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Looking at the ILI9341 datasheet Electrical Characteristics, I just can't find information about power consumption. The information is also missing from the LCD module datasheet (ER-TFT024-3).
I know that ILI9341 supports sleep modes where power is low, but I can't find data on power consumption under regular conditions.

My intention is to power the LCD (not the backlight!) from MCU pin under the assumption that continuous current will be in the 20mA neighborhood, or even less than that. (I'll drive the backlight by a MOSFET).

  • Is it common to drive low-power peripherals from MCU IO pin? Are there any pitfalls except from the current rating (and voltage) of the IO pin?
  • Does anyone have some experience with ILI9341 or similar module, and can confirm my assumptions about its low power consumption?

Update

When measuring VDDI + VCI with multimeter I observe a flat 8mA...

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  • \$\begingroup\$ The current consumption of the peripheral IC may have positive spikes, which may fry the pin. \$\endgroup\$
    – Mike Spark
    Commented Oct 30, 2018 at 22:36
  • \$\begingroup\$ I consider MCU I/O pins as signal outputs, not as power sources - I might use them directly to light an LED, but never to supply power to other devices. \$\endgroup\$
    – Peter Bennett
    Commented Oct 31, 2018 at 0:49

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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" 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 "partial" 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.

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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.

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