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MAX3243E: MAX3243E

SUJIT GHOSH
Prodigy 30 points
Part Number: MAX3243E

Can output of two RS-232 drivers remain shorted together for ever?

  • 0
    TI__Guru 52282 points

    Hi Sujit,

    Short answer:  No - you can't have more than 1 short at a time so the time limit is 0. Please see note 3 on the short circuit output current  from datasheet (included/highlighted below)

    So anytime two or more drivers are shorted we will consider breaking the parts recommended conditions.  

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 30 points

    Hi,

    I believe you answered for output of the driver being shorted to ground. My question is a bit different. I want to know if output of two drivers can be connected together, meaning DOUT1 is connected to DOUT2. The duration for which they remain connected together may be continuous/indefinite.

  • 0 in reply to SUJIT GHOSH
    TI__Guru 52282 points

    Hi Sujit,

    Shorting to each other can be worse than shorting to ground since drivers can have a swing of V+ - V- which is greater than V+ or V- to ground. So the answer is still no - you shouldn't do that - if the part breaks its because we don't suggest its used like that. 

    Ultimately it comes down to how hot the junction is - which is determined by multiple factors - ambient temperature, power dissipation, junction temperature limit, and thermal characteristics. 

    Junction temperature needs to stay below 150C

    TJ = P_tot * R_Theta_JA(effective)  + TA. 

    We list R_Theta_JA - but not R_Theta_JA(effective) you have to do your own thermal analysis in system to find that value. If you use the one in the datasheet your calculations will be wrong.  

    If the power burned causes TJ to be greater than 150C the part will break. 

    The issue comes down to:

    1. We don't guarantee a max junction temperature - it will be 150C but we don't list it in datasheet.

    2. We generally don't measure shorts in time - it either will break or it won't. Longer soak times could decrease lifetime due to excessive wear and tear. 

    3. R_Theta_JA listed in our datasheet is measured in an ideal setup that does not match how the parts will be used - this value will change. 

    Essentially - the question that you are asking is more complicated than yes/no. Since RS-232 has mechanical definitions it is generally easier to prevent shorts from shorts occurring or having a system to allow for quick remedies to shorts - driver to driver shorts is not a common need - so its very avoidable. 

    Best,

    Parker Dodson