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MAX3243: source/sink current capability on RTS/CTS lines

Art Mecina
Genius 16655 points
Part Number: MAX3243

Hello Guys,

Good day. Or customer have the following inquiries:

"I have an industrial computer that is using the MAX3243 ICs for some of the serial RS-232 ports.

I have a couple 232LPTTL33 level shifters that I am connecting to the computer's serial ports.

The serial port that is using the MAX3243 IC crashes the computer when connected to the 232LPTTL33 level shifter.

The com port that uses the mother board does not cause a crash.

The 232LPTTL33 level shifter needs <40MA from the handshaking lines to power the device.

Should the MAX3243 be able to supply this?"

Thanks and regards,

Art

  • 0
    TI__Mastermind 48108 points

    Art, 

    When you say "The COM port that uses the mother board does not cause a crash." Is that with the 232LPTTL33 level shifts and the MAX3243 IC? 

    Do you know the pins that are being used on the MAX3243 IC for this application? 

    What voltage level is the MAX3243 being powered at?

    -Tyler

  • 0 in reply to Tyler Townsend
    TI__Genius 16655 points

    Hello Tyler,

    Unfortunately, this is the only information the customer has on the motherboard.

    Thanks and regards,

    Art

  • 0
    TI__Mastermind 48108 points

    Art,

    Looking at the recommended operating conditions for High & Low level input current, the max value is +-1uA. There shouldn't be current in the mA unless there is a short. Please make sure that the RS232 connections are made properly according to the handshaking diagram:

    In the event that an electrical short has occurred with the MAX3243 driver, we can expect the short circuit current to typically fall around +-35mA, with a max of +-60mA (according to the datasheet) which would make sense why the motherboard might crash since Ios = +-60mA > 40mA handshaking requirement. 

    Regards,

    -Tyler

  • 0 in reply to Tyler Townsend
    TI__Genius 16655 points

    Thanks Tyler this is very helpful.

    Upon checking, the customer found out that the computer crash was caused by the Tx and RX pins being swapped. Not sure why that would cause excess current draw to make the computer crash. Any thoughts on why this would draw more current?

    Thanks and regards,

    Art

  • 0 in reply to Art Mecina
    TI__Guru 53575 points

    Hi Art,

    Swapping these pins can certainly cause excess current draw. When two TX signals are connected together, it is possible for each driver to drive the opposate polarity signal. This essentially looks like a short circuit to the system and may cause safe systems to intervene before damage can occur.

    Regards,
    Eric Schott