Circuit Note CN-0034 Devices Connected/Referenced Circuit Designs Using Analog Devices Products Apply these product pairings quickly and with confidence. For more information and/or support call 1-800-AnalogD (1-800-262-5643) or visit www.analog.com/circuit. AD5426/AD5432/ AD5443 8-Bit/10-Bit/12-Bit Multiplying DACs AD8065 High Performance FastFETTM Amplifier ADR01 Low Noise Precision Reference Unipolar, Precision DC Digital-to-Analog Conversion Using the AD5426/AD5432/AD5443 8-Bit to12-Bit DACs This circuit is a high performance, unipolar, precision dc DAC configuration that employs the AD5426/AD5432/AD5443 family of precision multiplying DACs, the AD8065 low noise operational amplifier (op amp), and the ADR01 precision reference. Since the op amp dictates the overall circuit performance in terms of precision or speed, the AD8065, a high precision, low noise op amp is well matched for performancedriven applications. This circuit also uses the ADR01, which is a high accuracy, high stability, 10 V precision voltage reference. Because voltage reference temperature coefficient and longterm drift are primary considerations for applications requiring high precision conversion, this device is an ideal candidate. The input offset voltage of an op amp is multiplied by the variable noise gain (due to the code-dependent output resistance of the DAC) of the circuit. A change in this noise gain between two adjacent digital codes produces a step change in the output voltage due to the amplifier’s input offset voltage. This output voltage change is superimposed on the desired change in output between the two codes and gives rise to a differential linearity error that, if large enough, could cause the DAC to be nonmonotonic. In general, the input offset voltage should be a fraction of an LSB to ensure monotonic behavior when stepping through codes. For the 12-bit AD5443, the LSB size is 10 V/212 = 2.44 mV, while the input offset voltage of the AD8065 is only 0.4 mV. CIRCUIT DESCRIPTION This circuit utilizes the AD5426/AD5432/AD5443 CMOS, current output DACs that provide 8-bit, 10-bit, and 12-bit operation, respectively. Because this is a current output DAC, an op amp is required for current-to-voltage (I-V) conversion at the output of the DAC. Since an op amp’s bias current and offset voltage are both important selection criteria for precision current output DACs, this circuit employs the AD8065 op amp, which has ultralow offset voltage (0.4 mV typical) and bias current (2 pA typical). The AD8065 and the AD5426/AD5432/ AD5443 can be easily configured to provide a 2-quadrant multiplying operation or a unipolar output voltage swing, as shown in Figure 1. When an output amplifier is connected in unipolar mode, the output voltage is given by VOUT = −VREF × (D/2N) where D is the digital word loaded to the DAC and N is the number of bits: D = 0 to 255 (8-bit AD5426); D = 0 to 1023 (10-bit AD5432); and D = 0 to 4095 (12-bit AD5443). VDD1 = +5.0V VDD VDD = +12V C1 VDD VIN VOUT VREF ADR01 0.1µF AD5426/ AD5432/ AD5443 SYNC SCLK SDIN RFB IOUT1 A1 A1 AD8065 VOUT = 0V TO –VREF IOUT2 VDD GND VSS = –12V 10µF 0.1µF MICROCONTROLLER AGND VSS 10µF 0.1µF VDD1 10µF 0.1µF NOTES 1. C1 PHASE COMPENSATION (1pF TO 5pF) MAY BE REQUIRED IF A1 IS A HIGH SPEED AMPLIFIER. 08269-001 CIRCUIT FUNCTION AND BENEFITS Figure 1. Unipolar Output Precision DC Configuration (Simplified Schematic) COMMON VARIATIONS The OP1177 is another excellent op amp candidate for the I-V conversion circuit. It also provides a low offset voltage (15 µV typical) and ultralow bias current (0.5 nA typical). Rev. 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CN-0034 Circuit Note The 10.0 V ADR01 reference can be replaced by either the ADR02 or ADR03, which are low noise references available from the same reference family as the ADR01 and provide 5.0 V and 2.5 V, respectively. The ADR445 and ADR441 ultralow noise references are suitable substitutes that also provide 5.0 V and 2.5 V, respectively. Note that the size of the reference input voltage is restricted by the rail-to-rail voltage of the operational amplifier selected. Data Sheets LEARN MORE ADR03 Data Sheet. ADIsimPower Design Tool. Analog Devices. ADR441 Data Sheet. Kester, Walt. 2005.The Data Conversion Handbook. Analog Devices. Chapters 3 and 7. ADR445 Data Sheet. MT-015 Tutorial, Basic DAC Architectures II: Binary DACs. Analog Devices. MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of AGND and DGND. Analog Devices. MT-033 Tutorial, Voltage Feedback Op Amp Gain and Bandwidth. Analog Devices. AD5426 Data Sheet. AD5432 Data Sheet. AD5443 Data Sheet. AD8065 Data Sheet. ADR01 Data Sheet. ADR02 Data Sheet. OP1177 Data Sheet. REVISION HISTORY 7/09—Rev. 0 to Rev. A Updated Format .................................................................. Universal MT-035 Tutorial, Op Amp Inputs, Outputs, Single-Supply, and Rail-to-Rail Issues. Analog Devices. MT-101 Tutorial, Decoupling Techniques. Analog Devices. Voltage Reference Wizard Design Tool. Analog Devices. (Continued from first page) "Circuits from the Lab" are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the "Circuits from the Lab" in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the "Circuits from the Lab". Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any "Circuits from the Lab" at any time without notice, but is under no obligation to do so. Trademarks and registered trademarks are the property of their respective owners. ©2008–2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN08269-0-7/09(A) Rev. A | Page 2 of 2