TLC555CPWRG4 datasheet(17/42 Pages) TI

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VDD

2/3 VDD

1/3 VDD

GND

tPHL

tPLH

tc(H)

tc(L)

PLH

c(H)

PHL

c(L)

PLH

C (R

R ) In 3

exp

C (R

r )

C (R

r ) In 3

exp

C (R

R )

TLC555

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SLFS043I – SEPTEMBER 1983 – REVISED JULY 2019

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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

ron during discharge adds to RB to provide another source of timing error in the calculation when RB is very low.

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

TLC555CPWRG4 Datasheet(PDF) 17 Page - Texas Instruments