Building a Stable DAC External Reference Circuit

Precision voltage referencesIntroductionOne reason why designing a data conversion system is such a challenge is the fact that the system accuracy very much depends on the accuracy of the voltage established by the internal or external DC voltage reference. The voltage reference is used to produce a precise value of output voltage for setting the full-scale input of the data conversion system. In an analog-to-digital converter(ADC), the DC voltage reference together with the analog input signal is used to generate the digitized output signal.And in a digital-to-analog converter (DAC), the DACselects and produces an analog output from the DC refer-ence voltage according to the digital input signal presented at the input of the DAC. Any errors in the reference volt-age over the operating temperature range will adversely affect the linearity and spurious free dynamic range (SFDR) of the ADC/DAC. Practically all voltage refer-ences vary with time or environmental factors such as humidity, pressure, and temperature. As a result most CMOS ADCs/DACs have internal references suitable only for applications demanding ≤12-bit resolution eventhough the converter may be capable of higher resolution.Modern CMOS converters operate from 3.3-V or 5-V sup-plies, which limits the on-chip voltage reference to aband-gap reference. By way of the external reference pins provided on the chip, an external precision reference can also be connected to a CMOS ADC or DAC. A precision external voltage reference has a much lower temperature coefficient, thermal hysteresis, and long-term drift than an on-chip band-gap voltage reference; therefore, in applications demanding high accuracy (14-bit or 16-bit ADCs/DACs), an external precision voltage reference is often required.Precision voltage references are available with varying degrees of precision and initial accuracy over someoperating temperature range. But often what is not obvi-ous when reading a manufacturer’s data sheet is how theinitial accuracy of the device is affected by other key device parameters such as line regulation, load regulation, initial voltage error, output voltage temperature coefficient (TC),output voltage noise, turn-on settling time, thermal hyste-resis, quiescent supply current, and long-term stability.The design originsModern voltage references are constructed using the energy-band-gap voltage of integrated transistors, buried zener diodes, and junction field-effect transistors. Each technology offers inherent performance characteristics that can be enhanced with compensation networks or additional active circuitry. The basis topologies for the band-gap, buried zener, and XFET references are shown in Figures 1, 2, and 3, respectively.Texas Instruments Incorporated Data AcquisitionBy Perry Miller, Application Specialist—Data Converters, Texas Instruments, Dallas,and Doug Moore, Managing Director, Thaler Corp., Tucson, Arizona Continued on next pageTexas Instruments IncorporatedData AcquisitionBand-gap referenceAt its simplest, a band-gap reference is simply two tran-sistors with different emitter areas used for generating a voltage proportional to absolute temperature. V BE1and V BE2have opposite temperature coefficients. The voltage V CC is converted to a current I 1and I 2that are mirrored to the output branch. The output equation is(1)where λis the scale factor, V BE1is the base-emitter volt-age of the larger of the two transistors, and V BE2is thebase-emitter voltage of the second transistor.The band-gap references are widely used in ADC/DAC converters as well as for external reference source because they are fairly inexpensive. Generally, they are used in system designs where a maximum accuracy of 10 bits is required. Band-gap references typically have an initial error of 0.5–1.0% and a TC of 25–50 ppm/°C. The output voltage noise is typically 15–30 µV p-p (0.1–10 Hz) with a long-term stability of 20–30 ppm/1000 hrs.Zener referenceThe zener voltage reference and feedback amplifier shown in Figure 2 are used to provide a very stable output. A current source is used to bias a 6.3-V zener diode. The zener voltage is divided by the resistor network R1 and R2.This voltage is applied to the non-inverting input of the operational amplifier, which amplifies the voltage to the required output voltage. The amplifier gain is determined by the resistor networks R3 and R4, where G = 1 + R4/R3.A 6.3-V zener diode is used because it is the most stable zener diode over time and temperature.The output equation is(2)Buried zener diode references are more expensive than band-gap references but provide a higher performance level. They typically have an initial error of 0.01–0.04%, a TC of 1–10 ppm/°C, and less than 10-µV p-p (0.1- to 10-Hz)),V V (V V BE2BE1BE1O −λ+=noise. The long-term stability is typically 6–15 ppm/1000hrs. Buried zener-based references are frequently used for 12-bit, 14-bit, and higher resolution systems because the performance of the buried zener-based references can be extended by incorporating nonlinear temperature com-pensation networks into the design. The compensation network is trimmed at several temperatures to optimize the electrical performance over the operating tempera-ture range.XFET referenceThe XFET reference is a new reference technique that consists of two junction field-effect transistors, one of which has an extra channel implant to raise the pinch-off voltage. The two JFETs are run at the same drain current.The difference in pinch-off voltage is amplified and used to form a voltage reference. The general equation is(3)where ∆V P is the difference in pinch-off voltage betweenthe two FETs and I PTAT is the positive temperature coefficient correction current.The simplified schematic for the XFET reference is shown in Figure 3.The XFET references are relatively new and provide a performance level between band-gap and zener refer-ences.The initial error is typically 0.06%, a TC of 10 ppm/°C,and 15-µV p-p (0.1- to 10-Hz) noise. The long-term stability is 0.2 ppm/1000 hrs.Reference selection for a 14-bit converterSpecified parameters for voltage references include line regulation, load regulation, initial voltage error, output voltage temperature coefficient (TC), output voltage noise, turn-on settling time, thermal hysterisis, quiescent supply current, and long term stability.The most important parameters for data acquisition systems design are initial error, output voltage tempera-ture coefficient (TC), thermal hysteresis, noise, and long-term stability of the voltage reference device.Table 1 summarizes the major error sources for the three references that are compared in this application note. The data represents the highest grade for each)(R3),(I R1R3R2R1V V PTAT P O +++∆=Table 1. Voltage reference major error sources (all information is based on published data sheets)Continued from previous page× V . ZR3R41R2R1R2V O++=Texas Instruments Incorporated Data Acquisitionrespective model in the 8-pin plastic DIP package over the industrial temperature range (–40°C to +85°C). The poorest-performing references are band-gap type and are not included in this summary. Buried zener diodes have better overall performance than band-gap devices and the XFET references. The buried zener reference with a third-order temperature compensation network (VRE3050) is the best performer with respect to initial error, TC, and thermal hysteresis.Explanation of parametersInitial error—The output voltage tolerance of a refer-ence after the device is turned on and warmed up. It is usually measured without a load applied. In many applica-tions, initial error is the most important specification.Often instrument manufacturers will specify a reference with a tight initial error so they do not have to perform room-temperature systems calibration after assembly.Temperature coefficient (TC)—A change in output voltage due to change in temperature usually expressed in ppm/°C. It is the second most important specification after initial accuracy. For many instrument manufacturers,a voltage reference with a temperature coefficient less than 1 ppm/°C makes it possible not to have to perform a system temperature calibration, a slow and costly process.Of the three TC specification methods (slope, butterfly,and box), the box method is most commonly used. A box is formed by the min/max limits for the nominal output voltage over the operating temperature range. The equa-tion follows.(4)6MIN MAX nominal MIN MAX 10)T (T V V V TC ×−×−=This method corresponds more accurately to the method of test and provides a closer estimate of actual error than the other methods. The box method guarantees limits for the temperature error but does not specify the exact shape and slope of the device under test. Assuming a 5-V reference with a 0.6-ppm/°C TC over the industrial tem-perature range, a plot of the box calculation method would appear as in Figure 4.A designer who needs a 14-bit accurate data acquisition system over the industrial temperature range (–40°C to +85°C) will need a voltage reference with a TC of 1.0 ppm/°C if the reference is allowed to contribute an error equivalent to 1 LSB. For 1/2 LSB equivalent error from the reference, a voltage reference with a tempera-ture coefficient of 0.5 ppm/°C would be needed. Figure 5shows the required reference TC vs. ∆T change from25°C for resolution rang-ing from 8 bits to 20 bits.Thermal hysteresis—A change in output voltage as a result of a tempera-ture change. When references experience a temperature change and return to the initial tem-perature, they do not always have the same initial output voltage.Thermal hysteresis is dif-ficult to correct and is a major error source in sys-tems that experience tem-perature changes of 25°C or more. Voltage refer-ence manufacturers are starting to include this important specification in their datasheets.Continued on next pageTexas Instruments IncorporatedData AcquisitionNoise (1/f and broadband)—Electrical noise on the output of a voltage reference. It can include wideband ther-mal noise and narrowband 1/f noise.Wideband noise can be effectively filtered with a simple RC network. 1/f noise is inherent in the reference and cannot be filtered. It is specified in the 0.1- to 10-Hz range. Low 1/f noise refer-ences are important in precision designs.Long-term drift—A slow change inoutput voltage that occurs over months of operation. Long-term drift is usually expressed in ppm/1000 hrs. In zener references, the long-term drift is typi-cally 6 ppm/1000 hrs. and decreases atan exponential rate over time. Additional temperature burn-in of the reference can accelerate the stability of a zener reference. The XFET reference has excellent long-term stability—0.2 ppm/1000 hrs.Turn-on settling time—A change in voltage over a specified time interval after the power is applied. Most references settle to 0.1% in less than 10 µs. Turn-on settling time is important for portable battery systems that conserve energy by powering the circuitry only for short periods of time.Line regulation—An error produced by a change in the input voltage. This dc specification does not include the effects of ripple voltage or line transients.Load regulation—An error produced by a change in load current. Like line regulation, this dc specification does not include the effects of load transients.PCB layout—Poor printed circuit board layout can adversely affect the performance of the reference. Poor layout can affect the output voltage, noise, and thermal performance of the device. Inherent stress in the PCB can also be transferred to the reference and can shift the out-put voltage.ConclusionIt has been shown that a number of key parameters must be evaluated before selecting an external reference for a high-resolution data acquisition system. The XFET refer-ence is suitable for systems that will be held at a constant temperature and where good long-term stability of the reference is important. In 14-bit conversion systems that are designed for the industrial operating temperature range, the VRE3050 is the preferred device because of its better initial error, TC, and thermal hysteresis performance.References1.Analog Devices Inc., Low Noise, Micropower,Precision Reference ADR293 Datasheet.2.Paul R. Gray and Robert G. Meyer, Analysis and Design of Analog Integrated Circuits ,3rd ed. (John Wiley & Sons, Inc., 1992).3.Maxim Corp., MAX6250, Low Noise Precision,+2.5 V +4.096 V +5 V Voltage Reference Datasheet.4.Texas Instruments, THS1265, 12-bit, 65 MSPS,IF Sampling Communications A/D converter.5.Texas Instruments, THS1470, 14-bit, 70 MSPS,IF Sampling Communications A/D converter.6.Thaler Corp., Precision Reference VRE3050Datasheet.Continued from previous pageIMPORTANT NOTICETexas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. 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DESCRIPTION
The DAC904 is a high-speed, Digital-to-Analog Converter (DAC) offering a 14-bit resolution option within the family of highperformance converters. Featuring pin compatibility among family members, the DAC908, DAC900, and DAC902 provide a component selection option to an 8-, 10-, and 12-bit resolution, respectively. All models within this family of DACs support update rates in excess of 165MSPS with excellent dynamic performance, and are especially suited to fulfill the demands of a variety of applications.
The advanced segmentation architecture of the DAC904 is optimized to provide a high Spurious-Free Dynamic Range (SFDR) for single-tone, as well as for multi-tone signals— essential when used for the transmit signal path of communication systems.
The DAC904 is available in SO-28 and TSSOP-28 packages.

电子课程设计题目：函数信号发生器的设计学院：机械工程学院班级：测控技术与仪器071班作者：学号：指导教师：2010年7月7日摘要：该函数发生器采用AT89S51 单片机作为控制核心，外围采用数字/模拟转换电路（DAC0832）、运放电路（1458N）等。

电路采用AT89S51单片机和一片DAC0832数模转换器组成函数信号发生器，在单片机的输出端口接DAC0832进行DA转换，再通过运放进行波形调整，最后输出波形接在示波器上显示。

它具有价格低、性能高和在低频范围内稳定性好、操作方便、体积小、耗电少等特点。

由于采用了1458N运算放大器，使其电路更加具有较高的稳定性能，性能比高。

此电路清晰，出现故障容易查找错误，操作简单、方便。

本设计主要应用AT89S51作为控制核心。

硬件电路简单，软件功能完善，控制系统可靠，性价比较高等特点，具有一定的使用和参考价值。

关键词：AT89S51、DAC0832、波形调整【Abstract】： For special requirement the function generator usingAT89S51 microcontroller as the control, external analog / digital conversion circuit (DAC0832), op-amp circuit (1458C) and so on. AT89S51 microcontroller circuit and an integral function DAC0832 digital-signal generator, the microcontroller output port connected to DA converter DAC0832, and then wave through the op amp to adjust the final output connected to the oscilloscope waveform display. It has a low cost, high performance and low frequency range, good stability, easy operation, small size, low power consumption and so on. As a result of 1458G operational amplifier circuit to a more stable performance with high performance is high. The circuit clear, easy to find failure error, simple and convenient.The design of the main application AT89S51 as the control center. Simple hardware circuit, software, functional, and reliable control system, high cost performance characteristics, has some use and reference.Key words:AT89S51, DAC0832, waveform adjust目录1、设计概述1.1、设计任务----------------------------------4 1.2、方案选择与论证----------------------------41.3、系统设计框图------------------------------52、硬件电路设计--------------------------------53、软件系统设计3.1、阶梯波设计思想及流程图--------------------133.3、三角波和正弦波设计思想--------------------144、系统软件仿真4.1、protues仿真原理图------------------------154.2、仿真波形图--------------------------------165、课程设计心得体会---------------------------176、参考文献------------------------------------177、附录附录一：protel原理图----------------------------18 附录二：PCB图 ----------------------------------18 附录三：焊接后的电路板实物图---------------------19 附录四：实际电路板调试后发生阶梯波图-------------19附录五：实验源程序-------------------------------191.1设计任务与要求：1采用AT89S51及DAC0832设计函数信号发生器；2输出信号为正弦波或三角波或阶梯波；3输出信号频率为100Hz，幅度-5V—+5V可调；4必须具有信号输出及外接电源、公共地线接口，程序在线下载接口。

FEATURES DESCRIPTIONAPPLICATIONSR FBI OUTGNDV DDV REFCSCLKSDIDAC8811SLAS411A–NOVEMBER2004–REVISED DECEMBER2004 16-Bit,Serial Input Multiplying Digital-to-Analog Converter•±0.5LSB DNL The DAC8811multiplying digital-to-analog converter •16-Bit Monotonic(DAC)is designed to operate from a single2.7-V to5.5-V supply.•±1LSB INL•Low Noise:12nV/√Hz The applied external reference input voltage VREFdetermines the full-scale output current.An internal •Low Power:I DD=2µAfeedback resistor(R FB)provides temperature tracking •+2.7V to+5.5V Analog Power Supplyfor the full-scale output when combined with an •2mA Full-Scale Current±20%,external I-to-V precision amplifier.with V REF=10VA serial data interface offers high-speed,three-wire•50-MHz Serial Interfacemicrocontroller-compatible inputs using data-in(SDI),•0.5µs Settling Time clock(CLK),and chip-select(CS).•4-Quadrant Multiplying ReferenceThe DAC8811is packaged in space-saving8-lead •Reference Bandwidth:10MHzSON and MSOP packages.•±10V Reference Input•Reference Dynamics:-105THD•Tiny8-Lead3x3mm SON and3x5mmMSOP Packages•Industry-Standard Pin Configuration•Automatic Test Equipment•Instrumentation•Digitally Controlled Calibration•Industrial Control PLCsPlease be aware that an important notice concerning availability,standard warranty,and use in critical applications of TexasInstruments semiconductor products and disclaimers thereto appears at the end of this data sheet.PRODUCTION DATA information is current as of publication date.Copyright©2004,Texas Instruments Incorporated Products conform to specifications per the terms of the TexasInstruments standard warranty.Production processing does notnecessarily include testing of all parameters.元器件交易网ABSOLUTE MAXIMUM RATINGSDAC8811SLAS411A–NOVEMBER 2004–REVISED DECEMBER 2004This integrated circuit can be damaged by ESD.Texas Instruments recommends that all integratedcircuits be handled with appropriate precautions.Failure to observe proper handling and installation procedures can cause damage.ESD damage can range from subtle performance degradation to complete device failure.Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.PACKAGE/ORDERING INFORMATION (1)MINIMUM RELATIVE DIFFERENTIAL PACKAGE-SPECIFIED TRANSPORT ACCURACYNONLINEARITYLEADTEMPERATUREPACKAGE ORDERING MEDIA,PRODUCT (LSB)(LSB)(DESIGNATOR)RANGE MARKINGNUMBER QUANTITY DAC8811C ±1±1MSOP-8(DGK)-40°C to +85°C D11DAC8811ICDGKT Tape and Reel,250DAC8811C ±1±1MSOP-8(DGK)-40°C to +85°C D11DAC8811ICDGKR Tape and Reel,2500DAC8811C ±1±1SON-8(DRB)-40°C to +85°C D11DAC8811ICDRBT Tape and Reel,250DAC8811C ±1±1SON-8(DRB)-40°C to +85°C D11DAC8811ICDRBR Tape and Reel,2500DAC8811B ±2±1MSOP-8(DGK)-40°C to +85°C D11DAC8811IBDGKT Tape and Reel,250DAC8811B ±2±1MSOP-8(DGK)-40°C to +85°C D11DAC8811IBDGKR Tape and Reel,2500DAC8811B ±2±1SON-8(DRB)-40°C to +85°C D11DAC8811IBDRBT Tape and Reel,250DAC8811B±2±1SON-8(DRB)-40°C to +85°CD11DAC8811IBDRBRTape and Reel,2500(1)For the most current specifications and package information,see the Package Option Addendum located at the end of this data sheet or refer to our web site at .over operating free-air temperature range (unless otherwise noted)(1)DAC8811UNIT V DD to GND-0.3to +7V Digital input voltage to GND -0.3to +V DD +0.3V V (I OUT )to GND-0.3to +V DD +0.3V Operating temperature range -40to +105°C Storage temperature range-65to +150°C Junction temperature range (T J max)+125°CPower dissipation (T J max -T A )/R ΘJAThermal impedance,R ΘJA 55°C/W Lead temperature,soldering Vapor phase (60s)215°C Lead temperature,soldering Infrared (15s)220°C ESD rating,HBM 1500V ESD rating,CDM 1000V (1)Stresses above those listed under absolute maximum ratings may cause permanent damage to the device.Exposure to absolute maximum conditions for extended periods may affect device reliability.2元器件交易网ELECTRICAL CHARACTERISTICSDAC8811 SLAS411A–NOVEMBER2004–REVISED DECEMBER2004V DD =+2.7V to+5.5V;IOUT=Virtual GND,GND=0V;VREF=10V;TA=full operating temperature.All specifications-40°Cto+85°C,unless otherwise noted.DAC8811PARAMETER CONDITIONS MIN TYP MAX UNITS STATIC PERFORMANCE(1)Resolution16BitsRelative accuracy DAC8811C±1LSBRelative accuracy DAC8811B±2LSBDifferential nonlinearity±1LSBOutput leakage current Data=0000h,T A=+25°C10nAOutput leakage current Data=0000h,T A=T MAX10nAFull-scale gain error All ones loaded to DAC register±1±4mVFull-scale tempco±3ppm/°COUTPUT CHARACTERISTICS(2)Output current2mAOutput capacitance Code dependent50pFREFERENCE INPUTVREF Range-1515VInput resistance5kΩInput capacitance5pFLOGIC INPUTS AND OUTPUT(2)Input low voltage V IL V DD=+2.7V0.6VV IL V DD=+5V0.8V Input high voltage V IH V DD=+2.7V 2.1VV IH V DD=+5V 2.4V Input leakage current I IL10µAInput capacitance C IL10pFINTERFACE TIMINGClock input frequency f CLK50MHzClock pulse width high10nsClock pulse width low10nsCS to Clock setup time0nsClock to CS hold time10nsData setup time5nsData hold time10nsPOWER REQUIREMENTSV DD 2.7 5.5VI DD(normal operation)Logic inputs=0V5µAV DD=+4.5V to+5.5V V IH=V DD and V IL=GND35µAV DD=+2.7V to+3.6V V IH=V DD and V IL=GND1 2.5µAAC CHARACTERISTICSOutput voltage settling time0.5µsReference multiplying BW V REF=5V PP,Data=FFFFh10MHzV REF=0V to10V,DAC glitch impulse2nV/sData=7FFFh to8000h to7FFFhFeedthrough error V OUT/V REF Data=0000h,V REF=100kHz-70dBDigital feedthrough2nV/s(1)Linearity calculated using a reduced code range of48to4047;output unloaded.(2)Specified by design and characterization;not production tested.3元器件交易网 PIN ASSIGNMENTSDRB PACKAGEDGK PACKAGER VR VDAC8811SLAS411A–NOVEMBER2004–REVISED DECEMBER2004 ELECTRICAL CHARACTERISTICS(continued)V DD =+2.7V to+5.5V;IOUT=Virtual GND,GND=0V;VREF=10V;TA=full operating temperature.All specifications-40°Cto+85°C,unless otherwise noted.DAC8811PARAMETER CONDITIONS MIN TYP MAX UNITS Total harmonic distortion-105dBOutput spot noise voltage12nV/√HzTable1.TERMINAL FUNCTIONSPIN NAME DESCRIPTION1CLK Clock input;positive edge triggered clocks data into shift registerSerial register input;data loads directly into the shift register MSB first.Extra 2SDIleading bits are ignored.3R FB Internal matching feedback resistor.Connect to external op amp output.DAC reference input pin.Establishes DAC full-scale voltage.Constant input 4V REFresistance versus code.DAC current output.Connects to inverting terminal of external precision I/V op 5I OUTamp.6GND Analog and digital ground.7V DD Positive power supply input.Specified operating range of2.7V to5.5V.Chip-select;active low digital input.Transfers shift register data to DAC register 8CSon rising edge.See Table2for operation.4元器件交易网TYPICAL CHARACTERISTICS:V DD =+5V1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0819216384245763276840960495125734465536I N L (L S B )Digital Input CodeT A =+25_C1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0D N L (L S B )T A =+25_C819216384245763276840960495125734465536Digital Input Code1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0T A =−40_CD N L (L S B )819216384245763276840960495125734465536Digital Input Code1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0T A =−40_CI N L (L S B )819216384245763276840960495125734465536Digital Input Code1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0I N L (L S B )T A =+85_C819216384245763276840960495125734465536Digital Input Code 1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0D N L (L S B )T A =+85_C819216384245763276840960495125734465536Digital Input CodeDAC8811SLAS411A–NOVEMBER 2004–REVISED DECEMBER 2004At T A =+25°C,+V DD =+5V,unless otherwise noted.LINEARITY ERROR DIFFERENTIAL LINEARITY ERRORvs DIGITAL INPUT CODEvs DIGITAL INPUT CODEFigure 1.Figure 2.LINEARITY ERROR DIFFERENTIAL LINEARITY ERRORvs DIGITAL INPUT CODEvs DIGITAL INPUT CODEFigure 3.Figure 4.LINEARITY ERROR DIFFERENTIAL LINEARITY ERRORvs DIGITAL INPUT CODEvs DIGITAL INPUT CODEFigure 5.Figure 6.5元器件交易网1.61.41.21.00.80.60.40.2000.51.01.52.02.53.03.54.04.55.0Logic Input Voltage (V)S u p p l y C u r r e n t , I D D (m A )60−6−12−18−24−30−36−42−48−54−60−66−72−78−84−90−96−102−108−114101001k10k100k1M10M100MA t t e n u a t i o n (dB )Bandwidth(Hz)Time (0.1µs/div)O u t p u t V o l t a g e (5V /d i v )Time (0.2µs/div)O u t p u t V o l t a g e (50m V /d i v )DAC8811SLAS411A–NOVEMBER 2004–REVISED DECEMBER 2004TYPICAL CHARACTERISTICS:V DD =+5V (continued)At T A =+25°C,+V DD =+5V,unless otherwise noted.SUPPLY CURRENTvs LOGIC INPUT VOLTAGEREFERENCE MULTIPLYING BANDWIDTHFigure 7.Figure 8.DAC GLITCHDAC SETTLING TIMEFigure 9.Figure 10.6元器件交易网TYPICAL CHARACTERISTICS:V DD =+2.7V1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0I N L (L S B )T A =+25_C819216384245763276840960495125734465536Digital Input Code1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0D N L (L S B )T A =+25_C819216384245763276840960495125734465536Digital Input Code1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0T A =−40_CI N L (L S B )819216384245763276840960495125734465536Digital Input Code T A =−40_C1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0D N L (L S B )819216384245763276840960495125734465536Digital Input Code1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0I N L (L S B )T A =+85_C819216384245763276840960495125734465536Digital Input Code 1.00.80.60.40.20−0.2−0.4−0.6−0.8−1.0D N L (L S B )T A =+85_C819216384245763276840960495125734465536Digital Input CodeDAC8811SLAS411A–NOVEMBER 2004–REVISED DECEMBER 2004At T A =+25°C,+V DD =+2.7V,unless otherwise noted.LINEARITY ERROR DIFFERENTIAL LINEARITY ERRORvs DIGITAL INPUT CODEvs DIGITAL INPUT CODEFigure 11.Figure 12.LINEARITY ERROR DIFFERENTIAL LINEARITY ERRORvs DIGITAL INPUT CODEvs DIGITAL INPUT CODEFigure 13.Figure 14.LINEARITY ERROR DIFFERENTIAL LINEARITY ERRORvs DIGITAL INPUT CODEvs DIGITAL INPUT CODEFigure 15.Figure 16.7元器件交易网THEORY OF OPERATIONV REFGNDI OUTV OUT +*V REF CODE65536(1)V OV REFDAC8811SLAS411A–NOVEMBER 2004–REVISED DECEMBER 2004The DAC8811is a single channel current output,16-bit digital-to-analog converter (DAC).The architecture,illustrated in Figure 17,is an R-2R ladder configuration with the three MSBs segmented.Each 2R leg of the ladder is either switched to GND or the I OUT terminal.The I OUT terminal of the DAC is held at a virtual GND potential by the use of an external I/V converter op amp.The R-2R ladder is connected to an external reference input V REF that determines the DAC full-scale current.The R-2R ladder presents a code independent load impedance to the external reference of 5k Ω±25%.The external reference voltage can vary in a range of -15V to 15V,thus providing bipolar I OUT current operation.By using an external I/V converter and the DAC8811R FB resistor,output voltage ranges of -V REF to V REF can be generated.Figure 17.Equivalent R-2R DAC CircuitWhen using an external I/V converter and the DAC8811R FB resistor,the DAC output voltage is given by Equation 1:Each DAC code determines the 2R leg switch position to either GND or I OUT .Because the DAC outputimpedance as seen looking into the I OUT terminal changes versus code,the external I/V converter noise gain will also change.Because of this,the external I/V converter op amp must have a sufficiently low offset voltage such that the amplifier offset is not modulated by the DAC I OUT terminal impedance change.External op amps with large offset voltages can produce INL errors in the transfer function of the DAC8811due to offset modulation versus DAC code.For best linearity performance of the DAC8811,an op amp (OPA277)is recommended (Figure 18).This circuit allows V REF swinging from -10V to +10V.Figure 18.Voltage Output Configuration8元器件交易网SDI CLKCSAPPLICATION INFORMATIONStabilityCircuitV OUTPositive Voltage Output CircuitDAC8811SLAS411A–NOVEMBER 2004–REVISED DECEMBER 2004THEORY OF OPERATION (continued)Figure 19.DAC8811Timing Diagram Table 2.Control Logic Truth Table (1)CLK CS Serial Shift Register DAC Register X H No effectLatched ↑+L Shift register data advanced one bit Latched X H No effectLatchedX ↑+Shift register data transferred to DAC registerNew data loaded from serial register(1)↑+Positive logic transition;X =Don't careTable 3.Serial Input Register Data Format,Data Loaded MSB FirstB15B0Bit (MSB)B14B13B12B11B10B9B8B7B6B5B4B3B2B1(LSB)DataD15D14D13D12D11D10D9D8D7D6D5D4D3D2D1D0For a current-to-voltage design (see Figure 20),the DAC8811current output (I OUT )and the connection with the inverting node of the op amp should be as short as possible and according to correct PCB layout design.For each code change there is a step function.If the GBP of the op amp is limited and parasitic capacitance is excessive at the inverting node then gain peaking is possible.Therefore,for circuit stability,a compensation capacitor C1(4pF to 20pF typ)can be added to the design,as shown in Figure 20.Figure 20.Gain Peaking Prevention Circuit With Compensation CapacitorAs Figure 21illustrates,in order to generate a positive voltage output,a negative reference is input to the DAC8811.This design is suggested instead of using an inverting amp to invert the output due to tolerance errors of the resistor.For a negative reference,V OUT and GND of the reference are level-shifted to a virtual ground and a -2.5V input to the DAC8811with an op amp.9元器件交易网V OUTBipolar Output CircuitV OUT+ǒD32,768*1ǓV REF(2)V OUT10 k W10 k W+2.5V(+10V)Programmable Current Source CircuitI L +(R2)R3)ńR1R3VREFD(3)DAC8811SLAS411A–NOVEMBER2004–REVISED DECEMBER2004APPLICATION INFORMATION(continued)Figure21.Positive Voltage Output CircuitThe DAC8811,as a2-quadrant multiplying DAC,can be used to generate a unipolar output.The polarity of the full-scale output I OUT is the inverse of the input reference voltage at V REF.Some applications require full4-quadrant multiplying capabilities or bipolar output swing.As shown in Figure22, external op amp U4is added as a summing amp and has a gain of2X that widens the output span to5V.A 4-quadrant multiplying circuit is implemented by using a 2.5-V offset of the reference voltage to bias U4.According to the circuit transfer equation given in Equation2,input data(D)from code0to full scale produces output voltages of V OUT=-2.5V to V OUT=+2.5V.External resistance mismatching is the significant error in Figure22.Figure22.Bipolar Output CircuitA DAC8811can be integrated into the circuit in Figure23to implement an improved Howland current pump forprecise voltage to current conversions.Bidirectional current flow and high voltage compliance are two features of the circuit.With a matched resistor network,the load current of the circuit is shown by Equation3:10元器件交易网ZO+R1ȀR3(R1)R2)R1(R2Ȁ)R3Ȁ)*R1Ȁ(R2)R3)(4)V REFR244OUTCross-ReferenceDAC8811 SLAS411A–NOVEMBER2004–REVISED DECEMBER2004The value of R3in the previous equation can be reduced to increase the output current drive of U3.U3can drive ±20mA in both directions with voltage compliance limited up to15V by the U3voltage supply.Elimination of the circuit compensation capacitor C1in the circuit is not suggested as a result of the change in the output impedance Z O,according to Equation4:As shown in Equation4,with matched resistors,Z O is infinite and the circuit is optimum for use as a current source.However,if unmatched resistors are used,Z O is positive or negative with negative output impedance being a potential cause of oscillation.Therefore,by incorporating C1into the circuit,possible oscillation problems are eliminated.The value of C1can be determined for critical applications;for most applications,however,a value of several pF is suggested.Figure23.Programmable Bidirectional Current Source CircuitThe DAC8811has an industry-standard pinout.Table4provides the cross-reference information.Table4.Cross-ReferenceSPECIFIEDTEMPERATURE PACKAGE PACKAGE CROSS-PRODUCT INL(LSB)DNL(LSB)RANGE DESCRIPTION OPTION REFERENCE PART DAC8811ICDGK±1±1-40°C to+85°C8-Lead MicroSOIC MSOP-8N/ADAC8811IBDGK±2±1-40°C to+85°C8-Lead MicroSOIC MSOP-8AD5543BRMDAC8811ICDRB±1±1-40°C to+85°C8-Lead Small Outline SON-8N/ADAC8811IBDRD±2±1-40°C to+85°C8-Lead Small Outline SON-8N/A N/A±2±1-40°C to+85°C8-Lead SOIC SOIC-8AD5543BR11元器件交易网PACKAGING INFORMATIONOrderable Device Status (1)Package Type Package Drawing Pins Package Qty Eco Plan (2)Lead/Ball FinishMSL Peak Temp (3)DAC8811IBDGKR ACTIVE MSOP DGK 82500TBD Call TI Call TIDAC8811IBDGKT ACTIVE MSOP DGK 8250TBD Call TILevel-1-220C-UNLIMDAC8811IBDRBR ACTIVE SON DRB 83000TBD CU POST PLATE Level-1-240C-UNLIM DAC8811IBDRBT ACTIVE SON DRB 8250TBD CU POST PLATE Level-1-240C-UNLIMDAC8811ICDGKR ACTIVE MSOP DGK 82500TBD Call TI Level-1-220C-UNLIM DAC8811ICDGKT ACTIVE MSOP DGK 8250TBD Call TI Level-1-220C-UNLIM DAC8811ICDRBR ACTIVE SON DRB 83000TBD CU SNPB Level-1-240C-UNLIM DAC8811ICDRBTACTIVESONDRB8250TBDCU SNPBLevel-1-240C-UNLIM(1)The marketing status values are defined as follows:ACTIVE:Product device recommended for new designs.LIFEBUY:TI has announced that the device will be discontinued,and a lifetime-buy period is in effect.NRND:Not recommended for new designs.Device is in production to support existing customers,but TI does not recommend using this part in a new design.PREVIEW:Device has been announced but is not in production.Samples may or may not be available.OBSOLETE:TI has discontinued the production of the device.(2)Eco Plan -The planned eco-friendly classification:Pb-Free (RoHS)or Green (RoHS &no Sb/Br)-please check /productcontent for the latest availability information and additional product content details.TBD:The Pb-Free/Green conversion plan has not been defined.Pb-Free (RoHS):TI's terms "Lead-Free"or "Pb-Free"mean semiconductor products that are compatible with the current RoHS requirements for all 6substances,including the requirement that lead not exceed 0.1%by weight in homogeneous materials.Where designed to be soldered at high temperatures,TI Pb-Free products are suitable for use in specified lead-free processes.Green (RoHS &no Sb/Br):TI defines "Green"to mean Pb-Free (RoHS compatible),and free of Bromine (Br)and Antimony (Sb)basedflame retardants (Br or Sb do not exceed 0.1%by weight in homogeneous material)(3)MSL,Peak Temp.--The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications,and peak solder temperature.Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided.TI bases its knowledge and belief on information provided by third parties,and makes no representation or warranty as to the accuracy of such information.Efforts are underway to better integrate information from third parties.TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.TI and TI suppliers consider certain information to be proprietary,and thus CAS numbers and 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