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SN65C3223E: Outputs Not Enabled

David Cummings30
Prodigy 30 points
Part Number: SN65C3223E

I’m working with the SN65C3223E in an application where we need to connect to a device via RS232. In this application, we do not need the automatic power down feature and have configured the circuit to disable the power down and always enable the receivers. The interface circuit is configured with capacitor values referenced in the application information for 3 V to 5.5 V supplies.

At the SN65C3223E, I’m measuring the following:

  • !FORCEOFF = 5.03 V
  • FORCEON = 5.03 V
  • !EN = 4.6 mV
  • !INVALID = 3.01 V

Based on the datasheet, I believe the drivers and receivers should be enabled however, when input signals are applied, there are no outputs on either the driver or receiver.

Am I misunderstanding how the SN65C3223E should be configured? What could cause the SN65C3223E outputs to not be enabled?

Thank you!

Dave

  • 0
    TI__Intellectual 2885 points

    Hi Dave,

    Your setup seems to be correct. What is your VCC? If you are using 3 V I would suggesting using their corresponding capacitors values (same thing for 5 V). How are you powering the FORCE ON/OFF? I would use these capacitors to try and get the most ideal test condition.

  • 0 in reply to Matt Mendez
    TI__Intellectual 2885 points
    Also,

    You may want to check charge pump voltage values to make sure they are outputting the correct voltage. What kind of input signal are you using? You could verify that it is reaching the VIH and VIL.
  • 0 in reply to Matt Mendez
    Prodigy 30 points
    Hi Matt,

    Thank you for the suggestions.

    Our interface board is supplied both 3.3 V and 5 V. For VCC, we are using the 5 V. As per your recommendation, we have changed the capacitors to the values for the 5 V.

    Regarding the FORCE ON/OFF signals, they have been hard-wired to VCC as we don’t plan to use the auto power-down feature in this application.

    For the DIN, we have tested with a couple signal sources: (1) 3.3 V GPIO signal, and (2) external 3.3 V power supply. For RIN, we have also tested with a couple signal sources: (1) RS-232 interface CTS/RTS pins, and (2) external +/-9 V power supply.

    We are currently re-checking all connections throughout the circuit and will double-check the charge pump voltages. However, based on notes from the earlier tests, it doesn’t appear as though we were reaching the appropriate output voltages.

    Regards,
    Dave
  • 0 in reply to David Cummings30
    TI__Intellectual 2885 points

    Hi David,

    I would recommend verifying that the capacitors are placed correctly, because they would be at fault if the charge pumps are not working correctly. Did you say you had measured V+ and V-? If the problem persists, I would suggest trying another IC as that one may not be functioning correctly.

  • 0 in reply to Matt Mendez
    Prodigy 30 points

    Matt,

    Yes, we had measured V+ and V- and were only seeing about 200 mV. We re-checked all the capacitors and connections. Lastly, we swapped out the IC for another one and the circuit now appears to be working properly.

    Thanks!

    Dave