TLC555: Frequency deviation

Part Number: TLC555
Other Parts Discussed in Thread: TLC3555,

Tool/software:

Hi, Team.

We have received an inquiry from one of our customers regarding their circuit design.
They are currently considering using Texas Instruments' timer IC, TLC555I, for their clock generation circuit.

As background, their objective is to establish a frequency generation circuit as an alternative to crystal oscillators in the 100kHz to 1MHz range, which have been increasingly discontinued in recent years.

In this context, they are exploring the possibility of generating a clock signal in the range of 300 to 400kHz using the TLC555I.
They would like to know what level of frequency deviation can be expected in such a configuration.

We understand that the deviation may vary depending on the circuit configuration and environmental conditions, but any reference data or guidance you could provide would be greatly appreciated.

Best regards,

  • Hello Okutsu-san,

    For this task, I'll skip TLC555 and take the speed upgrade of TLC3555

    I my calculator, a nominal 325.4kHz, I see a 9% frequency range even with good passive tolerance. TLC555 would be wider.

    RD is a series pin 7 (DISCH) resistor.     

    Tolerance Standard Circuit Nominal Short DC Long DC Slow Freq Fast Freq
    5% VDD V 5 5 5 5 5
    0.1% RA Ohm 1000 999 1001 1001 999
    0.1% RB Ohm 2000 2002 1998 2002 1998
    1% RD Ohm 150 151.5 148.5 148.5 148.5
    1% C F 6.80E-10 6.73E-10 6.87E-10 6.87E-10 6.732E-10
    20% RON Ohm 11 8.8 13.2 13.2 8.8
    2.0% THRESHOLD % ratio 66.67% 65.33% 68.00% 68.00% 65.33%
    2.0% TRIGGER % ratio 33.33% 32.67% 34.00% 32.67% 34.00%
    10% TPLH s 8.00E-08 8.8E-08 7.2E-08 8.8E-08 7.2E-08
    10% TPHL s 6.70E-08 6E-08 7.37E-08 7.37E-08 6.03E-08
     
    Output
    Table
    Duty Cycle ratio 49.22% 47.82% 50.61% 49.48% 49.16%
    Frequency Hz 325398 333334 317417 301505 353775
    Time base s 3.07E-06 3.00E-06 3.15E-06 3.32E-06 2.83E-06

    What precision in frequency is needed? 

    I believe an oscillator built from a very high speed comparator would be more frequency stable.