LMC555: Timing Shift with Temperature

User,

There are no setup conditions for that typical parameter. I have to assume that figure 1 with switches 2 and 4 closed as the related previous used those switch settings. This is 10k and 100nF for a timing interval of 1.1ms. The timing delay tempco is based propagation delay drift, threshold comparator drift and the pin 7 on resistance drift. All of that adds up to 75ppm/C.

I quickly checked a different setup 4685 ohms and 923 pF that had a pulse time positive tempco of 300ppm/C. The higher level is due to propagation delay drift that is a pulse width adder so it adds more error percentage to shorter pulses. Therefore longer pulses will have less error and drift.

I have to search for threshold tempco information. Pin 7 on resistance will set the capacitor starting voltage but that is expected to be insignificant unless Ra is low value. this resistance increases with temperature.

In any case LMC555 is a general purpose timer so auto calibration using better accuracy standard caps may be required. This would likely add more cost than an alternate approach without onboard standards.

User,

The internal equal value three resistor divider are inherently well matching FET based resistors and the comparator thresholds should only vary a few millivolts. Device to device should match fairly well. However, I recommend that you test more samples. to prove this out.