NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUAR Y 2002
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
D
Timing From Microseconds to Hours
D
Astable or Monostable Operation
D
Adjustable Duty Cycle
D
TTL-Compatible Output Can Sink or Source
up to 200 mA
D
Designed To Be Interchangeable With
Signetics NE555, SA555, and SE555
description
These devices are precision timing circuits
capable of producing accurate time delays or
oscillation. In the time-delay or monostable mode
of operation, the timed interval is controlled by a
single external resistor and capacitor network. In
the astable mode of operation, the frequency and
duty cycle can be controlled independently with
two external resistors and a single external
capacitor.
The threshold and trigger levels normally are
two-thirds and one-third, respectively, of VCC.
These levels can be altered by use of the
control-voltage terminal. When the trigger input
falls below the trigger level, the flip-flop is set and
the output goes high. If the trigger input is above
the trigger level and the threshold input is above
the threshold level, the flip-flop is reset and the output is low. The reset (RESET) input can override all other
inputs and can be used to initiate a new timing cycle. When RESET goes low, the flip-flop is reset and the output
goes low . When the output is low, a low-impedance path is provided between discharge (DISCH) and ground.
The output circuit is capable of sinking or sourcing current up to 200 mA. Operation is specified for supplies of
5 V to 15 V. With a 5-V supply, output levels are compatible with TTL inputs.
The NE555 is characterized for operation from 0°C to 70°C. The SA555 is characterized for operation from
–40°C to 85°C. The SE555 is characterized for operation over the full military range of –55°C to 125°C.
AVAILABLE OPTIONS
PACKAGE
TAVTHRES MAX
VCC = 15 V
SMALL
OUTLINE
(D, PS)
CHIP
CARRIER
(FK)
CERAMIC
DIP
(JG)
PLASTIC
DIP
(P)
PLASTIC
THIN SHRINK
SMALL OUTLINE
(PW)
0°C to 70°C11.2 V NE555D
NE555PS — — NE555P NE555PW
–40°C to 85°C11.2 V SA555D — — SA555P —
–55°C to 125°C10.6 V SE555D SE555FK SE555JG SE555P —
The D package is available taped and reeled. Add the suffix R to the device type (e.g., NE555DR). The PS and PW packages
are only available taped and reeled.
Copyright 2002, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
2
3
4
8
7
6
5
GND
TRIG
OUT
RESET
VCC
DISCH
THRES
CONT
NE555 ...D, P, PS, OR PW PACKAGE
SA555 ...D OR P PACKAGE
SE555 . . . D, JG, OR P PACKAGE
(TOP VIEW)
32120 19
910111213
4
5
6
7
8
18
17
16
15
14
NC
DISCH
NC
THRES
NC
NC
TRIG
NC
OUT
NC
SE555 . . . FK PACKAGE
(TOP VIEW)
NC
GND
NC
CONT
NC VCC
NC
NC
RESET
NC
NC – No internal connection
On products compliant to MIL-PRF-38535, all parameters are tested
unless otherwise noted. On all other products, production
processing does not necessarily include testing of all parameters.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
2POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
FUNCTION TABLE
RESET TRIGGER
VOLTAGE†THRESHOLD
VOLTAGE†OUTPUT DISCHARGE
SWITCH
Low Irrelevant Irrelevant Low On
High <1/3 VDD Irrelevant High Off
High >1/3 VDD >2/3 VDD Low On
High >1/3 VDD <2/3 VDD As previously established
†Voltage levels shown are nominal.
functional block diagram
1
S
R
R1
TRIG
THRES
VCC CONT
RESET
OUT
DISCH
GND
Î
Î
Î
Î
ÎÎ
Î
Î
Pin numbers shown are for the D, JG, P, PS, and PW packages.
NOTE A: RESET can override TRIG, which can override THRES.
4
8
5
6
2
1
7
3
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)†
Supply voltage, VCC (see Note 1) 18 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input voltage (CONT, RESET, THRES, and TRIG) VCC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output current ±225 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Continuous total dissipation See Dissipation Rating Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Package thermal impedance, θJA (see Note 2): D package 97°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
P package 85°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PS package 95°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PW package 149°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Case temperature for 60 seconds: FK package 260°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds: D, P, PS, or PW package 260°C. . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 60 seconds: JG package 300°C. . . . . . . . . . . . . . . . . . . .
Storage temperature range, Tstg –65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
†Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only , and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may af fect device reliability.
NOTES: 1. All voltage values are with respect to GND.
2. The package thermal impedance is calculated in accordance with JESD 51-7.
DISSIPATION RATING TABLE
PACKAGE TA ≤ 25°C
POWER RATING DERATING F ACTOR
ABOVE TA = 25°CTA = 70°C
POWER RATING TA = 85°C
POWER RATING TA = 125°C
POWER RATING
FK 1375 mW 11.0 mW/°C880 mW 715 mW 275 mW
JG (SE555) 1050 mW 8.4 mW/°C672 mW 546 mW 210 mW
recommended operating conditions
MIN MAX UNIT
VCC
Su
pp
ly voltage
SA555, NE555 4.5 16
V
V
CC
Supply
voltage
SE555 4.5 18
V
VIInput voltage (CONT, RESET, THRES, and TRIG) VCC V
IOOutput current ±200 mA
NE555 0 70
TAOperating free-air temperature SA555 –40 85 °C
SE555 –55 125
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
4POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
electrical characteristics, VCC = 5 V to 15 V, TA = 25°C (unless otherwise noted)
PARAMETER TEST CONDITIONS SE555 NE555
SA555 UNIT
MIN TYP MAX MIN TYP MAX
THRES voltage level
VCC = 15 V 9.4 10 10.6 8.8 10 11.2
V
THRES
voltage
level
VCC = 5 V 2.7 3.3 4 2.4 3.3 4.2
V
THRES current (see Note 3) 30 250 30 250 nA
VCC =15V
4.8 5 5.2 4.5 5 5.6
TRIG voltage level
V
CC =
15
V
TA = –55°C to 125°C 3 6
V
TRIG
voltage
level
VCC =5V
1.45 1.67 1.9 1.1 1.67 2.2
V
V
CC =
5
V
TA = –55°C to 125°C 1.9
TRIG current TRIG at 0 V 0.5 0.9 0.5 2 µA
RESET voltage level
0.3 0.7 1 0.3 0.7 1
V
RESET
voltage
level
TA = –55°C to 125°C 1.1
V
RESET current
RESET at VCC 0.1 0.4 0.1 0.4
mA
RESET
current
RESET at 0 V –0.4 –1–0.4 –1.5
mA
DISCH switch off-state current 20 100 20 100 nA
VCC =15V
9.6 10 10.4 9 10 11
CONT voltage (o
p
en circuit)
V
CC =
15
V
TA = –55°C to 125°C 9.6 10.4
V
CONT
voltage
(open
circuit)
VCC =5V
2.9 3.3 3.8 2.6 3.3 4
V
V
CC =
5
V
TA = –55°C to 125°C 2.9 3.8
V
CC
= 15 V, 0.1 0.15 0.1 0.25
CC ,
IOL = 10 mA TA = –55°C to 125°C 0.2
V
CC
= 15 V, 0.4 0.5 0.4 0.75
CC ,
IOL = 50 mA TA = –55°C to 125°C 1
V
CC
= 15 V, 2 2.2 2 2.5
Low-level out
p
ut voltage
CC ,
IOL = 100 mA TA = –55°C to 125°C 2.7
V
Low
-
level
out ut
voltage
VCC = 15 V, IOL = 200 mA 2.5 2.5
V
VCC = 5 V,
IOL = 3.5 mA TA = –55°C to 125°C 0.35
V
CC
= 5 V, 0.1 0.2 0.1 0.35
CC ,
IOL = 5 mA TA = –55°C to 125°C 0.8
VCC = 5 V, IOL = 8 mA 0.15 0.25 0.15 0.4
V
CC
= 15 V, 13 13.3 12.75 13.3
CC ,
IOH = –100 mA TA = –55°C to 125°C 12
High-level output voltage VCC = 15 V, IOH = –200 mA 12.5 12.5 V
V
CC
= 5 V, 3 3.3 2.75 3.3
CC ,
IOH = –100 mA TA = –55°C to 125°C 2
Output low, VCC = 15 V 10 12 10 15
Su
pp
ly current
,
No load VCC = 5 V 3 5 3 6
mA
Supply
current
Output high, VCC = 15 V 9 10 9 13
mA
g
No load VCC = 5 V 2 4 2 5
NOTE 3: This parameter influences the maximum value of the timing resistors RA and RB in the circuit of Figure 12. For example, when
VCC = 5 V, the maximum value is R = RA + RB ≈ 3.4 MΩ, and for VCC = 15 V, the maximum value is 10 MΩ.
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
operating characteristics, VCC = 5 V and 15 V
PARAMETER TEST
SE555 NE555
SA555 UNIT
MIN TYP MAX MIN TYP MAX
Initial error Each timer, monostable§
0.5% 1.5%* 1% 3%
Initial
error
of timing interval‡Each timer, astable
A =
1.5% 2.25%
Temperature coefficient Each timer, monostable§
30 100* 50 pp
m/
°
C
of timing interval Each timer, astable
A =
90 150
ppm/°C
Suppl
y
-volta
g
e sensitivit
y
Each timer, monostable§
0.05 0.2* 0.1 0.5
%/V
yg y
of timing interval Each timer, astable
A =
0.15 0.3
%/V
Output-pulse rise time CL = 15 pF,
TA = 25°C100 200* 100 300 ns
Output-pulse fall time CL = 15 pF,
TA = 25°C100 200* 100 300 ns
* On products compliant to MIL-PRF-38535, this parameter is not production tested.
†For conditions shown as MIN or MAX, use the appropriate value specified under recommended operating conditions.
‡Timing interval error is defined as the difference between the measured value and the average value of a random sample from each process
run.
§Values specified are for a device in a monostable circuit similar to Figure 9, with the following component values: RA = 2 kΩ to 100 kΩ,
C = 0.1 µF.
Values specified are for a device in an astable circuit similar to Figure 12, with the following component values: RA = 1 kΩ to 100 kΩ,
C = 0.1 µF.
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
6POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS†
Figure 1
ÏÏÏÏÏ
TA = 125°C
ÏÏÏÏ
TA = 25°C
IOL – Low-Level Output Current – mA
ÏÏÏÏ
ÏÏÏÏ
VCC = 5 V
LOW-LEVEL OUTPUT VOLTAGE
vs
LOW-LEVEL OUTPUT CURRENT
ÏÏÏÏ
ÏÏÏÏ
TA = –55°C
0.1
0.04
0.01 1 2 4 7 10 20 40 70 100
0.07
1
0.4
0.7
10
4
7
0.02
0.2
2
– Low-Level Output Voltage – VVOL
Figure 2
ÏÏÏÏ
ÏÏÏÏ
VCC = 10 V
LOW-LEVEL OUTPUT VOLTAGE
vs
LOW-LEVEL OUTPUT CURRENT
– Low-Level Output Voltage – VVOL
IOL – Low-Level Output Current – mA
0.1
0.04
0.01 1 2 4 7 10 20 40 70 100
0.07
1
0.4
0.7
10
4
7
0.02
0.2
2
ÏÏÏÏÏ
TA = 125°C
ÏÏÏÏ
ÏÏÏÏ
TA = 25°C
ÏÏÏÏÏ
ÏÏÏÏÏ
TA= –55°C
Figure 3
TA = 125°C
TA = 25°C
TA = –55°C
ÏÏÏÏ
ÏÏÏÏ
VCC = 15 V
LOW-LEVEL OUTPUT VOLTAGE
vs
LOW-LEVEL OUTPUT CURRENT
– Low-Level Output Voltage – VVOL
IOL – Low-Level Output Current – mA
0.1
0.04
0.01 1 2 4 7 10 20 40 70 100
0.07
1
0.4
0.7
10
4
7
0.02
0.2
2
Figure 4
1
0.6
0.2
0
1.4
1.8
2.0
0.4
1.6
0.8
1.2
–
IOH – High-Level Output Current – mA
ÏÏÏÏ
TA = 125°C
ÏÏÏÏ
ÏÏÏÏ
TA = 25°C
100704020107421
ÏÏÏÏÏÏ
VCC = 5 V to 15 V
ÏÏÏÏ
TA = –55°C
DROP BETWEEN SUPPLY VOLTAGE AND OUTPUT
vs
HIGH-LEVEL OUTPUT CURRENT
VCC VOH – Voltage Drop – V
)
(
†Data for temperatures below 0°C and above 70°C are applicable for SE555 circuits only.
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
7
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS†
Figure 5
5
4
2
1
0
9
3
567891011
– Supply Current – mA
7
6
8
SUPPLY CURRENT
vs
SUPPLY VOLTAGE
10
12 13 14 15
TA = 25°C
TA = 125°C
TA = –55°C
Output Low ,
No Load
CC
I
VCC – Supply Voltage – V
Figure 6
1
0.995
0.990
0.9850510
1.005
1.010
NORMALIZED OUTPUT PULSE DURATION
(MONOSTABLE OPERATION)
vs
SUPPLY VOLTAGE
1.015
15 20
CC
VPulse Duration Relative to Value at = 10 V
VCC – Supply Voltage – V
Figure 7
1
0.995
0.990
0.985
–75 –25 25
1.005
1.010
NORMALIZED OUTPUT PULSE DURATION
(MONOSTABLE OPERATION)
vs
FREE-AIR TEMPERATURE
1.015
75 125
Pulse Duration Relative to Value at = 25
TA – Free-Air Temperature – °C
–50 0 50 100
VCC = 10 V
TAC
°
Figure 8
150
100
50
0
200
250
300
– Propagation Delay Time – ns
PROPAGATION DELAY TIME
vs
LOWEST VOLTAGE LEVEL
OF TRIGGER PULSE
Lowest Voltage Level of T rigger Pulse
TA = –55°C
TA = 125°C
TA = 25°C
tpd
TA = 0°C
TA = 70°C
0 0.1 × VCC 0.2 × VCC 0.3 × VCC 0.4 × VC
C
†Data for temperatures below 0°C and above 70°C are applicable for SE555 series circuits only.
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
8POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
monostable operation
For monostable operation, any of these timers can be connected as shown in Figure 9. If the output is low,
application of a negative-going pulse to the trigger (TRIG) sets the flip-flop (Q goes low), drives the output high,
and turns off Q1. Capacitor C then is charged through RA until the voltage across the capacitor reaches the
threshold voltage of the threshold (THRES) input. If TRIG has returned to a high level, the output of the threshold
comparator resets the flip-flop (Q goes high), drives the output low, and discharges C through Q1.
VCC
(5 V to 15 V)
RARL
Output
GND
OUT
VCC
CONT
RESET
DISCH
THRES
TRIGInput
Î
58
4
7
6
2
3
1
Pin numbers shown are for the D, JG, P, PS, and PW packages.
Figure 9. Circuit for Monostable Operation
Voltage – 2 V/div
Time – 0.1 ms/div
ÏÏÏÏÏÏ
Capacitor Voltage
Output Voltage
Input Voltage
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
RA = 9.1 kΩ
CL = 0.01 µF
RL = 1 kΩ
See Figure 9
Figure 10. Typical Monostable Waveforms
Monostable operation is initiated when TRIG
voltage falls below the trigger threshold. Once
initiated, the sequence ends only if TRIG is high
at the end of the timing interval. Because of the
threshold level and saturation voltage of Q1,
the output pulse duration is approximately
tw = 1.1RAC. Figure 11 is a plot of the time
constant for various values of RA and C. The
threshold levels and charge rates both are directly
proportional to the supply voltage, VCC. The timing
interval is, therefore, independent of the supply
voltage, so long as the supply voltage is constant
during the time interval.
Applying a negative-going trigger pulse
simultaneously to RESET and TRIG during the
timing interval discharges C and reinitiates the
cycle, commencing on the positive edge of the
reset pulse. The output is held low as long as the
reset pulse is low. To prevent false triggering,
when RESET is not used, it should be connected
to VCC.
– Output Pulse Duration – s
C – Capacitance – µF
10
1
10–1
10–2
10–3
10–4
1001010.10.01
10–5
0.001
tw
RA = 10 MΩ
RA = 10 kΩ
RA = 1 kΩ
RA = 100 kΩ
RA = 1 MΩ
Figure 11. Output Pulse Duration vs Capacitance
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
astable operation
As shown in Figure 12, adding a second resistor , R B, to the circuit of Figure 9 and connecting the trigger input
to the threshold input causes the timer to self-trigger and run as a multivibrator. The capacitor C charges through
RA and RB and then discharges through RB only . Therefore, the duty cycle is controlled by the values of RA and
RB.
This astable connection results in capacitor C charging and discharging between the threshold-voltage level
(≈0.67 ×VCC) and the trigger-voltage level (≈0.33 ×VCC). As in the monostable circuit, charge and discharge
times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.
GND
OUT
VCC
CONT
RESET
DISCH
THRES
TRIG
C
RB
RA
Output
RL
0.01 µF
VCC
(5 V to 15 V)
(see Note A)
ÎÎ
NOTE A: Decoupling CONT voltage to ground with a capacitor can
improve operation. This should be evaluated for individual
applications.
Open
58
4
7
6
2
3
1
Pin numbers shown are for the D, JG, P, PS, and PW packages.
Figure 12. Circuit for Astable Operation
Voltage – 1 V/div
Time – 0.5 ms/div
tH
Capacitor Voltage
Output Voltage
tL
ÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏ
RA = 5 k
W
RL = 1 k
W
RB = 3 k
W
See Figure 12
C = 0.15 µF
Figure 13. Typical Astable Waveforms
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
astable operation (continued)
Figure 13 shows typical waveforms generated during astable operation. The output high-level duration tH and
low-level duration tL can be calculated as follows:
tH
+
0.693 (RA
)
RB) C
tL
+
0.693 (RB) C
Other useful relationships are shown below.
period
+
tH
)
tL
+
0.693 (RA
)
2RB)C
frequency
[
1.44
(RA
)
2RB)C
Output driver duty cycle
+
tL
tH
)
tL
+
RB
RA
)
2RB
Output waveform duty cycle
Low t high ratio
+
tL
tH
+
RB
RA
)
RB
-o-
+
tH
tH
)
tL
+
1–RB
RA
)
2RB
f – Free-Running Frequency – Hz
C – Capacitance – µF
100 k
10 k
1 k
100
10
1
10
0
1010.10.01
0.1
0.001
RA + 2 RB = 10 MΩ
RA + 2 RB = 1 MΩ
RA + 2 RB = 100 kΩ
RA + 2 RB = 10 kΩ
RA + 2 RB = 1 kΩ
Figure 14. Free-Running Frequency
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
11
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
missing-pulse detector
The circuit shown in Figure 15 can be used to detect a missing pulse or abnormally long spacing between
consecutive pulses in a train of pulses. The timing interval of the monostable circuit is retriggered continuously
by the input pulse train as long as the pulse spacing is less than the timing interval. A longer pulse spacing,
missing pulse, or terminated pulse train permits the timing interval to be completed, thereby generating an
output pulse as shown in Figure 16.
Figure 15. Circuit for Missing-Pulse Detector
VCC (5 V to 15 V)
DISCH
OUT
VCC
RESET
RLRA
A5T3644
C
THRES
GND
CONT
TRIG
Input
0.01 µF
ÏÏÏ
Output
48
3
7
6
2
5
1
Pin numbers shown are shown for the D, JG, P, PS, and PW packages.
Figure 16. Completed-Timing Waveforms
for Missing-Pulse Detector
Time – 0.1 ms/div
Voltage – 2 V/div
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
VCC = 5 V
RA = 1 kΩ
C = 0.1 µF
See Figure 15
Capacitor Voltage
ÏÏÏÏÏ
ÏÏÏÏÏ
Output Voltage
Input Voltage
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
12 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
frequency divider
By adjusting the length of the timing cycle, the basic circuit of Figure 9 can be made to operate as a frequency
divider. Figure 17 shows a divide-by-three circuit that makes use of the fact that retriggering cannot occur during
the timing cycle.
Voltage – 2 V/div
Time – 0.1 ms/div
Capacitor Voltage
Output Voltage
Input Voltage
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
VCC = 5 V
RA = 1250 Ω
C = 0.02 µF
See Figure 9
Figure 17. Divide-by-Three Circuit Waveforms
pulse-width modulation
The operation of the timer can be modified by modulating the internal threshold and trigger voltages, which is
accomplished by applying an external voltage (or current) to CONT. Figure 18 shows a circuit for pulse-width
modulation. A continuous input pulse train triggers the monostable circuit, and a control signal modulates the
threshold voltage. Figure 19 shows the resulting output pulse-width modulation. While a sine-wave modulation
signal is illustrated, any wave shape could be used.
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
THRES
GND C
RA
RL
VCC (5 V to 15 V)
Output
DISCH
OUT
VCC
RESET
TRIG
CONT
Modulation
Input
(see Note A)
Clock
Input
NOTE A: The modulating signal can be direct or capacitively coupled
to CONT. For direct coupling, the effects of modulation
source voltage and impedance on the bias of the timer
should be considered.
48
3
7
6
2
5
Pin numbers shown are for the D, JG, P, PS, and PW packages.
1
Figure 18. Circuit for Pulse-Width Modulation
Voltage – 2 V/div
Time – 0.5 ms/div
ÏÏÏÏÏÏ
Capacitor Voltage
ÏÏÏÏÏ
ÏÏÏÏÏ
Output Voltage
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
Clock Input Voltage
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
RA = 3 kΩ
C = 0.02 µF
RL = 1 kΩ
See Figure 18
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
Modulation Input Voltage
Figure 19. Pulse-Width-Modulation Waveforms
pulse-position modulation
As shown in Figure 20, any of these timers can be used as a pulse-position modulator. This application
modulates the threshold voltage and, thereby, the time delay, of a free-running oscillator. Figure 21 shows a
triangular-wave modulation signal for such a circuit; however, any wave shape could be used.
RB
Modulation
Input
(see Note A) CONT
TRIG
RESET VCC
OUT
DISCH
VCC (5 V to 15 V)
RLRA
C
GND
THRES
NOTE A: The modulating signal can be direct or capacitively coupled
to CONT. For direct coupling, the effects of modulation
source voltage and impedance on the bias of the timer
should be considered.
Pin numbers shown are for the D, JG, P, PS, and PW packages.
48
3
7
6
2
5
Output
Figure 20. Circuit for Pulse-Position Modulation Figure 21. Pulse-Position-Modulation Waveforms
Voltage – 2 V/div
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
RA = 3 kΩ
RB = 500 Ω
RL = 1 kΩ
See Figure 20
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
Capacitor Voltage
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
Output Voltage
ÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏ
Modulation Input Voltage
Time – 0.1 ms/div
NE555, SA555, SE555
PRECISION TIMERS
SLFS022C – SEPTEMBER 1973 – REVISED FEBRUARY 2002
14 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
sequential timer
Many applications, such as computers, require signals for initializing conditions during start-up. Other
applications, such as test equipment, require activation of test signals in sequence. These timing circuits can
be connected to provide such sequential control. The timers can be used in various combinations of astable
or monostable circuit connections, with or without modulation, for extremely flexible waveform control. Figure 22
shows a sequencer circuit with possible applications in many systems, and Figure 23 shows the output
waveforms.
S
VCC
RESET VCC
OUT
DISCH
GND
CONT
TRIG
48
3
7
6
1
5
2
THRES
RC
CC
0.01
CC = 14.7 µF
RC = 100 kΩOutput C
RESET VCC
OUT
DISCH
GND
CONT
TRIG
48
3
7
6
1
5
2
THRES
RB33 kΩ
0.001
0.01
µF
CB = 4.7 µF
RB = 100 kΩ
Output BOutput A
RA = 100 kΩ
CA = 10 µF
µF
0.01
µF
0.001
33 kΩ
RA
THRES
2
5
1
6
7
3
84
TRIG
CONT
GND
DISCH
OUT
VCC
RESET
µF
µF
CB
CA
Pin numbers shown are for the D, JG, P, PS, and PW packages.
NOTE A: S closes momentarily at t = 0.
Figure 22. Sequential Timer Circuit
Voltage – 5 V/div
t – Time – 1 s/div
ÏÏÏÏÏ
See Figure 22
ÏÏÏ
Output A
ÏÏÏ
ÏÏÏ
Output B
ÏÏÏ
Output C
ÏÏÏ
t = 0
ÏÏÏÏÏ
twC = 1.1 RCCC
ÏÏ
twC
ÏÏÏÏÏ
twB = 1.1 RBCB
ÏÏÏÏÏÏ
twA = 1.1 RACA
ÏÏ
ÏÏ
twA
ÏÏÏ
ÏÏÏ
twB
Figure 23. Sequential Timer Waveforms
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