如何看芯片资料

How to Read a DatasheetPrepared for the WIMS outreach program5/6/02, D. GroverIn order to use a PIC microcontroller, a flip-flop, a photodetector, or practically any electronic device, you need to consult a datasheet. This is theto.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 .LM555TimerGeneral DescriptionThe LM555is 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.Featuresn Direct n Timing n Operates n Adjustable n Output n Output n Temperature n Normally n Available Applicationsn Precision n Pulse n Sequential DS007851-1有时常规描述（GeneralDescription ）会给出一些其它地方没提到的特性或者用法。

特性（确认电气特性所在的条件以及特殊情况。

通常叫做等效原理图，该原理不是该芯片中必须的，但是该芯片将按照里面的来运作。

它能帮助解释在数据手册中未被描述的行为。

能把这个电路在面包板上搭出来吗？除非您知道那些并未给出参数的晶体管的参数。

总会有一个日期。

数据手册变动，尤其是预备版或者修正版，核对一下日期。

555MLDS007851-3Top ViewNumber Package Marking Media TransportLM555CM LM555CM RailsLM555CMX LM555CM 2.5k Units TapeLM555CMM Z551k Units TapeLM555CMMX Z55 3.5k Units TapeLM555CN LM555CN RailsOrdering Information ）下，可以找到带有完整零件编号的该器件的每个变种列表。

通常开始的几个字母是行业标准或者厂商标识, 接着的是常规标识（“555”）。

后缀通常给出封装类型（贴片安装型或直插型），温度范围（宽范围型，当然也会更贵），速度（快速型，当然也会更贵），以及其它各种如功耗，电压范围等等。

--相关器件，如它可替换的，可直接替换的，或者可以被其它替换的器件--提供编程或者配置该器件的信息（寄存器等）--与其它器件之间的连接（包括输入/输出特性）DS007851-4DS007851-19Output Voltage vs.Output Source CurrentDS007851-20Output Voltage vs.Sink CurrentDS007851-21Output Voltage vs.Output Sink CurrentDS007851-22Output Voltage vs.Sink CurrentDS007851-23LM555图表被用来描述那些不容易放在表格里的特性。

通常几个被变化--上文中，供电电流被测量当输入电压被改变时，并同时显示了三种温度下的值。

注意25C是近似室温（77F）的温度。

数据手册的第6页被省略。

The voltage across the capacitor then increases exponen-tially for a period of t =1.1R A C,at the end of which time the voltage equals 2/3V CC .The comparator then resets the flip-flop which in turn discharges the capacitor and drives the output to its low state.Figure 2shows 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 be connected to V CC to avoid any possibility of false trig-gering.Figure 3is a nomograph for easy determination of R,C val-ues for various time delays.OPERATIONcircuit is connected as shown in Figure 4(pins connected)it will trigger itself and free run as a multivibrator.external capacitor charges through R A +R B through R B .Thus the duty cycle may be ratio of these two resistors.this mode of operation,the capacitor charges and charges between 1/3V CC and 2/3V CC .As in the triggered mode,the charge and discharge times,and therefore the quency are independent of the supply voltage.DS007851-5FIGURE 1.MonostableDS007851-6CC =5VTop Trace:Input 5V/Div.TIME =0.1ms/DIV.Middle Trace:Output 5V/Div.A =9.1k ΩBottom Trace:Capacitor Voltage 2V/Div.=0.01µFFIGURE 2.Monostable WaveformsDS007851-7FIGURE 3.Time DelayDS007851-8FIGURE 4.AstableLM555并非所有的数据手册应用示例都写得这么充分，有时你仅得到一个不完整的原理图。

对于更复杂的器件，例如微控制器，不同的方面可能被放在不同的部分--例如，时钟电路在一处，而复位电路却在另一处。

阅读整个部分确保正确的使用器件以及提供了所有需要的元件。

应用注意。

这个波形有助于电路调试。

8-11页被省略。

SUPPORT POLICYNATIONAL’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:support devices or systems are devices or systems which,(a)are intended for surgical implant 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 ofsupport device or system whose failure to perform can be reasonably expected to cause the failurethe life support device or system,or to affectsafety or effectiveness.National Semiconductor CorporationAmericasTel:1-800-272-9959 Fax:1-800-737-7018 Email:support@ National SemiconductorEuropeFax:+49(0)180-5308586Email:europe.support@Deutsch Tel:+49(0)6995086208English Tel:+44(0)8702402171Français Tel:+33(0)141918790National SemiconductorAsia Pacific CustomerResponse GroupTel:65-2544466Fax:65-2504466Email:ap.support@National SemiconductorJapan Ltd.Tel:81-3-5639-7560Fax:81-3-5639-7507 Molded Dual-In-Line Package(N) NS Package Number N08E封装轮廓图也可以作为引脚编号的一个参考，如果你对引脚编号有疑问的话。