SA555: R, C value considerations

Hiromu Susami

Intellectual 1110 points

Part Number: SA555
Other Parts Discussed in Thread: TLC3555-Q1, TLC555

Hi team,

I have 3 questions.

I want to drive Astable Operation with 20us:L, 40us:H. Planning to use RA, RB:1330orm, C:0.022uF.

In addition to the R and C tolerances, what parameters are taken into account to calculate the output variation?
What are the recommended resistance and capacitance values? Of the system. What are the advantages and disadvantages of using higher resistance or capacitance?
Is there information on the actual resistance range between pin1-2, 2-6, 6-8 ? I understand that they all have the same resistance value.

Regards,
Hiromu

3 months ago

+1 Ron Michallick 3 months ago

TI__Guru**** 170096 points

Hello Hiromu,

Hiromu Susami said:
In addition to the R and C tolerances, what parameters are taken into account to calculate the output variation?

Propagation delay for 16kHz will introduce roughly a 4% error in the simple formulas. So change R to 1.27k ohms

Hiromu Susami said:
What are the recommended resistance and capacitance values? Of the system. What are the advantages and disadvantages of using higher resistance or capacitance?

See data sheet figure 6-7 for reasonable values. For high R low C, parasitic capacitances and leakages (input bias current) have more effect. For low R and high C, more supply current.

If more accuracy is needed, TLC3555-Q1 is best of the generic timers.

0 Hiromu Susami 3 months ago in reply to Ron Michallick

TI__Intellectual 1110 points

Hi Ron,

Thank you for your comment. Could you also comment on this?

Hiromu Susami said:
Is there information on the actual resistance range between pin1-2, 2-6, 6-8 ? I understand that they all have the same resistance value.

Regards,
Hiromu