TLC555-Q1 Datasheet, PDF (9/25 Pages) Texas Instruments – LinCMOS™ TIMER

www.ti.com
TLC555-Q1
SLFS078B – OCTOBER 2006 – REVISED OCTOBER 2015
Feature Description (continued)
Monostable operation is initiated when TRIG voltage falls below the trigger threshold. Once initiated, the
sequence ends only if TRIG is high for at least 10 µs before the end of the timing interval. When the trigger is
grounded, the comparator storage time can be as long as 10 µs, which limits the minimum monostable pulse
width to 10 µs. Because of the threshold level and saturation voltage of Q1, the output pulse duration is
approximately t_w = 1.1R_AC. Figure 4 is a plot of the time constant for various values of R_A and C. The threshold
levels and charge rates both are directly proportional to the supply voltage, V_CC. The timing interval is, therefore,
independent of the supply voltage, so long as the supply voltage is constant during the time interval.
Applying a negative-going trigger pulse simultaneously to RESET and TRIG during the timing interval discharges
C and reinitiates the cycle, commencing on the positive edge of the reset pulse. The output is held low as long
as the reset pulse is low. To prevent false triggering, when RESET is not used, it should be connected to V_CC.
R_A = 9.1 kW
C_L = 0.01 mF
R_L = 1 kW
See Figure 9
10
R_A = 10 MW
1
R_A = 1 MW
Input Voltage
10^−1
10^−2
Output Voltage
Capacitor Voltage
Time − 0.1 ms/div
Figure 4. Typical Monostable Waveforms
10^−3
10^−4
R_A = 100 kW
R_A = 10 kW
R_A = 1 kW
10^−5
0.001
0.01
0.1
1
10
100
C − Capacitance − mF
Figure 5. Output Pulse Duration vs Capacitance
8.3.2 A-stable Operation
As shown in Figure 6, adding a second resistor, R_B, to the circuit of and connecting the trigger input to the
threshold input causes the timer to self-trigger and run as a multi-vibrator. The capacitor C charges through R_A
and R_B and then discharges through R_B only. Therefore, the duty cycle is controlled by the values of R_A and R_B.
This astable connection results in capacitor C charging and discharging between the threshold-voltage level (≈
0.67 × V_CC) and the trigger-voltage level (≈ 0.33 × V_CC). As in the mono-stable circuit, charge and discharge
times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.
Copyright © 2006–2015, Texas Instruments Incorporated
Product Folder Links: TLC555-Q1
Submit Documentation Feedback
9