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TLC555: 10% frequency accuracy with 5V supply?

AnBer
Mastermind 31375 points

Part Number: TLC555
Other Parts Discussed in Thread: LMC555, NE555, LM555, NA555, SE555, SA555

Team,

Goal: Build 40kHz oscillator with an accuracy in frequency of +/-10% at 5V supply voltage.

According to this FAQ/Article an oscillator with 3% accuracy can be built with the TLC555:
[FAQ] How do I design a-stable timer, oscillator, circuits using LMC555, TLC555, LM555, NA555, NE555, SA555, or SE555?
https://e2e.ti.com/support/clock-and-timing/f/48/t/879112

According to the TLC555 data sheet, the threshold voltage can vary from 2.7 to 3.9 V (3.3 V nominal voltage). The same applies to the trigger voltage, which can vary from 1.26 V to 2.06 V (1.66 V nominal voltage).
simulating the switching behavior (via TI TLC555 spice model provided) and changing the switching thresholds to a worst-case scenario (e.g. U_th = 2.7V and U_tr = 2.06V), we see the output frequency changing a lot (typically between 20kHz and 80kHz).
How does the TLC555 still manage to produce such a precise frequency with such imprecise switching thresholds?

Thanks in advance

A.