AN-1238 APPLICATION NOTE One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com High Accuracy, Bipolar Voltage Output Digital-to-Analog Conversion Using the AD5765 DAC CIRCUIT FUNCTION AND BENEFITS This circuit provides high accuracy, bipolar data conversion using the AD5765, a quad, 16-bit, serial input, bipolar voltage output, digital-to-analog converter (DAC). This circuit uses the ADR420 precision reference to achieve optimal DAC performance over a full operating temperature range. The only external components needed for this precision 16-bit DAC are a reference voltage source, decoupling capacitors on the supply pins and reference inputs, and an optional short-circuit current-setting resistor. This implementation, therefore, leads to savings in cost and reduced board space. The circuit is well suited for both closed-loop servo control and open-loop control applications. There are four possible sources of error to consider when choosing a voltage reference for high accuracy applications: initial accuracy, long-term drift, temperature coefficient of the output voltage, and output voltage noise. Table 2 lists other 2.048 V precision reference candidates from Analog Devices, Inc., and their respective attributes. +5V ADR420 2 VOUT 6 GND VIN 4 +5V –5V CIRCUIT DESCRIPTION 10µF 10µF 100nF 100nF 100nF BIN/2sCOMP SDIN 3 SDIN SDO 4 SDO REFAB NC REFCD NC AVSS AVDD REFGND SCLK AGNDA 24 VOUTA 23 VOUTA VOUTB 22 VOUTB AGNDB 21 AD5765 CLR 5 CLR AGNDC 20 LDAC 6 LDAC VOUTC 19 VOUTC D0 7 D0 VOUTD 18 VOUTD D1 8 D1 AGNDD 17 RSTIN 10µF ISCC AVSS PGND AVDD DVCC 10 11 12 13 14 15 16 DGND 9 RSTOUT 10µF The AVDD supply range is from +4.75 V to +5.25 V. The AVSS supply range is from −4.75 V to −5.25 V. The nominal full-scale output voltage range is ±4.096 V. SYNC 2 100nF 100nF A precision voltage reference must be used in order for the DAC to achieve the optimum performance over its full operating temperature range. The AD5765 incorporates reference buffers, which eliminate the need for both a positive and negative external reference and associated buffers. This leads to further savings in both cost and board space. Because the voltages applied to the reference inputs (REFAB, REFCD) are used to generate the buffered positive and negative internal references for the DAC cores, any error in the external voltage reference is reflected in the outputs of the device. NC = NO CONNECT 10µF +5V +5V –5V Figure 1. High Accuracy, Bipolar Configuration of the AD5765 DAC Using a Precision Reference Table 2. Precision 2.048 V References Part ADR430 ADR420 Initial Accuracy, Maximum (mV) ±1 ±1 Long-Term Drift, Typical (ppm) 40 50 08273-001 • • • 1 SCLK RSTIN The AD5765 is a high performance DAC that offers guaranteed monotonicity, integral nonlinearity (INL) of ±1 LSB (C grade device), low noise, and a 10 µs settling time. Performance is guaranteed over the following supply voltage ranges: SYNC RSTOUT Description Complete quad, 16-bit, high accuracy DAC Precision 4.096 V voltage reference 100nF Product AD5765 ADR420 BIN/2sCOMP 32 31 30 29 28 27 26 25 Table 1. Devices Connected/Referenced Temperature Drift, Maximum (ppm/°C) 3 3 Rev. A | Page 1 of 2 0.1 Hz to 10 Hz Noise, Typical (µV p-p) 3.5 1.75 AN-1238 Application Note In any circuit where accuracy is important, careful consideration of the power supply and ground return layout helps to ensure the rated performance. The printed circuit board (PCB) on which the AD5765 is mounted must be designed so that the analog and digital sections are physically separated and confined to certain areas of the board. If the AD5765 is in a system where multiple devices require an AGND-to-DGND connection, make the connection at one point only. The star ground point is established as close as possible to the device. The AD5765 must have ample supply bypassing of 10 µF in parallel with 0.1 µF on each supply, located as close to the package as possible, ideally right up against the device. The 10 µF capacitors are the tantalum bead type. The 0.1 µF capacitor must have low effective series resistance (ESR) and low effective series inductance (ESL), such as the common ceramic types, which provide a low impedance path to ground at high frequencies to handle transient currents due to internal logic switching. LEARN MORE The power supply traces of the AD5765 must be as wide as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals, such as clocks, must be shielded with digital ground to avoid radiating noise to other parts of the board and must never be run near the reference inputs. A ground line routed between the SDIN and SCLK lines helps reduce crosstalk between them (not required on a multilayer board, which has a separate ground plane; however, it is helpful to separate the lines). It is essential to minimize noise on the reference inputs because it couples through to the DAC output. Avoid crossover of digital and analog signals. Traces on opposite sides of the board must run at right angles to each other. This reduces the effects of feedthrough on the board. A microstrip technique is recommended but not always possible with a double-sided board. In this technique, the component side of the board is dedicated to the ground plane, and signal traces are placed on the solder side. Best layout and performance are achieved with at least a 4-layer multilayer board, where there are a ground plane layer, a power supply layer, and two signal layers. 6/13—Rev. 0 to Rev. A Document Title Changed from CN-0073 to AN-1238 ....... Universal Changes to Table 2 ........................................................................................1 Kester, Walt. 2005. The Data Conversion Handbook. Analog Devices. Chapters 3 and 7. 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-101 Tutorial, Decoupling Techniques. Analog Devices. Voltage Reference Wizard Design Tool. Data Sheets and Evaluation Boards AD5765 Data Sheet. AD5765 Evaluation Board. ADR420 Data Sheet. REVISION HISTORY 6/09—Revision 0: Initial Version ©2009–2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. AN08273-0-6/13(A) Rev. A | Page 2 of 2