really really be stressing it?
-Any recommendations about the filter cap to use on the 3V source?
-Should VCI simply be tied to V_LOGIC? This is implied but never stated outright.

It would be awfully helpful to have an example schematic aside from the partial one on page 7 of the datasheet. I believe I've pieced the necessary connections together after reading every pin description in the datasheet, but it would be reassuring to see this in schematic form.

~Justine
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CF Kelsey

Administrator
Staff member
Hi Justine,

Thanks for reaching out. That looks like a very cool product!

-Can/should I drive V_LOGIC externally from a 3V source? If so would 3.3V really really be stressing it?.

V_LOGIC should just have a 1uF capacitor tying it to ground. It's max voltage is 2.75, so you don't want to connect 3.3v. It's driven internally as long as VCI is above 2.6v.

-Any recommendations about the filter cap to use on the 3V source?
The best capacitor for reducing any ringing is a tantalum capacitor but they are generally not REACH compliant so we use ceramic capacitors.
Sometimes the capacitor will expand and contract and the PCB will act like a speaker causing an audible sound. A through-hole capacitor instead of SMT will fix this

The values for the capacitors can be found on page 7 of the datasheet.

-Should VCI simply be tied to V_LOGIC? This is implied but never stated outright.

VCI should not be tied to V_LOGIC unless you're using a VCI below 2.6V.
 

justine.haupt

New member
Because one can't ever be too sure, would you mind taking a quick look at this schematic to see if anything's obviously amiss? Note that BS0-BS2 are tied to GND to select SPI.

cfoledschem.png


~Justine
 

CF Kelsey

Administrator
Staff member
Hi Justine,

I just looked quickly - my only note is that it doesn't look like you have Vss tied to an external ground
 
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