NE556 — Dual Precision CMOS/Bipolar Timer IC

Overview

The NE556 (LM556 / SA556) is a dual precision timing circuit in a 14-pin DIP/SOIC package manufactured by Texas Instruments, STMicroelectronics, and ON Semiconductor. Containing two fully independent 555-type timers sharing common power supply (VCC) and ground (GND) pins, each half can generate accurate time delays or oscillations from microseconds up to hours.

Operating across a supply range of 4.5V to 16.0V DC, both output drivers can sink or source up to 200mA. The NE556 is ideal for dual-stage timing applications, two-tone sirens, cascaded pulse generators, and PWM motor/LED controllers where two 555 timers are required in a single IC package.

Quick reference


Supply Voltage (`VCC`)	4.5 V to 16.0 V DC
Output Sink / Source Current	Up to $200\text{ mA}$ per channel
Independent Timers	2 (Timer 1 and Timer 2)
Operating Modes	Astable (Oscillator), Monostable (One-Shot), PWM, Bistable
Timing Accuracy	$< 1\%$ typical drift across temperature
Max Oscillation Frequency	Up to $500\text{ kHz}$
Package	14-pin DIP / SOIC-14

Pinout (DIP-14 Package)

text

             ┌───┴───┐
     1DISCH 1│ 1   14│ VCC
     1THRES 2│       │13 2DISCH
    1CONT  3│       │12 2THRES
     1RESET 4│ NE556 │11 2CONT
      1OUT  5│       │10 2RESET
     1TRIG  6│       │9  2OUT
       GND  7│       │8  2TRIG
             └───────┘

Pin	Name	Timer	Description
1	`1DISCH`	Timer 1	Discharge pin (Open-collector transistor to GND)
2	`1THRES`	Timer 1	Threshold input pin (Triggers output LOW when $V > \frac{2}{3}V_{CC}$ )
3	`1CONT`	Timer 1	Control voltage pin (Access to $\frac{2}{3}V_{CC}$ reference divider)
4	`1RESET`	Timer 1	Active-Low Reset pin (Forces output LOW when $<0.4\text{V}$ )
5	`1OUT`	Timer 1	Timer 1 Output (Push-pull, drives up to 200mA)
6	`1TRIG`	Timer 1	Trigger input pin (Triggers output HIGH when $V < \frac{1}{3}V_{CC}$ )
7	`GND`	Common	Common Ground reference (0 V)
8	`2TRIG`	Timer 2	Trigger input pin
9	`2OUT`	Timer 2	Timer 2 Output
10	`2RESET`	Timer 2	Active-Low Reset pin
11	`2CONT`	Timer 2	Control voltage pin
12	`2THRES`	Timer 2	Threshold input pin
13	`2DISCH`	Timer 2	Discharge pin
14	`VCC`	Common	Positive Supply Power pin (+4.5V to +16.0V DC)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{CC}$	4.5	12.0	16.0	V	DC
Supply Current (Both Timers)	$I_{CC}$	—	6.0	12.0	mA	$V_{CC} = 5\text{V}, V_{OUT} = \text{Low}$
High Output Voltage Drop	$V_{OH}$	$V_{CC}-1.5$	$V_{CC}-1.2$	—	V	$I_{SOURCE} = 100\text{mA}, V_{CC} = 15\text{V}$
Low Output Voltage	$V_{OL}$	—	0.1	0.25	V	$I_{SINK} = 10\text{mA}, V_{CC} = 5\text{V}$
Trigger Voltage Threshold	$V_{TRIG}$	1.45	1.67	1.9	V	$V_{CC} = 5\text{V}$
Threshold Voltage Level	$V_{THRES}$	3.1	3.33	3.5	V	$V_{CC} = 5\text{V}$

Typical Applications

Cascaded Sequential Timer (Delayed Pulse Generator)

Timer 1 operates as a monostable one-shot. When Timer 1's output (1OUT) completes its pulse and drops LOW, it triggers Timer 2 (2TRIG) to start a second timed pulse.