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NA556: What does temperature coefficient of timing interval means?

Art Mecina
Genius 16625 points
Part Number: NA556
Other Parts Discussed in Thread: NA555

Hi E2E,

Good day!

I am posting on behalf of one of our customer.
The customer wants to know what does the "temperature coefficient of timing interval mean"?

This was indicated in the device's table of electrical characteristics of the datasheet.
Datasheet:  http://www.ti.com/lit/ds/symlink/na556.pdf

Thanks in advance!

Regards,

Art

  • 0
    TI__Guru**** 155696 points

    Hello Art,

    The "temperature coefficient of timing interval" means the change in the time of the period (one shot 't' or '1/F' a-stable). The input time used in this calculation is measured at minimum and maximum rated device temperatures.

    The slope of delta time / delta centigrade at any given two temperatures (other than MIN and MAX) may or may not be higher.  

  • 0 in reply to Ron Michallick
    TI__Genius 16625 points

    Hi Ron,

    Thanks for the prompt response!
    I will inform the customer  and notify you if he has further clarifications.

    Regards,

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16625 points

    Hi Ron,

    Good day!
    We received a follow-up inquiry from our customer, hope you can help us on this one as well. Below is the inquiry:

    "So for astable operation if we have a value at TA= 25°C , the t=1/F value for TB = x °C will be t(TB)= t(TA)*(150/10^6)^(TA-TB) ?
    so at 125°C we have 1,5% less than on t(TA) value, and for -55°C , t is higher 1,2% than t(TA) ?"

    Thanks!

    Art 

  • 0 in reply to Art Mecina
    TI__Guru**** 155696 points

    Art,

    For astable operation meeting the requirements of note 5 the typical change in time is 150ppm/C. The temperature range for NA556 is -40C to 105C so the change is (105C+40C) * 150ppm/C = 21750ppm = 2.175% difference with no regard to whether the longer time (lower frequency) occurs at -40C or 105C. 

    Ideally the temperature coefficient would be fixed so the drift is linear across temperature. However this is not always the case especially on better than typical devices; the curve over temperature have have higher order components. Devices that are worse than typical are more likely to be linear as the 1st order effect will dominate. 

    The data sheet specification is only a typical value with no limits and this drift only includes NA555 drift. The drift of the timing resistors and more importantly the timing capacitor must be considered separately.

  • 0 in reply to Ron Michallick
    TI__Genius 16625 points

    Hi Ron,

    Thanks again for the fast response!
    I'll notify you in case customer has further inquiries.

    Best regards,

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16625 points

    Hi Ron,

    The customer is satisfied with the answer.

    Again, thank you for the excellent support!

    Best regards,

    Art