GND

PLH

c(H)

T

A

B

PHL

T

B

on

PHL

c(L)

T

B

on

PLH

T

A

B

t

t

C (R

R ) In 3

exp

t

C (R

r )

t

t

C (R

r ) In 3

exp

t

C (R

R )

é

ù

æ

ö

-

=

+

-

+

ê

ú

ç

÷

+

ê

ú

è

ø

ë

û

é

ù

æ

ö

-

=

+

-

+

ê

ú

ç

÷

+

ê

ú

è

ø

ë

û

17

TLC555

www.ti.com

SLFS043I – SEPTEMBER 1983 – REVISED JULY 2019

Product Folder Links: TLC555

Submit Documentation Feedback

Copyright © 1983–2019, Texas Instruments Incorporated

Feature Description (continued)

The formulas (1-7) do not account for any propagation delay times from the TRIG and THRES inputs to DISCH

output. These delay times add directly to the period and overcharge the capacitor which creates differences

between calculated and actual values that increase with frequency. In addition, the internal on-state resistance

The equations below provide better agreement with measured values. The formulas Equation 8 represent the

actual low and high times when used at higher frequencies because propagation delay and discharge on

resistance is added to the formulas. Because the formulas are complex, a calculation tool, TLC555 Design

Calculator can be used to calculate the component values.

(8)

Figure 14. Trigger and Threshold Voltage Waveform