如何阅读Datasheet

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.) LM555 Timer General Description The LM555 is a highly stable device for generating accurate time delays or oscillation. Additional terminals are provided for triggering or resetting if desired. In the time delay mode of operation, 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 accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output circuit can source or sink up to 200mA or drive TTL circuits. Features n Direct replacement for SE555/NE555 n Timing from microseconds through hours n Operates in both astable and monostable modes n Adjustable duty cycle n Output can source or sink 200 mA n Output and supply TTL compatible n Temperature stability better than 0.005% per ˚C n Normally on and normally off output n Available in 8-pin MSOP package Applications n Precision timing n Pulse generation n Sequential timing n Time delay generation n Pulse width modulation n Pulse position modulation n Linear ramp generator Schematic Diagram DS007851-1 February 2000 LM 555 Tim er © 2000 National Semiconductor Corporation DS007851 www.national.com Dale Grover There will always be a date. Datasheets do change, especially if Preliminary or Advance. Check the date! Dale Grover Look up here to see if the datasheet is Advance Information or Preliminary. Dale Grover Sometimes the General Description will tell you about a feature or usage not mentioned anywhere else! For example, you might need to hold a specific pin low for some operation. Dale Grover Features tell you general characteristics--always check the Electrical Characteristics for conditions and exceptions. Dale Grover Usually called the Equivalent Schematic Diagram, this schematic isn't what is necessarily in the device, but the device acts as if this was what was inside. It can help explain behavior that isn't otherwise described in the datasheet. Could you duplicate this circuit on a breadboard? Only if you knew what the characteristics of the transistors were--which are not given. Dale Grover Dale Grover Dale Grover Dale Grover Dale Grover Dale Grover Application suggestions can often tell you quickly if this device is in the ballpark for what you want to do, but these lists are often very general. Dale Grover Dale Grover Connection Diagram Ordering Information Package Part Number Package Marking Media Transport NSC Drawing 8-Pin SOIC LM555CM LM555CM Rails M08A LM555CMX LM555CM 2.5k Units Tape and Reel 8-Pin MSOP LM555CMM Z55 1k Units Tape and Reel MUA08A LM555CMMX Z55 3.5k Units Tape and Reel 8-Pin MDIP LM555CN LM555CN Rails N08E Dual-In-Line, Small Outline and Molded Mini Small Outline Packages DS007851-3 Top View LM 55 5 www.national.com 2 Dale Grover Make sure you're looking at the pinout for the correct package. In the back pages you'll find drawings of the package types. Here all the packages have the same pinout--that's not always the case! Dale Grover Under Ordering Information you'll find a list of every variation of this device along with the COMPLETE part number. Often the first few letters are either industry-standard or identify the manufacturer (e.g., PIC). The generic identifier comes next ("555"). Suffixes generally give 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. Dale Grover Other elements in datasheets: --Related devices, such as devices this supercedes, exactly replaces, or is replaced by --Block diagrams of internals --Information to support programming or configuring the device (registers, etc.) --Interfacing with other devices (including input/output characteristics) Dale Grover Dale Grover 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 +18V Power Dissipation (Note 3) LM555CM, LM555CN 1180 mW LM555CMM 613 mW Operating Temperature Ranges LM555C 0˚C to +70˚C Storage Temperature Range −65˚C to +150˚C Soldering Information Dual-In-Line Package Soldering (10 Seconds) 260˚C Small Outline Packages (SOIC and MSOP) Vapor Phase (60 Seconds) 215˚C Infrared (15 Seconds) 220˚C See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” for other methods of soldering surface mount devices. Electrical Characteristics (Notes 1, 2) (TA = 25˚C, VCC = +5V to +15V, unless othewise specified) Parameter Conditions Limits Units LM555C Min Typ Max Supply Voltage 4.5 16 V Supply Current VCC = 5V, RL = ∞ VCC = 15V, RL = ∞ (Low State) (Note 4) 3 10 6 15 mA Timing Error, Monostable Initial Accuracy 1 % Drift with Temperature RA = 1k to 100kΩ, 50 ppm/˚C C = 0.1µF, (Note 5) Accuracy over Temperature 1.5 % Drift with Supply 0.1 %/V Timing Error, Astable Initial Accuracy 2.25 % Drift with Temperature RA, RB = 1k to 100kΩ, 150 ppm/˚C C = 0.1µF, (Note 5) Accuracy over Temperature 3.0 % Drift with Supply 0.30 %/V Threshold Voltage 0.667 x VCC Trigger Voltage VCC = 15V 5 V VCC = 5V 1.67 V Trigger Current 0.5 0.9 µA Reset Voltage 0.4 0.5 1 V Reset Current 0.1 0.4 mA Threshold Current (Note 6) 0.1 0.25 µA Control Voltage Level VCC = 15V VCC = 5V 9 2.6 10 3.33 11 4 V Pin 7 Leakage Output High 1 100 nA Pin 7 Sat (Note 7) Output Low VCC = 15V, I7 = 15mA 180 mV Output Low VCC = 4.5V, I7 = 4.5mA 80 200 mV LM 555 www.national.com3 Dale Grover Absolute Maximum Ratings tell you what will damage the chip--NOT the maximum operating limits! Dale Grover Dale Grover See Note 2 for details. Dale Grover Dale Grover Dale Grover Dale Grover Dale Grover Dale Grover Electrical Characteristics are sometimes split into DC (power supply, static input/ouput characteristics) and AC or Timing, these tell you what you can count on. Dale Grover Design to the minimum and maximum limits, not to the typical. This gives you an idea of the likely behavior, but not the worst-case. Good, robust design does not count on the typical! Dale Grover Dale Grover Dale Grover Dale Grover Dale Grover Dale Grover Watch out--the datasheet might discuss more than one part! Dale Grover Dale Grover Pay attention to the conditions noted. Here the device is at a specific temperature. Often, plots later on in the datasheet will show temperature-related parameters (as well as those dependent on supply voltage, speed, etc.). Electrical Characteristics (Notes 1, 2) (Continued) (TA = 25˚C, VCC = +5V to +15V, unless othewise specified) Parameter Conditions Limits Units LM555C Min Typ Max Output Voltage Drop (Low) VCC = 15V ISINK = 10mA 0.1 0.25 V ISINK = 50mA 0.4 0.75 V ISINK = 100mA 2 2.5 V ISINK = 200mA 2.5 V VCC = 5V ISINK = 8mA V ISINK = 5mA 0.25 0.35 V Output Voltage Drop (High) ISOURCE = 200mA, VCC = 15V 12.5 V ISOURCE = 100mA, VCC = 15V 12.75 13.3 V VCC = 5V 2.75 3.3 V Rise Time of Output 100 ns Fall Time of Output 100 ns Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func- tional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guar- antee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 3: For operating at elevated temperatures the device must be derated above 25˚C based on a +150˚C maximum junction temperature and a thermal resistance of 106˚C/W (DIP), 170˚C/W (S0-8), and 204˚C/W (MSOP) junction to ambient. Note 4: Supply current when output high typically 1 mA less at VCC = 5V. Note 5: Tested at VCC = 5V and VCC = 15V. Note 6: This will determine the maximum value of RA + RB for 15V operation. The maximum total (RA + RB) is 20MΩ. Note 7: No protection against excessive pin 7 current is necessary providing the package dissipation rating will not be exceeded. Note 8: Refer to RETS555X drawing of military LM555H and LM555J versions for specifications. LM 55 5 www.national.com 4 Dale Grover (Here is Note 2 in large print) Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional,but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Dale Grover Typical Performance Characteristics Minimuim Pulse Width Required for Triggering DS007851-4 Supply Current vs. Supply Voltage DS007851-19 High Output Voltage vs. Output Source Current DS007851-20 Low Output Voltage vs. Output Sink Current DS007851-21 Low Output Voltage vs. Output Sink Current DS007851-22 Low Output Voltage vs. Output Sink Current DS007851-23 LM 555 www.national.com5 Dale Grover Graphs are used to describe characteristics that can't be captured easily in a table. Often several things are being varied--above, supply current is measured as voltage is changed, but this is also being show for three different temperatures. Note that 25C is roughly room temperature (77F). Dale Grover Page 6 of the datasheet is omitted. Dale Grover Applications Information MONOSTABLE OPERATION In this mode of operation, the timer functions as a one-shot (Figure 1). The external capacitor is initially held discharged by a transistor inside the timer. Upon application of a nega- tive trigger pulse of less than 1/3 VCC to pin 2, the flip-flop is set which both releases the short circuit across the capacitor and drives the output high. The voltage across the capacitor then increases exponen- tially for a period of t = 1.1 RA C, at the end of which time the voltage equals 2/3 VCC. The comparator then resets the flip-flop which in turn discharges the capacitor and drives the output to its low state. Figure 2 shows the waveforms gener- ated in this mode of operation. Since the charge and the threshold level of the comparator are both directly propor- tional to supply voltage, the timing internal is independent of supply. During the timing cycle when the output is high, the further application of a trigger pulse will not effect the circuit so long as the trigger input is returned high at least 10µs before the end of the timing interval. However the circuit can be reset during this time by the application of a negative pulse to the reset terminal (pin 4). The output will then remain in the low state until a trigger pulse is again applied. When the reset function is not in use, it is recommended that it be connected to VCC to avoid any possibility of false trig- gering. Figure 3 is a nomograph for easy determination of R, C val- ues for various time delays. NOTE: In monostable operation, the trigger should be driven high before the end of timing cycle. ASTABLE OPERATION If the circuit is connected as shown in Figure 4 (pins 2 and 6 connected) it will trigger itself and free run as a multivibrator. The external capacitor charges through RA + RB and dis- charges through RB. Thus the duty cycle may be precisely set by the ratio of these two resistors. In this mode of operation, the capacitor charges and dis- charges between 1/3 VCC and 2/3 VCC. As in the triggered mode, the charge and discharge times, and therefore the fre- quency are independent of the supply voltage. DS007851-5 FIGURE 1. Monostable DS007851-6 VCC = 5V Top Trace: Input 5V/Div. TIME = 0.1 ms/DIV. Middle Trace: Output 5V/Div. RA = 9.1kΩ Bottom Trace: Capacitor Voltage 2V/Div. C = 0.01µF FIGURE 2. Monostable Waveforms DS007851-7 FIGURE 3. Time Delay DS007851-8 FIGURE 4. Astable LM 555 www.national.com7 Dale Grover Not all datasheet application examples are so well written--sometimes you just get the raw schematics. For more complex devices, such as microcontrollers, different aspects might be handled in different sections--for example, a clock circuit in one part, a reset circuit in another. Read over all the sections to make sure you are using the device correctly and have supplied all the necessary components. Dale Grover Here are example circuits and application notes. Note too that often there are other sources for application information, such as separate Application Notes available from the manufacturer. Dale Grover These waveforms would be helpful in debugging a circuit! Dale Grover Pages 8-11 have been omitted. Dale Grover Physical Dimensions inches (millimeters) unless otherwise noted (Continued) LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 www.national.com Molded Dual-In-Line Package (N) NS Package Number N08E LM 55 5 Ti m er National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. Dale Grover The package outlines can also be a source for pin-numbering if you are in doubt. Note that plastic DIP is the most common package for prototyping. Avoid surface mount packages (e.g., SOIC, MSOP, PQFP), though with the proper socket PLCC packages can be soldered to relatively easily (but not used in a plastic prototype board without an adapter). There is great variation in pricing depending on package type (and other factors such as temperature range, speed, etc.), so be sure to double-check part numbers. Dale Grover Finally, remember that datasheets can always be in error. But just like programming, 99% of errors are user errors. If you find what you think is an error, make sure you have the most recent datasheet, and send a polite query to the appropriate technical support. Newsgroups such as sci.electronics.design might be useful to query first.