Editing 555 timer IC (section)

==Design==
Depending on the manufacturer, the standard 555 package incorporated the equivalent of 25 [[transistor]]s, 2 [[diode]]s, and 15 [[resistor]]s on a [[silicon]] chip packaged into an 8-pin [[dual in-line package]] (DIP-8).<ref>{{cite web |title=Oral History Hans Camenzind Historic 555 Integrated Circuit Page6 |url=http://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page6.htm |website=Semiconductor Museum |access-date=2022-02-27}}</ref> Variants available included the 556 (a DIP-14 combining two complete 555s on one chip),<ref name="Signetics_1973_555-556_Databook"/> and 558 / 559 (both variants were a DIP-16 combining four reduced-functionality timers on one chip).<ref name="Signetics_1985_Linear_Databook"/>

The '''NE555''' parts were commercial temperature range, 0&nbsp;°C to +70&nbsp;°C, and the '''SE555''' part number designated the military temperature range, −55&nbsp;°C to +125&nbsp;°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.<ref name="Intersil_ICM7555-556_Datasheet"/><ref name="TI_LMC555_Datasheet"/><ref name="TI_TLC555_Datasheet"/><ref name="TI_TLC551_Datasheet"/>

=== 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:<ref name="Signetics_1985_Linear_Databook"/>
* {{font color||#D5FFD5|Voltage divider}}: Between the positive [[Voltage source|supply voltage]] V<sub>CC</sub> and the [[Ground (electricity)|ground]] GND is a [[voltage divider]] consisting of three identical [[resistor]]s (5{{nbsp}}[[ohm|kΩ]] for bipolar timers, 100{{nbsp}}kΩ or higher for CMOS) to create reference voltages for the [[analog comparator]]s. CONTROL is connected between the upper two resistors, allowing an external voltage to control the reference voltages:
** When CONTROL is not driven, this divider creates an upper reference voltage of {{frac|2|3}} V<sub>CC</sub> and a lower reference voltage of {{frac|1|3}} V<sub>CC</sub>.
** When CONTROL is driven, the upper reference voltage will instead be V<sub>CONTROL</sub> and the lower reference voltage will be {{frac|1|2}} V<sub>CONTROL</sub>.
* {{font color||#FFEEAA|Threshold comparator}}: The [[comparator]]'s negative input is connected to voltage divider's upper reference voltage, and the comparator's positive input is connected to THRESHOLD.
* {{font color||#FFAAAA|Trigger comparator}}: The [[comparator]]'s positive input is connected to voltage divider's lower reference, and the comparator's negative input is connected to TRIGGER.
* {{font color||#AAAAFF|Latch}}: A [[Set-Reset latch|set-reset latch]] stores the [[State (computer science)|state]] of the timer and is controlled by the two comparators. RESET overrides the other two inputs, thus the latch (and therefore the entire timer) can be reset at any time.
* {{font color||#FFAAEE|Output}}: The output of the latch is followed by an output stage with [[Push–pull output|push{{ndash}}pull]] output drivers that can supply up to 200{{nbsp}}mA for bipolar timers, lower for CMOS timers.
* {{font color||#AAEEFF|Discharge}}: Also, the output of the latch controls a [[transistor]] acting as an [[electronic switch]] that connects DISCHARGE to ground.

<gallery mode="packed" widths="200px" heights="200px">
File:NE555 Bloc Diagram.svg|555 internal block diagram<ref name="TI_NE555_Datasheet"/>
File:NE555 Internal Circuit.svg|555 internal schematic of bipolar version
File:C555 Internal Circuit.svg|555 internal schematic of CMOS version
</gallery>

===Pinout===
The [[pinout]] of the 8-pin 555 timer<ref name="TI_NE555_Datasheet"/> and 14-pin 556 dual timer<ref name="TI_NE556_Datasheet"/> 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.<ref name="Signetics_1985_Linear_Databook"/>

{| class="wikitable"
! 555 pin# !! 556 {{Nowrap|(unit 1)}} !! 556 {{Nowrap|(unit 2)}} !! Pin name !! Pin direction !! Pin description<ref name="TI_NE555_Datasheet"/><ref name="TI_NE556_Datasheet"/><ref name="Signetics_1985_Linear_Databook"/>
|-
| {{yes|1}} || colspan="2" | {{center|7}} || {{center|GND}} || {{center|Power}}
|| Ground supply: this pin is the [[Ground (electricity)#Electronics|ground]] reference voltage (zero volts).<ref name="Book-IC-Timer-Cookbook"/>
|-
| {{yes|2}} || {{center|6}} || {{center|8}} || {{center|{{overline|TRIGGER}}}} || {{center|Input}}
|| Trigger: when ''V''<sub>TRIGGER</sub> falls below {{Frac|1|2}} ''V''<sub>CONTROL</sub> ({{Frac|1|3}} ''V''<sub>CC</sub>, except when CONTROL is driven by an external signal), OUTPUT goes to the high state and a timing interval starts.<ref name="Book-IC-Timer-Cookbook"/> As long as TRIGGER continues to be kept at a low voltage, OUTPUT will remain in the high state.
|-
| {{yes|3}} || {{center|5}} || {{center|9}} || {{center|OUTPUT}} || {{center|Output}}
|| Output: this pin is a [[push-pull output|push-pull]] (P.P.) output that is driven to either a low state (GND) or a high state (''V''<sub>CC</sub> minus approximately 1.7 volts for bipolar timers, or ''V''<sub>CC</sub> for CMOS timers).  
|-
| {{yes|4}} || {{center|4}} || {{center|10}} || {{center|{{overline|RESET}}}} || {{center|Input}}
|| 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 {{overline|TRIGGER}}, which in turn overrides THRESHOLD. If this pin is not used, it should be connected to ''V''<sub>CC</sub> to prevent electrical noise accidentally causing a reset.<ref name="Book-TTL-Cookbook">{{cite book |last1=Lancaster |first1=Don |author-link=Don Lancaster |title=TTL Cookbook |date=1974 |publisher=Sams |isbn=978-0672210358 }}</ref><ref name="Book-IC-Timer-Cookbook">{{cite book |last1=Jung |first1=Walt |author-link=Walt Jung |title=IC Timer Cookbook |date=1977 |publisher=Sams Publishing |isbn=978-0672219320 |edition=1}}</ref>
|-
| {{yes|5}} || {{center|3}} || {{center|11}} || {{center|CONTROL}} || {{center|Input}}
|| Control: this pin provides access to the internal [[voltage divider]] ({{Frac|2|3}} ''V''<sub>CC</sub> 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.<ref name="Signetics_1973_555-556_Databook"/>  If this pin is not used, it should be connected to a 10 [[Farad|nF]] [[decoupling capacitor]] (between this pin and GND) to ensure electrical noise doesn't affect the internal voltage divider.<ref name="Signetics_1985_Linear_Databook"/><ref name="Book-TTL-Cookbook"/><ref name="Book-IC-Timer-Cookbook"/>
|-
| {{yes|6}} || {{center|2}} || {{center|12}} || {{center|THRESHOLD}} || {{center|Input}}
|| Threshold: when the voltage at this pin is greater than ''V''<sub>CONTROL</sub> ({{Frac|2|3}} ''V''<sub>CC</sub> 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.<ref name="Book-IC-Timer-Cookbook"/>
|-
| {{yes|7}} || {{center|1}} || {{center|13}} || {{center|DISCHARGE}} || {{center|Output}}
|| 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.<ref name="Book-IC-Timer-Cookbook"/>
|-
| {{yes|8}} || colspan="2" | {{center|14}} || {{center|''V''<sub>CC</sub>}} || {{center|Power}}
|| 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|derivatives table]] in this article. [[Decoupling capacitor]](s) are generally applied (between this pin and GND) as a good practice.<ref>{{Cite book|last=Carr|first=Joseph|url=https://books.google.com/books?id=DyX_dKLyZVwC&q=555+%22decoupling+capacitor%22&pg=PA119|title=Linear IC Applications: A Designer's Handbook|date=1996-12-19|publisher=Newnes|isbn=978-0-7506-3370-3|pages=119|language=en}}</ref><ref name="Book-TTL-Cookbook"/>
|}

<gallery class="center" widths="200px" heights="200px">
File:555 Pinout.svg| Pinout of 555 single timer<ref name="TI_NE555_Datasheet"/><ref name="Signetics_1985_Linear_Databook"/>
File:NE556 pennen.svg| Pinout of 556 dual timer<ref name="TI_NE556_Datasheet"/><ref name="Signetics_1985_Linear_Databook"/>
</gallery>