APPLICATION INFORMATION

MONOSTABLE OPERATION

In the monostable mode,the timer functions as a

one-shot. Referring to figure 2 the external capaci-

tor is initially held discharged by a transistor inside

the timer.

Reset

Trigger

Out

3

2

48

7

6

5

1

TS555

R

C

Control Voltage

0.01 F

µ

Figure 2

CC

SUPPLY VOLTAGE, V

(V)

300

200

100

04

8

12

16

TYPICAL CHARACTERISTICS

Figure 1 : Supply Current (each timer) versus

Supply Voltage

The circuit triggers on a negative-goinginput signal

circuit remains in this state until the set time has

elapsed,even if it is triggered again during this

interval. The duration of the output HIGH state is

given by t = 1.1 R x C.

Notice that since the charge rate and the threshold

level of the comparator are both directly propor-

tional to supply voltage, the timing interval is inde-

pendent of supply. Applying a negative pulse

simultaneously to the Reset terminal (pin 4) and the

Trigger terminal (pin 2) during the timing cycle

discharges the external capacitor and causes the

cycle to start over. The timing cycle now starts on

the positive edge of the reset pulse. During the time

the reset pulse is applied, the output is driven to its

LOW state.

When a negative trigger pulse is applied to pin 2,

the flip-flop is set, releasing the short circuit across

the external capacitor and driving the output HIGH.

The voltage across the capacitor increases expo-

nentially with the time constant

τ =R x C.

When the voltage across the capacitor equals 2/3

discharges the capacitor rapidly and drives the

output to its LOW state.

Figure 3 shows the actual waveforms generated in

this mode of operation.

When Reset is not used, it should be tied high to

avoid any possible or false triggering.

CAPACITOR VOLTAGE = 2.0V/div

Ω

Ω

µ

t = 0.1 ms / div

INPUT = 2.0V/div

OUTPUT VOLTAGE = 5.0V/div

R = 9.1k , C = 0.01 F , R = 1.0k

L

Figure 3

TS555C,I,M

8/12