NHD-2.4 IM0 voltage level

Magnus Thomé

I would guess IM0 is nothing but a logic input to set the ST7789 in 8 or 16 bit mode. So I was a bit surprised the schematics suggest to connect it to the backlight 3.1V. As a logic input it should be okay to do it that way but it looked a bit of an odd choice. So I just want to double check if this is mandatory due to something odd that I missed :-)

 

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7 comments

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  • Engineering Support
    Community moderator

    Hi,

    As you have noted the IM connections are for setting the interface type as per Section 8.3 of the ST7789VI specification for Mode II. There is no special reason for the IM0 signal using the Backlight Supply over the Logic supply, as these signals only require to either pulled high or tied low depending on the interface selection.

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  • Magnus Thomé
    • Edited

    Thanks! Just wanted to be sure 🙂

    Another question, I'm making prototype boards but haven't yet a sample of the display to check that this works correctly: as I see it a 20 Ohm resistor from 5V to drive the backlight should work fine to get the correct current and voltage?

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  • Engineering Support
    Community moderator

    Hi,

    Can you clarify if you are looking to use a 5V source for this display (NHD-2.4-240320CF-CSXN#-F)?

    If so, you will need to create a voltage divider with a second resistor to reduce your 5V source to 3.3V.

    Note: VOUT = VS*R2 / (R1+R2)

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  • Magnus Thomé

    Thanks for getting back to me. I have 3.3V supply for the display controller (and 3.3V logic signals) but also have 5V available for the backlight. I have another manufacturer display which I run the backlight directly to 3.3V but it runs a bit hot that way.

     

     

     

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  • Engineering Support
    Community moderator

    Hi,

    Thank you for the clarification, the backlight for this display typically will require 3.1V for operation, however, as you can see in the table below, the maximum voltage the backlight should accept is no more than 3.5V, so a 3.3V logic signal is not an issue to use.

    However, while the display may function off of a higher voltage, you can risk permanent damage to the LEDs if operating above the maximum voltage range.

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  • Magnus Thomé

    Thank you 🙂👍

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  • Engineering Support
    Community moderator

    Happy to help.

    Please let us know if you have any further questions.

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