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TLC555-Q1: TLC555-Q1 thermal tolerance

David Park
Expert 5400 points
Part Number: TLC555-Q1
Other Parts Discussed in Thread: TL431-Q1, OPA2377-Q1, NE555, TLC555

Hi,

Customer would like to use TLC555-Q1 for oscillator about 100Hz~200Hz.

It has to used in full thermal range so tolerance is important.

In the datasheet, threshold voltage is from 2.7V ~ 3.9V at Vdd=5V.

How many does this voltage range make the tolerance if there is not a tolerance of external component?

In my calculation, R1=2.89k, R2=11.54k, C=1uF, frequency is 100Hz.

I adopted 2.7V~3.9V to Vc and frequency is varied from 91Hz~107Hz in a result. +/-10%

Am I correct?

For reducing tolerance, I will recommend to add TL431-Q1 for 3.3V reference and OPA2377-Q1 for filter to CONT pin.

If these are adopted, can I assume that tolerance is 0.5% without tolerance of external component?

Thanks.

  • 0
    TI__Guru*** 139956 points

    David,

    The actual tolerance for CONT pin and THRESHOLD trip voltage is much better than data sheet limits suggests.

    Those limits are nearly same as NE555 timer limits set in the early 1970's.  The "resistors"  in TLC555-Q1 (actually two PMOS per "resistor")  will change with voltage and temperature however the matching is very good so voltage is quite stable.

    If you still want to externally control CONT pin, use (2 or 3) resistors to create a2/3 VCC voltage on OPA2377-Q1 input and buffer that to TLC555-Q1 CONT pin.  The TL431-Q1 is not needed and it is not beneficial.

    Here is sample data for TLC555 threshold voltage (5V supply).

  • 0 in reply to Ron Michallick
    TI__Guru*** 139956 points

    David,

    Here is a small sample size lab evaluation across temperature for CONT pin and threshold value.

    TLC555 Lab Temperature Testing.pptx