� High Current Drive Capability (200mA) The LM555/NE555/SA555 is a highly stable controller
� Adjustable Duty Cycle capable of producing accurate timing pulses. With a
� Temperature Stability of 0.005%/�C monostable operation, the time delay is controlled by one
� Timing From �Sec to Hours external resistor and one capacitor. With an astable
� Turn off Time Less Than 2�Sec operation, the frequency and duty cycle are accurately
controlled by two external resistors and one capacitor.
� Precision Timing
� Pulse Generation 1
� Time Delay Generation 8-SOP
� Sequential Timing
Internal Block Diagram
R R R
GND 1 8 Vcc
Comp. Discharging Tr.
Trigger 2 7 Discharge
Output 3 OutPut F/F 6 Threshold
Reset 4 Control
�2002 Fairchild Semiconductor Corporation
Absolute Maximum Ratings (TA = 25�C)
Parameter Symbol Value Unit
Lead Temperature (Soldering 10sec) VCC 16 V
Operating Temperature Range TLEAD 300 �C
SA555 PD 600 mW
Storage Temperature Range
TOPR 0 ~ +70 �C
-40 ~ +85
TSTG -65 ~ +150 �C
(TA = 25�C, VCC = 5 ~ 15V, unless otherwise specified)
Parameter Symbol Conditions Min. Typ. Max. Unit
Supply Voltage VCC -
4.5 - 16 V
Supply Current (Low Stable) (Note1) ICC VCC = 5V, RL =
VCC = 15V, RL = - 3 6 mA
Timing Error (Monostable)
Initial Accuracy (Note2) - 7.5 15 mA
Drift with Temperature (Note4)
Drift with Supply Voltage (Note4) ACCUR RA = 1k to100k - 1.0 3.0 %
t/T C = 0.1�F
0.1 0.5 %/V
Timing Error (Astable) ACCUR RA = 1k to 100k - 2.25 - %
Intial Accuracy (Note2) t/T C = 0.1�F
Drift with Temperature (Note4) 150 ppm/�C
Drift with Supply Voltage (Note4) t/VCC VCC = 15V
Control Voltage VC VCC = 5V 0.3 %/V
VCC = 15V
Threshold Voltage VTH VCC = 5V 9.0 10.0 11.0 V
Threshold Current (Note3) ITH
Trigger Voltage VTR - 2.6 3.33 4.0 V
Trigger Current ITR VCC = 5V
Reset Voltage VRST VCC = 15V - 10.0 - V
Reset Current IRST VTR = 0V
- 3.33 - V
Low Output Voltage VOL -
- - 0.1 0.25 �A
High Output Voltage VOH VCC = 15V
ISINK = 10mA 1.1 1.67 2.2 V
Rise Time of Output (Note4) tR ISINK = 50mA
Fall Time of Output (Note4) tF VCC = 5V 4.5 5 5.6 V
Discharge Leakage Current ILKG ISINK = 5mA
VCC = 15V 0.01 2.0 �A
ISOURCE = 200mA
ISOURCE = 100mA 0.4 0.7 1.0 V
VCC = 5V
ISOURCE = 100mA 0.1 0.4 mA
- - 0.06 0.25 V
0.3 0.75 V
- 0.05 0.35 V
12.5 - V
12.75 13.3 V
2.75 3.3 - V
- 100 - ns
- 100 - ns
- 20 100 nA
1. When the output is high, the supply current is typically 1mA less than at VCC = 5V.
2. Tested at VCC = 5.0V and VCC = 15V.
3. This will determine the maximum value of RA + RB 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.
Table 1 below is the basic operating table of 555 timer:
Table 1. Basic Operating Table
Threshold Voltage Trigger Voltage Reset(PIN 4) Output(PIN 3) Discharging Tr.
(Vth)(PIN 6) (Vtr)(PIN 2) (PIN 7)
Don't care Don't care Low Low ON
Vth > 2Vcc / 3 Vth > 2Vcc / 3 High Low ON
Vcc / 3 < Vth < 2 Vcc / 3 Vcc / 3 < Vth < 2 Vcc / 3 High - -
Vth < Vcc / 3 Vth < Vcc / 3 High High OFF
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
4 8 101 =1k
RESET Vcc C1 R AA
Trigger DISCH 7 C2 10k 100k 1M 10M
RL 2 TRIG
THRES 6 Capacitance(uF) 100
GND CONT 5 10-2
10-5 10-4 10-3 10-2 10-1 100 101 102
Figure 1. Monoatable Circuit Figure 2. Resistance and Capacitance vs.
Figure 3. Waveforms of Monostable Operation
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, VC1 increases exponentially with the time constant t=RA*C and reaches 2Vcc/3
at td=1.1RA*C. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC, the longer it takes
for the VC1 to reach 2Vcc/3. In other words, the time constant RAC 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 RA 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.
Figure 4. Waveforms of Monostable Operation (abnormal)
2. Astable Operation
RA 100 (RA+2RB)
4 8 1 1k
RESET Vcc 100k
DISCH 7 Capacitance(uF) 1E-3
2 TRIG 100m
3 OUT C1
GND CONT 5
RL 1 C2
1 10 100 1k 10k 100k
Figure 5. Astable Circuit Figure 6. Capacitance and Resistance vs. Frequency
Figure 7. Waveforms of Astable Operation
An astable timer operation is achieved by adding resistor RB 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 VC1 increases by exponential
function with the time constant (RA+RB)*C.
When the VC1, 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 RB and the discharging Tr. When the VC1 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
VC1 rises again.
In the above process, the section where the timer output is high is the time it takes for the VC1 to rise from Vcc/3 to 2Vcc/3,
and the section where the timer output is low is the time it takes for the VC1 to drop from 2Vcc/3 to Vcc/3. When timer output
is high, the equivalent circuit for charging capacitor C1 is as follows:
Vcc C1 Vc1(0-)=Vcc/3
C1 d----v---c----1-- = V-----c---c-----�----V----(---0-------) (1)
dt RA + RB
VC1(0+) = VCC / 3 (2)
VC1(t) = � 2-- (---R-----A-----+-----Rt----B-----)--C-----1-- (3)
VC C 1
Since the duration of the timer output high state(tH) is the amount of time it takes for the VC1(t) to reach 2Vcc/3,
VC1(t) = 23-- VCC = 1 � 2-- (---R-----A-----+---t--HR----B-----)--C-----1-- (4)
3 -� (5)
tH = C1(RA + RB)In2 = 0.693(RA + RB)C1
The equivalent circuit for discharging capacitor C1, when timer output is low is, as follows:
C1 VC1(0-)=2Vcc/3 RD
C1 d----v---C-----1-- + -----------1----------- VC1 = 0 (6)
dt RA + RB
(RA + RD)C1
VC1(t) = 2-- V (7)
3 C Ce
Since the duration of the timer output low state(tL) is the amount of time it takes for the VC1(t) to reach Vcc/3,
1-- 2-- - ----------------t--L------------------
3 3 (RA + RD)C1
VC = VCCe (8)
tL = C1(RB + RD)In2 = 0.693(RB + RD)C1 (9)
Since RD is normally RB>>RD although related to the size of discharging Tr.,
Consequently, if the timer operates in astable, the period is the same with
'T=tH+tL=0.693(RA+RB)C1+0.693RBC1=0.693(RA+2RB)C1' 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.
frequency, f = -1-- = (---R-----A-----+--1---2.--4--R-4---B-----)--C-----1- (11)
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.
Figure 8. Waveforms of Frequency Divider Operation
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.
4 8 RA
Trigger RESET Vcc 7
2 TRIG DISCH
3 OUT Input
GND CONT 5 C
Figure 9. Circuit for Pulse Width Modulation Figure 10. Waveforms of Pulse Width Modulation
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.
4 8 RA
RESET Vcc 7
3 OUT Modulation
GND CONT 5 C
Figure 11. Circuit for Pulse Position Modulation Figure 12. Waveforms of pulse position modulation
6. Linear Ramp
When the pull-up resistor RA in the monostable circuit shown in Figure 1 is replaced with constant current source, the VC1
increases linearly, generating a linear ramp. Figure 13 shows the linear ramp generating circuit and Figure 14 illustrates the
generated linear ramp waveforms.
4 8 RE R1
2 TRIG DISCH 7 R2
THRES 6 C1
GND CONT 5
Figure 13. Circuit for Linear Ramp Figure 14. Waveforms of Linear Ramp
In Figure 13, current source is created by PNP transistor Q1 and resistor R1, R2, and RE.
IC = V-----C-----C-----�-----V----E-- (12)
Here, VE is
VE = VBE + --------R----2--------- VC C ( 13 )
R1 + R2
For example, if Vcc=15V, RE=20k, R1=5kW, R2=10k, and VBE=0.7V,
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 VC is a linear ramp function as shown in Figure 14. The gradient S of the linear ramp function is defined as
S = -V----p-----�----p-- ( 14 )
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 VC comes out as follows:
The above equation divided on both sides by T gives us
V--- = Q-------/--T-- ( 16 )
and may be simplified into the following equation.
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.
Mechanical Dimensions LM555/NE555/SA555
Package Dimensions in millimeters
6.40 �0.20 ( 0.79 )
0.252 �0.008 0.031
#1 #8 0.46 �0.10
MAX 9.20 �0.20
5.08 MAX 3.30 �0.30
0.200 0.130 �0.012
7.62 3.40 �0.20 0.33 MIN
0.300 0.134 �0.008 0.013
Mechanical Dimensions (Continued)
Dimensions in millimeters
8-SOP MIN 0.1~0.25
( 0.56 )
MAX 4.92 �0.20
#4 #5 0.41 �0.10
6.00 �0.30 1.80 MAX
0.236 �0.012 0.071
+0.10 3.95 �0.20 0~8�
0.15 -0.05 0.156 �0.008 MAX0.10
Ordering Information Package Operating Temperature
8-DIP 0 ~ +70�C
Product Number 8-SOP
LM555CN Operating Temperature
LM555CM Package 0 ~ +70�C
Product Number 8-SOP Operating Temperature
NE555N -40 ~ +85�C
Product Number 8-SOP
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY
PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY
LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER
DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
LIFE SUPPORT POLICY
FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems 2. A critical component in any component of a life support
which, (a) are intended for surgical implant into the body, device or system whose failure to perform can be
or (b) support or sustain life, and (c) whose failure to reasonably expected to cause the failure of the life support
perform when properly used in accordance with device or system, or to affect its safety or effectiveness.
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
11/29/02 0.0m 001
2002 Fairchild Semiconductor Corporation
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