(5 V to 15 V)

Output

GND

OUT

CONT

RESET

DISCH

THRES

TRIG

Input

5

8

4

7

6

2

3

1

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

NA555, NE555, SA555, SE555

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SLFS022H – SEPTEMBER 1973 – REVISED JUNE 2010

APPLICATION INFORMATION

Monostable Operation

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

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

threshold voltage of the threshold (THRES) input. If TRIG has returned to a high level, the output of the threshold

comparator resets the flip-flop (Q goes high), drives the output low, and discharges C through Q1.

Figure 9. Circuit for Monostable Operation

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

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

Copyright © 1973–2010, Texas Instruments Incorporated

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9

Product Folder Link(s): NA555 NE555 SA555 SE555