LM4682 LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and DC Volume Control Literature Number: SNAS271D OBSOLETE September 24, 2011 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and DC Volume Control General Description Key Specifications The LM4682 is a fully integrated single supply, high efficiency audio power amplifier solution. The LM4682 utilizes a proprietary balanced pulse-width modulation technique that lowers output noise and THD and improves PSRR when compared to conventional pulse width modulators. The LM4682 also features a stereo headphone amplifier that delivers 60mW into a 32 headset with less than 0.5% THD. The LM4682's DC volume control has a +30dB to -48dB range when speakers are driven and a range of +13dB to - 65dB when headphones are connected. All amplifiers are protected by thermal shutdown. Additionally, all amplifiers incorporate output current limiting function to protect their outputs from short circuit. The LM4682 features a low-power consumption shutdown mode. And its efficiency reaches 85% for a 10W output power with an 8 load. External heatsink is not required when playing music. The IC features click and pop reduction circuitry that minimizes audible popping during device turn-on and turn-off. The LM4682 is available in a 48-lead LLP package, ideal for portable and desktop computer applications. PO at THD+N = 10%, VDD = 14V THD+N at 1kHz at 6W into 8 (Power Amp) Efficiency at 7W into 8 Total quiescent power supply current Total shutdown power supply current THD+N 1kHz, 20mW, 32 (Headphone) Single supply range 10W (typ) 0.2% (typ) 84% (typ) 52mA (typ) 0.1mA (typ) 0.02% (typ) 8.5V to 15V Features Pulse-width modulator. DC Volume Control Stereo headphone amplifier. "Click and pop" suppression circuitry. Micropower shutdown mode. 48 lead LLP package (No heatsink required). Applications Flat Panel Displays Televisions Multimedia Monitors Boomer(R) is a registered trademark of National Semiconductor Corporation. (c) 2011 National Semiconductor Corporation 201196 201196 Version 5 Revision 2 www.national.com Print Date/Time: 2011/09/24 10:13:06 LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and DC Volume Control LM4682 LM4682 Block Diagram 20119622 Block Diagram for LM4682 www.national.com 2 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 Connection Diagram LLP Package 20119618 Top View Order Number LM4682SQ See NS Package Number SQA48A (LLP Package) 3 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com FIGURE 1. Typical Stereo Audio Amplifier with Headphone Selection Circuit 20119630 LM4682 Typical Application www.national.com 4 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Input Voltage Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature (Note 6) Storage Temperature 15.5V -0.3V to VDD +0.3V Internally Limited 2000V 200V 150C Operating Ratings TMIN TA TMAX Supply Voltage -40C TA +85C 8.5V VDD 15V Thermal Resistance (LLP Package) -65C TA 150C Soldering Information LLP Package Electrical Characteristics (Note 1, Note 2) Temperature Range JA 28C/W JC 20C/W (Note 1, Note 2, Note 7) The following specifications apply for VDD = 12V, VOLVDD = 5V, RL = 8, LC filter values as shown in Figure 1, unless otherwise specified. Limits apply for TA = 25C. LM4682 Symbol VDD Parameter Conditions Operating Supply Voltage Range Typica l Max Min 12 15 8.5 Units V Quiescent Power Supply Current, Class D Mode VIN = 0VRMS, VHPSEL = 0V 52 70 mA Quiescent Power Supply Current, Headphone Mode VIN = 0VRMS, VHPSEL = 12V 30 40 mA ISD Quiescent Power Supply Current, Shutdown Mode SDB = 0V 0.1 RIN Input Resistance in Both Modes VOLVDD DC Reference Supply Voltage VIH Minimum Logic High Input Voltage VIL Maximum Logic Low Input Voltage VHPIH HP Sense High Input Voltage VHPIL HP Sense Low Input Voltage IS mA 8 k 5.5 SDB, MUTEB pins 3 V 0.7xVOLVDD V 0.3xVOLVDD V VDD-1 VDD/2 V V Power Amplifiers POR Output Power, Per Channel THD+N 1%, fIN = 1kHz PD1 Power Dissipation PO = 7W/Chan, fIN = 1kHz 2.6 W EFF1 Efficiency PO = 7W/Chan, fIN = 1kHz 84.4 % THD+N Harmonic Distortion + Noise PO = 6W/Chan, fIN = 1kHz 0.2 % VNOISE Output Noise Voltage, RMS. A-Weighted RSOURCE = 50, CIN = 1F, BW = 8Hz to 22kHz A-weighted, input referred 13 V 6.0 5.5 W VRIPPLE = 200mVpp, 1kHz, VIN = 0, input referred PSRR Power Supply Rejection Ratio f = 50Hz 94 f = 60Hz 94 f 100Hz 93 f = 120Hz 93 f = 1kHz 84 5 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 dB www.national.com LM4682 Vapor Phase (60 sec.) 215C Infrared (15 sec.) 220C See AN-450 "Surface Mounting and their Effects on Product Reliability" for other methods of soldering surface mount devices. Absolute Maximum Ratings (Note 2) LM4682 LM4682 Symbol Parameter Conditions Typica l Max Min Units Headphone Amplifiers PO Power Out Per Channel THD+N 1%, RL = 32, fIN = 1kHz 80 THD+N Distortion + Noise PO = 20mW, RL = 32, fIN = 1kHz 0.02 % VNOISE Output Noise Voltage, RMS RIN = 50, CIN = 1F, BW = 20Hz to 20kHz A-weighted, input referred 9 V PSRR Power Supply Rejection Ratio (Referred to Input) 200mV, 1kHz, VIN = 0, RL = 32 88 dB Electrical Characteristics for Volume Control 60 mW (Note 1, Note 2) The following specifications apply for VDD = 12V. Limits apply for TA = 25C. LM4682 Symbol CRANGE AM Parameter Gain Range Mute Gain Conditions Units (Limits ) Typical (Note 8) Limit (Note 7) VOL_CTL voltage = VOLVDD voltage, No Load Power Amplifier Headphone Amplifier 30 13 29 12 dB (min) dB (min) VOL_CTL voltage = 0.069 x VOLVDD No Load Power Amplifier Headphone Amplifier -48 -65 -46 -63 dB (min) dB (min) VMUTE voltage = 0V, No Load Power Amplifier Headphone Amplifier -80 -70 -60 -60 dB (max) dB (max) Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: "Absolute Maximum Ratings" indicate limits beyond which damage to the device may occur. "Operating Ratings" indicate conditions for which the device is functional, but do not guarantee specific performance limits. "Electrical Characteristics" state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 3: For operating at case temperatures above 25C, the device must be derated based on a 150C maximum junction temperature and a thermal resistance of JA = 28C/W (junction to ambient). Note 4: Human body model, 100pF discharged through a 1.5k resistor. Device pin 16 has ESD HBM rating = 1500V. Note 5: Machine Model 220pF-240pF discharged through all pins. Note 6: The operating junction temperature maximum is 150C. Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 8: Typicals are measured at 25C and represent the parametric norm. www.national.com 6 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 Typical Performance Characteristics (Power Amplifier) THD+N vs Frequency VDD = 9V, RL = 8, PO = 1W THD+N vs Frequency VDD = 12V, RL = 8, PO = 1W 20119658 20119659 THD+N vs Frequency VDD = 15V, RL = 8, PO = 1W THD+N vs Output Power Per Channel VDD = 9V, fIN = 1kHz, RL = 8 20119661 20119660 THD+N vs Output Power Per Channel VDD = 12V, fIN = 1kHz, RL = 8 THD+N vs Output Power Per Channel VDD = 15V, fIN = 1kHz, RL = 8 20119662 20119663 7 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 THD+N vs Output Power Per Channel VDD = 12V, fIN = 10kHz, RL = 8 THD+N vs Output Power Per Channel VDD = 12V, fIN = 20Hz, RL = 8 20119664 20119665 Output Power vs Supply Voltage fIN = 1kHz, RL = 8 Amplifiers Gain vs Frequency VDD = 9V, RL = 8, PO = 1W 20119667 20119647 Amplifiers Gain vs Frequency VDD = 12V, RL = 8, PO = 1W Amplifiers Gain vs Frequency VDD = 15V, RL = 8, PO = 1W 20119648 www.national.com 20119649 8 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 PSRR vs Frequency VDD = 9V PSRR vs Frequency VDD = 12V 20119644 20119645 PSRR vs Frequency VDD = 15V Class-D Amplifier Dissipation vs Load Dissipation Per Channel, VDD = 9V, RL = 8 (both channels driven and measured) 20119646 20119638 Class-D Amplifier Dissipation vs Load Dissipation Per Channel, VDD = 15V, RL = 8 (both channels driven and measured) Class-D Amplifier Dissipation vs Load Dissipation Per Channel, VDD = 12V, RL = 8 (both channels driven and measured) 20119640 20119639 9 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 Efficiency vs Output Power VDD = 9V, RL = 8 (both channels driven and measured) Efficiency vs Output Power VDD = 12V, RL = 8 (both channels driven and measured) 20119641 20119642 Efficiency vs Output Power VDD = 15V, RL = 8 (both channels driven and measured) Output Power vs Load Resistance VDD = 9V, fIN = 1kHz (both channels driven and measured) 20119655 20119643 Output Power vs Load Resistance VDD = 12V, fIN = 1kHz (both channels driven and measured) Output Power vs Load Resistance VDD = 15V, fIN = 1kHz (both channels driven and measured) 20119657 20119656 www.national.com 10 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 Power Supply Current vs Power Supply Voltage Class-D Amplifier Gain vs Volume Control Voltage VDD = 15V 20119654 20119628 Typical Performance Characteristics (Headphone Amplifier) THD+N vs Frequency VDD = 9V, RL = 32, PO = 20mW THD+N vs Frequency VDD = 12V, RL = 32, PO = 20mW 20119651 20119652 11 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 THD+N vs Frequency VDD = 15V, RL = 32, PO = 20mW THD+N vs Output Power VDD = 9V, RL = 32, fIN = 1kHz 20119668 20119653 THD+N vs Output Power VDD = 12V, RL = 32, fIN = 1kHz THD+N vs Output Power VDD = 15V, RL = 32, fIN = 1kHz 20119669 20119670 Output Power vs Supply Voltage Per Channel fIN = 1kHz, RL = 32 Power Supply Current vs Power Supply Voltage 20119650 20119671 www.national.com 12 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 Headphone Amplifier Gain vs Volume Control Voltage VDD = 15V 20119629 13 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 Class D amplifiers. The headphone control of the output configuration is shown in Table 1. General Features SYSTEM FUNCTIONAL INFORMATION TABLE 1. Headphone Controls Modulation Technique Unlike typical Class D amplifiers that use single-ended comparators to generate a pulse-width modulated switching waveform and RC timing circuits to set the switching frequency, the LM4682 uses a balanced differential floating modulator. Oscillation is a result of injecting complimentary currents onto the respective plates of a floating, on-die capacitor. The value of the floating capacitor and value of the components in the modulator's feedback network set the nominal switching frequency at 450kHz. Modulation results from imbalances in the injected currents. The amount of current imbalance is directly proportional to the applied input signal's magnitude and frequency. Using a balanced, floating modulator produces a Class D amplifier that is immune to common mode noise sources such as substrate noise. This noise occurs because of the high frequency, high current switching in the amplifier's output stage. The LM4682 is immune to this type of noise because the modulator, the components that set its switching frequency, and even the load all float with respect to ground. The balanced modulator's pulse width modulated output drives the gates of the LM4682's H-bridge configured output power MOSFETs. The pulse-train present at the power MOSFETs' output is applied to an LC low pass filter that removes the 450kHz energy component. The filter's output signal, which is applied to the driven load, is an amplified replica of the audio input signal. HP Sense Pin, HPSEL 0 Class D Amps Active 1 Class D Amps Inactive Under Voltage Protection The under voltage protection disables the output driver section of the LM4682 while the supply voltage is below 8V. This condition may occur as power is first applied or during low line conditions, changes in load resistance, or when power supply sag occurs. The under voltage protection ensures that all of the LM4682's power MOSFETs are off. This action eliminates shoot-through current and minimizes output transients during turn-on and turn-off. The under voltage protection gives the digital logic time to stabilize into known states, further minimizing turn on output transients. Power Supply Sequencing In order to stabilize LM4682 before any operation, a powerup sequence for the power supplies is recommended. The Power VDD should be applied first. Without deactivating the mute and shutdown function of the amplifiers, the VOLVDD is then applied. Prior to removing the two supply voltages, activate shutdown and mute. Turn-On Time The LM4682 has an internal timer that determines the amplifier's turn-on time. After power is first applied or the part returns from shutdown, the nominal turn-on time is 600ms. This delay allows all externally applied capacitors to charge to a final value of VDD/2. Further, during turn-on, the outputs are muted. This minimizes output transients that may occur while the part settles into its quiescent operating mode. Shutdown Function The LM4682's active-low shutdown function allows the user to place the amplifier in a shutdown mode while the system power supply remains active. Activating shutdown stops the output switching waveform and minimizes the quiescent current. Applying logic "0" to SDB pin enables the shutdown function. Applying logic "1" to SDB pin disables the shutdown function and restores full amplifier operation. Output Stage Current Limit and Fault Detection Protection The output stage MOSFETs are protected against output conditions that could otherwise compromise their operational status. The first stage of protection is output current limiting. When conditions that require high currents to drive a load, the LM4682's current limit circuitry clamps the output current at a nominal value of 2.5A. The output waveform is present, but may be clipped or its amplitude reduced. The same 2.5A nominal current limit also occurs if the amplifier outputs are shorted together or either output is shorted to VDD or GND. The second stage of protection is an onboard fault detection circuit that continuously monitors the signal on each output MOSFET's gate and compares it against the respective drain voltage. When a condition is detected that violates a MOSFET's Safe Operating Area (SOA) and the drive signal is disconnected from the output MOSFETs' gates. The fault detect circuit maintains this protective condition for approximately 600ms, at which time the drive signal is reconnected. If the fault condition is no longer present, normal operation resumes. If the fault condition remains, however, the drive signal is again disconnected. Mute Function The LM4682's active-low mute function allows the user to place the amplifier outputs in muted mode while the amplifier's analog input signals remain active. Activating mute internally removes the analog input signal from the Class D and headphone amplifier inputs. While muted the amplifier inputs and outputs retain in their VDD/2 operational bias. Applying logic "0" to MUTEB pin activates mute. Applying logic "1" to MUTEB pin deactivates mute. The MUTEB pin is pulldown internally to put both Class D and headphone amplifier outputs mute. Stereo Headphone Amplifier The LM4682's stereo headphone amplifier operates continuously, even while the Class D amplifiers are active. When using headphones to listen to program material, it is usually desirable to stop driving external speakers. This is easily achieved by using the active high HPSEL input. As shown in typical application schematic in Figure 1, with no headphones connected to the headphone jack, the input voltage applied to the HPSEL pin is a logic low. In this state, the Class D amplifiers are active and able to drive external speakers. When headphones are plugged into the headphone jack, the switch inside the jack is opened. This changes the voltage applied to the HPSEL pin to a logic high, shutting off the LM4682's www.national.com Thermal Protection The LM4682 has thermal shutdown circuitry that monitors the die temperature. Once the LM4682 die temperature reaches 170C, the LM4682 disables the output switching waveform and remains disabled until the die temperature falls below 140C (typ). 14 201196 Version 5 Revision 2 Output Stage Configuration Print Date/Time: 2011/09/24 10:13:06 DC Volume Control The LM4682 has an internal stereo volume control whose setting is a function of the DC voltage applied to the volume control pin VOLCTL. The LM4682 volume control consists of 31 steps, which are individually selected by a variable DC voltage level on the VOLCTL pin. A linear type 100k potentiometer is used to adjust the VOLCTL voltage in the LM4682 demonstration board as shown in application circuit (see Figure 1). The resistance value of potentiometer fall in the range from 10k to 15 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 100k is recommended to be used with only small amount of current dissipation and large enough for the VOLCTL pin to function properly. The Volume Control Characteristics of LM4682 can be found in the Typical Performance Characteristics section. The gain range of Class D amplifiers are from -48dB to 30dB. The gain range of headphone amplifiers are from -65dB to 13dB. Each gain step corresponds to specific input voltage of both Class D amplifiers and headphone amplifiers are shown in Table 2. To minimize the effect of noise on the volume control VOLCTL pin, which can affect the selected gain level, hysteresis has been implemented. The amount of hysteresis corresponds to half of the step width. For highest accuracy, the voltage shown in the "recommended voltage" column of the table is used to select a desired gain. The recommended voltage is exactly halfway between the two closest transitions to the next highest or next lowest gain levels. Over-Modulation Protection The LM4682's over-modulation protection is a result of the preamplifier's inability to produce signal magnitudes that equal the power supply voltages. Since the preamplifier's output magnitude will always be less than the supply voltage, the duty cycle of the amplifier's switching output will never reach zero. Peak modulation is limited to a nominal 95%. LM4682 TABLE 2. Volume Control Table Voltage Range (% of VOLVDD) Step Voltage Range (V), VOLVDD = 5V Gain (dB) Low High Recommended Low High Recommended Class D Amplifier 1 77.50% 100.00% 100.000% 3.875 5.000 5.000 29.97 13.06 2 75.00% 78.50% 76.875% 3.750 3.925 3.844 28.97 12.07 3 72.50% 76.25% 74.375% 3.625 3.813 3.719 27.97 11.07 4 70.00% 73.75% 71.875% 3.500 3.688 3.594 26.96 10.06 5 67.50% 71.25% 69.375% 3.375 3.563 3.469 25.98 9.07 6 65.00% 68.75% 66.875% 3.250 3.438 3.344 24.97 8.07 7 62.50% 66.25% 64.375% 3.125 3.313 3.219 23.95 7.05 8 60.00% 63.75% 61.875% 3.000 3.188 3.094 21.98 5.08 9 57.50% 61.25% 59.375% 2.875 3.063 2.969 19.95 3.05 10 55.00% 58.75% 56.785% 2.750 2.983 2.844 17.96 1.06 11 52.50% 56.25% 54.375% 2.625 2.813 2.719 15.97 -0.93 12 50.00% 53.75% 51.875% 2.500 2.688 2.594 13.99 -2.91 13 47.50% 51.25% 49.375% 2.375 2.563 2.469 11.99 -4.91 14 45.00% 48.75% 46.875% 2.250 2.438 2.344 9.95 -6.96 15 42.50% 46.25% 44.375% 2.125 2.313 2.219 7.96 -8.94 16 40.00% 43.75% 41.875% 2.000 2.188 2.094 5.96 -10.95 17 37.50% 41.25% 39.375% 1.875 2.063 1.969 3.99 -12.91 18 35.00% 38.75% 36.875% 1.750 1.938 1.844 2.03 -14.87 19 32.50% 36.25% 34.375% 1.625 1.813 1.719 -0.02 -16.92 20 30.00% 33.75% 31.875% 1.500 1.688 1.594 -2.11 -19.02 21 27.50% 31.25% 29.375% 1.375 1.563 1.469 -4.16 -21.06 22 25.00% 28.75% 26.875% 1.250 1.438 1.344 -5.97 -22.87 23 22.50% 26.25% 24.375% 1.125 1.313 1.219 -8.77 -25.68 24 20.00% 23.75% 21.875% 1.000 1.188 1.094 -12.06 -28.96 25 17.50% 21.25% 19.375% 0.875 1.063 0.969 -14.84 -31.75 26 15.00% 18.75% 16.875% 0.750 0.938 0.844 -17.36 -34.26 27 12.50% 16.25% 14.375% 0.625 0.813 0.719 -20.89 -37.79 28 10.00% 13.75% 11.875% 0.500 0.688 0.594 -26.92 -43.83 29 7.50% 11.25% 9.375% 0.375 0.563 0.469 -32.95 -49.85 30 5.00% 8.75% 6.875% 0.250 0.438 0.344 -38.97 -55.88 31 0.00% 6.25% 0.000% 0.000 0.313 0.000 -48.03 -64.94 www.national.com 16 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 Headphone Amplifier SUPPLY BYPASSING The major source of noises to be taken care and applying bypassing technique in using LM4682 are those transients response coming from its output stage. During the switching operations of the output stage of LM4682, the switching frequencies vary when the internal modulator react to the input signals. This creates a band of switching transients giving back to the power supply terminals of LM4682. A single capacitor may not bypass those transients well. Two capacitors which values are closed to each other are used to bypass this range of frequencies to the ground. 10F tantalum capacitors and 4.7F ceramic capacitors are needed for this kind of decoupling of LM4682 switching operation. This results an improvement in terms of both stability and audio performance of LM4682. In addition, these capacitors should be placed as close as possible to each IC's supply pin(s) using leads as short as possible. Apart from the power supply de-coupling capacitors, the four bootstrapping capacitors (at pins BST1_A, BST2_A, BST1_B and BST2_B) should also be placed close to their corresponding pins. This could minimize the undesirable switching noise coupled to the supply rail. The LM4682 has two different sets of VDD pins: a set for power VDD (PVDD_A and P VDD _B) and a set for signal VDD _A and HP_ VDD. The parallel combination of the low value ceramic (4.7F) and high value tantalum (10F) should be used to bypass the power VDD pins. A small value (1F) ceramic or tantalum can be used to bypass the signal VDD _A and HP_ VDD pin. RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT Figures 2 through 6 show the recommended four-layer PCB board layout that is optimized for the 48-pin LLP packaged LM4682 and associated external components. This circuit is designed for use with an external 12V supply and 8 speakers (or load resistors). Apply 12V and ground to board's VDD and GND terminals respectively. And apply 5V to the VOLVDD (refer to power supply sequencing for details). Connect speakers (or load resistors) between the board's OUTA + and OUTA-, and between the board's OUTB+ and OUTB-. Apply the stereo input signals to IN_A and IN_B. When designing the layout of the PCB layout, please pay attention to the output terminals of LM4682. OUTPUT STAGE FILTERING The LM4682 requires a low pass filter connected between the amplifier's bridge output and the load. Figure 1 shows the recommended LC filter. A minimum value of 22H is recommended. As shown in Figure 1, using the values of the components connected between the amplifier BTL outputs and the load achieves a 2nd-order lowpass filter response which optimizes the amplifier's performance within the audio band. THD+N MEASUREMENTS AND OUT OF AUDIO BAND NOISE THD+N (Total Harmonic Distortion plus Noise) is a very important parameter by which all audio amplifiers are measured. 17 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 Often it is shown as a graph where either the output power or frequency is changed over the operating range. A very important variable in the measurement of THD+N is the bandwidth-limiting filter at the input of the test equipment. Class D amplifiers, by design, switch their output power devices at a much higher frequency than the accepted audio range (20Hz - 20kHz). Alternately switching the output voltage between VDD and GND allows the LM4682 to operate at much higher efficiency than that achieved by traditional Class AB amplifiers. Switching the outputs at high frequency also increases the out-of-band noise. Under normal circumstances the output lowpass filter significantly reduces this out-of-band noise. If the low pass filter is not optimized for a given switching frequency, there can be significant increase in out-of-band noise. THD+N measurements can be significantly affected by out-of-band noise, resulting in a higher than expected THD+N measurement. To achieve a more accurate measurement of THD, the test equipment's input bandwidth of the must be limited. Some common upper filter points are 22kHz, 30kHz, and 80kHz. The input filter limits the noise component of the THD+N measurement to a smaller bandwidth resulting in a more real-world THD+N value. Application Hints LM4682 20119626 FIGURE 2. Top Layer 20119627 FIGURE 3. Top Silkscreen Layer www.national.com 18 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 20119623 FIGURE 4. Upper Middle Layer 20119624 FIGURE 5. Lower Middle Layer 19 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 20119625 FIGURE 6. Bottom Layer www.national.com 20 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 Revision History Rev Date 1.0 02/22/06 Initial WEB release of the document. Description 1.1 02/24/06 Edited art 201196 71 (changed the y-axis unit from mA to mW. 1.2 03/08/06 Did few texts clean-up and re-released D/S to the WEB (per Kevin H.). 1.3 06/29/06 Added 2 columns on ( Gain dB) Table 2 and re-released the D/S to the WEB (per Alex CK Wong). 1.4 04/09/08 Added volume control curves and input some text edits. 1.5 04/15/08 Changed the titles on curves 20119628 and 29. 1.6 04/21/08 Text edits. 21 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM4682SQ NS Package Number SQA48A www.national.com 22 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 LM4682 Notes 23 201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06 www.national.com LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and DC Volume Control Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH(R) Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise(R) Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise(R) Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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