EVAL-SSM2375Z

Evaluation Board User Guide UG-196 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 Evaluation Board for SSM2375 Filterless Class-D Audio Amplifier enables a low EMI mode, which significantly reduces the radiated emissions at the Class-D outputs, particularly above 100 MHz. With this option selected, the SSM2375 can pass FCC Class B radiated emissions testing with a 50 cm unshielded speaker cable without any external filtering. PACKAGE CONTENTS EVAL-SSM2375Z evaluation board OTHER SUPPORTING DOCUMENTATION SSM2375 data sheet GENERAL DESCRIPTION The SSM2375 is a fully integrated, high efficiency, Class-D audio amplifier. It is designed to maximize performance for mobile phone applications. The application circuit requires a minimum of external components and operates from a single 2.5 V to 5.5 V supply. It is capable of delivering 3 W of continuous output power with less than 1% THD + N driving a 3 Ω load from a 5.0 V supply. EVALUATION BOARD OVERVIEW The SSM2375 evaluation board carries a complete application circuit for driving a loudspeaker. Figure 1 shows the top view of the evaluation board, and Figure 2 shows the bottom view. 09393-002 09393-001 Spread spectrum pulse density modulation (PDM) is used to provide lower EMI-radiated emissions compared with other Class-D architectures. The inherent randomized nature of spread spectrum PDM eliminates clock intermodulation (beating effect) of several amplifiers in close proximity. The SSM2375 includes an optional modulation select pin that The device also includes a flexible gain select pin that only requires one series resistor to select among 0 dB, 3 dB, 6 dB, 9 dB, or 12 dB. The benefit of this is to improve gain matching between multiple SSM2375 devices within a single application as compared to using external resistors to set gain. This user guide describes how to configure and use the SSM2375 evaluation board. It is recommended that this user guide be read in conjunction with the SSM2375 data sheet, which provides specifications, internal block diagrams, and application guidance for the amplifier IC. Figure 2. SSM2375 Evaluation Board Bottom View Figure 1. SSM2375 Evaluation Board Top View PLEASE SEE THE LAST PAGE FOR AN IMPORTANT WARNING AND LEGAL TERMS AND CONDITIONS. Rev. 0 | Page 1 of 8 UG-196 Evaluation Board User Guide TABLE OF CONTENTS Package Contents.............................................................................. 1  Output Configuration...................................................................3  Other Supporting Documentation................................................. 1  Power Supply Configuration .......................................................3  General Description ......................................................................... 1  Component Selection ...................................................................3  Evaluation Board Overview ............................................................ 1  Getting Started...................................................................................5  Revision History ............................................................................... 2  What to Test ...................................................................................5  Setting Up the Evaluation Board .................................................... 3  Evaluation Board Schematic and Artwork.....................................6  Input Configuration ..................................................................... 3  Ordering Information.......................................................................8  Shutdown Mode............................................................................ 3  Bill of Materials..............................................................................8  Gain Configuration ...................................................................... 3  REVISION HISTORY 4/11—Revision 0: Initial Version Rev. 0 | Page 2 of 8 Evaluation Board User Guide UG-196 SETTING UP THE EVALUATION BOARD INPUT CONFIGURATION A 4-pin header (H2) on the middle left side of the board feeds the audio signal into the board (see Figure 1). If the input audio signal is differential (IN+ and IN−), three pins of H2 are used for IN+, IN−, and signal ground. For a single-ended audio input, only two pins of H2 are used. One is for the signal ground and the other is for either IN+ or IN−. If IN+ is used, place a jumper between Pin 3 and Pin 4 of H2, shorting IN− to ground. If IN− is used, place the jumper between Pin 1 and Pin 2 of H2, connecting IN+ to ground. For optimal THD and SNR performance as specified in the SSM2375 data sheet, remove the entire EMI filter, short across the ferrite bead terminals, and open the capacitor terminals. POWER SUPPLY CONFIGURATION The 2-pin header, H1, is used to power the board. Care must be taken to connect the dc power with correct polarity and voltage. Reverse polarity or overvoltage may damage the board permanently. The maximum supply current is approximately 0.33 A when driving an 8 Ω load and when the input voltage is 5 V. Do not allow VDD to exceed 5.5 V. SHUTDOWN MODE COMPONENT SELECTION The 2-pin header, J1, is used to turn on and off the SSM2375 amplifier. Placing a jumper across Pin 1 and Pin 2 of H1 puts the SSM2375 in normal operation. Removing the jumper shuts down the SSM2375 so that only a minimum current (about 20 nA) is drawn from the power supply. Selecting the proper components is the key to achieving the performance required at the cost budgeted. GAIN CONFIGURATION Two headers, H3 and J3, control the SSM2375 analog gain. By placing a jumper across two pins of H3, the amplifier’s gain pin can be connected to GND or VDD. Three jumper settings are used: between the center pin and the left pin (HI), between the center pin and the right pin (LO), and no jumper (open). Placing a jumper on J3 removes the 47 kΩ resistor (R3) between the gain pin and H3. Gain settings between 0 dB and 12 dB are available; see Table 1 for configuration details. J3 Short Short Short Open Open H3 LO Open HI LO HI If the desired gain must be adjusted beyond the available gain settings (see the Gain Configuration section), a series resistor can be placed in the input signal path. This creates a voltage divider with the 80 kΩ input resistance on each input pin, allowing an arbitrary reduction of the input signal. Note that input signal attenuation directly reduces SNR performance; therefore, large values compared to the built-in input resistance should be avoided. These components are populated with 0 Ω values on the evaluation board. Input Coupling Capacitor Selection—C1 and C2 The input coupling capacitors, C1 and C2, should be large enough to couple the low frequency signal components in the incoming signal but small enough to reject unnecessary extremely low frequency signals. For music signals, the cutoff frequency is typically between 20 Hz and 30 Hz. The value of the input capacitor is calculated by Table 1. Gain Configuration Gain 0 dB 3 dB 6 dB 9 dB 12 dB Input Gain Resistor Selection—R1 and R2 Configuration Short gain pin to GND Gain pin unconnected Short gain pin to VDD Gain pin through 47 kΩ to GND Gain pin through 47 kΩ to VDD C = 1/(2πRIN fc) where: RIN = 80 kΩ + (R1 or R2). fc is the desired cutoff frequency. OUTPUT CONFIGURATION The output connector, H4, is located on the right side of the board (see Figure 1). H4 can drive a loudspeaker whose impedance should be no less than 3 Ω. Output Ferrite Beads—B1 and B2 Because the SSM2375 does not typically require any external LC output filters due to a low noise modulation scheme, no output filter is installed on the evaluation board. In this case, thick wire connects the empty pads of B1 and B2, and the capacitor pads are left unpopulated. If the speaker length exceeds 10 cm, place Ferrite Bead B1 and Ferrite Bead B2 in the output paths, and use Capacitors C6 and C7 to couple the output terminals to ground, as shown in the schematic in Figure 3. Some recommended ferrite beads are listed in Table 2. Some users may want to use inductors for applications with specific EMI vs. audio performance constraints; see Table 3 for recommendations. The output beads, B1 and B2, are necessary components for filtering out the EMI caused at the switching output nodes when the length of the speaker wire is greater than 10 cm. The penalty for using ferrite beads for EMI filtering is slightly worse noise and distortion performance at the system level due to the nonlinearity of the beads. Ensure that these beads have enough current conducting capability while providing sufficient EMI attenuation. The current rating needed for an 8 Ω load is approximately 420 mA, and impedance at 100 MHz should be ≥120 Ω. In addition, the lower the dc resistance (DCR) of these beads, the better for minimizing their power consumption. Table 2 describes the recommended beads. Rev. 0 | Page 3 of 8 UG-196 Evaluation Board User Guide Output Shunting Capacitors Output Inductors There are two output-shunting capacitors, C6 and C7, that work with the ferrite beads, B1 and B2. Use small size (0603 or 0402), multilayer ceramic capacitors made of X7R or C0G (NP0) materials. Note that the capacitors can be used in pairs: a capacitor with small capacitance (up to 100 pF) plus a capacitor with a larger capacitance (less than 1 nF). This configuration provides thorough EMI reduction for the entire frequency spectrum. If the bill of materials must be minimized, a single capacitor of approximately 470 pF can be used with acceptable performance in many cases. If inductors are preferred for EMI filtering at the output nodes, choose components with an inductance of less than 2.2 μH. The higher the inductance, the lower the EMI is at the output; however, cost and power consumption are higher. Using 0.47 μH to 2.2 μH inductors is recommended, and the current rating (and saturation current) should exceed 600 mA for an 8 Ω load. Table 3 shows the recommended inductors. Table 2. Recommended Output Beads Part No. BLM18PG121SN1D MPZ1608S101A MPZ1608S221A BLM18EG221SN1D Manufacturer Murata TDK TDK Murata Z (Ω) 120 100 220 220 IMAX (mA) 2000 3000 2000 2000 DCR (Ω) 0.05 0.03 0.05 0.05 Size (mm) 1.6 × 0.8 × 0.8 1.6 × 0.8 × 0.8 1.6 × 0.8 × 0.8 1.6 × 0.8 × 0.8 L (μH) 0.47 1.0 0.47 1.0 2.2 IMAX (mA) 1400 1200 1100 800 790 DCR (Ω) 0.07 0.12 0.12 0.19 0.1 Size (mm) 3.2 × 1.6 × 0.85 3.2 × 1.6 × 0.85 2.0 × 1.25 × 0.5 2.0 × 1.25 × 0.5 3.2 × 2.5 × 1.55 Table 3. Recommended Output Inductors Part No. LQM31PNR47M00 LQM31PN1R0M00 LQM21PNR47MC0 LQM21PN1R0MC0 LQH32CN2R2M53 Manufacturer Murata Murata Murata Murata Murata Rev. 0 | Page 4 of 8 Evaluation Board User Guide UG-196 GETTING STARTED To ensure proper operation, carefully follow Step 1 through Step 5. WHAT TO TEST 1. • 2. 3. 4. 5. Place a jumper between Pin 1 and Pin 2 of J1 to enable the amplifier. For most audio quality testing, the EMI filtering (B1/B2 and C6/C7) must be removed. Short across the B1 and B2 terminals to make a direct connection from device output to the H5 speaker header. Connect the load to the audio output connector, H5. Connect the audio input to the board in either differential mode or single-ended mode, depending on the application. Connect the power supply with the proper polarity and voltage. • • • • • Rev. 0 | Page 5 of 8 Electromagnetic interference (EMI)—connect wires for the speakers, making sure they are the same length as the wires required for the actual application environment; then complete the EMI test. Signal-to-noise ratio. Output noise—make sure to use an A-weighted filter to filter the output before reading the measurement meter. Maximum output power. Distortion. Efficiency. Rev. 0 | Page 6 of 8 HDR1X4 1 2 3 4 H2 VDD ACTIVE C2 0.22uF R1 R2 0 J1 HDR1X2 0 + C5 A3 A2 A1 B1 Figure 3. Schematic of the SSM2375 Evaluation Board 47k R3 J3 HDR1X2 C4 10uF CAP POL VDD GAIN SD IN- IN+ C3 0.1uF VDD EDGE OUT- OUT+ U1 SSM2375 1 2 3 HDR1X3 600103 H3 B2 B3 C3 POWER HEADER H1 HDR1X2 C2 VDD VDD GND C1 C1 0.22uF 22uF Alum. Elec throughole, near H1 (nopop) J2 HDR1X2 H4 HDR1X2 NO POP 0-ohm VDD B2 MPZ1608S221A 0-ohm short short B1 MPZ1608S221A NOPOP C7 NOPOP 510pF C6 510pF OUT- OUT+ H5 HDR1X2 UG-196 Evaluation Board User Guide EVALUATION BOARD SCHEMATIC AND ARTWORK 09393-003 UG-196 09393-007 09393-004 Evaluation Board User Guide Figure 4. Top Layer Copper 09393-008 09393-005 Figure 7. Bottom Layer Copper Figure 8. Top Silkscreen 09393-009 09393-006 Figure 5. Second Layer Copper—GND Plane Figure 6. Third Layer Copper—VDD Plane Figure 9. Bottom Silkscreen Rev. 0 | Page 7 of 8 UG-196 Evaluation Board User Guide ORDERING INFORMATION BILL OF MATERIALS Table 4. Qty 1 2 1 1 1 2 2 2 1 6 1 1 Reference Designator U1 C1, C2 C3 C4 C5 C6, C7 B1, B2 R1, R2 R3 H1, H4, H5, J1 to J3 H2 H3 Description IC, SSM2375 Capacitor, 22 nF, 25 V, 10%, X7R, 0805 Capacitor, ceramic 0.1 μF, 50 V, Y5V, 0603 Capacitor, ceramic 10 μF, 10 V, X5R, 0805 Capacitor, 47 μF, 25 V electrolytic Capacitor, ceramic, 510 pF, 50 V, 2%, 0603 Wire short Resistor, 0.0 Ω, 1/8 W, 0805 Resistor, 47 kΩ, 1/10 W, 1%, 0603 Connector, header, 2-position, 0.100" single gold Connector, header, 4-position, 0.100" single gold Connector, header, 3-position, 0.100" single gold Supplier/Part No. Analog Devices/SSM2375CBZ Panasonic/ECJ-2YB1E224K Panasonic/ECJ-1VF1H104Z Murata/GRM21BR61A106KE19L Nichicon/UFW1E470MDD Murata/GRM1885C1H511JA01D N/A Panasonic/P0.0ATR-ND Panasonic/ERJ-3EKF4702V Tyco/826629-2 Tyco/826629-3 Tyco/826629-4 ESD Caution ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality. Legal Terms and Conditions By using the evaluation board discussed herein (together with any tools, components documentation or support materials, the “Evaluation Board”), you are agreeing to be bound by the terms and conditions set forth below (“Agreement”) unless you have purchased the Evaluation Board, in which case the Analog Devices Standard Terms and Conditions of Sale shall govern. Do not use the Evaluation Board until you have read and agreed to the Agreement. Your use of the Evaluation Board shall signify your acceptance of the Agreement. This Agreement is made by and between you (“Customer”) and Analog Devices, Inc. (“ADI”), with its principal place of business at One Technology Way, Norwood, MA 02062, USA. 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