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[Question] Ch341a and 5v to 3.3v with logic converter

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    [Question] Ch341a and 5v to 3.3v with logic converter

    zz0.8tpitu4y0i8zzI bought a ch341a (I'm waiting for it to arrive) and I noticed that the programmer has a bug that the data pins go to 5v when the VCC pin is at 3.3v (which is the voltage I'm looking for).

    Instead of doing the 3.3v mod, I'm thinking of converting the 5v to 3.3v with an 8 channel TXS0108E through the ZIF socket but I don't know if that would work, because it has to circulate voltage and also information.

    What I am looking for is something that will convert from 5v to 3.3v but without modifying the ch341a.

    I can't buy the ch341a 1.6v that has the switches (through aliexpress website), because where I live I can't make purchases that come from china.

    Logic Level Converter

    I understand that the CH341A is not recommended (as LibreBoot webpage says) for the voltage 5v data output bug, it is for that reason that I want to know if a logic converter would work, since in itself, there are no converters 5v to 3.3v when there are 5v to 1.8v con (the latter that comes with the purchase of ch341a):

    LibreBoot Quote:
    Alternatively, you might work around the voltage issue by using an adapter with logic-level converter, making sure to have matching vcc going into the flash. Use of a logic level converter would be quite flexible, in this scenario, and you could use it to set many voltages such as 1.8v or 3.3v.

    Not covered on that eevblog page: the WP/HOLD pins (pins 3 and 7) must be held high via pull-up resistors, but on CH341A dongles, they are directly connected to 3.3V DC (continuity with pin 8). It is advisable to cut these two connections, to the WP and HOLD pins, and jump the cuts using pull-up resistors instead. A value between 1k to 10k (ohms) should be fine.

    In the event of a surge, like for example you connect the clip wrongly and cause a short circuit between two pins, lack of pull-up resistors on WP/HOLD could cause a direct short between VCC/ground, which would cause a lot of heat build up and possibly fire (and definitely damaged circuitry). On SOIC8, pin 3 is WP and 4 is GND, so a direct 3.3v connection there is quite hazardous for that reason; all the more reason to use a pull-up resistor.

    Supply Voltage

    Historically, all boards that Libreboot supports happened to have SPI NOR chips which work at 3.3V DC. With the recent addition of Chromebooks whose chips are rated for 1.8V DC, this can no longer be assumed.

    Inspect the chip on your board for a part number, look up the datasheet for it. Find out and make note of the power supply voltage it needs. If it doesn't match the voltage output by your external flashing hardware, you should only connect it to the chip through an adapter or logic level converter, never directly.
    Here's my idea, that i dont know if it will work:

    Click image for larger version  Name:	ch34a.png Views:	0 Size:	88.9 KB ID:	3277654

    I want to use this programmer for SPI and I2C chips that uses 3.3v input.

    But i dont know how to do the WP/HOLD pins to the programmer because in Libreboot webpage the image is not clear to do the mod...

    Any help will be appreciated!

    like this?
    Attached Files


      Seems that are many ways to do the mod, i want to do a mod like this (with a 5v-3.3v switch with solder and lift up 28pin) to switch between 5v and 3.3:
      Click image for larger version

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      It will work? Or I would like to know if the logic converter also works as an alternative to avoid modify the programmer.

      Libreboot images seems confusing to do the WP/HOLD mod. The pictures is low quality and I can't see which pins/tracks to solder/cut. According to what I saw in the pictures, i understood the following and I modified the pictures (although I would require validation if what I indicated in the modified pictures is correct)

      Click image for larger version

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      Modified image to try to understand which pins/tracks to solder/cut:

      Click image for larger version

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      I hope anyone can help me, I understand that the questions I am asking are too basic....
      Attached Files


        What I am looking for is something that will convert from 5v to 3.3v but without modifying the ch341a.
        Maybe this circuit for every wire?

        For 3.3v mod Sorin has the video about no point...? Current is so small that voltage easy drop, I guess.
        Attached Files
        Last edited by harp; 05-26-2024, 01:29 AM.


          WP/HOLD mod
          Attached Files


            the mod i posted doesnt need a switch, the 5v / 3v3 jumper selects the voltage


              I think the logic converter is the best solution so far.


                i dont - lift 1 pin and add 1 wire and it's fully 3.3v compatable.
                to make it 5v just put a jumper between the 5v and 3.3v pins to bypass the regulator.