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Rev. 1.0.3

Features

· High Current Drive Capability (200mA)
· Adjustable Duty Cycle
· Temperature Stability of 0.005%/

· Timing From

Sec to Hours

· Turn off Time Less Than 2

Sec

Applications

· Precision Timing
· Pulse Generation
· Time Delay Generation
· Sequential Timing

Description

The LM555/NE555/SA555 is a highly stable controller
capable of producing accurate timing pulses. With a
monostable operation, the time delay is controlled by one
external resistor and one capacitor. With an astable
operation, the frequency and duty cycle are accurately
controlled by two external resistors and one capacitor.

8-DIP

8-SOP

Internal Block Diagram

F/F

OutPut

Stage

1
1
1
1

7
7
7
7

5
5
5
5

2
2
2
2

3
3
3
3

4
4
4
4

6
6
6
6

8
8
8
8

Comp.

Discharging Tr.

Vref

Vcc

Discharge

Threshold

Control

Voltage

GND

Trigger

Output

Reset

LM555/NE555/SA555

Single Timer

LM555/NE555/SA555

3
3

Electrical Characteristics

= 25

C, V

= 5 ~ 15V, unless otherwise specified)

Notes:

Notes:
1. When the output is high, the supply current is typically 1mA less than at V

= 5V.

2. Tested at V

= 5.0V and V

= 15V.

3. This will determine the maximum value of R

+ R

for 15V operation, the max. total R = 20M

, and for 5V operation, the max.

total R = 6.7M

4. These parameters, although guaranteed, are not 100% tested in production.

Parameter

Symbol

Conditions

Min.

Typ.

Max.

Unit

Supply Voltage

4.5

Supply Current (Low Stable) (Note1)

= 5V, R

= 15V, R

7.5

Timing Error (Monostable)
Initial Accuracy (Note2)
Drift with Temperature (Note4)
Drift with Supply Voltage (Note4)

ACCUR

= 1k

to100k

C = 0.1

1.0

0.1

3.0

0.5

ppm/

%/V

Timing Error (Astable)
Intial Accuracy (Note2)
Drift with Temperature (Note4)
Drift with Supply Voltage (Note4)

ACCUR

= 1k

to 100k

C = 0.1

2.25

150

0.3

ppm/

%/V

Control Voltage

= 15V

9.0

10.0

11.0

= 5V

2.6

3.33

4.0

Threshold Voltage

= 15V

10.0

= 5V

3.33

Threshold Current (Note3)

-
-
-
-

0.1

0.25

Trigger Voltage

= 5V

1.1

1.67

2.2

= 15V

4.5

5.6

Trigger Current

= 0V

0.01

2.0

Reset Voltage

RST

-
-
-
-

0.4

0.7

1.0

Reset Current

RST

-
-
-
-

0.1

0.4

Low Output Voltage

= 15V

SINK

= 10mA

SINK

= 50mA

0.06

0.3

0.25
0.75

V
V

= 5V

SINK

= 5mA

0.05

0.35

High Output Voltage

= 15V

SOURCE

= 200mA

SOURCE

= 100mA

12.75

12.5
13.3

V
V

= 5V

SOURCE

= 100mA

2.75

3.3

Rise Time of Output (Note4)

-
-
-
-

100

Fall Time of Output (Note4)

-
-
-
-

100

Discharge Leakage Current

LKG

-
-
-
-

100

LM555/NE555/SA555

4
4

Application Information

Table 1 below is the basic operating table of 555 timer:

When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or
the trigger voltage. Only when the high signal is applied to the reset terminal, the timer's output changes according to
threshold voltage and trigger voltage.
When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer's internal discharge Tr.
turns on, lowering the threshold voltage to below 1/3 of the supply voltage. During this time, the timer output is maintained
low. Later, if a low signal is applied to the trigger voltage so that it becomes 1/3 of the supply voltage, the timer's internal
discharge Tr. turns off, increasing the threshold voltage and driving the timer output again at high.

1. Monostable Operation

Table 1. Basic Operating Table

Threshold Voltage

)(PIN 6)

Trigger Voltage

)(PIN 2)

Reset(PIN 4)

Output(PIN 3)

Discharging Tr.

(PIN 7)

Don't care

Low

> 2Vcc / 3

High

Low

Vcc / 3 < V

< 2 Vcc / 3

Vcc / 3 < V

< 2 Vcc / 3

High

< Vcc / 3

High

OFF

-5

-4

-3

-2

-1

0
0

1
1

2
2

-3

-2

-1

0
0

1
1

2
2

10M

10k

100

R
R
R
R

A
A
A

=1k

a
p
a
ci

t
a
n
ce(u

)

a
p
a
ci

t
a
n
ce(u

)

a
p
a
ci

t
a
n
ce(u

)

a
p
a
ci

t
a
n
ce(u

)

Time Delay(s)

Figure 1. Monoatable Circuit

Figure 2. Resistance and Capacitance vs.

Time delay(t

d
d

)
)
)
)

Figure 3. Waveforms of Monostable Operation

RESET

Vcc

DISCH

THRES

CONT

GND

OUT

TRIG

+Vcc

Trigger

LM555/NE555/SA555

5
5

Figure 1 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls
below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's
internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C1
and setting the flip-flop output at the same time.
The voltage across the external capacitor C1, V

increases exponentially with the time constant t=R

*C and reaches 2Vcc/3

at td=1.1R

*C. Hence, capacitor C1 is charged through resistor R

. The greater the time constant R

C, the longer it takes

for the V

to reach 2Vcc/3. In other words, the time constant R

C controls the output pulse width.

When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop,
turning the discharging Tr. on. At this time, C1 begins to discharge and the timer output converts to low.
In this way, the timer operating in the monostable repeats the above process. Figure 2 shows the time constant relationship
based on R

and C. Figure 3 shows the general waveforms during the monostable operation.

It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer
output turns low. That is, although the output remains unaffected even if a different trigger pulse is applied while the output is
high, it may be affected and the waveform does not operate properly if the trigger pulse voltage at the end of the output pulse
remains at below Vcc/3. Figure 4 shows such a timer output abnormality.

2. Astable Operation

Figure 4. Waveforms of Monostable Operation (abnormal)

100m

1
1
1
1

100

10k

100k

1E-3

0.01

0.1

1
1
1
1

100

10M

100k

10k

+2R

)
)
)
)

a
p
a
cit

a
n
ce(u

)

a
p
a
cit

a
n
ce(u

)

a
p
a
cit

a
n
ce(u

)

a
p
a
cit

a
n
ce(u

)

Fr equency(Hz)

Figure 5. Astable Circuit

Figure 6. Capacitance and Resistance vs. Frequency

RESET

Vcc

DISCH

THRES

CONT

GND

OUT

TRIG

+Vcc

LM555/NE555/SA555

6
6

An astable timer operation is achieved by adding resistor R

to Figure 1 and configuring as shown on Figure 5. In the astable

operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multi
vibrator. When the timer output is high, its internal discharging Tr. turns off and the V

increases by exponential

function with the time constant (R

)*C.

When the V

, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high,

resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges
through the discharging channel formed by R

and the discharging Tr. When the V

falls below Vcc/3, the comparator

output on the trigger terminal becomes high and the timer output becomes high again. The discharging Tr. turns off and the
V

rises again.

In the above process, the section where the timer output is high is the time it takes for the V

to rise from Vcc/3 to 2Vcc/3,

and the section where the timer output is low is the time it takes for the V

to drop from 2Vcc/3 to Vcc/3. When timer output

is high, the equivalent circuit for charging capacitor C1 is as follows:

Since the duration of the timer output high state(t

) is the amount of time it takes for the V

(t) to reach 2Vcc/3,

Figure 7. Waveforms of Astable Operation

Vcc

Vc1(0-)=Vcc/3

dvc1

-------------

Vcc V 0-

( )

RA RB

-------------------------------

( )

VC1 0+

(

)

VCC 3

( )

VC1 t

( )

VCC 1

2
3

---

RA RB

(

)

------------------------------------

( )

LM555/NE555/SA555

7
7

The equivalent circuit for discharging capacitor C1, when timer output is low is, as follows:

Since the duration of the timer output low state(

) is the amount of time it takes for the V

(t) to reach Vcc/3,

Since R

is normally R

>>R

although related to the size of discharging Tr.,

=0.693R

(10)

Consequently, if the timer operates in astable, the period is the same with
'T=t

=0.693(RA+R

+0.693R

=0.693(R

+2R

' because the period is the sum of the charge time and discharge

time. And since frequency is the reciprocal of the period, the following applies.

3. Frequency divider

By adjusting the length of the timing cycle, the basic circuit of Figure 1 can be made to operate as a frequency divider. Figure
8. illustrates a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle.

VC1 t

( )

2
3

---

VCC V

2
3

---

RA RB

(

)

------------------------------------

( )

tH C1 RA RB

(

)

In2

0.693 RA RB

(

)

( )

(0-)=2Vcc/3

dvC1

--------------

RA RB

-----------------------

VC1 0

( )

VC1 t

( )

2
3

---

RA RD

(

)

-------------------------------------

( )

1
3

---

VCC

2
3

---

RA RD

(

)

-------------------------------------

( )

tL C1 RB RD

(

)

In2

0.693 RB RD

(

)

( )

frequency,

1
T

---

1.44

RA 2RB

(

)

----------------------------------------

( )

LM555/NE555/SA555

8
8

4. Pulse Width Modulation

The timer output waveform may be changed by modulating the control voltage applied to the timer's pin 5 and changing the
reference of the timer's internal comparators. Figure 9 illustrates the pulse width modulation circuit.
When the continuous trigger pulse train is applied in the monostable mode, the timer output width is modulated according to
the signal applied to the control terminal. Sine wave as well as other waveforms may be applied as a signal to the control
terminal. Figure 10 shows the example of pulse width modulation waveform.

5. Pulse Position Modulation

If the modulating signal is applied to the control terminal while the timer is connected for the astable operation as in Figure 11,
the timer becomes a pulse position modulator.
In the pulse position modulator, the reference of the timer's internal comparators is modulated which in turn modulates the
timer output according to the modulation signal applied to the control terminal.
Figure 12 illustrates a sine wave for modulation signal and the resulting output pulse position modulation : however, any wave
shape could be used.

Figure 8. Waveforms of Frequency Divider Operation

Figure 9. Circuit for Pulse Width Modulation

Figure 10. Waveforms of Pulse Width Modulation

CONT

GND

Vcc

DISCH

THRES

RESET

TRIG

OUT

+Vcc

Trigger

Output

Input

LM555/NE555/SA555

9
9

6. Linear Ramp

When the pull-up resistor RA in the monostable circuit shown in Figure 1 is replaced with constant current source, the V

increases linearly, generating a linear ramp. Figure 13 shows the linear ramp generating circuit and Figure 14 illustrates the
generated linear ramp waveforms.

In Figure 13, current source is created by PNP transistor Q1 and resistor R1, R2, and R

For example, if Vcc=15V, R

=20k

, R1=5kW, R2=10k

, and V

=0.7V,

=0.7V+10V=10.7V

Ic=(15-10.7)/20k=0.215mA

CONT

GND

Vcc

DISCH

THRES

RESET

TRIG

OUT

+Vcc

Modulation

Output

Figure 11. Circuit for Pulse Position Modulation

Figure 12. Waveforms of pulse position modulation

Figure 13. Circuit for Linear Ramp

Figure 14. Waveforms of Linear Ramp

RESET

Vcc

DISCH

THRES

CONT

GND

OUT

TRIG

+Vcc

Output

VCC VE

---------------------------

( )

Here, VE is

VE VBE

R1 R2

----------------------

VCC

( )

LM555/NE555/SA555

When the trigger starts in a timer configured as shown in Figure 13, the current flowing through capacitor C1 becomes a
constant current generated by PNP transistor and resistors.
Hence, the V

is a linear ramp function as shown in Figure 14. The gradient S of the linear ramp function is defined as

follows:

Here the Vp-p is the peak-to-peak voltage.
If the electric charge amount accumulated in the capacitor is divided by the capacitance, the V

comes out as follows:

V=Q/C

(15)

The above equation divided on both sides by T gives us

and may be simplified into the following equation.

S=I/C

(17)

In other words, the gradient of the linear ramp function appearing across the capacitor can be obtained by using the constant
current flowing through the capacitor.
If the constant current flow through the capacitor is 0.215mA and the capacitance is 0.02

F, the gradient of the ramp function

at both ends of the capacitor is S = 0.215m/0.022

= 9.77V/ms.

Vp p

----------------

( )

V
T

----

Q T

------------

( )

LM555/NE555/SA555

Mechanical Dimensions

Package

Dimensions in millimeters

6.40

0.20

3.30

0.30

0.130

0.012

3.40

0.20

0.134

0.008

0.252

0.008

9.20

0.20

0.79

2.54

0.100

0.031

()

0.46

0.10

0.018

0.004

0.060

0.004

1.524

0.10

0.362

0.008

9.60

0.378

MAX

5.08

0.200

0.33

0.013

7.62

0~15

0.300

MAX

MIN

0.25

+0.10

0.05

0.010

+0.004

0.002

8-DIP

LM555/NE555/SA555

Mechanical Dimensions

(Continued)

Package

Dimensions in millimeters

4.92

0.20

0.194

0.008

0.41

0.10

0.016

0.004

1.27

0.050

5.72

0.225

1.55

0.20

0.061

0.008

0.1~0.25

0.004~0.001

6.00

0.30

0.236

0.012

3.95

0.20

0.156

0.008

0.50

0.20

0.020

0.008

5.13

0.202

MAX

0~8

0.56

0.022

()

1.80

0.071

MAX0.10

MAX0.004

MAX

MIN

0.10

-0.05

0.15

0.004

-0.002

0.006

8-SOP

LM555/NE555/SA555

Ordering Information

Product Number

Package

Operating Temperature

LM555CN

8-DIP

0 ~ +70

LM555CM

8-SOP

Product Number

Package

Operating Temperature

NE555N

8-DIP

0 ~ +70

NE555D

8-SOP

Product Number

Package

Operating Temperature

SA555

8-DIP

-40 ~ +85

SA555D

8-SOP

LM555/NE555/SA555

11/29/02 0.0m 001

Stock#DSxxxxxxxx

2002 Fairchild Semiconductor Corporation

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which, (a) are intended for surgical implant into the body,

or (b) support or sustain life, and (c) whose failure to

perform when properly used in accordance with
instructions for use provided in the labeling, can be

reasonably expected to result in a significant injury of the

user.

2. A critical component in any component of a life support

device or system whose failure to perform can be

reasonably expected to cause the failure of the life support

device or system, or to affect its safety or effectiveness.

www.fairchildsemi.com

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PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY
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