SSM2356

2 × 2W Filterless Class-D Stereo Audio Amplifier SSM2356 FEATURES Filterless stereo Class-D amplifier with Σ-Δ modulation No sync necessary when using multiple Class-D amplifiers from Analog Devices, Inc. 2 × 2W into 4 Ω load and 2x1.4 W into 8 Ω load at 5.0 V supply with 103 dB signal-to-noise ratio (SNR) Single-supply operation from 2.5 V to 5.5 V 20 nA shutdown current; left/right channel control Short-circuit and thermal protection Available in a 16-ball, 1.66 mm × 1.66 mm WLCSP Pop-and-click suppression Built-in resistors that reduce board component count User-selectable 6 dB or 18 dB gain setting User-selectable ultralow EMI emission mode The SSM2356 features a high efficiency, low noise modulation scheme that requires no external LC output filters. The modulation continues to provide high efficiency even at low output power. It operates with 92% efficiency at 1.4 W into 8 Ω or 85% efficiency at 2.0 W into 4 Ω from a 5.0 V supply and has an SNR of >103 dB. Spread-spectrum pulse density modulation is used to provide lower EMI-radiated emissions compared with other Class-D architectures. The SSM2356 includes an optional modulation select pin (ultralow EMI emission mode) that significantly reduces the radiated emissions at the Class-D outputs, particularly above 100 MHz. The SSM2356 has a micropower shutdown mode with a typical shutdown current of 20 nA. Shutdown is enabled by applying a logic low to the SDNR and SDNL pins. The device also includes pop-and-click suppression circuitry that minimizes voltage glitches at the output during turn-on and turn-off, reducing audible noise on activation and deactivation. The fully differential input of the SSM2356 provides excellent rejection of common-mode noise on the input. Input coupling capacitors can be omitted if the dc input common-mode voltage is approximately VDD/2. The preset gain of SSM2356 can be selected between 6 dB and 18 dB with no external components and no change to the input impedance. Gain can be further reduced to a user-defined setting by inserting series external resistors at the inputs. The SSM2356 is specified over the commercial temperature range (−40°C to +85°C). It has built-in thermal shutdown and output short-circuit protection. It is available in a 16-ball, 1.66 mm × 1.66 mm wafer level chip scale package (WLCSP). VBATT 2.5V TO 5.5V VDD OUTR+ MODULATOR (Σ-Δ) BIAS BIAS FET DRIVER OUTR– APPLICATIONS Mobile phones MP3 players Portable gaming Portable electronics GENERAL DESCRIPTION The SSM2356 is a fully integrated, high efficiency, stereo 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 2 × 2W of continuous output power with 100 29 100 Min Typ 1.42 0.75 1.8 0.94 2.0 1.3 2.5 1 1.7 92 90 0.004 0.004 VDD − 1 Max Unit W W W W W W W W % % % % V dB dB kHz mV V dB dB mA mA mA mA mA mA nA dB dB kΩ V V ms μs kΩ μVrms dB Efficiency η Total Harmonic Distortion + Noise Input Common-Mode Voltage Range Common-Mode Rejection Ratio Channel Separation Average Switching Frequency Differential Output Offset Voltage POWER SUPPLY Supply Voltage Range Power Supply Rejection Ratio THD + N VCM CMRRGSM XTALK fSW VOOS VDD PSRR (DC) PSRRGSM ISY Supply Current (stereo) Shutdown Current GAIN CONTROL Closed-Loop Gain Input Impedance SHUTDOWN CONTROL Input Voltage High Input Voltage Low Turn-On Time Turn-Off Time Output Impedance NOISE PERFORMANCE Output Voltage Noise Signal-to-Noise Ratio 1 ISD Gain Gain ZIN VIH VIL tWU tSD ZOUT en SNR SDNR/SDNL rising edge from GND to VDD SDNR/SDNL falling edge from VDD to GND SDNR/SDNL = GND VDD = 3.6 V, f = 20 Hz to 20 kHz, inputs are ac grounded, Gain = 6 dB, A-weighted PO = 1.4 W, RL = 8 Ω Note that, although the SSM2356 has good audio quality above 2 W per channel, continuous output power beyond 2 W per channel must be avoided due to device packaging limitations. Rev. 0 | Page 3 of 16 SSM2356 ABSOLUTE MAXIMUM RATINGS Absolute maximum ratings apply at 25°C, unless otherwise noted. Table 2. Parameter Supply Voltage Input Voltage Common-Mode Input Voltage ESD Susceptibility Storage Temperature Range Operating Temperature Range Junction Temperature Range Lead Temperature Range (Soldering, 60 sec) Rating 6V VDD VDD 4 kV −65°C to +150°C −40°C to +85°C −65°C to +165°C 300°C THERMAL RESISTANCE θJA (junction to air) is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. θJA and θJB (junction to board) are determined according to JESD51-9 on a 4-layer printed circuit board (PCB) with natural convection cooling. Table 3. Thermal Resistance Package Type 16-ball, 1.66 mm × 1.66 mm WLCSP θJA 66 θJB 19 Unit °C/W ESD CAUTION Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rev. 0 | Page 4 of 16 SSM2356 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS BALL A1 INDICATOR 2 1 OUTL+ VDD A OUTL– GND B SDNL EDGE GAIN SDNR C INL+ D 08084-002 3 4 VDD OUTR+ GND OUTR– INL– INR– INR+ TOP VIEW (BALL SIDE DOWN) Not to Scale Figure 2. Pin Configuration (Top Side View) Table 4. Pin Function Descriptions Bump A1 B1 C1 D1 D2 C4 C3 D3 D4 B2 B4 A4 B3 A2 A3 C2 Mnemonic OUTL+ OUTL− SDNL INL+ INL− SDNR GAIN INR− INR+ GND OUTR− OUTR+ GND VDD VDD EDGE Description Noninverting Output for Left Channel. Inverting Output for Left Channel. Shutdown, Left Channel. Active low digital input. Noninverting Input for Left Channel. Inverting Input for Left Channel. Shutdown, Right Channel. Active low digital input. Gain select between 6 dB and 18 dB. Inverting Input for Right Channel. Noninverting Input for Right Channel. Ground. Inverting Output for Right Channel. Noninverting Output for Right Channel. Ground. Power Supply. Power Supply. Edge Control (Low Emission Mode); active high digital input. Rev. 0 | Page 5 of 16 SSM2356 TYPICAL PERFORMANCE CHARACTERISTICS 100 RL = 8Ω + 33µH GAIN = 6dB VDD = 2.5V 100 VDD = 3.6V 10 RL = 4Ω + 15µH GAIN = 18dB VDD = 2.5V 10 THD + N (%) THD + N (%) 1 1 VDD = 3.6V 0.1 0.1 0.01 VDD = 5V 0.01 VDD = 5V 08084-101 0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10 OUTPUT POWER (W) OUTPUT POWER (W) Figure 3. THD + N vs. Output Power into 8 Ω, AV = 6 dB 100 RL = 8Ω + 33µH GAIN = 18dB VDD = 2.5V 100 VDD = 3.6V 10 Figure 6. THD + N vs. Output Power into 4 Ω, AV = 18 dB VDD = 5V GAIN = 6dB RL = 8Ω + 33µH 10 1 THD + N (%) THD + N (%) 1 0.1 0.25W 0.01 1W 0.1 0.01 VDD = 5V 0.001 0.5W 08084-102 0.001 0.01 0.1 1 10 100 1k FREQUENCY (Hz) 10k 100k OUTPUT POWER (W) Figure 4. THD + N vs. Output Power into 8 Ω, AV = 18 dB 100 RL = 4Ω + 15µH GAIN = 6dB VDD = 2.5V Figure 7. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 6 dB 100 VDD = 5V GAIN = 18dB RL = 8Ω + 33µH 10 10 THD + N (%) VDD = 3.6V 0.1 THD + N (%) 1 1 1W 0.1 0.01 VDD = 5V 08084-103 0.01 0.5W 0.001 10 0.25W 0.001 0.01 0.1 1 10 100 1k FREQUENCY (Hz) 10k 100k OUTPUT POWER (W) Figure 5. THD + N vs. Output Power into 4 Ω, AV = 6 dB Figure 8. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 18 dB Rev. 0 | Page 6 of 16 08084-106 0.001 0.0001 08084-105 0.001 0.0001 0.0001 10 08084-104 0.001 0.0001 0.001 0.0001 SSM2356 100 VDD = 5V GAIN = 6dB RL = 4Ω + 15µH 100 VDD = 3.6V GAIN = 18dB RL = 8Ω + 33µH 10 10 THD + N (%) THD + N (%) 1 1 0.5W 0.1 0.1 2W 0.01 0.5W 1W 08084-107 0.01 0.25W 0.001 10 0.125W 100 1k FREQUENCY (Hz) 10k 100k 100 1k FREQUENCY (Hz) 10k 100k Figure 9. THD + N vs. Frequency, VDD = 5 V, RL = 4 Ω, AV = 6 dB 100 VDD = 5V GAIN = 18dB RL = 4Ω + 15µH Figure 12. THD + N vs. Frequency, VDD = 3.6 V, RL = 8 Ω, AV = 18 dB 100 VDD = 3.6V GAIN = 6dB RL = 4Ω + 15µH 10 10 THD + N (%) 2W 0.1 0.5W THD + N (%) 1 1 1W 0.1 0.25W 0.01 1W 08084-108 08084-111 08084-112 0.01 0.001 10 100 1k FREQUENCY (Hz) 10k 100k 0.001 10 0.5W 100 1k FREQUENCY (Hz) 10k 100k Figure 10. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 18 dB 100 VDD = 3.6V GAIN = 6dB RL = 8Ω + 33µH Figure 13. THD + N vs. Frequency, VDD = 3.6 V, RL = 4 Ω, AV = 6 dB 100 VDD = 3.6V GAIN = 18dB RL = 4Ω + 15µH 10 10 THD + N (%) THD + N (%) 1 1 1W 0.1 0.5W 0.1 0.25W 0.01 0.25W 0.125W 0.01 0.5W 08084-109 0.001 10 100 1k FREQUENCY (Hz) 10k 100k 0.001 10 100 1k FREQUENCY (Hz) 10k 100k Figure 11. THD + N vs. Frequency, VDD = 3.6 V, RL = 8 Ω, AV = 6 dB Figure 14. THD + N vs. Frequency, VDD = 3.6 V, RL = 4 Ω, AV = 18 dB Rev. 0 | Page 7 of 16 08084-110 0.001 10 SSM2356 100 VDD = 2.5V GAIN = 6dB RL = 8Ω + 33µH 100 VDD = 2.5V GAIN = 18dB RL = 4Ω + 15µH 0.5W 10 10 THD + N (%) 0.25W 0.1 0.0625W 0.01 THD + N (%) 1 1 0.1 1.25W 0.01 0.25W 08084-113 100 1k FREQUENCY (Hz) 10k 100k 100 1k FREQUENCY (Hz) 10k 100k Figure 15. THD + N vs. Frequency, VDD = 2.5 V, RL = 8 Ω, AV = 6 dB 100 VDD = 2.5V GAIN = 18dB RL = 8Ω + 33µH SUPPLY CURRENT (mA) Figure 18. THD + N vs. Frequency, VDD = 2.5 V, RL = 4 Ω, AV = 18 dB 7.0 ISY FOR BOTH CHANNELS GAIN = 6dB 10 6.5 6.0 4Ω + 15µH 5.5 THD + N (%) 1 0.25W 8Ω + 33µH 0.1 0.0625W 5.0 NO LOAD 0.01 0.125W 0.001 10 4.5 08084-114 100 1k FREQUENCY (Hz) 10k 100k 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) Figure 16. THD + N vs. Frequency, VDD = 2.5 V, RL = 8 Ω, AV = 18 dB 100 VDD = 2.5V GAIN = 6dB RL = 4Ω + 15µH SUPPLY CURRENT (mA) Figure 19. Supply Current vs. Supply Voltage, AV = 6 dB 7.5 7.0 6.5 4Ω + 15µH 6.0 8Ω + 33µH 5.5 5.0 NO LOAD 4.5 ISY FOR BOTH CHANNELS GAIN = 18dB 10 0.5W THD + N (%) 1 0.1 0.25W 0.01 0.125W 08084-115 100 1k FREQUENCY (Hz) 10k 100k 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) Figure 17. THD + N vs. Frequency, VDD = 2.5 V, RL = 4 Ω, AV = 6 dB Figure 20. Supply Current vs. Supply Voltage, AV = 18 dB Rev. 0 | Page 8 of 16 08084-118 0.001 10 4.0 2.5 08084-117 4.0 2.5 08084-116 0.001 10 0.125W 0.001 10 SSM2356 2.0 f = 1kHz 1.8 GAIN = 6dB RL = 8Ω + 33µH 1.6 OUTPUT POWER (W) OUTPUT POWER (W) 3.5 f = 1kHz GAIN = 18dB 3.0 RL = 4Ω + 15µH 2.5 2.0 10% 1.5 1% 1.0 0.5 0 2.5 1.4 1.2 1.0 0.8 1% 0.6 0.4 0.2 08084-119 10% 3.0 3.5 4.0 4.5 5.0 3.0 3.5 4.0 4.5 5.0 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) Figure 21. Maximum Output Power vs. Supply Voltage, RL = 8 Ω, AV = 6 dB 1.8 f = 1kHz GAIN = 18dB 1.6 RL = 8Ω + 33µH 1.4 OUTPUT POWER (W) Figure 24. Maximum Output Power vs. Supply Voltage, RL = 4 Ω, AV = 18 dB 100 90 80 70 VDD = 3.6V VDD = 5V VDD = 2.5V 1.0 0.8 10% EFFICIENCY (%) 1.2 60 50 40 30 20 10 GAIN = 6dB RL = 8Ω + 33µH POUT FOR BOTH CHANNELS 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 OUTPUT POWER (W) 08084-123 08084-124 1% 0.6 0.4 0.2 08084-120 0 2.5 0 3.0 3.5 4.0 4.5 5.0 SUPPLY VOLTAGE (V) Figure 22. Maximum Output Power vs. Supply Voltage, RL = 8 Ω, AV = 18 dB 3.5 f = 1kHz GAIN = 6dB 3.0 RL = 4Ω + 15µH 2.5 EFFICIENCY (%) Figure 25. Efficiency vs. Output Power into 8 Ω 100 90 80 VDD = 5V OUTPUT POWER (W) 70 60 50 40 30 20 VDD = 2.5V VDD = 3.6V 2.0 10% 1.5 1% 1.0 0.5 0 2.5 10 3.0 3.5 4.0 4.5 5.0 08084-121 0 0 0.5 1.0 1.5 2.0 2.5 3.0 GAIN = 6dB RL = 4Ω + 15µH POUT FOR BOTH CHANNELS 3.5 4.0 4.5 5.0 5.5 6.0 OUTPUT POWER (W) SUPPLY VOLTAGE (V) Figure 23. Maximum Output Power vs. Supply Voltage, RL = 4 Ω, AV = 6 dB Figure 26. Efficiency vs. Output Power into 4 Ω Rev. 0 | Page 9 of 16 08084-122 0 2.5 SSM2356 0.8 GAIN = 6dB RL = 8Ω + 33µH 0.7 I , P SY OUT FOR BOTH CHANNELS 0.6 SUPPLY CURRENT (A) 0 VDD = 5V –10 –20 –30 CMRR (dB) 08084-125 0.5 0.4 VDD = 2.5V 0.3 0.2 VDD = 3.6V –40 –50 –60 –70 –80 0.1 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 OUTPUT POWER (W) –90 100 1k FREQUENCY (Hz) 10k 100k 08084-129 08084-131 08084-130 –100 10 Figure 27. Supply Current vs. Output Power into 8 Ω 1.6 GAIN = 6dB RL = 4Ω + 15µH 1.4 I , P SY OUT FOR BOTH CHANNELS 1.2 SUPPLY CURRENT (A) Figure 30. CMRR vs. Frequency 0 VDD = 5V –10 –20 –30 PSRR (dB) 08084-126 1.0 0.8 VDD = 2.5V 0.6 0.4 VDD = 3.6V –40 –50 –60 –70 –80 0.2 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 OUTPUT POWER (W) –90 –100 10 100 1k FREQUENCY (Hz) 10k 100k Figure 28. Supply Current vs. Output Power into 4 Ω 0 VDD = 5V VOUT = 500mV rms RL = 8Ω + 33µH 6 5 4 –40 VOLTAGE (V) Figure 31. PSRR vs. Frequency –20 CHANNEL SEPARATION (dB) SD INPUT 3 2 OUTPUT 1 0 –60 RIGHT TO LEFT –80 –100 LEFT TO RIGHT 1 10 100 1k 10k 100k 08084-133 –1 –2 –2 –120 FREQUENCY (Hz) 0 2 4 6 8 TIME (ms) 10 12 14 16 18 Figure 29. Crosstalk v. Frequency Figure 32. Turn-On Response Rev. 0 | Page 10 of 16 SSM2356 7 6 5 4 VOLTAGE (V) 3 2 1 0 –1 –2 –110 OUTPUT SD INPUT –90 –70 –50 –30 –10 10 30 50 70 08084-132 TIME (µs) Figure 33. Turn-Off Response Rev. 0 | Page 11 of 16 SSM2356 TYPICAL APPLICATION CIRCUITS 10µF 0.1µF VDD GAIN CONTROL VDD OUTR+ MODULATOR (Σ-Δ) BIAS INTERNAL OSCILLATOR BIAS 80kΩ INL+ 22nF REXT INL– 80kΩ GAIN GAIN EXTERNAL GAIN SETTINGS = 160kΩ/(80kΩ + R EXT ) {GAIN = GND} = 640kΩ/(80kΩ + R EXT ) {GAIN = VBATT} 08084-003 VBATT 2.5V TO 5.5V SSM2356 RIGHT AUDIO IN+ RIGHT AUDIO IN– SHUTDOWN–R 22nF R EXT INR+ 22nF REXT INR– 80kΩ SDNR 80kΩ FET DRIVER OUTR– EDGE CONTROL EDGE SHUTDOWN–L LEFT AUDIO IN+ LEFT AUDIO IN– 22nF R EXT SDNL GAIN CONTROL OUTL+ MODULATOR (Σ-Δ) GND FET DRIVER GND OUTL– Figure 34. Stereo Differential Input Configuration 10µF 0.1µF VDD GAIN CONTROL VDD VBATT 2.5V TO 5.5V SSM2356 RIGHT AUDIO IN+ 22nF R EXT INR+ 22nF REXT SHUTDOWN–R INR– 80kΩ SDNR 80kΩ OUTR+ MODULATOR (Σ-Δ) BIAS INTERNAL OSCILLATOR BIAS EDGE CONTROL EDGE FET DRIVER OUTR– SHUTDOWN–L LEFT AUDIO IN+ 22nF R EXT SDNL 80kΩ INL+ GAIN CONTROL GAIN INL– 80kΩ OUTL+ MODULATOR (Σ-Δ) GND FET DRIVER GND OUTL– 22nF REXT GAIN EXTERNAL GAIN SETTINGS = 160kΩ/(80kΩ + R EXT ) {GAIN = GND} = 640kΩ/(80kΩ + R EXT ) {GAIN = VBATT} 08084-004 Figure 35. Stereo Single-Ended Input Configuration Rev. 0 | Page 12 of 16 SSM2356 APPLICATIONS INFORMATION OVERVIEW The SSM2356 stereo Class-D audio amplifier features a filterless modulation scheme that greatly reduces the external component count, conserving board space and, thus, reducing systems cost. The SSM2356 does not require an output filter but, instead, relies on the inherent inductance of the speaker coil and the natural filtering of the speaker and human ear to fully recover the audio component of the square wave output. Most Class-D amplifiers use some variation of pulse-width modulation (PWM), but the SSM2356 uses Σ-Δ modulation to determine the switching pattern of the output devices, resulting in a number of important benefits. Σ-Δ modulators do not produce a sharp peak with many harmonics in the AM frequency band, as pulsewidth modulators often do. Σ-Δ modulation provides the benefits of reducing the amplitude of spectral components at high frequencies, that is, reducing EMI emission that might otherwise be radiated by speakers and long cable traces. Due to the inherent spread-spectrum nature of Σ-Δ modulation, the need for oscillator synchronization is eliminated for designs incorporating multiple SSM2356 amplifiers. The SSM2356 also integrates overcurrent and temperature protection. • • • • System power-up/power-down Mute/unmute Input source change Sample rate change The SSM2356 has a pop-and-click suppression architecture that reduces these output transients, resulting in noiseless activation and deactivation. EMI NOISE The SSM2356 uses a proprietary modulation and spreadspectrum technology to minimize EMI emissions from the device. For applications having difficulty passing FCC Class B emission tests, the SSM2356 includes a modulation select pin (ultralow EMI emission mode) that significantly reduces the radiated emissions at the Class-D outputs, particularly above 100 MHz. Figure 36 shows SSM2356 EMI emission tests performed in a certified FCC Class-B laboratory in normal emissions mode (EDGE = GND). Figure 37 shows SSM2356 EMI emission with EDGE = VDD, placing the device in low emissions mode. 60 50 GAIN SELECTION The preset gain of SSM2356 can be selected between 6 dB and 18 dB with no external components and no change to the input impedance. A major benefit of fixed input impedance is that there is no need to recalculate input corner frequency (Fc) when gain is adjusted. The same input coupling components can be used for both gain settings. It is possible to adjust the SSM2356 gain by using external resistors at the input. To set a gain lower than 18 dB (or 6 dB when GAIN = VDD), refer to Figure 34 for the differential input configuration and Figure 35 for the single-ended configuration. Calculate the external gain configuration as follows: When GAIN = GND External Gain Settings = 160 kΩ/(80 kΩ + REXT) When GAIN = VDD External Gain Settings = 640 kΩ/(80 kΩ + REXT) (dBµV) 40 (dBµV) 30 20 10 130 230 330 430 530 630 730 830 930 1000 FREQUENCY (MHz) Figure 36. EMI Emissions from SSM2356, 1-Channel, 12 cm Cable, EDGE = GND 60 50 40 POP-AND-CLICK SUPPRESSION Voltage transients at the output of audio amplifiers may occur when shutdown is activated or deactivated. Voltage transients as low as 10 mV can be heard as an audio pop in the speaker. Clicks and pops can also be classified as undesirable audible transients generated by the amplifier system and, therefore, as not coming from the system input signal. Such transients may be generated when the amplifier system changes its operating mode. For example, the following can be sources of audible transients: 30 20 10 130 230 330 430 530 630 730 830 930 1000 FREQUENCY (MHz) Figure 37. EMI Emissions from SSM2356, 1-Channel, 12 cm Cable, EDGE = VDD Rev. 0 | Page 13 of 16 08084-006 0 30 [1] HORIZONTAL [2] VERTICAL FCC CLASS-B LIMIT 08084-005 0 30 [1] HORIZONTAL [2] VERTICAL FCC CLASS-B LIMIT SSM2356 The measurements for Figure 36 and Figure 37 were taken in an FCC-certified EMI laboratory with a 1 kHz input signal, producing 0.5 W output power into an 8 Ω load from a 5 V supply. Cable length was 12 cm, unshielded twisted pair speaker cable. Note that reducing the supply voltage greatly reduces radiated emissions. affecting efficiency. Use large traces for the power supply inputs and amplifier outputs to minimize losses due to parasitic trace resistance. Proper grounding guidelines help to improve audio performance, minimize crosstalk between channels, and prevent switching noise from coupling into the audio signal. To maintain high output swing and high peak output power, the PCB traces that connect the output pins to the load and supply pins should be as wide as possible to maintain the minimum trace resistances. It is also recommended that a large ground plane be used for minimum impedances. In addition, good PCB layout isolates critical analog paths from sources of high interference. High frequency circuits (analog and digital) should be separated from low frequency circuits. Properly designed multilayer PCBs can reduce EMI emission and increase immunity to the RF field by a factor of 10 or more, compared with double-sided boards. A multilayer board allows a complete layer to be used for the ground plane, whereas the ground plane side of a double-sided board is often disrupted by signal crossover. If the system has separate analog and digital ground and power planes, the analog ground plane should be directly beneath the analog power plane, and, similarly, the digital ground plane should be directly beneath the digital power plane. There should be no overlap between analog and digital ground planes or between analog and digital power planes. OUTPUT MODULATION DESCRIPTION The SSM2356 uses three-level, Σ-Δ output modulation. Each output can swing from GND to VDD and vice versa. Ideally, when no input signal is present, the output differential voltage is 0 V because there is no need to generate a pulse. In a real-world situation, there are always noise sources present. Due to this constant presence of noise, a differential pulse is generated, when required, in response to this stimulus. A small amount of current flows into the inductive load when the differential pulse is generated. However, most of the time, output differential voltage is 0 V, due to the Analog Devices three-level, Σ-Δ output modulation. This feature ensures that the current flowing through the inductive load is small. When the user wants to send an input signal, an output pulse is generated to follow input voltage. The differential pulse density is increased by raising the input signal level. Figure 38 depicts three-level, Σ-Δ output modulation with and without input stimulus. OUTPUT = 0V OUT+ OUT– +5V 0V +5V 0V +5V 0V –5V INPUT CAPACITOR SELECTION The SSM2356 does not require input coupling capacitors if the input signal is biased from 1.0 V to VDD − 1.0 V. Input capacitors are required if the input signal is not biased within this recommended input dc common-mode voltage range, if high-pass filtering is needed, or if a single-ended source is used. If highpass filtering is needed at the input, the input capacitor and the input resistor of the SSM2356 form a high-pass filter whose corner frequency is determined by the following equation: fC = 1/(2π × RIN × CIN) The input capacitor can significantly affect the performance of the circuit. Not using input capacitors degrades both the output offset of the amplifier and the dc PSRR performance. 08084-007 VOUT OUTPUT > 0V OUT+ OUT– VOUT OUTPUT < 0V OUT+ OUT– VOUT +5V 0V +5V 0V +5V 0V +5V 0V +5V 0V 0V –5V PROPER POWER SUPPLY DECOUPLING To ensure high efficiency, low total harmonic distortion (THD), and high PSRR, proper power supply decoupling is necessary. Noise transients on the power supply lines are short-duration voltage spikes. These spikes can contain frequency components that extend into the hundreds of megahertz. The power supply input must be decoupled with a good quality, low ESL, low ESR capacitor, greater than 4.7 μF. This capacitor bypasses low frequency noises to the ground plane. For high frequency transient noises, use a 0.1 μF capacitor as close as possible to the VDD pin of the device. Placing the decoupling capacitor as close as possible to the SSM2356 helps to maintain efficient performance. Figure 38. Three-Level, Σ-Δ Output Modulation With and Without Input Stimulus LAYOUT As output power continues to increase, care must be taken to lay out PCB traces and wires properly among the amplifier, load, and power supply. A good practice is to use short, wide PCB tracks to decrease voltage drops and minimize inductance. Ensure that track widths are at least 200 mil for every inch of track length for the lowest dc resistance (DCR), and use 1 oz. or 2 oz. copper PCB traces to further reduce IR drops and inductance. A poor layout increases voltage drops, consequently Rev. 0 | Page 14 of 16 SSM2356 OUTLINE DIMENSIONS 1.700 1.660 SQ 1.620 0.660 0.600 0.540 SEATING PLANE 4 3 2 1 A BALL A1 IDENTIFIER 0.290 0.260 0.230 1.20 BSC B C D 0.40 BSC TOP VIEW (BALL SIDE DOWN) 0.430 0.400 0.370 0.07 COPLANARITY 0.230 0.200 0.170 BOTTOM VIEW (BALL SIDE UP) 040209-B Figure 4. 16-Ball Wafer Level Chip Scale Package [WLCSP] (CB-16-4) Dimensions shown in millimeters ORDERING GUIDE Model SSM2356CBZ-REEL1 SSM2356CBZ-REEL71 EVAL-SSM2356Z1 1 Temperature Range −40°C to +85°C −40°C to +85°C Package Description 16-Ball Wafer Level Chip Scale Package [WLCSP] 16-Ball Wafer Level Chip Scale Package [WLCSP] Evaluation Board Package Option CB-16-4 CB-16-4 Branding Y1R Y1R Z = RoHS Compliant Part. Rev. 0 | Page 15 of 16 SSM2356 NOTES ©2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D08084-0-5/09(0) Rev. 0 | Page 16 of 16