Circuit Note CN-0226 Devices Connected/Referenced Circuits from the Lab(R) 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/CN0226. AD5116 Single-Channel, 64-Position, Push-Button, 8% Resistor Tolerance, Nonvolatile Digital Potentiometer SSM2375 Filterless, High Efficiency, Mono 3 W Class-D Audio Amplifier AD8515 1.8 V Low Power CMOS Rail-to-Rail Input/Output Operational Amplifier ADA4051-2 1.8 V, Micropower, Zero-Drift, Dual Rail-toRail Input/Output Op Amp Portable Audio Amplifier with Volume Control The volume is controlled manually with a simple push-button interface to a 64-position digital potentiometer. An automatic store function retains the last volume setting, and an LED provides visual information of the maximum/minimum volume. EVALUATION AND DESIGN SUPPORT Circuit Evaluation Boards CN-0226 Circuit Evaluation Board (EVAL-CN0226-EB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials The SSM2375 Class-D driver amplifier provides up to 3 W output power into 3 load, with 93% power efficiency at 5 V, built in pop and click suppression, and shutdown mode. CIRCUIT FUNCTION AND BENEFITS The circuit shown in Figure 1 is a complete low cost, low power, mono audio amplifier with volume control, glitch reduction, and a 3 W Class-D output driver. VDD The circuit provides a preconditioning input stage, allowing compatibility with a wide range of audio input signals and can be powered with a cell battery. AUDIO INPUT 220nF 33k VDD 33k 1F AD8515 33k VDD VDD S2 PUSH-UP BUTTON AD5116 A VDD PU VDD PD S3 PUSH-DOWN BUTTON 1.8k 110k 47nF W 10k VDD ASE GND B 1/2 ADA4051-2 SSM2375 47nF S1 SHUTDOWN BUTTON 10059-001 1/2 ADA4051-2 Figure 1. Audio Volume Control (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 (c)2017 Analog Devices, Inc. All rights reserved. CN-0226 Circuit Note This circuit employs the 64-position AD5116 digital potentiometer in conjunction with the SSM2375 Class-D amplifier, dual ADA4051-2, and single AD8515 op amps, providing an ease of use circuit for low power and/or portable applications. The input signal is filtrated by a high-pass filter that removes any dc offset voltage and centers the signal between the supply rails. The high pass filter also improves the power supply rejection (PSR). A separate filter is provided for the VDD/2 bias voltage, as shown in Figure 2. AUDIO INPUT 33k Figure 3 shows the THD + N performance of the circuit operating on a 5 V power supply with a 4 + 15 H load. Note that the THD + N increases at the 2 W output power level. 100 10 0.1 220nF 33k 2.0W OUTPUT 1.0W OUTPUT 0.5W OUTPUT 0.01 33k BIAS VOLTAGE FILTER HIGH-PASS FILTER 10059-002 1F 1 0.001 10 Figure 2. Input Filter Configuration 100 1k FREQUENCY (Hz) 10k 100k 10059-003 VDD A third push-button is provided on the board to shut down the audio output. THD + N (%) CIRCUIT DESCRIPTION Figure 3. THD + N Performance of Circuit Using 5 V Power Supply, 4 + 15 H Load, Gain = 3 dB The filter formed by the 1 F capacitor and the 33 k divider resistors has a cutoff frequency of approximately 10 Hz. The high pass filter formed by the 33 k resistor and the 220 nF capacitor has a cutoff frequency of approximately 22 Hz. Audio Input Signal Level Calculation The SSM2375 output power is given by The bias voltage filter rejects supply noise at 10 Hz and above. The AD5116 is configured in the potentiometer mode, thereby attenuating the audio input signal and is available in 80 k, 10 k, and 5 k resistance values. Selecting the resistance represents a trade-off between linearity, noise, bandwidth, and total harmonic distortion (THD) performance. The 10 k option was chosen for the circuit in Figure 1, although the 5 k option yields a slight reduction in noise. The dual AD8515 is a low cost, low power, rail-to-rail, input/ output operational amplifier and is used to buffer the audio signal and drives the A terminal of the AD5116. Output Power (W) = (IN x GAIN )2 RLOAD where: IN is the rms input voltage or VPEAK /2. RLOAD is the speaker impedance. GAIN is the linear gain, by default 1.4125 (3 dB). The SSM2375 gain can be set from 0 dB to 12 dB in 3 dB steps, as shown in Table 1. Table 1. SSM2375 Gain Configurations One-half of the ADA4051-2 op amp provides the low impedance VDD/2 bias voltage to the B terminal of the AD5116. Setting the bias voltage at VDD/2 provides optimum signal headroom and best THD performance. The other half of the ADA4051-2 op amp is used to buffer the W terminal output of the AD5116. The AD5116 provides an automatic store feature that ensures it retains the last volume position. The ASE pin has a double function when the automatic store is enabled. The pin indicates when the end of the resistance has been reached, which indicates the maximum/minimum volume. An LED is provided for visual information of the event. The SSM2375 is a high efficiency Class-D amplifier that provides up to 3 W output power. The device provides a 12 dB gain with a built in pop and click suppression circuit that minimizes the transition glitches from the digital potentiometer. Gain Setting (dB) 12 9 6 3 0 GAIN Pin Configuration Tie to VDD through 47 k resistor Tie to GND through 47 k resistor Tie to VDD Open Tie to GND Optimum layout, grounding, and decoupling techniques must be utilized to achieve the desired performance (see the MT-031 and MT-101 tutorials). As a minimum, a 4-layer printed circuit board (PCB) must be used with one ground plane layer, one power plane layer, and two signal layers. A complete design support package including schematic, layout, assembly, and bill of materials (BOM) is available at www.analog.com/CN0226-DesignSupport. Rev. 0 | Page 2 of 5 Circuit Note CN-0226 It is also possible to externally implement an automatic shutdown to improve the attenuation at minimum volume using a D-type flip-flop, as shown in Figure 4. COMMON VARIATIONS The circuit can be configured for ultralow power operation. If the circuit is used in a low power system, all three op amps can be replaced with the quad AD8508, which provides a very low supply current of 20 A per amplifier and allows full functionality at a supply of 2.5 V. VDD VDD VDD AD5116 VDD SSM2375 PRE GND CONTROL LOGIC BLOCK D D-TYPE FLIP-FLOP SD Q PUSH-DOWN BUTTON CLR PU PUSH-UP BUTTON 10k VDD GND 1F Figure 4. Automatic Shutdown Mode Rev. 0 | Page 3 of 5 10059-004 PD Q CLK ASE ADAPTIVE DEBOUNCER VDD CN-0226 Circuit Note CIRCUIT EVALUATION AND TEST Setup and Test The circuit is tested using standard audio test equipment and methods. Connect the equipment as shown in Figure 5. Connect the power supply to the EVAL-CN0226-EB1Z board. Equipment Needed Use standard audio test methods to make the required measurements. The following equipment is required: Figure 6 shows a photograph of the EVAL-CN0226-EB1Z board. EVAL-CN0226-EB1Z evaluation board DC power supply (2.7 V to 5.5 V) Audio Precision 2700 series audio analyzer or equivalent Audio Precision AUX-0025 filter or equivalent Functional Block Diagram POWER SUPPLY 2.7V TO 5.5V J3-1 AUDIO INPUT J2 COM J3-2 AUDIO OUTPUT J1 AUDIO PRECISION AUX-0025 FILTER Figure 5. Test Setup Functional Diagram Rev. 0 | Page 4 of 5 10059-006 AUDIO PRECISION 2700 SERIES AUDIO ANALYZER 10059-005 EVAL-CN0226-EB1Z Figure 6. Photo of EVAL-CN0226-EB1Z Circuit Note CN-0226 LEARN MORE Data Sheets and Evaluation Boards CN-0226 Design Support Package: www.analog.com/CN0226-DesignSupport CN-0226 Evaluation Board (EVAL-CN0226-EB1Z) MT-031 Tutorial. Grounding Data Converters and Solving the Mystery of "AGND" and "DGND". Analog Devices. SSM2375 Data Sheet AD5116 Data Sheet AD8515 Data Sheet MT-091 Tutorial. Digital Potentiometers. Analog Devices. ADA4051-2 Data Sheet MT-101 Tutorial. Decoupling Techniques. Analog Devices. Kitchin, Charles. AN-581 Application Note. Biasing and Decoupling Op Amps in Single Supply Applications. Analog Devices. REVISION HISTORY 4/2017--Revision 0: Initial Version Usach Merino, Miguel. Insight into digiPOT Specifications and Architecture Enhances AC Performance. Analog Dialogue, (Volume 45, August 2011), Analog Devices. (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. (c)2017 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN10059-0-4/17(0) Rev. 0 | Page 5 of 5