ADC0816/ADC08178-Bit µP Compatible A/D Converters with 16-Channel MultiplexerGeneral DescriptionThe ADC0816,ADC0817data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital con-verter,16-channel multiplexer and microprocessor compat-ible control logic.The 8-bit A/D converter uses successive approximation as the conversion technique.The converter features a high impedance chopper stabilized comparator,a 256R voltage divider with analog switch tree and a succes-sive approximation register.The 16-channel multiplexer can directly access any one of 16-single-ended analog signals,and provides the logic for additional channel expansion.Sig-nal conditioning of any analog input signal is eased by direct access to the multiplexer output,and to the input of the 8-bit A/D converter.The device eliminates the need for external zero and full-scale adjustments.Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE ®outputs.The design of the ADC0816,ADC0817has been optimized by incorporating the most desirable aspects of several A/D conversion techniques.The ADC0816,ADC0817offers high speed,high accuracy,minimal temperature dependence,ex-cellent long-term accuracy and repeatability,and consumes minimal power.These features make this device ideally suited to applications from process and machine control to consumer and automotive applications.For similar perfor-mance in an 8-channel,28-pin,8-bit A/D converter,see the ADC0808,ADC0809data sheet.(See AN-258for more in-formation.)Featuresn Easy interface to all microprocessorsn Operates ratiometrically or with 5V DC or analog span adjusted voltage referencen 16-channel multiplexer with latched control logic n Outputs meet TTL voltage level specificationsn 0V to 5V analog input voltage range with single 5V supplyn No zero or full-scale adjust requiredn Standard hermetic or molded 40-pin DIP packagen Temperature range −40˚C to +85˚C or −55˚C to +125˚C n Latched TRI-STATE outputn Direct access to “comparator in”and “multiplexer out”for signal conditioningn ADC0816equivalent to MM74C948n ADC0817equivalent to MM74C948-1Key Specificationsn Resolution8Bitsn Total Unadjusted Error ±1⁄2LSB and ±1LSBn Single Supply 5V DC n Low Power15mW nConversion Time100µsBlock DiagramTRI-STATE ®is a registered trademark of National Semiconductor Corporation.DS005277-1June 1999ADC0816/ADC08178-Bit µP Compatible A/D Converters with 16-Channel Multiplexer©1999National Semiconductor Corporation Connection DiagramOrdering InformationTEMPERATURE RANGE−40˚C to +85˚CError±1⁄2Bit Unadjusted ADC0816CCN ADC0816CCJ±1Bit UnadjustedADC0817CCN Package OutlineN40A Molded DIPJ40A Hermetic DIP Dual-In-Line PackageDS005277-6Order Number ADC0816CCN or ADC0817CCNSee NS Package Number N40A 2Absolute Maximum Ratings(Notes1,2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.Supply Voltage(V CC)(Note3) 6.5V Voltage at Any Pin−0.3V to(V CC+0.3V) Except Control InputsVoltage at Control Inputs−0.3V to15V (START,OE,CLOCK,ALE,EXPANSION CONTROL,ADD A,ADD B,ADD C,ADD D)Storage Temperature Range−65˚C to+150˚C Package Dissipation at T A=25˚C875mW Lead Temp.(Soldering,10seconds)Dual-In-Line Package(Plastic)260˚C Molded Chip Carrier PackageVapor Phase(60seconds)215˚C Infrared(15seconds)220˚C ESD Susceptibility(Note9)400VOperating Conditions(Notes1,2) Temperature Range(Note1)T MIN≤T A≤T MAX ADC0816CCN,ADC0817CCN−40˚C≤T A≤+85˚C Range of V CC(Note1) 4.5V DC to6.0V DC Voltage at Any Pin0V to V CC Except Control InputsVoltage at Control Inputs0V to15V (START,OE,CLOCK,ALE,EXPANSION CONTROL, ADD A,ADD B,ADD C,ADD D)Electrical CharacteristicsConverter Specifications:V CC=5V DC=V REF(+),V REF(−)=GND,V IN=V COMPARATOR IN,T MIN≤T MAX and f CLK=640kHz unless otherwise stated.Symbol Parameter Conditions Min Typ Max Units ADC0816Total Unadjusted Error25˚C±1⁄2LSB(Note5)T MIN to T MAX±3⁄4LSBADC0817Total Unadjusted Error0˚C to70˚C±1LSB(Note5)T MIN to T MAX±11⁄4LSBInput Resistance From Ref(+)to Ref(−) 1.0 4.5kΩAnalog Input Voltage Range(Note4)V(+)or V(−)GND−0.10V CC+0.10V DCV REF(+)Voltage,Top of Ladder Measured at Ref(+)V CC V CC+0.1V Voltage,Center of Ladder V CC/2−0.1V CC/2V CC/2+0.1VV REF(−)Voltage,Bottom of Ladder Measured at Ref(−)−0.10V Comparator Input Current f c=640kHz,(Note6)−2±0.52µAElectrical CharacteristicsDigital Levels and DC Specifications:ADC0816CCN,ADC0817CCN—4.75V≤V CC≤5.25V,−40˚C≤T A≤+85˚C unless other-wise noted.Symbol Parameter Conditions Min Typ Max Units ANALOG MULTIPLEXERR ON Analog Multiplexer ON(Any Selected Channel)Resistance T A=25˚C,R L=10k 1.53kΩT A=85˚C6kΩT A=125˚C9kΩ∆R ON∆ON Resistance Between Any(Any Selected Channel)75Ω2Channels R L=10kI OFF+OFF Channel Leakage Current V CC=5V,V IN=5V,T A=25˚C10200nAT MIN to T MAX 1.0µAI OFF(−)OFF Channel Leakage Current V CC=5V,V IN=0,T A=25˚C−200nAT MIN to T Max−1.0µA3Electrical Characteristics(Continued)Digital Levels and DC Specifications:ADC0816CCN,ADC0817CCN—4.75V≤V CC≤5.25V,−40˚C≤T A≤+85˚C unless other-wise noted.Symbol Parameter Conditions Min Typ Max Units CONTROL INPUTSV IN(1)Logical“1”Input Voltage V CC−1.5VV IN(0)Logical“0”Input Voltage 1.5VI IN(1)Logical“1”Input Current V IN=15V 1.0µA(The Control Inputs)I IN(0)Logical“0”Input Current V IN=0−1.0µA(The Control Inputs)I CC Supply Current f CLK=640kHz0.3 3.0mADATA OUTPUTS AND EOC(INTERRUPT)V OUT(1)Logical“1”Output Voltage I O=−360µA,T A=85˚C V CC−0.4VI O=−300µA,T A=125˚CV OUT(0)Logical“0”Output Voltage I O=1.6mA0.45VV OUT(0)Logical“0”Output Voltage EOC I O=1.2mA0.45VI OUT TRI-STATE Output Current V O=V CC 3.0µAV O=0−3.0µA Electrical CharacteristicsTiming Specifications:V CC=V REF(+)=5V,V REF(−)=GND,t r=t f=20ns and T A=25˚C unless otherwise noted.Symbol Parameter Conditions Min Typ Max Units t WS Minimum Start Pulse Width(Figure5)(Note7)100200nst WALE Minimum ALE Pulse Width(Figure5)100200nst s Minimum Address Set-Up Time(Figure5)2550nsT H Minimum Address Hold Time(Figure5)2550nst D Analog MUX Delay Time R S=OΩ(Figure5)1 2.5µs from ALEt H1,t H0OE Control to Q Logic State C L=50pF,R L=10k(Figure8)125250nst1H,t0H OE Control to Hi-Z C L=10pF,R L=10k(Figure8)125250nst C Conversion Time f c=640kHz,(Figure5)(Note8)90100116µsf c Clock Frequency106401280kHz t EOC EOC Delay Time(Figure5)08+2µs ClockPeriods C IN Input Capacitance At Control Inputs1015pFC OUT TRI-STATE Output At TRI-STATE Outputs(Note8)1015pFCapacitanceNote1:Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.DC and AC electrical specifications do not apply when operating the device beyond its specified operating conditions.Note2:All voltages are measured with respect to GND,unless otherwise specified.Note3:A zener diode exists,internally,from V CC to GND and has a typical breakdown voltage of7V DC.Note4:Two on-chip diodes are tied to each analog input which will forward conduct for analog input voltages one diode drop below ground or one diode drop greater than the V CC supply.The spec allows100mV forward bias of either diode.This means that as long as the analog V IN does not exceed the supply voltage by more than100mV,the output code will be correct.To achieve an absolute0V DC to5V DC input voltage range will therefore require a minimum supply voltage of4.900 V DC over temperature variations,initial tolerance and loading.Note5:Total unadjusted error includes offset,full-scale,and linearity errors.See Figure3.None of these A/Ds requires a zero or full-scale adjust.However,if an all zero code is desired for an analog input other than0.0V,or if a narrow full-scale span exists(for example:0.5V to4.5V full-scale)the reference voltages can be adjusted to achieve this.See Figure13.Note6:Comparator input current is a bias current into or out of the chopper stabilized comparator.The bias current varies directly with clock frequency and has little temperature dependence(Figure6).See paragraph4.0.Note7:If start pulse is asynchronous with converter clock or if f c>640kHz,the minimum start pulse width is8clock periods plus2µs.For synchronous operation at f c≤640kHz take start high within100ns of clock going low.Note8:The outputs of the data register are updated one clock cycle before the rising edge of EOC.Note9:Human body model,100pF discharged through a1.5kΩresistor.4Functional DescriptionMultiplexer:The device contains a16-channel single-ended analog signal multiplexer.A particular input channel is se-lected by using the address decoder.Table1shows the input states for the address line and the expansion control line to select any channel.The address is latched into the decoder on the low-to-high transition of the address latch enable sig-nal.TABLE1.Selected Address Line Expansion Analog Channel D C B A Control IN0L L L L HIN1L L L H HIN2L L H L HIN3L L H H HIN4L H L L HIN5L H L H HIN6L H H L HIN7L H H H HIN8H L L L HIN9H L L H HIN10H L H L HIN11H L H H HIN12H H L L HIN13H H L H HIN14H H H L HIN15H H H H HAll Channels OFF X X X X LX=don’t care Additional single-ended analog signals can be multiplexed to the A/D converter by disabling all the multiplexer inputs using the expansion control.The additional external signals are connected to the comparator input and the device ground. Additional signal conditioning(i.e.,prescaling,sample and hold,instrumentation amplification,etc.)may also be added between the analog input signal and the comparator input.CONVERTER CHARACTERISTICSThe ConverterThe heart of this single chip data acquisition system is its 8-bit analog-to-digital converter.The converter is designed to give fast,accurate,and repeatable conversions over a wide range of temperatures.The converter is partitioned into3 major sections:the256R ladder network,the successive ap-proximation register,and the comparator.The converter’s digital outputs are positive true.The256R ladder network approach Figure1was chosen over the conventional R/2R ladder because of its inherent monotonicity,which guarantees no missing digital codes. Monotonicity is particularly important in closed loop feedback control systems.A non-monotonic relationship can cause os-cillations that will be catastrophic for the system.Additionally, the256R network does not cause load variations on the ref-erence voltage.The bottom resistor and the top resistor of the ladder net-work in Figure1are not the same value as the remainder of the network.The difference in these resistors causes the output characteristic to be symmetrical with the zero and full-scale points of the transfer curve.The first output transi-tion occurs when the analog signal has reached+1⁄2LSB and succeeding output transitions occur every1LSB later up to full-scale.DS005277-2FIGURE1.Resistor Ladder and Switch Tree5Functional Description(Continued)Timing DiagramDS005277-3FIGURE2.3-Bit A/D Transfer CurveDS005277-4FIGURE3.3-Bit A/D Absolute Accuracy CurveDS005277-5FIGURE4.Typical Error CurveDS005277-7FIGURE5.6Timing Diagram(Continued)The successive approximation register(SAR)performs8it-erations to approximate the input voltage.For any SAR typeconverter,n-iterations are required for an n-bit converter.Figure2shows a typical example of a3-bit converter.In theADC0816,ADC0817,the approximation technique is ex-tended to8bits using the256R network.The A/D converter’s successive approximation register(SAR)is reset on the positive edge of the start conversion(SC)pulse.The conversion is begun on the falling edge ofthe start conversion pulse.A conversion in process will be in-terrupted by receipt of a new start conversion pulse.Con-tinuous conversion may be accomplished by tying theend-of-conversion(EOC)output to the SC input.If used inthis mode,an external start conversion pulse should be ap-plied after power up.End-of-conversion will go low between0and8clock pulses after the rising edge of start conversion.The most important section of the A/D converter is the com-parator.It is this section which is responsible for the ulimateaccuracy of the entire converter.It is also the comparatordrift which has the greatest influence on the repeatability ofthe device.A chopper-stabilized comparator provides themost effective method of satisfying all the converter require-ments.The chopper-stabilized comparator converts the DC inputsignal into an AC signal.This signal is then fed through ahigh gain AC amplifier and has the DC level restored.Thistechnique limits the drift component of the amplifier since thedrift is a DC component which is not passed by the AC am-plifier.This makes the entire A/D converter extremely insen-sitive to temperature,long term drift and input offset errors.Figure4shows a typical error curve for the ADC0816asmeasured using the procedures outlined in AN-179.7Typical Performance CharacteristicsTRI-STATE Test Circuits and Timing DiagramsApplications InformationOPERATION1.0RATIOMETRIC CONVERSIONThe ADC0816,ADC0817is designed as a complete Data Acquisition System (DAS)for ratiometric conversion sys-tems.In ratiometric systems,the physical variable being measured is expressed as a percentage of full-scale which is not necessarily related to an absolute standard.The voltage input to the ADC0816is expressed by the equation(1)V IN =Input voltage into the ADC0816V fs =Full-scale voltage V Z =Zero voltageD X =Data point being measured D MAX =Maximum data limit D MIN =Minimum data limitDS005277-18FIGURE parator I IN vs V IN(V CC =V REF =5V)DS005277-19FIGURE 7.Multiplexer R ON vs V IN(V CC =V REF =5V)DS005277-9DS005277-10FIGURE 8. 8Applications Information(Continued)A good example of a ratiometric transducer is a potentiom-eter used as a position sensor.The position of the wiper is di-rectly proportional to the output voltage which is a ratio of the full-scale voltage across it.Since the data is represented as a proportion of full-scale,reference requirements are greatly reduced,eliminating a large source of error and cost for many applications.A major advantage of the ADC0816, ADC0817is that the input voltage range is equal to the sup-ply range so the transducers can be connected directly across the supply and their outputs connected directly into the multiplexer inputs,(Figure9).Ratiometric transducers such as potentiometers,strain gauges,thermistor bridges,pressure transducers,etc.,are suitable for measuring proportional relationships;however, many types of measurements must be referred to an abso-lute standard such as voltage or current.This means a sys-tem reference must be used which relates the full-scale volt-age to the standard volt.For example,if V CC=V REF= 5.12V,then the full-scale range is divided into256standard steps.The smallest standard step is1LSB which is then20 mV.2.0RESISTOR LADDER LIMITATIONSThe voltages from the resistor ladder are compared to the selected input8times in a conversion.These voltages are coupled to the comparator via an analog switch tree which is referenced to the supply.The voltages at the top,center and bottom of the ladder must be controlled to maintain proper operation.The top of the ladder,Ref(+),should not be more positive than the supply,and the bottom of the ladder,Ref(−),should not be more negative than ground.The center of the ladder voltage must also be near the center of the supply because the analog switch tree changes from N-channel switches to P-channel switches.These limitations are automaticaly sat-isfied in ratiometric systems and can be easily met in ground referenced systems.Figure10shows a ground referenced system with a sepa-rate supply and reference.In this system,the supply must be trimmed to match the reference voltage.For instance,if a 5.12V reference is used,the supply should be adjusted to the same voltage within0.1V.The ADC0816needs less than a milliamp of supply current so developing the supply from the reference is readily ac-complished.In Figure11a ground references system is shown which generates the supply from the reference.The buffer shown can be an op amp of sufficient drive to supply the millliamp of supply current and the desired bus drive,or if a capacitive bus is driven by the outputs a large capacitor will supply the transient supply current as seen in Figure12. The LM301is overcompensated to insure stability when loaded by the10µF output capacitor.The top and bottom ladder voltages cannot exceed V CC and ground,respectively,but they can be symmetrically less than V CC and greater than ground.The center of the ladder volt-age should always be near the center of the supply.The sen-sitivity of the converter can be increased,(i.e.,size of the LSB steps decreased)by using a symmetrical reference sys-tem.In Figure13,a2.5V reference is symmetrically cen-tered about V CC/2since the same current flows in identical resistors.This system with a2.5V reference allows the LSB to be half the size of the LSB in a5V reference system.DS005277-11FIGURE9.Ratiometric Conversion System9Applications Information(Continued)DS005277-12FIGURE10.Ground ReferencedConversion System Using Trimmed SupplyDS005277-13FIGURE11.Ground Referenced Conversion System withReference Generating V CC SupplyDS005277-14FIGURE12.Typical Reference and Supply Circuit10Applications Information(Continued)3.0CONVERTER EQUATIONSThe transition between adjacent codes N and N +1is given by:(2)The center of an output code N is given by:(3)The output code N for an arbitrary input are the integers within the range:(4)where:V IN =Voltage at comparator input V REF =Voltage at Ref(+)V REF =Voltage at Ref(−)V TUE =Total unadjusted error voltage (typicallyV REF (+)÷512)4.0ANALOG COMPARATOR INPUTSThe dynamic comparator input current is caused by the pe-riodic switching of on-chip stray capacitances These are connected alternately to the output of the resistor ladder/switch tree network and to the comparator input as part of the operation of the chopper stabilized comparator.The average value of the comparator input current varies di-rectly with clock frequency and with V IN as shown in Figure 6.If no filter capacitors are used at the analog or comparator in-puts and the signal source impedances are low,the com-parator input current should not introduce converter errors,as the transient created by the capacitance discharge will die out before the comparator output is strobed.If input filter capacitors are desired for noise reduction and signal conditioning they will tend to average out the dynamic comparator input current.It will then take on the characteris-tics of a DC bias current whose effect can be predicted con-ventionally.See AN-258for further discussion.DS005277-15FIGURE 13.Symmetrically Centered Reference11Typical ApplicationMicroprocessor Interface TablePROCESSOR READ WRITE INTERRUPT (COMMENT)8080MEMRMEMWINTR (Thru RST Circuit)8085RD WR INTR (Thru RST Circuit)Z-80RD WR INT (Thru RST Circuit,Mode 0)SC/MP NRDS NWDS SA (Thru Sense A)6800VMA •φ2•R/WVMA •Q 2•R/WIRQA or IRQB (Thru PIA)DS005277-16*Address latches needed for 8085and SC/MP interfacing the ADC0816,17to a microprocessor 12Physical Dimensionsinches (millimeters)unless otherwise notedLIFE 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: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 AmericasTel:1-800-272-9959Fax:1-800-737-7018Email:support@National Semiconductor EuropeFax:+49(0)180-5308586Email:europe.support@Deutsch Tel:+49(0)180-5308585English Tel:+49(0)180-5327832Français Tel:+49(0)180-5329358Italiano Tel:+49(0)180-5341680National Semiconductor Asia Pacific Customer Response Group Tel:65-2544466Fax:65-2504466Email:sea.support@National Semiconductor Japan Ltd.Tel:81-3-5639-7560Fax:81-3-5639-7507Molded Dual-In-Line Package (N)NS Package Number N40AADC0816/ADC08178-Bit µP Compatible A/D Converters with 16-Channel MultiplexerNational 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.。
