Circuit Note CN-0226 Devices Connected/Referenced Single-Channel, 64-Position, Push-Button, AD5116 8% Resistor Tolerance, Nonvolatile Digital Potentiometer Circuits from the Lab reference designs are engineered and tested for quick and easy system integration to help solve todays Filterless, High Efficiency, Mono 3 W SSM2375 Class-D Audio Amplifier analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0226. 1.8 V Low Power CMOS Rail-to-Rail AD8515 Input/Output Operational Amplifier 1.8 V, Micropower, Zero-Drift, Dual Rail-to- ADA4051-2 Rail Input/Output Op Amp Portable Audio Amplifier with Volume Control The volume is controlled manually with a simple push-button EVALUATION AND DESIGN SUPPORT interface to a 64-position digital potentiometer. An automatic Circuit Evaluation Boards store function retains the last volume setting, and an LED provides CN-0226 Circuit Evaluation Board (EVAL-CN0226-EB1Z) visual information of the maximum/minimum volume. 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, CIRCUIT FUNCTION AND BENEFITS built in pop and click suppression, and shutdown mode. The circuit shown in Figure 1 is a complete low cost, low power, The circuit provides a preconditioning input stage, allowing mono audio amplifier with volume control, glitch reduction, and compatibility with a wide range of audio input signals and can a 3 W Class-D output driver. be powered with a cell battery. V AUDIO INPUT DD V DD 33k 220nF 33k 1F 33k AD8515 V DD S2 V DD PUSH-UP AD5116 BUTTON V A DD V DD PU PD V S3 DD 47nF W PUSH-DOWN 10k BUTTON 1.8k ASE SSM2375 GND B 1/2 ADA4051-2 110k 47nF 1/2 ADA4051-2 S1 SHUTDOWN BUTTON 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due Fax: 781.461.3113 2017 Analog Devices, Inc. All rights reserved. to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) 10059-001CN-0226 Circuit Note A third push-button is provided on the board to shut down the CIRCUIT DESCRIPTION audio output. This circuit employs the 64-position AD5116 digital Figure 3 shows the THD + N performance of the circuit operating potentiometer in conjunction with the SSM2375 Class-D amplifier, dual ADA4051-2, and single AD8515 op amps, on a 5 V power supply with a 4 + 15 H load. Note that the providing an ease of use circuit for low power and/or portable THD + N increases at the 2 W output power level. applications. 100 The input signal is filtrated by a high-pass filter that removes any dc offset voltage and centers the signal between the supply rails. 10 The high pass filter also improves the power supply rejection (PSR). A separate filter is provided for the VDD/2 bias voltage, as shown 1 in Figure 2. V AUDIO INPUT DD 0.1 33k 220nF 2.0W OUTPUT 33k 0.01 1.0W OUTPUT 0.5W OUTPUT 1F 33k 0.001 BIAS VOLTAGE HIGH-PASS 10 100 1k 10k 100k FILTER FILTER FREQUENCY (Hz) Figure 2. Input Filter Configuration 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 Audio Input Signal Level Calculation high pass filter formed by the 33 k resistor and the 220 nF The SSM2375 output power is given by capacitor has a cutoff frequency of approximately 22 Hz. 2 (IN GAIN) The bias voltage filter rejects supply noise at 10 Hz and above. Output Power (W) = R LOAD The AD5116 is configured in the potentiometer mode, thereby where: attenuating the audio input signal and is available in 80 k, IN is the rms input voltage or VPEAK /2. 10 k, and 5 k resistance values. Selecting the resistance RLOAD is the speaker impedance. represents a trade-off between linearity, noise, bandwidth, and GAIN is the linear gain, by default 1.4125 (3 dB). total harmonic distortion (THD) performance. The 10 k option was chosen for the circuit in Figure 1, although the 5 k option The SSM2375 gain can be set from 0 dB to 12 dB in 3 dB steps, yields a slight reduction in noise. as shown in Table 1. The dual AD8515 is a low cost, low power, rail-to-rail, input/ Table 1. SSM2375 Gain Configurations output operational amplifier and is used to buffer the audio Gain Setting (dB) GAIN Pin Configuration signal and drives the A terminal of the AD5116. 12 Tie to VDD through 47 k resistor One-half of the ADA4051-2 op amp provides the low impedance 9 Tie to GND through 47 k resistor VDD/2 bias voltage to the B terminal of the AD5116. Setting the 6 Tie to VDD bias voltage at VDD/2 provides optimum signal headroom and 3 Open best THD performance. 0 Tie to GND The other half of the ADA4051-2 op amp is used to buffer the W terminal output of the AD5116. Optimum layout, grounding, and decoupling techniques must be utilized to achieve the desired performance (see the MT-031 The AD5116 provides an automatic store feature that ensures it and MT-101 tutorials). As a minimum, a 4-layer printed circuit retains the last volume position. The ASE pin has a double board (PCB) must be used with one ground plane layer, one function when the automatic store is enabled. The pin indicates power plane layer, and two signal layers. when the end of the resistance has been reached, which indicates the maximum/minimum volume. An LED is provided for visual A complete design support package including schematic, layout, information of the event. assembly, and bill of materials (BOM) is available at www.analog.com/CN0226-DesignSupport. 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. Rev. 0 Page 2 of 5 10059-002 THD + N (%) 10059-003