How to Read a Datasheet Prepared for the WIMS outreach program 5/6/02, D. Grover In order to use a PIC microcontroller, a flip-flop, a photodetector, or practically any electronic device, you need to consult a datasheet. This is the document that the manufacturer provides telling you • the typical device performance • minimum and maximum requirements and characteristics • what you can do to the device without harming it • suggested uses and hints Manufacturers want you, the designer, to have a successful experience with their device. They are trying to be helpful. They don’t always succeed. The datasheet on the following pages is a relatively good datasheet. It tries to concisely tell you everything you need to know about the device, a common 555 timer chip (the duct-tape of the electronics hobbyist). Most datasheets for ICs follow the same general layout. You don’t have to understand everything in a datasheet. There’s a lot of information that might not be of any use to you. The annotations that follow try to point out parts of the datasheet that you should pay particular attention to. Where do you find datasheets? Nowadays you can find almost any datasheet on the internet, often in PDF (Acrobat) form. For example, the LM555 datasheet from National Semiconductor is on their website at www.national.com. What is the LM555? The LM555 is a timer chip that uses external resistors and capacitors to generate either a single pulse of a certain duration, or a continuous sequence of pulses with a variety of pulse widths possible. Because it is a very general purpose collection of functional blocks such as comparators, a flip-flop, internal voltage divider, high power output stage, and so on, a number of different timing-related functions are possible. Entire books have been written about the 555, though it is often used when another IC would work better. (See for example the CD4538 timer chip.)LM555TimerGeneral DescriptionThe LM555 is a highly stable device for generating accuratetime delays or oscillation. Additional terminals are providedfor triggering or resetting if desired. In the time delay mode ofoperation, the time is precisely controlled by one external re-sistor and capacitor. For astable operation as an oscillator,the free running frequency and duty cycle are accuratelycontrolled with two external resistors and one capacitor. Thecircuit may be triggered and reset on falling waveforms, andthe output circuit can source or sink up to 200mA or driveTTL circuits.Featuresn Direct replacement for SE555/NE555n Timing from microseconds through hoursn Operates in both astable and monostable modesn Adjustable duty cyclen Output can source or sink 200 mAn Output and supply TTL compatiblen Temperature stability better than 0.005% per ˚Cn Normally on and normally off outputn Available in 8-pin MSOP packageApplicationsn Precision timingn Pulse generationn Sequential timingn Time delay generationn Pulse width modulationn Pulse position modulationn Linear ramp generatorSchematic DiagramDS007851-1February 2000LM555 Timer© 2000 National Semiconductor Corporation DS007851 www.national.comThere will always be a date. Datasheets do change,especially if Preliminary or Advance. Check the date!Look up here to see if the datasheet isAdvance Information or Preliminary.Sometimes the General Descriptionwill tell you about a feature orusage not mentioned anywhere else! For example, you might need tohold a specific pin low for someoperation.Features tell you generalcharacteristics--always check the ElectricalCharacteristics for conditions andexceptions.Usually called the Equivalent Schematic Diagram, this schematic isn't what isnecessarily in the device, but the device acts as if this was what was inside. It can helpexplain behavior that isn't otherwise described in the datasheet. Could you duplicatethis circuit on a breadboard? Only if you knew what the characteristics of thetransistors were--which are not given.Applicationsuggestions can oftentell you quickly if thisdevice is in theballpark for what youwant to do, but theselists are often verygeneral.Connection DiagramOrdering InformationPackage Part Number Package Marking Media Transport NSC Drawing8-Pin SOIC LM555CM LM555CM RailsM08ALM555CMX LM555CM 2.5k Units Tape and Reel8-Pin MSOP LM555CMM Z55 1k Units Tape and ReelMUA08ALM555CMMX Z55 3.5k Units Tape and Reel8-Pin MDIP LM555CN LM555CN Rails N08EDual-In-Line, Small Outlineand Molded Mini Small Outline PackagesDS007851-3Top ViewLM555www.national.com 2Make sure you're looking atthe pinout for the correctpackage. In the back pagesyou'll find drawings of thepackage types. Here all thepackages have the samepinout--that's not always thecase!Under Ordering Information you'll find a list of every variation of this device along with theCOMPLETE part number. Often the first few letters are either industry-standard or identifythe manufacturer (e.g., PIC). The generic identifier comes next ("555"). Suffixes generallygive package type (surface mount and through hole types), temperature range (wider range= more expensive), speed (faster = more expensive), and other variations such as power,voltage range, etc.Other elements in datasheets:--Related devices, such as devices this supercedes, exactly replaces, or is replacedby--Block diagrams of internals--Information to support programming or configuring the device (registers, etc.)--Interfacing with other devices (including input/output characteristics)Absolute Maximum Ratings (Note 2)If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and specifications.Supply Voltage +18VPower Dissipation (Note 3)LM555CM, LM555CN 1180 mWLM555CMM 613 mWOperating Temperature RangesLM555C 0˚C to +70˚CStorage Temperature Range −65˚C to +150˚CSoldering InformationDual-In-Line PackageSoldering (10 Seconds) 260˚CSmall Outline Packages(SOIC and MSOP)Vapor Phase (60 Seconds) 215˚CInfrared (15 Seconds) 220˚CSee AN-450 “Surface Mounting Methods and Their Effecton Product Reliability” for other methods of solderingsurface mount devices.Electrical Characteristics (Notes 1, 2)(TA= 25˚C, VCC= +5V to +15V, unless othewise specified)Parameter Conditions Limits UnitsLM555CMin Typ MaxSupply Voltage 4.5 16 VSupply Current VCC= 5V, RL=∞VCC= 15V, RL=∞(Low State) (Note 4)310615 mATiming Error, MonostableInitial Accuracy 1%Drift with Temperature RA= 1k
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