SLFS022 – D1669, SEPTEMBER 1973—REVISED FEBRUARY 1992

NE555, SA555, SE555, SE555C

PRECISION TIMERS

POST OFFICE BOX 655303

9

APPLICATION INFORMATION

monostable operation

For monostable operation, any of these timers may be connected as shown in Figure 9. If the output is low,

application of a negative-going pulse to TRIG sets the flip-flop (Q goes low), drives the output high, and turns

voltage of THRES input. If TRIG has returned to a high level, the output of the threshold comparator will reset

the flip-flop (Q goes high), drive the output low, and discharge C through Q1.

VCC

(5 V to 15 V)

RA

RL

Output

GND

OUT

VCC

CONT

RESET

DISCH

THRES

TRIG

Input

Time – 0.1 ms/div

Capacitor Voltage

Output Voltage

Input Voltage

RA = 9.1 kΩ

CL = 0.01 µF

RL = 1 kΩ

See Figure 9

5

8

4

7

6

2

3

1

Pin numbers shown are for the D, JG, and P packages.

Figure 9. Circuit for Monostable Operation

Figure 10. Typical Monostable Waveforms

Monostable operation is initiated when TRIG

voltage falls below the trigger threshold. Once

initiated, the sequence ends only if TRIG is high at

the end of the timing interval. Because of the

threshold level and saturation voltage of Q1,

the output pulse duration is approximately

threshold levels and charge rates are both directly

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 re-initiates 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

C – Capacitance –

µF

10

1

10–1

10–2

10–3

10–4

100

10

1

0.1

0.01

10–5

0.001

Figure 11. Output Pulse Duration vs Capacitance

RA = 10 MΩ

RA = 10 kΩ

RA = 1 kΩ

RA = 100 kΩ

RA = 1 MΩ