Circuit Note CN-0052 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/circuits. AD5450/AD5451/ AD5452/AD5453 8-/10-/12-/14-Bit Multiplying DACs OP177 Ultra-Precision Operational Amplifier ADR01 Low Noise Precision 10 V Reference Unipolar, Precision DC, Digital-to-Analog Conversion Using the AD5450/AD5451/AD5452/AD5453 8-/10-/12-/14-Bit DACs CIRCUIT FUNCTION AND BENEFITS CIRCUIT DESCRIPTION The circuit described in this document is a high performance, unipolar, precision DAC configuration that employs the AD5450/ AD5451/AD5452/AD5453 family of precision multiplying DACs, the OP177 low noise, high precision operational amplifier (op amp), and the ADR01 precision 10 V reference. Because the op amp dictates the overall circuit dc performance in terms of precision, the OP177, a high precision, low noise op amp, is well matched for performance-driven 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 long-term drift are primary considerations for applications requiring high precision conversion, this device is also an ideal candidate. The circuit uses the AD5450/AD5451/AD5452/AD5453 CMOS, current-output DACs, which provide 8-, 10-, 12- and 14-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. Because an op amp bias current and offset voltage are both important selection criteria for precision current output DACs, this circuit employs the OP177 op amp, which has ultralow offset voltage (25 µV) and bias current (2 nA). The OP177 and the AD5450/AD5451/ AD5452/AD5453 can be easily configured to provide a twoquadrant multiplying operation or a unipolar output voltage swing, as shown in Figure 1. VDD = 5V VDD1 = 12V VDD VIN VOUT ADR01 VREF VREF 0.1µF AD5450/ AD5451/ AD5452/ AD5453 C1 = 1.8pF RFB VDD1 = 12V IOUT1 OP177 VOUT = 0 TO –VREF VSS = –12V VDD SYNC SCLK SDIN GND 10µF µCONTROLLER 0.1µF AGND VSS 10µF 0.1µF 10µF 0.1µF 08611-001 VDD1 Figure 1. Unipolar Precision DC Configuration (Simplified Schematic: Decoupling and All Connections Not Shown) Rev. A “Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, youare solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any“Circuit fromthe Lab”. (Continued on last page) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved. CN-0052 Circuit Note When an output amplifier is connected in unipolar mode, the output voltage is given by TA = 25°C VREF = 10V VDD = 5V 1.6 1.2 0.8 0.4 0 –0.4 –0.8 × (D/2N) –1.2 where D is the digital word loaded to the DAC, and N is the number of bits (D = 0 to 255 (8-bit AD5450); D = 0 to 1023 (10-bit AD5451); D = 0 to 4095 (12-bit AD5452); D = 0 to 16,383 (14-bit AD5453)). –1.6 –2.0 0 2048 4096 6144 8192 10,240 12,288 14,336 16,384 CODE 08611-002 VOUT = −VREF 2.0 INL (LSB) The AD5450/AD5451/AD5452/AD5453are designed on a 5 V CMOS process and operate from a VDD power supply of 2.5 V to 5.5 V. The DACs accept VREF input ranges up to 10 V, as shown with the ADR01 reference in Figure 1. The ADR01 requires a supply voltage (VDD1) of 12 V minimum and can be driven from the same supply voltage that powers the output amplifier. Figure 2. AD5453 14-Bit DAC Relative Accuracy Plot. 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, which, if large enough, may 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. Excellent grounding, layout, and decoupling techniques must be used for proper operation of the circuit. All power supply pins should be decoupled directly at the pin with a low inductance (low ESL) 0.1 µF ceramic capacitor. The connection to ground should be directly to a large area ground plane. Additional decoupling using a 1 µF to 10 µF electrolytic capacitor is recommended on each power supply where it enters the PC board. The decoupling capacitors are not shown in Figure 1 for simplicity. Relative accuracy or endpoint nonlinearity is one of the most widely used techniques in determining the accuracy performance of a DAC circuit. This is a measure of the maximum deviation from a straight line passing through the endpoints of the DAC transfer function. It is measured after adjusting for zero and full-scale error and is normally expressed in LSBs. Figure 2 shows the performance of the circuit shown in Figure 1 using the AD5453 14-bit DAC and an OP177 amplifier. To optimize high frequency performance, the I-V amplifier should be located as close to the DAC as possible. The AD5450/ AD5451/AD5452/AD5453 data sheets show the schematics and layouts used for the evaluation boards. COMMON VARIATIONS The OP1177 and AD8065 are other excellent op amp candidates for the I-V conversion circuit. They also provide a low offset voltage and ultralow bias current. The 10.0 V output ADR01 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 outputs, respectively. The ADR445 and ADR441 ultralow noise references are also suitable substitutes that 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. Rev. A | Page 2 of 3 Circuit Note CN-0052 LEARN MORE Data Sheets and Evaluation Boards Kester, Walt. The Data Conversion Handbook. Chapters 3, 7. Analog Devices, 2005. AD5450/AD5451/AD5452/AD5453 Data Sheets and Evaluation Boards. MT-015 Tutorial, Basic DAC Architectures II: Binary DACs. Analog Devices. OP177 Data Sheet. MT-033 Tutorial, Voltage Feedback Op Amp Gain and Bandwidth. Analog Devices. OP1177 Data Sheet. MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of AGND and DGND. Analog Devices. ADR02 Data Sheet. MT-035 Tutorial, Op Amp Inputs, Outputs, Single-Supply, and Rail-to-Rail Issues. Analog Devices. AD8065 Data Sheet. ADR01 Data Sheet. ADR03 Data Sheet. ADR441 Data Sheet. MT-101 Tutorial, Decoupling Techniques. Analog Devices. ADR445 Data Sheet. ADIsimPower Design Tool. Analog Devices. REVISION HISTORY Voltage Reference Wizard Design Tool. Analog Devices. 11/09—Rev. 0 to Rev. A Updated Format ................................................................. Universal 1/09—Revision 0: Initial Release (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. ©2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN08611-0-11/09(A) Rev. A | Page 3 of 3