Author Topic: Why do some displays operate at 3V and not 3.3V  (Read 1032 times)

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Offline alank2

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Why do some displays operate at 3V and not 3.3V
« on: March 19, 2017, 01:53:52 pm »
When looking through displays on eBay or at buydisplay.com, or here:

http://www.newhavendisplay.com/specs/NHD-C12832A1Z-FSRGB-FBW-3V.pdf

I noticed that there are a lot of displays that operate at 3V or other odd voltages.  Why would they design it to operate at 3V with a max of 3.3V?  Isn't 3.3V more or less a standard that a lot of pcb's operate with?  Why not 3.3V with a max of 3.6V ?

I've seen others that are 2.8V, etc., as well.  Is there any logic to this?
 

Offline joseph nicholas

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Re: Why do some displays operate at 3V and not 3.3V
« Reply #1 on: March 19, 2017, 02:47:54 pm »
I don't think designers design like that.  They design from the inside out and are not overly concerned about stuff like interfacing the display with an arduino and ebay fixed voltage boost or buck converter.
 

Offline dmills

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Re: Why do some displays operate at 3V and not 3.3V
« Reply #2 on: March 19, 2017, 03:16:43 pm »
Logic voltages have been getting lower for at least 40 years now.

A 1.8 - 3.3V (Abs Max) display is perfect for example for interfacing with a 2.5V or 1.8V io bank (Which is then a good fit for a DDR2 memory or something connected elsewhere on the same rail).

3.3V logic is common but anyone designing with a modern ASIC or FPGA would really prefer lower voltages, and IO in the 1.8-2.5V region seems commonplace at the moment in the sorts of applications that buy displays in volume.

I recently did a design where the ONLY use of the 5V rail was USB, time was 5V logic was everywhere.
All the logic action in that design was 2.5/1.8/1V, I did not even bother with 3.3V except to deal with the USB port and some external IO.

You design the PCB to match the device you want to drive, nobody designs a display to support an existing PCB (Every one of the stupid things has a different FPC pinout anyway!).
 

Offline Ian.M

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Re: Why do some displays operate at 3V and not 3.3V
« Reply #3 on: March 19, 2017, 03:23:56 pm »
Additionally, the ability to run down to 3.0V or slightly below vastly eases single cell LiPO powered applications as a simple buck converter can be used.   Anyway the ST7565R controller of the display you linked to is rated for operation up to 3.3V, so as long as your supply voltage tolerance is tight enough it can be run very close to 3.3V in a nominally 3.3V (but fractionally under) system.
 

Online BrianHG

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Re: Why do some displays operate at 3V and not 3.3V
« Reply #4 on: March 19, 2017, 04:54:41 pm »
If you are worried, just send you 3.3v VCC power through a Schottky diode.  It will then be powered by around 0.3v less.  The digital IO being fed only 0.3v more should be safe.
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