LM555CMM/NOPB - NATIONAL SEMICONDUCTOR

LM555

LM555 Timer

Literature Number: SNAS548B

LM555

Timer

General Description

The LM555 is a highly stable device for generating accurate

time delays or oscillation. Additional terminals are provided

for triggering or resetting if desired. In the time delay mode of

operation, the time is precisely controlled by one external

resistor and capacitor. For astable operation as an oscillator,

the free running frequency and duty cycle are accurately

controlled with two external resistors and one capacitor. The

circuit may be triggered and reset on falling waveforms, and

the output circuit can source or sink up to 200mA or drive

TTL circuits.

Features

nDirect replacement for SE555/NE555

nTiming from microseconds through hours

nOperates in both astable and monostable modes

nAdjustable duty cycle

nOutput can source or sink 200 mA

nOutput and supply TTL compatible

nTemperature stability better than 0.005% per ˚C

nNormally on and normally off output

nAvailable in 8-pin MSOP package

Applications

nPrecision timing

nPulse generation

nSequential timing

nTime delay generation

nPulse width modulation

nPulse position modulation

nLinear ramp generator

Schematic Diagram

00785101

July 2006

LM555 Timer

Connection Diagram

Dual-In-Line, Small Outline

and Molded Mini Small Outline Packages

00785103

Top View

Ordering Information

Package Part Number Package Marking Media Transport NSC Drawing

8-Pin SOIC LM555CM LM555CM Rails M08A

LM555CMX LM555CM 2.5k Units Tape and Reel

8-Pin MSOP LM555CMM Z55 1k Units Tape and Reel MUA08A

LM555CMMX Z55 3.5k Units Tape and Reel

8-Pin MDIP LM555CN LM555CN Rails N08E

LM555

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Absolute Maximum Ratings (Note 2)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage +18V

Power Dissipation (Note 3)

LM555CM, LM555CN 1180 mW

LM555CMM 613 mW

Operating Temperature Ranges

LM555C 0˚C to +70˚C

Storage Temperature Range −65˚C to +150˚C

Soldering Information

Dual-In-Line Package

Soldering (10 Seconds) 260˚C

Small Outline Packages

(SOIC and MSOP)

Vapor Phase (60 Seconds) 215˚C

Infrared (15 Seconds) 220˚C

See AN-450 “Surface Mounting Methods and Their Effect

on Product Reliability” for other methods of soldering

surface mount devices.

Electrical Characteristics (Notes 1, 2)

= 25˚C, V

= +5V to +15V, unless othewise specified)

Parameter Conditions Limits Units

LM555C

Min Typ Max

Supply Voltage 4.5 16 V

Supply Current V

= 5V, R

=∞

= 15V, R

=∞

(Low State) (Note 4)

15 mA

Timing Error, Monostable

Initial Accuracy 1%

Drift with Temperature R

= 1k to 100kΩ, 50 ppm/˚C

C = 0.1µF, (Note 5)

Accuracy over Temperature 1.5 %

Drift with Supply 0.1 %/V

Timing Error, Astable

Initial Accuracy 2.25 %

Drift with Temperature R

= 1k to 100kΩ, 150 ppm/˚C

C = 0.1µF, (Note 5)

Accuracy over Temperature 3.0 %

Drift with Supply 0.30 %/V

Threshold Voltage 0.667 x V

Trigger Voltage V

= 15V 5 V

= 5V 1.67 V

Trigger Current 0.5 0.9 µA

Reset Voltage 0.4 0.5 1 V

Reset Current 0.1 0.4 mA

Threshold Current (Note 6) 0.1 0.25 µA

Control Voltage Level V

= 15V

=5V

2.6

3.33

Pin 7 Leakage Output High 1 100 nA

Pin 7 Sat (Note 7)

Output Low V

= 15V, I

= 15mA 180 mV

Output Low V

= 4.5V, I

= 4.5mA 80 200 mV

LM555

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Electrical Characteristics (Notes 1, 2) (Continued)

= 25˚C, V

= +5V to +15V, unless othewise specified)

Parameter Conditions Limits Units

LM555C

Min Typ Max

Output Voltage Drop (Low) V

= 15V

SINK

= 10mA 0.1 0.25 V

SINK

= 50mA 0.4 0.75 V

SINK

= 100mA 2 2.5 V

SINK

= 200mA 2.5 V

=5V

SINK

= 8mA V

SINK

= 5mA 0.25 0.35 V

Output Voltage Drop (High) I

SOURCE

= 200mA, V

= 15V 12.5 V

SOURCE

= 100mA, V

= 15V 12.75 13.3 V

= 5V 2.75 3.3 V

Rise Time of Output 100 ns

Fall Time of Output 100 ns

Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.

Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which

guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit

is given, however, the typical value is a good indication of device performance.

Note 3: For operating at elevated temperatures the device must be derated above 25˚C based on a +150˚C maximum junction temperature and a thermal

resistance of 106˚C/W (DIP), 170˚C/W (S0-8), and 204˚C/W (MSOP) junction to ambient.

Note 4: Supply current when output high typically 1 mA less at VCC =5V.

Note 5: Tested at VCC = 5V and VCC = 15V.

Note 6: This will determine the maximum value of RA+R

Bfor 15V operation. The maximum total (RA+R

B)is20MΩ.

Note 7: No protection against excessive pin 7 current is necessary providing the package dissipation rating will not be exceeded.

Note 8: Refer to RETS555X drawing of military LM555H and LM555J versions for specifications.

LM555

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Typical Performance Characteristics

Minimuim Pulse Width

Required for Triggering

Supply Current vs.

Supply Voltage

00785104 00785119

High Output Voltage vs.

Output Source Current

Low Output Voltage vs.

Output Sink Current

00785120 00785121

Low Output Voltage vs.

Output Sink Current

Low Output Voltage vs.

Output Sink Current

00785122 00785123

LM555

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Typical Performance Characteristics (Continued)

Output Propagation Delay vs.

Voltage Level of Trigger Pulse

Output Propagation Delay vs.

Voltage Level of Trigger Pulse

00785124 00785125

Discharge Transistor (Pin 7)

Voltage vs. Sink Current

Discharge Transistor (Pin 7)

Voltage vs. Sink Current

00785126 00785127

LM555

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Applications Information

MONOSTABLE OPERATION

In this mode of operation, the timer functions as a one-shot

(Figure 1). The external capacitor is initially held discharged

by a transistor inside the timer. Upon application of a nega-

tive trigger pulse of less than 1/3 V

to pin 2, the flip-flop is

set which both releases the short circuit across the capacitor

and drives the output high.

The voltage across the capacitor then increases exponen-

tially for a period of t = 1.1 R

C, at the end of which time the

voltage equals 2/3 V

. The comparator then resets the

flip-flop which in turn discharges the capacitor and drives the

output to its low state. Figure 2 shows the waveforms gen-

erated in this mode of operation. Since the charge and the

threshold level of the comparator are both directly propor-

tional to supply voltage, the timing interval is independent of

supply.

During the timing cycle when the output is high, the further

application of a trigger pulse will not effect the circuit so long

as the trigger input is returned high at least 10µs before the

end of the timing interval. However the circuit can be reset

during this time by the application of a negative pulse to the

reset terminal (pin 4). The output will then remain in the low

state until a trigger pulse is again applied.

When the reset function is not in use, it is recommended that

it be connected to V

to avoid any possibility of false

triggering.

Figure 3 is a nomograph for easy determination of R, C

values for various time delays.

NOTE: In monostable operation, the trigger should be driven

high before the end of timing cycle.

ASTABLE OPERATION

If the circuit is connected as shown in Figure 4 (pins 2 and 6

connected) it will trigger itself and free run as a multivibrator.

The external capacitor charges through R

and dis-

charges through R

. Thus the duty cycle may be precisely

set by the ratio of these two resistors.

In this mode of operation, the capacitor charges and dis-

charges between 1/3 V

and 2/3 V

. As in the triggered

mode, the charge and discharge times, and therefore the

frequency are independent of the supply voltage.

00785105

FIGURE 1. Monostable

00785106

VCC = 5V Top Trace: Input 5V/Div.

TIME = 0.1 ms/DIV. Middle Trace: Output 5V/Div.

RA= 9.1kΩBottom Trace: Capacitor Voltage 2V/Div.

C = 0.01µF

FIGURE 2. Monostable Waveforms

00785107

FIGURE 3. Time Delay

00785108

FIGURE 4. Astable

LM555

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Applications Information (Continued)

Figure 5 shows the waveforms generated in this mode of

operation.

The charge time (output high) is given by:

= 0.693 (R

And the discharge time (output low) by:

= 0.693 (R

Thus the total period is:

T=t

= 0.693 (R

+2R

The frequency of oscillation is:

Figure 6 may be used for quick determination of these RC

values.

The duty cycle is:

FREQUENCY DIVIDER

The monostable circuit of Figure 1 can be used as a fre-

quency divider by adjusting the length of the timing cycle.

Figure 7 shows the waveforms generated in a divide by three

circuit.

PULSE WIDTH MODULATOR

When the timer is connected in the monostable mode and

triggered with a continuous pulse train, the output pulse

width can be modulated by a signal applied to pin 5. Figure

8shows the circuit, and in Figure 9 are some waveform

examples.

00785109

VCC = 5V Top Trace: Output 5V/Div.

TIME = 20µs/DIV. Bottom Trace: Capacitor Voltage 1V/Div.

RA= 3.9kΩ

RB=3kΩ

C = 0.01µF

FIGURE 5. Astable Waveforms

00785110

FIGURE 6. Free Running Frequency

00785111

VCC = 5V Top Trace: Input 4V/Div.

TIME = 20µs/DIV. Middle Trace: Output 2V/Div.

RA= 9.1kΩBottom Trace: Capacitor 2V/Div.

C = 0.01µF

FIGURE 7. Frequency Divider

00785112

FIGURE 8. Pulse Width Modulator

LM555

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Applications Information (Continued)

PULSE POSITION MODULATOR

This application uses the timer connected for astable opera-

tion, as in Figure 10, with a modulating signal again applied

to the control voltage terminal. The pulse position varies with

the modulating signal, since the threshold voltage and hence

the time delay is varied. Figure 11 shows the waveforms

generated for a triangle wave modulation signal.

LINEAR RAMP

When the pullup resistor, R

, in the monostable circuit is

replaced by a constant current source, a linear ramp is

generated. Figure 12 shows a circuit configuration that will

perform this function.

Figure 13 shows waveforms generated by the linear ramp.

The time interval is given by:

.0.6V

00785113

VCC = 5V Top Trace: Modulation 1V/Div.

TIME = 0.2 ms/DIV. Bottom Trace: Output Voltage 2V/Div.

RA= 9.1kΩ

C = 0.01µF

FIGURE 9. Pulse Width Modulator

00785114

FIGURE 10. Pulse Position Modulator

00785115

VCC = 5V Top Trace: Modulation Input 1V/Div.

TIME = 0.1 ms/DIV. Bottom Trace: Output 2V/Div.

RA= 3.9kΩ

RB=3kΩ

C = 0.01µF

FIGURE 11. Pulse Position Modulator

00785116

FIGURE 12.

LM555

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Applications Information (Continued)

50% DUTY CYCLE OSCILLATOR

For a 50% duty cycle, the resistors R

and R

may be

connected as in Figure 14. The time period for the output

high is the same as previous, t

= 0.693 R

C. For the output

low it is t

Thus the frequency of oscillation is

Note that this circuit will not oscillate if R

is greater than 1/2

because the junction of R

and R

cannot bring pin 2

down to 1/3 V

and trigger the lower comparator.

ADDITIONAL INFORMATION

Adequate power supply bypassing is necessary to protect

associated circuitry. Minimum recommended is 0.1µF in par-

allel with 1µF electrolytic.

Lower comparator storage time can be as long as 10µs

when pin 2 is driven fully to ground for triggering. This limits

the monostable pulse width to 10µs minimum.

Delay time reset to output is 0.47µs typical. Minimum reset

pulse width must be 0.3µs, typical.

Pin 7 current switches within 30ns of the output (pin 3)

voltage.

00785117

VCC = 5V Top Trace: Input 3V/Div.

TIME = 20µs/DIV. Middle Trace: Output 5V/Div.

R1= 47kΩBottom Trace: Capacitor Voltage 1V/Div.

R2= 100kΩ

RE= 2.7 kΩ

C = 0.01 µF

FIGURE 13. Linear Ramp

00785118

FIGURE 14. 50% Duty Cycle Oscillator

LM555

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Physical Dimensions inches (millimeters) unless otherwise noted

Small Outline Package (M)

NS Package Number M08A

8-Lead (0.118” Wide) Molded Mini Small Outline Package

NS Package Number MUA08A

LM555

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Molded Dual-In-Line Package (N)

NS Package Number N08E

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the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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LM555 Timer

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