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参数资料
| 型号： | TLC555IP |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 模拟波形发生器 |
| 英文描述： | PULSE; RECTANGULAR, 1.2 MHz, TIMER, PDIP8 |
| 封装： | ROHS COMPLIANT, PLASTIC, DIP-8 |
| 文件页数： | 2/24页 |
| 文件大小： | 726K |
| 代理商： | TLC555IP |
TLC555
LinCMOS TIMER
SLFS043F SEPTEMBER 1983 REVISED FEBRUARY 2005
10
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
Connecting TRIG to THRES, as shown in Figure 3, causes the timer to run as a multivibrator. The capacitor CT
charges through RA and RB to the threshold voltage level (approximately 0.67 VDD) and then discharges through RB
only to the value of the trigger voltage level (approximately 0.33 VDD). The output is high during the charging cycle
(tc(H)) and low during the discharge cycle (tc(L)). The duty cycle is controlled by the values of RA, RB, and CT as shown
in the equations below.
t
c(H) [
C
T
(R
A )
R
B
)In2 (In2
+ 0.693)
t
c(L) [
C
T
R
B
In 2
Period
+ t
c(H) )
t
c(L) [
C
T
(R
A )
2R
B
)In2
Output driver duty cycle
+
t
c(L)
t
c(H) )
t
c(L)
[ 1–
R
B
R
A )
2R
B
Output waveform duty cycle
+
t
c(H)
t
c(H) )
t
c(L)
[
R
B
R
A )
2R
B
The 0.1-
F capacitor at CONT in Figure 3 decreases the period by about 10%.
The formulas shown above do not allow for any propagation delay times from the TRIG and THRES inputs to DISCH.
These delay times add directly to the period and create 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 or ron is very high.
The equations below provide better agreement with measured values.
t
c(H) +
C
T
(R
A )
R
B
)In
3– exp
–t
PLH
C
T
(R
B )
ron)
) t
PHL
t
c(L) +
C
T
(R
B )
ron)In
3– exp
–t
PHL
C
T
(R
A )
R
B
)
) t
PLH
These equations and those given earlier are similar in that a time constant is multiplied by the logarithm of a number
or function. The limit values of the logarithmic terms must be between In 2 at low frequencies and In 3 at extremely
high frequencies. For a duty cycle close to 50%, an appropriate constant for the logarithmic terms can be substituted
with good results. Duty cycles less than 50%
t
c(H)
t
c(H) )
t
c(L)
require that
t
c(H)
t
c(L)
< 1 and possibly RA ≤ ron. These
conditions can be difficult to obtain.
In monostable applications, the trip point on TRIG can be set by a voltage applied to CONT. An input voltage between
10% and 80% of the supply voltage from a resistor divider with at least 500-
A bias provides good results.
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