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MAX3222: Waht is the VOH Max value of Driver

Kenta Nabekura
Prodigy 10 points
Part Number: MAX3222

There is no stipulation for the maximum value on the data sheet, but would it be possible for you to disclose the upper limit of the actual value?

Thank you

  • 0
    Prodigy 10 points

    Additional question.
    The figure below shows the output voltage trend we measured.
    I see a variation of about ±0.4V, but is this within expectations?
    Also, please tell me the dominant factors that cause this variation.

    Thank you

  • +1 in reply to Kenta Nabekura
    Guru 275410 points

    The RS-232 bus voltages are regulated to nominally ±5.6 V. These voltages are generated with charge pumps, so the theoretical maximum is twice the input supply voltage. (The RS-232 specification allows anything between ±3 V and ±15 V.)

    The RS-232 specification defines a receiver's load as 5 kΩ ±2 kΩ. A charge pump has a noticeable output impedance, so if the load changes, the output voltage changes.

    I do not know the time scale of your measurements. When zoomin in, you should be able to see the switching frequency of the charge pump.

  • +1 in reply to Kenta Nabekura
    TI__Mastermind 46607 points

    Hi Nebekura-san,

    We don't guarantee a max output voltage - as Clemens mentioned changes in load will impact the output voltage strength. That being said as long as the RS-232 receiver receives >3V and < - 3V for logic low and high respectively  it should be okay at receiver end. 

    That being said - what is the time scale shown above? The signal looks noisy - like it could be possible it is coupling in a signal somewhere or the through the probe - because I don't really see any periodicity from the waveform above (which could be the charge pump - but this just looks like noise). 

    What is the load that you are driving  during this test? 

    Please let me know - because this could indicate an issue - or it could be something that isn't going to impact final application too much. 

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 10 points

    Clemens-san,

    Parker-san,

    Thank you for your reply!

    I understand that the theoretical nominal value is twice the input power supply voltage.

    The load at the time of measurement is data measured in a released state. Under a 3kΩ load condition, the output voltage value decreased by approximately 0.3V.

    Sorry at the lack of explanation.

    The horizontal axis of the pasted figure is the number of samples, not the time axis.

    The output values of each sample are listed. Since some variation was confirmed, I wanted to check whether this distribution was theoretically reasonable and to what extent the voltage value could fluctuate.

    Thank you,

  • +1 in reply to Kenta Nabekura
    TI__Mastermind 46607 points

    Hi Nebekura-san,

    Yes it is not completely unprecedented to have some noise coupled onto the line - and that is what it looks like - but since the loading doesn't seem to be causing too much of a concern on the "readability" of the data by the receiver - I wouldn't be too concerned - you can always add some filtering elements to the bus - as long as you respect the loading of the transceiver - to reduce the variation if you are still concerned by it.

    Best,

    Parker Dodson