Powering ILI9341 LCD from MCU IO pin
I was wondering this exact thing so I made some measurements.




Power mode
Refresh rate
Clock divider
Vcc current
Note




Normal
79 Hz
1
8-10 mA
Depends on image content


Normal
79 Hz
2
6 mA
Really ugly flicker.


Idle
119 Hz
1
5.13 mA



Idle
79 Hz
1
4.50 mA



Idle
61 Hz
1
4.16 mA



Idle
61 Hz
8
2.53 mA
Some flicker was (barely) noticeable, but only in large black areas.


Sleep
screen off
clock stopped
28 uA





Test conditions:
I only had the smallest 2.4&quot; panel at hand, one of the red pcb modules with SPI you can get everywhere. I've tested it with 3.3V Vcc supply and with SPI slowly writing bitmap font characters onto the screen, roughly at 1 full frame updated per second.
Keeping the MCU in reset (no screen content update) seemed to haveno effect on the screen's consumption.
As seen in the table, if you need to save power, the the current can be greatly reduced by changing TFT update rate, color depth and internal clocks. In Idle mode (command 39h), the grayscale DAC is powered off, leaving you just with on/off state for each subpixel. It saves approx. half the power.
Note that the framerate and clock control are setup separately for the normal mode (B1h) and idle (B2h).
I haven't experimented with the &quot;partial&quot; power mode, yet. It updates just a small portion of the screen, possibly further reducing power.
Regarding backlight current, 5mA already offered about the same contrast as a backlit FSTN (older technology) screen nearby. The monochrome text was still comfortable to read even with a 1000lm lamp on top of my desk. Much more comfortable at 11mA, though.
--
Note that these measurements highly depend on the panel and many other circumstances. I hope it provides some general idea and satisfies curiousity, should anyone ask the same question.