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MAX3221: Pin output is zero

zhao leo
Prodigy 70 points
Part Number: MAX3221

Hi everyone

I tested according to the recommended circuit diagram in the specification, the chip 12 and 16 pins are connected to 3.3V, when the chip 8 and 13 pins are connected to the 232 serial port of the computer, the output voltage is normal and the output command is normal. When I disconnect the computer 232 serial port, the chip Dout output voltage is 0.

What is the problem?

Thanks!

  • 0
    Guru 294520 points

    This is not a problem. Disconnecting RIN activates the auto-power-down feature.

  • 0
    TI__Mastermind 48237 points

    Hi Zhao,

    If the circuit is connected to allow for auto power-down - disconnecting the RIN pin will active the auto-power down feature of the device.

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 70 points

    FORCEON and FORCEOFF (pin8 and pin 13)are high, Automatic power-down is disabled 

    Automatic power-down can be disabled when FORCEON and FORCEOFF are high. With automatic powerdown plus enabled, the device activates automatically when a valid signal is applied to any receiver input. The device can automatically power down the driver to save power when the RIN input is unpowered

  • 0 in reply to zhao leo
    TI__Mastermind 48237 points

    Hi Zhao,

    Sorry I misread the original post - I apologize.

    Do you have a schematic - it will be much quicker for me to see if the design is correct if you can have a schematic snippet of this device - I don't need the entire system - but this part would be helpful. I understand if you can't - but RS-232 stuff is pretty standardized across the board so it would be helpful for you to shared - but DOUT shouldn't drop to zero unless its being disabled - and since you can still communicate it seems to some degree when everything is connected I don't think damage is high probability - but I want to double check the enable scheme.

    Has this problem been seen on multiple devices or just 1?

    Also are there any other problems - or is the problem that the output turns off when you disconnect it? If that is the only unexpected behavior in the system - why is a problem? The cable is connected - why do you need a signal out of an disconnected cable/ 

    Best,

    Parker Dodson