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MAX3221E: MAX3221E function not working

DAE SUN Kang
Prodigy 40 points
Part Number: MAX3221E

Hi TI Team,

I'm having a few issues using the TI MAX3221E.

I checked the charge pump and all pins are the same as the datasheet.

V+ : 5.6V and V- : -6.1V

However, RIN (pin 8) drops from -5V to -13V at power-on, receives a data swing below 0V and does not output to Rout (pin 9).

Do you have any idea? 

By the way, we implemented the exact same circuit on another board and that board works fine.

Thanks

  • 0
    TI__Guru 52182 points

    Hi,

    Is it possible for you  to share a schematic snippet of the RS-232 device? I want to make sure all the connections to the device make sense - as if the charge pumps are at 5.5V - 6V in magnitude nothing should be able to give -13V with respect to ground - the device shouldn't be generating that large of a signal.

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 40 points

    Hi, 

    RX_EN# (Pin 1): :Low

    DBG_TXEN (Pin 12/16) : High.

    Thx

  • 0 in reply to DAE SUN Kang
    TI__Guru 52182 points

    Hi,

    There is nothing that sticks out in the schematic that looks wrong - I do have a couple questions:

    1. Are the lines on DOUT and RIN pull-up / pull-down resistors? - generally speaking you shouldn't have components on these bus lines as the receiver should pull down the bus as its relatively lower input impedance. 

    2. I think VCC  = 3.3V - could you confirm that is the case? 

    With that being said I do think testing the IC with signal generator as the input and testing the output would be a good way to check if the IC is causing a problem - because right now this seems like a system issue and not necessarily the IC - but we can start looking at the IC directly to look for problems - as this device can't output -13V (it can take an input of -13V - but it can't create it)  - so I don't think its the IC directly. 

    Can you run a test where you input from a signal generator into the Rin pin (a swing of +/-5V would be good) and disconnect any load or cabling tot eh device and test.

    The RIN pin is a high impedance input - so it shouldn't be outputting anything. If you run the described test above and the RIN pin still tries to drop then something with the IC could be wrong - but there is nothing that would suggest that this part is even going to generate those voltages. 

    Of if I am confusing the issue - is the issue that you are starting with a -5V signal input and then putting in -13V into the pin?

    So please:

    1. If you can run a IC test using a signal generator to send data to the RIN pin to test to see if the part itself is working okay

    2. Or if you are already sending -5V and then it transitions to -13V with no output change please let me know if that is the case. 

    Best,

    Parker Dodson

  • +1 in reply to Parker Dodson
    Prodigy 40 points

    Hi,

    Thank you for your help.

    I resolved this issue.

    Thanks.

  • 0 in reply to DAE SUN Kang
    TI__Guru 52182 points

    Thank you for letting me know that the issue was resolved!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 40 points

    Something connection problem.