LM556 Dual Timer IC : Pin Diagram & Its Working

The dual timer chip is one kind of integrated circuit, used in different types of applications like the generation of pulse, delay, oscillator, and variety of timer applications. For instance, LM556 IC is a type of highly constant dual timer available in a 14-pin package. It includes two timers which share the equal power supply pins. For every timing function, timing can be provided through external components like resistor & capacitor. The timers used in this IC can operate independently by sharing simply VCC & GND. One frequent method to utilize the LM556 dual timer is by connecting both 555 IC circuits in monostable mode by connecting the o/p pin of the primary 555 timers to the trigger pin of the next 555 timers. When the o/p of the primary timer goes low, then the second timer will trigger.

What is the LM556 Dual Timer IC?

Definition: The LM556 IC is a dual timing chip and extremely stable controller, used to generate an exact time delay otherwise oscillation. For every timing function, timing can be given through external components like a resistor as well as a capacitor. The LM556 is the dual timer IC, so it includes two timers in it. Same like to the IC LM555, this IC is also used in different applications. The working of this IC can be done by using CMOS technology.

LM556 IC Pin Configuration

The pin diagram of IC LM556 includes the following.

LM556 IC Pin Configuration
LM556 IC Pin Configuration

Pins 1 & 13 (Discharge Pins): The output of open collector discharges a capacitor among two intervals (in phase with output). When the voltage gets 2/3 of the voltage supply, toggles the o/p from high to low.

Pins 2 &12 (Threshold Pins): These pins evaluates the applied voltage toward the terminal through a 2/3 Vcc of the reference voltage. The voltage amplitude which is applied to this terminal can be accountable for the FF’s set state.

Pins 3 & 11(Control Voltage): These pins control the levels of trigger & threshold to determine the pulse width of the o/p waveform. When an external voltage is applied to these pins, then these are used for modulating the o/p waveform

Pins 4 & 10 (Reset Pins): When a negative pulse is applied to these pins, then a timer can be reset or disable. When these pins are not used for the purpose of reset, then they must be linked to VCC for avoiding fake triggering

Pins 5 & 9 (Out): Generally, these pins are connected to load when it is the single pin including o/p driven waveform

Pins 6 & 8 (Trigger): These pins are accountable for the alteration of the FF from set to reset. So, the timer o/p mainly depends on the amplitude of the exterior trigger pulse which is applied to these pins

Pin 7 (Ground): This is a ground pin

Pin 14 (Vcc): This is a voltage supply pin.

LM556 IC Features

The features of the LM556 dual timer IC include the following.

  • Replacement can be done directly for ICs like SE556 or NE556
  • This IC operates in two modes like astable and monostable
  • It restores Two 555 timers
  • The duty cycle can be adjustable
  • The output is normally ON & normally OFF
  • It is compatible with output and supply TTL
  • The stability of temperature is superior to 0.005% /˚C

LM556 IC Specifications

The specifications of the LM556 dual timer IC include the following.

  • In a single package, two precision timers are available
  • The operating voltage of this IC is +5V and can withstand the highest of +18V.
  • The sink current of the o/p pin is 200mA
  • Supply current is 10mA
  • Operating temperature ranges from 0 to 70°C
  • It is available in two packages like 14-pin SOIC & MDIP

LM556 Ratings

The ratings of this IC will show the necessity of voltage & power for an exact device. So the ratings are listed below.

  • Input voltage 5V
  • Supply voltage 18V
  • Output current +/- 225 mA
  • Thermal impedance 86 degree C/W
  • Storage temperature -65 to 150 degree C
  • Load temperature of 300 degrees C

Where to Use?

The dual timer IC like the LM556 IC includes two timers in it. Equivalent to the IC LM555, this IC is also used in various applications by using CMOS technology. This IC is available with two timers with enhanced characteristics. So if you are looking to replace 555 timers IC with the modern one, this is the best choice for you.

LM556 IC Circuit

The LM556 IC is available in a single package including two timers and this IC is perfect in the applications of sequential timing. The connection of these ICs can be done like this, the first-timer output is connected to the i/p of the next timer using a capacitor with a value of 0.001μF. The circuit diagram of this IC is shown below.

LM556 IC Circuit
LM556 IC Circuit

From the above circuit, the trigger and threshold inputs to the first-timer are pins 2 & 6 whereas the output pin is pin5. Here, the output pin is inverse always with both the input pins. Similarly, the output of the second IC is pin 9 whereas the input pins are pin 8 & 12. So the output pin is inverse to the input pins.

In the process, a 0.001μF capacitor will charge to whatever voltage is there at the pin 5, so the voltage of this capacitor will be given to the input of the next IC which will overturn the condition of two timers ICs. Here ‘t1’ delay can be determined through the first half & ‘t2’ delay through the next half delay.

The first portion of the IC can be started for a moment by connecting Pin6 to the GND. Once it is timed out, then the second portion of the timer will begin. The time duration can be determined through 1.1R2C2.


The applications of the LM556 IC include the following.

  • Generation of Time Delay
  • Industrial Controls
  • Tone Burst Generator
  • PWM/Pulse Width Modulation
  • Touch Tone Encoder
  • Generation of Pulse
  • Controlling of Traffic Light
  • Accuracy Timing
  • Frequency Division
  • Sequential Timing circuits
  • Shaping of pulse
  • Missing pulse detectors
  • PPM/Pulse position modulation
  • Linear ramp generator

Thus, this is all about an overview of the LM556 dual timer IC, pin configuration, circuit diagram with working, specifications, features, and applications. Here is a question for you, what are the advantages of LM556 IC?