Circuit Note CN-0317 Devices Connected/Referenced Circuits from the Lab® reference designs are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0317. AD2S1210 Variable Resolution, 10-Bit to 16-Bit Resolverto-Digital Converter with Reference Oscillator AD8397 Dual, Rail-to-Rail, High Output Current Amplifier Integrated High Current Driver for 10-Bit to 16-Bit Resolver-to-Digital Converter EVALUATION AND DESIGN SUPPORT CIRCUIT FUNCTION AND BENEFITS Circuit Evaluation Boards AD2S1210 Evaluation Board (EVAL-AD2S1210SDZ) System Demonstration Platform, SDP-B (EVAL-SDP-CB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials The circuit shown in Figure 1 is a high performance, resolverto-digital converter (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range. The AD8397 high current driver can supply 310 mA into a 32 Ω load and eliminates the requirement for discrete push-pull buffer solutions. Common applications of RDCs are in automotive and industrial markets to provide motor shaft position and/or velocity feedback. TO DUPLICATE BUFFER CIRCUIT 120pF R2 AD2S1210 15.4kΩ EXC EXC +12V R1 VCM (1) = +2.5V VCM (OUT) = +5.7V 10kΩ 1/2 AD8397 VCM (2) = +3.75V R3 +2.5V 3.6V p-p +12V 22kΩ VOUT +5.7V 5.54V p-p R4 10kΩ NOTES 1. VCM (1) IS THE COMMON-MODE VOLTAGE OF THE EXCITATION OUTPUTS. 2. VCM (2) IS THE COMMON-MODE VOLTAGE OF THE AMPLIFIER SET BY R3 AND R4. 3. VCM (OUT) IS THE BUFFER OUTPUT COMMON-MODE VOLTAGE. 11348-001 +5V C1 +2.5V 3.6V p-p Figure 1. High Current Buffer Using the AD8397 for the AD2S1210 RDC Excitation Signal Output (Simplified Schematic: Decoupling and All Connections Not Shown) Rev. 0 Circuits from the Lab reference designs 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, you are 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 toanycausewhatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage) 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 ©2014 Analog Devices, Inc. All rights reserved. CN-0317 Circuit Note CIRCUIT DESCRIPTION The RDC simultaneously samples both input signals to provide digitized data to the digital engine, known as a Type II tracking loop. The Type II tracking loop is responsible for the position and velocity calculations. A typical application circuit is shown in Figure 2. The AD2S1210 is a complete 10-bit to 16-bit resolution tracking RDC, which includes an on-chip programmable sine wave oscillator that provides the excitation for resolvers. Because of harsh operating environments, the AD2S1210 (C grade and D grade) are specified over the extended industrial temperature range of −40°C to +125°C. Due to resolver input signal requirements, the excitation buffer must provide a single-ended current of up to 200 mA. The buffer circuit shown in Figure 1 also provides gain to the AD2S1210 excitation output signal, in addition to current drive capability. The high current driver shown in Figure 1 uses the AD8397 dual op amp to amplify and level shift the AD2S1210 reference oscillator excitation outputs so that the interface to the resolver is optimized. The AD8397 is a low distortion, high output current, and wide output dynamic range amplifier that is ideal for resolvers. The AD8397 310 mA current drive capability for 32 Ω loads delivers the required power to a resolver without the conventional use of discrete push-pull output stages, which simplifies the driver circuit and consumes less power compared to the additional components required in the conventional push-pull circuitry. A similar driver stage is used for the complementary excitation output to achieve a fully differential signal used in driving the resolver primary winding. The AD8397 is available in a narrow 8-lead SOIC package specified over the industrial temperature range of −40°C to +85°C. A typical resolver has an input resistance in range of 100 Ω to 200 Ω, and the primary coil must be excited with 7 V rms. The converter accepts input signals in the range of 3.15 V p-p ±27%. The frequency range of the AD2S1210 is specified from 2 kHz to 20 kHz. A Type II tracking loop is employed to track the inputs and to convert the input sine and cosine information into a digital representation of the input angle and velocity. The maximum tracking rate of the device is specified at 3125 rps. At 16-bit resolution, the position output has a maximum accuracy error specification of ±5.3 arc min. The AD2S1210 operates on the 5 V supply, and the AD8397 that acts as output buffer circuit requires a 12 V supply to provide the required differential signal amplitude to the resolver. RDCs employ sinusoidal signals to determine the angular position and/or velocity of a resolver that is excited with a sine wave reference signal. The resolver excitation reference signal present on the primary winding is transformed into two sinusoidal, differential output signals: the sine and cosine. The amplitudes of the sine and cosine signals depend on the actual resolver position, the transformation ratio of the resolver, and the excitation signal amplitude. Figure 1 shows the schematic for the AD2S1210 and AD8397 configured as a differential driver. A very attractive aspect of the AD8397 is that its output can deliver high linear output current when driving heavy loads, up to 310 mA into a 32 Ω load while maintaining a −80 dBc spurious-free dynamic range (SFDR). Due to its high output current, the AD8397 can deliver the required power to a resolver without the need of a discrete push-pull circuit. S2 S4 5V S1 R1 BUFFER CIRCUIT 2 EXC EXC SIN AGND 1 SINLO 48 47 46 45 44 43 42 41 40 39 38 37 COS 10µF COSLO AVDD 10nF S3 BUFFER CIRCUIT REFBYP 10nF REFOUT 4.7µF R2 34 3 4 5V 8.192MHz 33 5 DGND 6 DVDD 7 CLKIN 8 XTALOUT 32 AD2S1210 29 9 28 10 27 11 12 20pF 26 25 13 14 15 16 17 18 19 20 21 22 23 24 VDRIVE 10nF 4.7µF Figure 2. AD2S1210 RDC Typical Application Circuit Rev. 0 | Page 2 of 7 11348-002 20pF 31 30 DGND 4.7µF VDRIVE 10nF 36 35 Circuit Note CN-0317 TO DUPLICATE BUFFER CIRCUIT C1 120pF 3.6V p-p R2 15.4kΩ AD2S1210 EXC 3.3Ω VOUT D2 R3 22kΩ R4 10kΩ 5.54V p-p +5.7V 4.7Ω AD8662 +12V 3.6V p-p VCM (OUT) = +5.7V Q1 BC846B D1 VCM (1) = +2.5V VCM (2) = +3.75V +2.5V +12V 2.2kΩ +12V R1 10kΩ EXC +12V 4.7Ω 3.3Ω Q2 BC856B 2.2Ω 11348-003 +2.5V +5V D1, D2: TS4148RY Figure 3. Discrete Push-Pull Driver Circuit The excitation output of the AD2S1210 typically delivers a 3.6 V p-p sinusoidal signal on the EXC and EXC outputs, which results in a 7.2 V p-p differential signal. The typical transformation ratio of an automotive resolver is 0.286. Therefore, if a unity-gain buffer is used in conjunction with the AD2S1210, the amplitude of the resolver outputs is approximately 2 V p-p differential. Such a signal has insufficient amplitude to meet the AD2S1210 input amplitude specification. Ideally, the sine and cosine inputs have amplitudes of 3.15 V p-p differential; therefore, the AD8397 must provide a gain of approximately 1.5. The gain of the excitation buffer shown in Figure 1 is set by the R1 and R2 resistors. During the circuit tests, the R1 and R2 resistors had a value of 10 kΩ and 15.4 kΩ, respectively, corresponding to a gain of 1.54. The EVAL-AD2S1210SDZ evaluation board provides jumper options that allow the use of either the integrated driver shown in Figure 1 or the discrete driver in Figure 3. Figure 4 shows the quality of the signals of the discrete pushpull circuit and the integrated buffer using the AD8397. Using the Rohde & Schwarz RTO1024, a fast Fourier transform (FFT) analyzes the output signal, and the fundamental and harmonics power are measured. The excitation frequency is set to 10 kHz. With the gain set to 1.54, the AD8397 provides an output signal of 5.54 V p-p in both configurations. The power in the fundamental is approximately 18 dBm into the 50 Ω typical input impedance of the RTO1024. The signal-to-noise-and-distortion (SINAD) and total harmonic distortion (THD) are then computed from the power values of the fundamental frequency and harmonics of the signal. For the push-pull circuit, SINAD = 50.9615 dB, and THD = 25.66%; for the AD8397 buffer, SINAD = 54.8 dB, and THD = 25.51%. This calculation makes both configurations comparable. There are jumper options on the EVAL-AD2S1210SDZ evaluation board to change R2 to 8.66 kΩ, which provides a gain of 0.866. This gain setting delivers 3.12 V p-p differential amplitude signals to the sine and cosine inputs for resolvers with transformation ratios of 0.5. The R3 and R4 resistors set the common-mode voltage of the amplifier to VCM (2) = 3.75 V. The common-mode voltage of the excitation outputs is VCM (1) = 2.5 V (midsupply), which translates into the buffer output common-mode voltage of approximately VCM (OUT) = 5.7 V (approximately one half the 12 V supply). Because the selected topology can operate on a single supply, the op amp selected for the buffer must also be able to operate with the single-supply rail. The AD8397 operates on a single supply of 12 V and has rail-to-rail outputs, making it an ideal choice. Rev. 0 | Page 3 of 7 30 PUSH-PULL BUFFER AD8397 BUFFER 18.186 20 18.135 10 0 –10 –20 –30 –40.998 –40.74 –36.84 –39.588 –40 –41.587 –42.56 –50 –44.031 –42.435 –46.954 –46.787 FOURTH FIFTH –60 FIRST SECOND THIRD FUNDAMENTAL Figure 4. Push-Pull and AD8397 Output Signal Comparison 11348-004 The buffer stage in Figure 1 reduces power and component count while achieving driving capability that the push-pull circuit offers. MEASUREMENTS POWER (dBm) The required current to drive the resolver is 200 mA for a 100 Ω to 200 Ω input resistance. The discrete solution shown in Figure 3 provides a push-pull output stage, which not only adds cost to the driver circuit but also consumes a small amount of quiescent power even when there is no signal present. CN-0317 Circuit Note The next step is to prove that AD8397 circuit can still pass the excitation signals even with the presence of a high current at its output. The test setup shown in Figure 5 determines the AD8397 circuit performance by sinking a current at the output. C1 120pF R2 15.4kΩ +2.5V 3.6V p-p EXC R1 10kΩ VCM (1) = +2.5V +12V VCM (OUT) = +5.7V 5.54V p-p +5.7V VOUT AD8397 A VCM (2) = +3.75V R3 22kΩ R4 10kΩ RESISTOR NETWORK ISINK 11348-005 +12V Figure 5. Test Setup for Sinking Current on AD8397 The AD8397 can deliver a high linear output current of up to 310 mA into a 32 Ω load. Resolver input resistance typically ranges from 100 Ω to 200 Ω. Figure 6 shows the excitation signals when sinking a current of 310 mA to the AD8397 output. The output is still able to maintain its signal strength and, therefore, able to drive a typical resolver. Recommendations Capacitor C1 in parallel with Resistor R2 forms a low-pass filter to filter out any noise that exists on the EXC and EXC outputs. When selecting the cutoff frequency of this filter, ensure that the phase shift of the carrier caused by the filter does not exceed the phase lock range of the AD2S1210. Note that C1 is not obligatory, because the resolver can filter out high frequency components from the AD2S1210 excitation output. During the circuit verification process, the outputs of the resolver were directly connected to the AD2S1210 inputs. Often in user applications, additional scaling resistors and/or passive RC filters are used. Additional passive components in front of the AD2S1210 device are acceptable; however, do not exceed the maximum phase lock range of the AD2S1210 as specified in the product data sheet. External passive components can result in amplitude mismatch error between the channels, which directly translates into position error. For this reason, it is recommended that at least 1% tolerance resistors and 5% tolerance capacitors be used in the signal path. The values of the components surrounding the AD2S1210 and AD8397 can be modified to meet the specific requirements of the application and sensor. For example, by modifying resistor values, the user can scale the bias voltage, amplitude, and maximum drive capability on the output of the buffer circuitry. COMMON VARIATIONS The buffer circuitry in Figure 1 can be used without any modifications with other Analog Devices, Inc., RDCs such as the AD2S1200 and AD2S1205. Adjust the passive components appropriately to change the output amplitude, drive capability, and offset voltage. Figure 6. Sinking 310 mA Current on AD8397 Output If connected to a resolver, the excitation signals from the AD8397 can generate sine and cosine signals within the AD2S1210 input range requirements. Rev. 0 | Page 4 of 7 Circuit Note CN-0317 CIRCUIT EVALUATION AND TEST Getting Started The EVAL-AD2S1210SDZ evaluation board is used to evaluate and test the AD2S1210 with the CN-0317 circuitry. A detailed schematic, layout, and bill of materials are available in the CN-0317 Design Support Package. To set up the circuit evaluation, take the following steps: 1. The EVAL-AD2S1210SDZ user guide provides complete instructions on using the hardware and software for the evaluation board. 2. Equipment Needed 3. The following equipment is needed: • 4. A PC with a USB port and Windows® 7 or later The EVAL-AD2S1210SDZ evaluation board The EVAL-SDP-CB1Z SDP-B controller board The EVAL-AD2S1210SDZ evaluation software A 9 V wall wart dc power supply (supplied with the EVAL-AD2S1210SDZ evaluation board) A resolver (such as the Tamagawa TS2620N21E11) 5. 6. 7. 9V SUPPLY J500 VDRIVE GND J703 J702 J701 AVDD GND DVDD GND DC JACK PC 12V 5V 5V B A B A B A ON-BOARD POWER SUPPLY USB RESOLVER θ J6 J2 EXE VDRIVE EXE DATA BUS DB0 TO DB15 EXC EXC SIN SIN SIN SIN AD2S1210 CS RD SAMPLE WR/FSYNC COS COS COS COS J5 EVAL-AD2S1210SDZ EVAL-SDP-CB1Z DVDD AVDD DB0 TO DB15 A, B, NM, DIR, DOS, LOT SAMPLE, WR/FSYNC, SCLK, SDI, SDO, A0, A1 26-WAY CONNECTOR 12-WAY CONNECTOR J3 J4 Figure 7. Functional Block Diagram of Test Setup Rev. 0 | Page 5 of 7 120-PIN CON A OR CON B SDP-B BOARD 11348-006 • • • • • Install the evaluation software supplied on the included evaluation software CD. Ensure that the EVAL-SDP-CB1Z board is disconnected from the USB port of the PC while installing the software. The PC may need to be restarted after the installation. Ensure that the various link options are configured as shown in Table 2 of the EVAL-AD2S1210SDZ user guide. Connect the SDP board to the evaluation board, as shown in Figure 7. Connect the 9 V power supply adapter included in the kit to Connecter J702 on the evaluation board. Connect the SDP board to the PC via the USB cable. Launch the evaluation software from the Analog Devices subfolder in the Programs menu. Connect the EXC, EXC, SIN, SIN, COS, and COS wires of the resolver to Connector J5 and Connector J6, as shown in Figure 7. CN-0317 Circuit Note Test When USB communications are established, the EVAL-SDPCB1Z can send, receive, and capture parallel data from the EVAL-AD2S1210SDZ. Figure 8 shows the evaluation software output display for the Acquisition tab when using the circuit to measure position and velocity. Figure 9 shows a photograph of the EVAL-AD2S1210SDZ evaluation board connected to the EVAL-SDP-CB1Z board. Complete information and details regarding test setup and calibration and how to use the evaluation software for data capture can be found in the EVAL-AD2S1210SDZ evaluation board user guide. Figure 8. Evaluation Software Output Display Showing Acquisition Tab Position and Velocity Data J702 J6 USB J5 J2 Figure 9. Photograph of EVAL-AD2S1210SDZ Evaluation Board Connected to EVAL-SDP-CB1Z SDP Board Rev. 0 | Page 6 of 7 Circuit Note CN-0317 LEARN MORE Data Sheets and Evaluation Boards CN-0317 Design Support Package. AD2S1210 Data Sheet UG-709 EVAL-AD2S1210SDZ Evaluation Board User Guide. AD8397 Data Sheet Szymczak, Jakub, et. al. Precision Resolver-to-Digital Converter Measures Angular Position and Velocity. Analog Dialogue 48-03, March 2014. Analog Devices. REVISION HISTORY 10/14—Revision 0: Initial Version Thomas, Mark. Dynamic Characteristics of Tracking Converters. AN-264 Application Note. Analog Devices. Gasking, John. Resolver-to-Digital Conversion. AN-263 Application Note. Analog Devices. Fu, Dennis. Digital Resolver Integration. AN-234 Application Note. Analog Devices. Fu, Dennis. Circuit Applications of the AD2S90 Resolver-toDigital Converter. AN-230 Application Note. Analog Devices. MT-030 Tutorial. Resolver-to-Digital Converters. Analog Devices. MT-031 Tutorial. Grounding Techniques. Analog Devices. MT-101 Tutorial. Decoupling Techniques. Analog Devices. CN-0192 Circuit Note. High Current Driver for the AD2S1210 Resolver-to-Digital Reference Signal Output. Analog Devices. CN-0276 Circuit Note. High Performance, 10-Bit to 16-Bit Resolver-to-Digital Converter. Analog Devices. “Chapter 3: Sensors” and “Chapter 6: Converters” in Linear Circuit Design Handbook. Ed. Hank Zumbahlen. Newnes, 2008. (Continued from first page) Circuits from the Lab reference designs 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 reference designs 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 reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab reference designs 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 reference designs at any time without notice but is under no obligation to do so. ©2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN11348-0-10/14(0) Rev. 0 | Page 7 of 7