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SE555: Output Pulse Duration over Temperatures

Shinichi Yokota
Genius 9715 points
Part Number: SE555


Hello,

Output pulse duration of SE555's mono-stable operation is estimated as tW = 1.1 × R × C. I'd like to ask how much the constant "1.1" in this equation can change over temperatures.

I guess this equation is derived from tW = -RC ln(1 - VTHRES/VCC), where the VTHRES/VCC is typically 2/3 in the SE555, and the "1.1" comes from -ln(1 - 2/3) = 1.0986 . The SE555 has the Min and Max specs of this THRES voltage level, VTHRES, in its data sheet, however, they are only at TA = 25 °C.

Best regards,
Shinichi Yokota

  • +1
    TI__Mastermind 26005 points

    Hello, 

    The constant will follow curve 7 in the product datasheet. The curve is normalized. For example if you wanted to calculate what the constant would be a little past T = 125 degrees C you would multiply the number on the plot by 1.1 which is the nominal value. 0.995*1.1 = 1.0945. The largest source of error will come from the RC components and temperature drift of these components should be accounted for.

    Best Regards, 

    Chris Featherstone