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    Application Board RS232 doesn't work with external Power but works with USB power

    Application Board RS232 doesn't work with external Power but works with USB power



    I had an issue with comunicating with the rs232 solved on this thread :

    But i have another issue now,

    I'm trying to use the board without the USB (by using the RS232 and external power).

    The external power is 3V3 while the USB provide 5V. I can use the RS232 with the USB, but not with the external power. My guess is that it has something to do with the "EX_POWER_CTL" pin on J601 (it seems to be some sort of power control). But there is nothing in the datasheet about that pin.

    Thank you in advance

    Datasheet :

    4 REPLIES 4

    Community Moderator
    Community Moderator

    Could you please check which configuration fits your requirements in chapter 2.3.1 (page 6) of the Application note you linked, and let us know if that solves your power source selection?

    I'm already using the external power configuration, it works to power the device but not for the communication with the Development Desktop 2.0 software.

    While powering it works with the usb plugged in (with the COM connection).

    The usb is providing 5V in the LDO to power the card in 3V3, while the external power is already 3V3. There is probably something about that.


    For external power, you can solder a lithium-ion battery either J105 or J106. The board even has built-in battery charger when the USB is plugged in. If you must use 3.3V directly, then change the J107 jumper to the "EX_POWER_3.3.V_IN" position, and connect your power source to J601 pin 16.

    Connect EX_POWER_CTL to ground to enable the high-side switch.


    Alternatively, you can remove the J107 jumper and connect your power directtly to +3.3V (pin 31-32 of J601)

    Thank you very much again,

    Using the EX_POWER3.3 with the EX_POWER_CTL at the ground worked i'm now able to read the data without the usb