1

S

R

R1

TRIG

THRES

CONT

RESET

OUT

DISCH

GND

4

8

5

6

2

1

7

3

NA555, NE555, SA555, SE555

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SLFS022I – SEPTEMBER 1973 – REVISED SEPTEMBER 2014

8 Detailed Description

8.1 Overview

The xx555 timer is a popular and easy to use for general purpose timing applications from 10 µs to hours or from

< 1mHz to 100 kHz. In the time-delay or mono-stable mode of operation, the timed interval is controlled by a

single external resistor and capacitor network. In the a-stable mode of operation, the frequency and duty cycle

can be controlled independently with two external resistors and a single external capacitor. Maximum output sink

and discharge sink current is greater for higher VCC and less for lower VCC.

8.2 Functional Block Diagram

A.

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

B.

RESET can override TRIG, which can override THRES.

8.3 Feature Description

8.3.1 Mono-stable Operation

For mono-stable 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.

Copyright © 1973–2014, Texas Instruments Incorporated

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