555 timer IC explained

555 timer IC
Type:Active, integrated circuit
Invented:Hans Camenzind (1971)
First Produced:1972
Symbol Caption:Internal block diagram

The 555 timer IC is an integrated circuit used in a variety of timer, delay, pulse generation, and oscillator applications. It is one of the most popular timing ICs due to its flexibility and price. Derivatives provide two (556) or four (558) timing circuits in one package. The design was first marketed in 1972 by Signetics[1] and used bipolar junction transistors. Since then, numerous companies have made the original timers and later similar low-power CMOS timers. In 2017, it was said that over a billion 555 timers are produced annually by some estimates, and that the design was "probably the most popular integrated circuit ever made".[2]

History

The timer IC was designed in 1971 by Hans Camenzind under contract to Signetics.[1] In 1968, he was hired by Signetics to develop a phase-locked loop (PLL) IC. He designed an oscillator for PLLs such that the frequency did not depend on the power supply voltage or temperature. Signetics subsequently laid off half of its employees due to the 1970 recession, and development on the PLL was thus frozen.[3] Camenzind proposed the development of a universal circuit based on the oscillator for PLLs and asked that he develop it alone, borrowing equipment from Signetics instead of having his pay cut in half. Camenzind's idea was originally rejected, since other engineers argued the product could be built from existing parts sold by the company; however, the marketing manager approved the idea.[4]

The first design for the 555 was reviewed in the summer of 1971. After this design was tested and found to be without errors, Camenzind got the idea of using a direct resistance instead of a constant current source, finding that it worked satisfactorily. The design change decreased the required 9 external pins to 8, so the IC could be fit in an 8-pin package instead of a 14-pin package. This revised version passed a second design review, and the prototypes were completed in October 1971 as the NE555V (plastic DIP) and SE555T (metal TO-5).[5] The 9-pin version had already been released by another company founded by an engineer who had attended the first review and had retired from Signetics; that firm withdrew its version soon after the 555 was released. The 555 timer was manufactured by 12 companies in 1972, and it became a best-selling product.[3]

The 555 found many applications beyond timers. Camenzind noted in 1997 that "nine out of 10 of its applications were in areas and ways I had never contemplated. For months I was inundated by phone calls from engineers who had new ideas for using the device."

Name

Several books report the name "555" timer IC derived from the three 5 kΩ resistors inside the chip.[6] [7] [8] However, in a recorded interview with an online transistor museum curator,[9] Hans Camenzind said "It was just arbitrarily chosen. It was Art Fury (marketing manager) who thought the circuit was gonna sell big who picked the name '555' timer IC.."[10]

Design

Depending on the manufacturer, the standard 555 package incorporated the equivalent of 25 transistors, 2 diodes, and 15 resistors on a silicon chip packaged into an 8-pin dual in-line package (DIP-8).[11] Variants available included the 556 (a DIP-14 combining two complete 555s on one chip), and 558 / 559 (both variants were a DIP-16 combining four reduced-functionality timers on one chip).

The NE555 parts were commercial temperature range, 0 °C to +70 °C, and the SE555 part number designated the military temperature range, −55 °C to +125 °C. These chips were available in both high-reliability metal can (T package) and inexpensive epoxy plastic (V package) form factors. Thus, the full part numbers were NE555V, NE555T, SE555V, and SE555T.

Low-power CMOS versions of the 555 are now available, such as the Intersil ICM7555 and Texas Instruments LMC555, TLC555, TLC551.

Internal schematic

The internal block diagram and schematic of the 555 timer are highlighted with the same color across all three drawings to clarify how the chip is implemented:

Pinout

The pinout of the 8-pin 555 timer and 14-pin 556 dual timer are shown in the following table. Since the 556 is conceptually two 555 timers that share power pins, the pin numbers for each half are split across two columns.

555 pin# 556 556 Pin name Pin direction Pin description
Ground supply: this pin is the ground reference voltage (zero volts).
Trigger: when VTRIGGER falls below VCONTROL (VCC, except when CONTROL is driven by an external signal), OUTPUT goes to the high state and a timing interval starts. As long as TRIGGER continues to be kept at a low voltage, OUTPUT will remain in the high state.
Output: this pin is a push-pull (P.P.) output that is driven to either a low state (GND) or a high state (VCC minus approximately 1.7 volts for bipolar timers, or VCC for CMOS timers).
Reset: a timing interval may be reset by driving this pin to GND, but the timing does not begin again until this pin rises above approximately 0.7 volts. This pin overrides, which in turn overrides THRESHOLD. If this pin is not used, it should be connected to VCC to prevent electrical noise accidentally causing a reset.[12] [13]
Control: this pin provides access to the internal voltage divider (VCC by default). By applying a voltage to this pin, the timing characteristics can be changed. In astable mode, this pin can be used to frequency-modulate the OUTPUT state. If this pin is not used, it should be connected to a 10 nF decoupling capacitor (between this pin and GND) to ensure electrical noise doesn't affect the internal voltage divider.
Threshold: when the voltage at this pin is greater than VCONTROL (VCC by default except when CONTROL is driven by an external signal), then the OUTPUT high state timing interval ends, causing OUTPUT to go to the low state.
Discharge: This pin is an open-collector (O.C.) output for bipolar timers, or an open-drain (O.D.) output for CMOS timers. This pin can be used to discharge a capacitor when OUTPUT is low. In bistable latch and bistable inverter modes, this pin is unused, which allows it to be used as an alternate output.
Positive supply: For bipolar timers, the supply voltage range is typically 4.5 to 16 volts (some are spec'ed for up to 18 volts, though most will operate as low as 3 volts). For CMOS timers, the supply voltage range is typically 2 to 15 volts (some are spec'ed for up to 18 volts, and some are spec'ed as low as 1 volt). See the supply min and max columns in the derivatives table in this article. Decoupling capacitor(s) are generally applied (between this pin and GND) as a good practice.[14]

Modes

The 555 IC has the following operating modes:

  1. Astable (free-running) mode – The 555 operates as an electronic oscillator. Applications include:
  2. Monostable (one-shot) mode – The 555 operates as a "one-shot" pulse generator. Applications include:
    • timers, missing pulse detection, bounce-free switches, touch switches, frequency dividers, triggered measurement of resistance or capacitance, PWM, etc.
  3. Bistable (latch) mode – The 555 operates as a set-reset latch. Applications include:
    • switch debouncing.
  4. Schmitt trigger (inverter) mode – the 555 operates as a Schmitt trigger inverter gate. Application:
    • Converts a noisy input into a clean digital output.

Astable

See also: Electronic oscillator.

+ Astable mode examples with common valuesR2 Duty cycle
0.1Hz (+0.048%) 100μF 8.2kΩ 68kΩ 52.8%
1Hz (+0.048%) 10μF 8.2kΩ 68kΩ 52.8%
10Hz (+0.048%) 1μF 8.2kΩ 68kΩ 52.8%
100Hz (+0.048%) 100nF 8.2kΩ 68kΩ 52.8%
1kHz (+0.048%) 10nF 8.2kΩ 68kΩ 52.8%
10kHz (+0.048%) 1nF 8.2kΩ 68kΩ 52.8%
100kHz (+0.048%) 100pF 8.2kΩ 68kΩ 52.8%

In the astable configuration, the 555 timer puts out a continuous stream of rectangular pulses having a specific period.

The astable configuration is implemented using two resistors,

R1

and

R2,

and one capacitor

C

. The threshold and trigger pins are both connected to the capacitor; thus they have the same voltage.

Its repeated operating cycle (starting with the capacitor uncharged) is:

  1. Since the capacitor's voltage will be below  VCC, the trigger pin causes the 555's internal latch to change state, causing OUT to go high and the internal discharge transistor to cut-off.
  2. Since the discharge pin is no longer short-circuited to ground, the capacitor starts charging via current from Vcc through the resistors

R1

and

R2

.
  1. Once the capacitor charge reaches  Vcc, the threshold pin causes the 555's internal latch to change state, causing OUT to go low and the internal discharge transistor to go into saturation (maximal-conductivity) mode.
  2. This discharge transistor provides a discharge path, so the capacitor starts discharging through

R2

.
  1. Once the capacitor's voltage drops below  VCC, the cycle repeats from step 1.

During the first pulse, the capacitor charges from 0 V to  VCC, however, in later pulses, it only charges from  VCC to  VCC. Consequently, the first pulse has a longer high time interval compared to later pulses. Moreover, the capacitor charges through both resistors but only discharges through

R2

, thus the output high interval is longer than the low interval. This is shown in the following equations:

The output high time interval of each pulse is given by:

thigh=ln(2)(R1+R2)C

The output low time interval of each pulse is given by:

tlow=ln(2)R2C

f

of the pulse is given by:

f=

1
thigh+tlow

=

1
ln(2)(R1+2R2)C

D

is given by:

D~(\%)=

thigh
thigh+tlow

100=

R1+R2
R1+2R2

100

where

t

is the time in seconds,

R

is the resistance in ohms,

C

is the capacitance in farads, and

ln(2)

is the natural logarithm of 2.

Resistor

R1

requirements:

R1

must be greater than
{VCC
2}{R

1}

, per Ohm's law.

Shorter duty cycle

To create an output high time shorter than the low time (i.e., a duty cycle less than 50%) a fast diode (i.e. 1N4148 signal diode) can be placed in parallel with R2, with the cathode on the capacitor side. This bypasses R2 during the high part of the cycle, so that the high interval depends only on R1 and C, with an adjustment based on the voltage drop across the diode. The low time is unaffected by the diode and so remains \ln(2) \, R_2 \, C \, . But the diode's forward voltage drop Vdiode slows charging on the capacitor, so the high time is longer than the often-cited \ln(2) \, R_1 \, C to become:

thigh=ln\left(

2VCC-3Vdiode
VCC-3Vdiode

\right)R1C,

where Vdiode is when the diode's "on" current is of VCC/R1 (which depends on the type of diode and can be found in datasheets or measured). When Vdiode is small relative to Vcc, this charging is faster and approaches \ln(2) \, R_1 \, C but is slower the closer Vdiode is to Vcc:

As an extreme example, when VCC = 5 V, and Vdiode = 0.7 V, high time is 1.00 R1C, which is 45% longer than the "expected" 0.693 R1C. At the other extreme, when Vcc = 15 V, and Vdiode = 0.3 V, the high time is 0.725 R1C, which is closer to the expected 0.693 R1C. The equation approaches 0.693 R1C as Vdiode approaches 0 V.

Voltage-controlled pulse-width modulation

In the previous example schematics, the control pin was not used, thus it should connected to ground through a 10 nF decoupling capacitor to shunt electrical noise. However if a time-varying voltage source was applied to the control pin, then the pulse widths would be dependent on the control voltage.

Monostable

See also: RC circuit.

Monostable mode produces an output pulse when the trigger signals drops below VCC. An RC circuit sets the output pulse's duration as the time

t

in seconds it takes to charge C to VCC:

t=ln(3)RC,

where

R

is the resistance in ohms,

C

is the capacitance in farads,

ln(3)

is the natural log of 3 constant. The output pulse duration can be lengthened or shortened as desired by adjusting the values of R and C. Subsequent triggering before the end of this timing interval won't affect the output pulse.

Example Values

+ Monostable mode examples with common valuesR
100 μs (−0.026%) 1 nF 91 kΩ
1 ms (−0.026%) 10 nF 91 kΩ
10 ms (−0.026%) 100 nF 91 kΩ
100 ms (−0.026%) 1 μF 91 kΩ
1 s (−0.026%) 10 μF 91 kΩ
10 s (−0.026%) 100 μF 91 kΩ

The timing table (right) shows common electronic component value solutions for various powers of 10 timings.

Scaling R and C by opposite powers of 10 will provide the same timing. For instance:

For each row in the example table (right), additional timing values can easily be created by adding one to three of the same resistor value in parallel and/or series. A second resistor in parallel, the new timing is half the table time. A second resistor in series, the new timing is double the table time.

Bistable SR latch

A 555 timer can act as an active-low SR latch (though without an inverted output) with two outputs: output pin is a push-pull output, discharge pin is an open-collector output (requires a pull-up resistor).

For the schematic on the right, a input signal connects to the pin and connecting a input signal to the pin. Thus, pulling momentarily low acts as a "set" and transitions the output to the high state (VCC). Conversely, pulling momentarily low acts as a "reset" and transitions the Out pin to the low state (GND).

No timing capacitors are required in a bistable configuration. The threshold input is grounded because it is unused.[15] The trigger and reset inputs may be held high via pull-up resistors if they are normally Hi-Z and only enabled by connecting to ground.

Bistable schmitt trigger inverter gate

See also: Inverter gate.

A 555 timer can be used to create a Schmitt trigger inverter gate with two outputs: output pin is a push-pull output, discharge pin is an open-collector output (requires a pull-up resistor).

For the schematic on the right, an input signal is AC-coupled through a low value series capacitor, then biased by identical high-resistance resistors

R1

and

R2

, which causes the signal to be centered at Vcc. This centered signal is connected to both the trigger and threshold input pins of the timer. The input signal must be strong enough to excite the trigger levels of the comparators to exceed the lower VCC and upper VCC thresholds in order to cause them to change state, thus providing the schmitt trigger feature.[16]

No timing capacitors are required in a bistable configuration.

Packages

In 1972, Signetics originally released the 555 timer in DIP-8 and TO5-8 metal can packages, and the 556 timer was released in a DIP-14 package.

In 2006, the dual 556 timer was available in through-hole packages as DIP-14 (2.54 mm pitch), and surface-mount packages as SO-14 (1.27 mm pitch) and SSOP-14 (0.65 mm pitch).

In 2012, the 555 was available in through-hole packages as DIP-8 (2.54 mm pitch), and surface-mount packages as SO-8 (1.27 mm pitch), SSOP-8 / TSSOP-8 / VSSOP-8 (0.65 mm pitch), BGA (0.5 mm pitch).

The MIC1555 is a CMOS 555-type timer with three fewer pins available in SOT23-5 (0.95 mm pitch) surface-mount package.

Specifications

These specifications apply to the original bipolar NE555. Other 555 timers can have different specifications depending on the grade (industrial, military, medical, etc.).

Part numberNE555
IC ProcessBipolar
Supply voltage (VCC)4.5 to 16 V
Supply current (VCC = +5 V)3 to 6 mA
Supply current (VCC = +15 V)10 to 15 mA
Output current (maximum)200 mA
Maximum Power dissipation600 mW
Power consumption (minimum operating)30 mW @ 5 V,
225 mW @ 15 V
Operating temperature0 to 70 °C

Derivatives

Numerous companies have manufactured one or more variants of the 555, 556, 558 timers over the past decades, under many different part numbers. The following is a partial list:

Manufacturer Part
number
Production
status
IC
process
Timers
total
Supply
min. (volt)
Supply
max. (volt)
Iq (μA)
at 5 V
supply
Frequency
max. (MHz)
Remarks Datasheet
Custom Silicon Solutions (CSS) CSS555 1 1.2 5.5 4.3 1.0 Internal EEPROM, requires programmer [17] [18] [19]
ZSCT1555 Bipolar 1 0.9 6 150 0.33 [20]
Japan Radio Company (JRC) NJM555 Bipolar 1 4.5 16 3000 0.1* Also available in SIP-8 package. [21]
MIC1555/7 CMOS 1* 2.7 18 240 5.0* Reduced pins & features (only astable & monostable & no reset for MIC1555, astable only for MIC1557), only available in SOT23-5, TSOT23-5, UTDFN-10 packages. [22]
MC1455 Bipolar 1 4.5 16 3000 0.1* [23]
ICM7555 CMOS 1 2 18 40 1.0 [24]
Renesas ICM7556 CMOS 2 2 18 80 1.0
Signetics NE555 Bipolar 1 4.5 16 3000 0.1* First 555 timer, DIP-8 or TO5-8 packages. [25] [26] [27] [28]
Signetics NE556 Bipolar 2 4.5 16 6000 0.1* First 556 timer, DIP-14 package.
Signetics NE558 Bipolar 4* 4.5 16 4800* 0.1* First 558 timer, DIP-16 package.
STMicroelectronics (ST) TS555 CMOS 1 2 16 110 2.7 [29]
Texas Instruments (TI) LM555 Bipolar 1 4.5 16 3000 0.1 [30]
Texas Instruments LM556 Bipolar 2 4.5 16 6000 0.1 [31]
Texas Instruments LMC555 CMOS 1 1.5 15 100 3.0 Also available in DSBGA-8 package. [32]
Texas Instruments NE555 Bipolar 1 4.5 16 3000 0.1* [33]
Texas Instruments NE556 Bipolar 2 4.5 16 6000 0.1* [34]
Texas Instruments TLC551 CMOS 1 1 15 170 1.8 [35]
Texas Instruments TLC552 CMOS 2 1 15 340 1.8 [36]
Texas Instruments TLC555 CMOS 1 2 15 170 2.1 [37]
Texas Instruments TLC556 CMOS 2 2 15 340 2.1 [38]
X-REL XTR655 1 2.8 5.5 170 4.0 Extreme (−60 °C to +230 °C), ceramic DIP-8 package or bare die. [39]
Table notes

556 dual timer

The dual version is called 556. It features two complete 555 timers in a 14-pin package; only the two power-supply pins are shared between the two timers.[34] [26] In 2020, the bipolar version was available as the NE556,[34] and the CMOS versions were available as the Intersil ICM7556 and Texas Instruments TLC556 and TLC552. See derivatives table in this article.[24] [38] [36]

558 quad timer

The quad version is called 558 and has four reduced-functionality timers in a 16-pin package designed primarily for monostable multivibrator applications.[49] [28] By 2014, many versions of 16-pin NE558 have become obsolete.[50]

Partial list of differences between 558 and 555 chips:[28]

See also

Further reading

Books
Books with timer chapters
Datasheets

External links

Notes and References

  1. News: Fuller. Brian. 15 August 2012. Hans Camenzind, 555 timer inventor, dies. EE Times. 27 December 2016.
  2. Book: Lowe, Doug. Electronics All-in-One For Dummies. 2017-02-06. Wiley . 978-1-119-32079-1. 339. The 555 timer chip, developed in 1970, is probably the most popular integrated circuit ever made. By some estimates, more than a billion of them are manufactured every year..
  3. Carmenzind. Hans. 三宅. 和司. 2010. タイマIC 555 誕生秘話. The birth of the 555 timer IC. トランジスタ技術 (Transistor Technology). ja. CQ出版. 47. 12. 73, 74. 0040-9413.
  4. Brian . Santo. 25 Microchips That Shook the World. May 2009 . IEEE Spectrum. 46. 5. 34–43. 10.1109/MSPEC.2009.4907384. 20539726.
  5. Web site: The 555 Timer IC – An Interview with Hans Camenzind . Ward . Jack . 2004 . The Semiconductor Museum . 2010-04-05.
  6. Book: Scherz. Paul. Practical Electronics for Inventors . 4th . Monk. Simon. 2016 . McGraw Hill . 978-1-259-58755-9. 687. The 555 gets its name from the three 5-kW +VCC R1 discharging path 555 R 2 C 6 resistors shown in the block diagram. These resistors act as a three-step voltage..
  7. Book: Kleitz, William. Digital electronics : a practical approach. Prentice Hall. 1990. 0-13-211657-X. 2nd. 401. 20218185. The 555 got its name from the three 5-kOhm resistors.
  8. Book: Simpson, Colin D. . Industrial electronics. Prentice Hall. 1996. 0-02-410622-4. 357. 33014077. The reference voltage for the comparators is established by a voltage divider consisting of three 5 - k2 resistors, which is where the name 555 is derived.
  9. Harry . GoldStein . March 3, 2003. The Irresistible Transistor. 2020-08-29. IEEE Spectrum. 40 . 3 . 42–47 . 10.1109/MSPEC.2003.1184435 .
  10. Web site: Oral History Hans Camenzind Historic 555 IC Page2. 2020-08-28. The Semiconductor Museum.
  11. Web site: Oral History Hans Camenzind Historic 555 Integrated Circuit Page6 . Semiconductor Museum . 2022-02-27.
  12. Book: Lancaster . Don . Don Lancaster . TTL Cookbook . 1974 . Sams . 978-0672210358 .
  13. Book: Jung . Walt . Walt Jung . IC Timer Cookbook . 1977 . Sams Publishing . 978-0672219320 . 1.
  14. Book: Carr, Joseph. Linear IC Applications: A Designer's Handbook. 1996-12-19. Newnes. 978-0-7506-3370-3. 119. en.
  15. Book: Buiting, Jan . 308 Circuits . 2003 . Elektor International Media . 978-0-905705-66-8 . en.
  16. Web site: 555 Timer as Schmitt Trigger . Electronics Hub . https://web.archive.org/web/20230315063926/https://www.electronicshub.org/555-timer-as-schmitt-trigger/ . March 15, 2023 . June 19, 2015 . live.
  17. Web site: CSS555 Datasheet . July 2012 . Custom Silicon Solutions . https://web.archive.org/web/20170629194001/http://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555_Spec_2.pdf . June 29, 2017 . live.
  18. Web site: CSS555 Part Search . Jameco Electronics .
  19. James . Senft . The Remarkable CSS555 . Nuts & Volts Magazine . https://web.archive.org/web/20200527061138/https://www.nutsvolts.com/magazine/article/february2016_CSS555TimerICs . May 27, 2020 . February 2016 . live.
  20. Web site: ZSCT1555 Datasheet . July 2006 . . https://web.archive.org/web/20170629181234/https://www.diodes.com/assets/Datasheets/ZSCT1555.pdf . June 29, 2017 . live.
  21. Web site: NJM555 Datasheet . November 2012 . . https://web.archive.org/web/20170629170934/http://www.njr.com/semicon/PDF/NJM555_E.pdf . June 29, 2017 . dead.
  22. Web site: MIC1555 Datasheet . March 2017 . . https://web.archive.org/web/20210421210319/http://ww1.microchip.com/downloads/en/DeviceDoc/20005730A.pdf . April 21, 2021 . live.
  23. Web site: MC1455 Datasheet . December 2009 . ON Semiconductor . https://web.archive.org/web/20200522114538/https://www.onsemi.com/pub/Collateral/MC1455-D.PDF . May 22, 2020 . live.
  24. Web site: ICM7555-556 Datasheet . June 2016 . . https://web.archive.org/web/20170629211905/http://www.intersil.com/content/dam/Intersil/documents/icm7/icm7555-56.pdf . June 29, 2017 . dead.
  25. Web site: Linear Vol1 Databook . 1972 . Signetics.
  26. Web site: 555/556 Timers Databook . 1973 . . https://web.archive.org/web/20210511041359/https://www.rfcafe.com/miscellany/cool-products/Signetics-555-556-Timer-1973-Databook.pdf . May 11, 2021 . live.
  27. Web site: Analog Applications Manual . 1979 . Signetics.
  28. Web site: Linear LSI Data and Applications Manual . 1985 . Signetics.
  29. Web site: TS555 Datasheet . June 2015 . . https://web.archive.org/web/20200526095316/https://www.st.com/content/ccc/resource/technical/document/datasheet/45/d5/c6/11/46/d3/4b/a3/CD00000893.pdf/files/CD00000893.pdf/jcr:content/translations/en.CD00000893.pdf . May 26, 2020 . live.
  30. Web site: LM555 Datasheet . January 2015 . . https://web.archive.org/web/20170629043122/http://www.ti.com/lit/ds/symlink/lm555.pdf . June 29, 2017 . live.
  31. Web site: LM556 Datasheet . October 2015 . . https://web.archive.org/web/20170629111822/http://www.ti.com/lit/ds/symlink/lm556.pdf . June 29, 2017 . dead .
  32. Web site: LMC555 Datasheet . July 2016 . . https://web.archive.org/web/20170628232001/http://www.ti.com/lit/ds/symlink/lmc555.pdf . June 28, 2017 . live.
  33. Web site: NE555 Datasheet . September 2014 . . https://web.archive.org/web/20170628232239/http://www.ti.com/lit/ds/symlink/ne555.pdf . June 28, 2017 . live.
  34. Web site: NE556 Datasheet . June 2006 . . https://web.archive.org/web/20170629045640/http://www.ti.com/lit/ds/symlink/ne556.pdf . June 29, 2017 . live.
  35. Web site: TLC551 Datasheet . September 1997 . . https://web.archive.org/web/20170629111015/http://www.ti.com/lit/ds/symlink/tlc551.pdf . June 29, 2017 . live.
  36. Web site: TLC552 Datasheet . May 1988 . . https://web.archive.org/web/20170629111022/http://www.ti.com/lit/ds/symlink/tlc552.pdf . June 29, 2017 . live.
  37. Web site: TLC555 Datasheet . August 2016 . . https://web.archive.org/web/20170628232326/http://www.ti.com/lit/ds/symlink/tlc555.pdf . June 28, 2017 . live.
  38. Web site: TLC556 Datasheet . September 1997 . . https://web.archive.org/web/20170629111759/http://www.ti.com/lit/ds/symlink/tlc556.pdf . June 29, 2017 . live.
  39. Web site: XTR655 Datasheet . August 2021 . X-REL Semiconductor . https://web.archive.org/web/20230710152544/https://www.easii-ic.com/wp-content/uploads/2021/08/EASii-IC-DS-XTR650-Versatile-Timer-Rev-3-August-21-DS-00100-11.pdf . July 10, 2023 . live.
  40. Book: Reick, Ullrich . Zeitgeber-IS B 555 / B 556 . de . Halbleiterwerk Frankfurt (Oder) . 1986-03-01 .
  41. Web site: ON Semiconductor Successfully Completes Acquisition of Fairchild Semiconductor . . https://web.archive.org/web/20200128124808/https://www.businesswire.com/news/home/20160919005796/en/Semiconductor-Successfully-Completes-Acquisition-Fairchild-Semiconductor-2.4 . January 28, 2020 . September 19, 2016 . live.
  42. Web site: Former Motorola group emerges as ON Semiconductor . . https://web.archive.org/web/20200608011400/https://www.eetimes.com/former-motorola-group-emerges-as-on-semiconductor/ . June 8, 2020 . August 5, 1999 . live.
  43. Web site: Renesas and Intersil Announce Final Regulatory Approval for Renesas' Acquisition of Intersil . . https://web.archive.org/web/20200613181551/https://www.renesas.com/us/en/about/press-center/news/2017/news20170222.html . June 13, 2020 . February 22, 2017 . live.
  44. Web site: Microchip Technology Completes Micrel Acquisition . Power Electronics . https://web.archive.org/web/20200522100320/https://www.powerelectronics.com/news/industry/article/21862805/microchip-technology-completes-micrel-acquisition . May 22, 2020 . August 12, 2015 . live.
  45. Web site: Texas Instruments completes acquisition of National Semiconductor . . https://web.archive.org/web/20200522101031/https://investor.ti.com/news-releases/news-release-details/texas-instruments-completes-acquisition-national-semiconductor . May 22, 2020 . September 23, 2011 . live.
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  47. Web site: Diodes Incorporated closes acquisition of Zetex . LEDs Magazine . https://web.archive.org/web/20200522102057/https://www.ledsmagazine.com/leds-ssl-design/driver-ics/article/16697918/diodes-incorporated-closes-acquisition-of-zetex-plc . May 22, 2020 . June 13, 2008 . live.
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