LM48520

LM48520 Boosted Stereo Class D Audio Power Amplifier with Output Speaker Protection and Spread Spectrum March 20, 2008 LM48520 Boosted Stereo Class D Audio Power Amplifier with Output Speaker Protection and Spread Spectrum General Description The LM48520 integrates a boost converter with a high efficiency Class D stereo audio power amplifier to provide up to 1W/ch continuous power into an 8Ω speaker when operating from 2.7V to 5.0V power supply with boost voltage (PV1) of 5.0V. The LM48520 utilizes a proprietary spread spectrum pulse width modulation technique that lowers RF interference and EMI levels. The Class D amplifier is a low noise, filterless PWM architecture that eliminates the output filter, reducing external component count, board area, power consumption, system cost, and simplifying design. The LM48520 is designed for use in mobile phones and other portable communication devices. The high (78%) efficiency extends battery life when compared to Boosted Class AB amplifiers. The LM48520 features a low-power consumption shutdown mode. Shutdown may be enabled by driving the Shutdown pin to a logic low (GND). Also, external leakage is minimized via control of the ground reference via the SWOUT pin . The LM48520 has 4 gain options which are pin selectable via Gain0 and Gain1 pins. Output short circuit prevents the device from damage during fault conditions. Superior click and pop suppression eliminates audible transients during powerup and shutdown. Key Specifications ■ Quiescent Power Supply Current ■ Output Power (RL = 8Ω, THD+N ≤ 1%, VDD = 3.3V,PV1 = 5.0V) 11.5mA (typ) 1.1W (typ) 0.04μA (typ) ■ Shutdown Current Features ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Click and Pop Suppression Low 0.04μA Shutdown Current 78% Efficiency Filterless Class D 2.7V - 5.0V operation 4 Adjustable Gain settings Adjustable output swing limiter with Soft Clipping Speaker Protection Short circuit protection on Audio Amps Independent Boost and Amplifier shutdown pins Applications ■ ■ ■ ■ ■ Mobile Phones PDAs Portable media Cameras Handheld games Boomer® is a registered trademark of National Semiconductor Corporation. © 2008 National Semiconductor Corporation 201987 www.national.com LM48520 Typical Application 20198701 FIGURE 1. Typical LM48520 Audio Amplifier Application Circuit www.national.com 2 LM48520 Connection Diagrams LM48520TL 20198702 Top View Order Number LM48520TL See NS Package Number TLA25AAA Micro SMD Marking 20198721 Top View X — Date Code T — Die Traceability G — Boomer Family I5 — LM48520TL 3 www.national.com LM48520 Pin Descriptions Pin Designator A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 C1 C2 C3 C4 C5 D1 D2 D3 D4 D5 E1 E2 E3 E4 E5 Pin Name VDD BstFB Soft Start SW_GND SW INR+ INRFB_GND INLINL+ V1 BstSD GND Gain0 PV1 AmpSD OUTR+ NC OUTL+ Gain1 VLimit OUTRPGND OUTLNC Power Supply Regulator Feedback Input. Connect BstFB to an external resistive voltage divider to set the boost output voltage. Soft start capacitor Booster ground Drain of the Internal FET switch Non-inverting right channel input Inverting right channel input Ground return for R1, R2 resistor divider Inverting left channel input Non-inverting left channel input Amplifier supply voltage. Connect to PV1. Regulator active low shutdown Ground Gain setting input 0 Amplifier H-bridge power supply. Connect to V1. Amplifier active low shutdown Non-inverting right channel output No connect Non-inverting left channel output Gain setting input 1 Set to control output clipping level Inverting right channel output Power ground Inverting left channel output No connect Pin Function www.national.com 4 LM48520 Absolute Maximum Ratings (Note 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (VDD, V1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature 6V −65°C to +150°C −0.3V to VDD + 0.3V Internally limited 2000V 200V 150°C Thermal Resistance  θJA (TL) 40.5 °C/W Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage (VDD) Amplifier Voltage (V1 ) Not under Boosted Condition Amplifier Voltage (PV1 ) Under Boosted Condition (Notes 1, 2) −40°C ≤ TA ≤ +85°C 2.7V ≤ VDD ≤ 5.0V 2.4V ≤ V1 ≤ 5.5V 3.0V ≤ PV1 ≤ 5.0V Electrical Characteristics VDD = 3.3V Symbol Parameter The following specifications apply for VDD = 3.3V, AV = 6dB, RL = 15µH + 8Ω +15µH, fIN = 1kHz, unless otherwise specified. Limits apply for TA = 25°C, R1 = 40.2kΩ, R2 = 16.2kΩ, V1 = PV1 = 5V, Vlimit = GND. All electrical specifications are for amplifier and booster. Conditions LM48520 Typical (Note 6) VIN = 0, RLOAD = ∞ IDD Quiescent Power Supply Current VDD = 2.7V VDD = 3.3V VDD = 5.0V ISD VSDIH VSDIL TWU VOS Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Wake-up Time Output Offset Voltage G0, G1 = GND RL = ∞ RL = ∞ G0 = VDD, G1 = GND G0 = GND, G1 = VDD RL = ∞ RL = ∞ G0, G1 = VDD RL = 15μH + 8Ω + 15μH THD+N = 1% (max), f = 1kHz, 22kHz, BW VDD = 3.3V RL = 15μH + 8Ω + 15μH THD+N = 10% (max), f = 1kHz, 22kHz, BW VDD = 3.3V PO = 500mW, f = 1kHz, THD+N Total Harmonic Distortion + Noise RL = 15μH + 8Ω + 15μH, VDD = 3.3V VDD = 3.6V, f = 20Hz – 20kHz Inputs to AC GND, A weighted 0.04 % VSHUTDOWN = GND For SD Boost, SD Amp For SD Boost, SD Amp Amplifier + Booster Wakeup 3 5 6 12 18 24 14.8 11.5 8.0 0.04 1.0 1.4 0.4 μA (max) V V ms mV dB dB dB dB 15.5 mA (max) Limit (Notes 7, 8) Units (Limits) AV Gain PO Output Power 1.1 0.87 W (min) 1.3 W εOS Output Noise 32 µVRMS 5 www.national.com LM48520 Symbol Parameter Conditions LM48520 Typical (Note 6) Limit (Notes 7, 8) Units (Limits) PSRR Power Supply Rejection Ratio VRIPPLE = 200mVP-P Sine, fRIPPLE = = 217Hz VRIPPLE = 200mVP-P Sine, fRIPPLE = = 1kHz VRIPPLE = 1VP-P, fRIPPLE = 217Hz PO = 1W, f = 1kHz, RL = 15μH + 8Ω + 15μH VDD = 3.3V VDD = 4.2V (Note 11) 82 79 67 dB dB dB CMRR Common Mode Rejection Ratio η Efficiency 78 1.24 2.5 1.9 3.2 % V Vpk (min) Vpk (max) VFB Vout clipped Feedback Pin Reference Voltage Output Voltage in clipped state with Vlimit = 2V, RL = 8Ω, VIN = 2VP soft clip activated Vout clipped = 8/3 (PV1 – 2Vlimit) Note 1: All voltages are measured with respect to the GND 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: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature, TA. The maximum allowable power dissipation is PDMAX = (TJMAX − TA) / θJA or the given in Absolute Maximum Ratings, whichever is lower. Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Note 5: Machine Model, 220pF–240pF discharged through all pins. Note 6: Typicals are measured at 25°C and represent the parametric norm. Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 9: Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to Vin for minimum shutdown current. Note 10: Shutdown current is measured with components R1 and R2 removed. Note 11: Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is unloaded). www.national.com 6 LM48520 Typical Performance Characteristics THD+N vs Frequency VDD = 2.7V, POUT = 800mW, RL = 8Ω THD+N vs Frequency VDD = 3.3V, POUT = 900mW, RL = 8Ω 20198703 20198704 THD+N vs Frequency VDD = 5.0V, POUT = 1W, RL = 8Ω THD+N vs Output Power VDD = 2.7V, RL = 8Ω 20198705 20198706 THD+N vs Output Power VDD = 3.3V, RL = 8Ω THD+N vs Output Power VDD = 5.0V, RL = 8Ω 20198707 20198708 7 www.national.com LM48520 Power Dissipation vs Output Power VDD = 2.7V, RL = 8Ω, f = 1kHz Power Dissipation vs Output Power VDD = 3.3V, RL = 8Ω, f = 1kHz 20198712 20198713 Power Dissipation vs Output Power VDD = 5.0V, RL = 8Ω, f = 1kHz Efficiency vs Output Power VDD = 2.7V, RL = 8Ω, f = 1kHz 20198714 20198709 Efficiency vs Output Power VDD = 3.3V, RL = 8Ω, f = 1kHz Efficiency vs Output Power VDD = 5.0V, RL = 8Ω, f = 1kHz 20198710 20198711 www.national.com 8 LM48520 CMRR vs Frequency VDD =3.3V, VRIPPLE = 1VP-P, RL = 8Ω PSRR vs Frequency VDD =3.3V, VRIPPLE = 200mVP-P, RL = 8Ω 20198722 20198723 Supply Current vs Supply Voltage No Load Output Power vs Supply Voltage RL = 8Ω, f = 1kHz 20198724 20198725 Boost Output Voltage vs Load Current VDD = 2.7V Boost Output Voltage vs Load Current VDD = 3.3V 20198726 20198727 9 www.national.com LM48520 Boost Output Voltage vs Load Current VDD = 5.0V 20198728 www.national.com 10 LM48520 Application Information GENERAL AMPLIFIER FUNCTION The LM48520 features a Class D audio power amplifier that utilizes a filterless modulation scheme, reducing external component count, conserving board space and reducing system cost. The outputs of the device transition from PV1 to GND with a 300kHz switching frequency. With no signal applied, the outputs (VLS+ and VLS-) switch with a 50% duty cycle, in phase, causing the two outputs to cancel. This cancellation results in no net voltage across the speaker, thus there is no current to the load in the idle state. With the input signal applied, the duty cycle (pulse width) of the LM48520 outputs changes. For increasing output voltage, the duty cycle of VLS+ increases, while the duty cycle of VLSdecreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. DIFFERENTIAL AMPLIFIER EXPLANATION The amplifier portion of the LM48520 is a fully differential amplifier that features differential input and output stages. A differential amplifier amplifies the difference between the two input signals. Traditional audio power amplifiers have typically offered only single-ended inputs resulting in a 6dB reduction in signal to noise ratio relative to differential inputs. The amplifier also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The amplifier can be used, however, as a single ended input amplifier while still retaining it's fully differential benefits. In fact, completely unrelated signals may be placed on the input pins. The amplifier portion of the LM48520 simply amplifies the difference between the signals. A major benefit of a differential amplifier is the improved common mode rejection ratio (CMRR) over single input amplifiers. The commonmode rejection characteristic of the differential amplifier reduces sensitivity to ground offset related noise injection, especially important in high noise applications. AMPLIFIER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM48520 is attributed to the region of operation of the transistors in the output stage. The Class D output stage acts as current steering switches, consuming negligible amounts of power compared to their Class AB counterparts. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET onresistance, along with switching losses due to gate charge. REGULATOR POWER DISSIPATION At higher duty cycles, the increased ON-time of the switch FET means the maximum output current will be determined by power dissipation within the LM48520 FET switch. The switch power dissipation from ON-time conduction is calculated by: PD(SWITCH) = DC x (IINDUCTOR(AVE))2 x RDS(ON) (W) Where DC is the duty cycle. (1) Class D amplifiers, while BstSD controls the regulator. Driving either inputs low disables the corresponding portion of the device, and reducing supply current. When the regulator is disabled, both FB_GND switches open, further reducing shutdown current by eliminating the current path to GND through the regulator feedback network. With the regulator disabled, there is still a current path from VDD, through the inductor and diode, to the amplifier power supply. This allows the amplifier to operate even when the regulator is disabled. The voltage at PV1 and V1 will be: VDD — [VD + (IL x DCR)] (2) Where VD is the forward voltage of the Schottky diode, IL is the current through the inductor, and DCR is the DC resistance of the inductor. Additionally, when the regulator is disabled, an external voltage between 2.4V and 5.5V can be applied directly to PV1 and V1 to power the amplifier. It is best to switch between ground and VDD for minimum current consumption while in shutdown. The LM48520 may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.1µA value. Increased THD+N may also be observed when a voltage of less than VDD is applied to AmpSD. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers, and switching DC-DC converters, is critical for optimizing device and system performance. Consideration to component values must be used to maximize overall system quality. The best capacitors for use with the switching converter portion of the LM48520 are multi-layer ceramic capacitors. They have the lowest ESR (equivalent series resistance) and highest resonance frequency, which makes them optimum for high frequency switching converters. When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage, they may provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from Taiyo-Yuden, AVX, and Murata. POWER SUPPLY BYPASSING FOR AMPLIFIER As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. The capacitor location on both PV1, V1 and VDD pins should be as close to the device as possible. SELECTING INPUT CAPACITOR FOR AUDIO AMPLIFIER Input capacitors, CIN, in conjunction with the input impedance of the LM48520 forms a high pass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to bias the signal to an optimal DC level. Assuming zero source impedance, the -3dB point of the high pass filter is given by: f(–3dB) = 1/2πRINCIN (3) SHUTDOWN FUNCTION The LM48520 features independent amplifier and regulator shutdown controls, allowing each portion of the device to be disabled or enabled independently. AmpSD controls the Choose CIN such that f-3dB is well below that lowest frequency of interest. Setting f-3dB too high affects the low-frequency responses of the amplifier. Use capacitors with low voltage 11 www.national.com LM48520 coefficient dielectrics, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies. Other factors to consider when designing the input filter include the constraints of the overall system. Although high fidelity audio requires a flat frequency response between 20Hz and 20kHz, portable devices such as cell phones may only concentrate on the frequency range of the frequency range of the spoken human voice (typically 300Hz to 4kHz). In addition, the physical size of the speakers used in such portable devices limits the low frequency response; in this case, frequencies below 150Hz may be filtered out. SELECTING OUTPUT CAPACITOR (CO) FOR BOOST CONVERTER A single 100µF low ESR tantalum capacitor provides sufficient output capacitance for most applications. Higher capacitor values improve line regulation and transient response. Typical electrolytic capacitors are not suitable for switching converters that operate above 500kHz because of significant ringing and temperature rise due to self-heating from ripple current. An output capacitor with excessive ESR reduces phase margin and causes instability. SELECTING INPUT CAPACITOR (Cs1) FOR BOOST CONVERTER An input capacitor is required to serve as an energy reservoir for the current which must flow into the coil each time the switch turns ON. This capacitor must have extremely low ESR, so ceramic is the best choice. We recommend a nominal value of 2.2µF, but larger values can be used. Since this capacitor reduces the amount of voltage ripple seen at the input pin, it also reduces the amount of EMI passed back along that line to other circuitry. SELECTING SOFTSTART (CSS) CAPACITOR The soft-start function charges the boost converter reference voltage slowly. This allows the output of the boost converter to ramp up slowly thus limiting the transient current at startup. Selecting a soft-start capacitor (CSS) value presents a trade off between the wake-up time and the startup transient current. Using a larger capacitor value will increase wake-up time and decrease startup transient current while the apposite effect happens with a smaller capacitor value. A general guideline is to use a capacitor value 1000 times smaller than the output capacitance of the boost converter (CO). A 0.1uF softstart capacitor is recommended for a typical application. SETTING THE OUTPUT VOLTAGE (V1) OF BOOST CONVERTER The output voltage is set using the external resistors R1 and R2 (see Figure 1). A value of approximately 13.3kΩ is recommended for R2 to establish a divider current of approximately 92µA. R1 is calculated using the formula: R1 = R2 X (V1/1.23 − 1) (4) Cf = 1 / (2 X R1 X fz) (5) SELECTING DIODES FOR BOOST The external diode used in Figure 1 should be a Schottky diode. A 20V diode such as the MBRS320T3 is recommended. The MBRS320T3 series of diodes are designed to handle a maximum average current of 3A. DUTY CYCLE The maximum duty cycle of the boost converter determines the maximum boost ratio of output-to-input voltage that the converter can attain in continuous mode of operation. The duty cycle for a given boost application is defined as: Duty Cycle = VOUT + VDIODE - VIN / VOUT + VDIODE - VSW This applies for continuous mode operation. SELECTING INDUCTOR VALUE Inductor value involves trade-offs in performance. Larger inductors reduce inductor ripple current, which typically means less output voltage ripple (for a given size of output capacitor). Larger inductors also mean more load power can be delivered because the energy stored during each switching cycle is: E = L/2 X (IP)2 Where “lp” is the peak inductor current. The LM48520 will limit its switch current based on peak current. With IP fixed, increasing L will increase the maximum amount of power available to the load. Conversely, using too little inductance may limit the amount of load current which can be drawn from the output. Best performance is usually obtained when the converter is operated in “continuous” mode at the load current range of interest, typically giving better load regulation and less output ripple. Continuous operation is defined as not allowing the inductor current to drop to zero during the cycle. Boost converters shift over to discontinuous operation if the load is reduced far enough, but a larger inductor stays continuous over a wider load current range. During the TBDµs ON-time, the inductor current ramps up TBDA and ramps down an equal amount during the OFFtime. This is defined as the inductor “ripple current”. It can also be seen that if the load current drops to about TBDmA, the inductor current will begin touching the zero axis which means it will be in discontinuous mode. A similar analysis can be performed on any boost converter, to make sure the ripple current is reasonable and continuous operation will be maintained at the typical load current values. MAXIMUM SWITCH CURRENT The maximum FET switch current available before the current limiter cuts in is dependent on duty cycle of the application. This is illustrated in a graph in the typical performance characterization section which shows typical values of switch current as a function of effective (actual) duty cycle. CALCULATING OUTPUT CURRENT OF BOOST CONVERTER (IAMP) As shown in Figure 2 which depicts inductor current, the load current is related to the average inductor current by the relation: 12 FEED-FORWARD COMPENSATION FOR BOOST CONVERTER Although the LM48520's internal Boost converter is internally compensated, the external feed-forward capacitor Cf is required for stability (see Figure 1). Adding this capacitor puts a zero in the loop response of the converter. The recommended frequency for the zero fz should be approximately 6kHz. Cf1 can be calculated using the formula: www.national.com LM48520 ILOAD = IIND(AVG) x (1 - DC) (6) tor, make certain that the continuous current rating is high enough to avoid saturation at peak currents, where: IIND = (PV1 / VDD) x ILOAD(BOOST) (10) Where "DC" is the duty cycle of the application. The switch current can be found by: ISW = IIND(AVG) + 1/2 (IRIPPLE) (7) A suitable core type must be used to minimize core (switching) losses, and wire power losses must be considered when selecting the current rating. Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency: IRIPPLE = DC x (VIN-VSW) / (f x L) (8) PCB Layout Guidelines High frequency boost converters require very careful layout of components in order to get stable operation and low noise. All components must be as close as possible to the LM48520 device. It is recommended that a four layer PCB be used so that internal ground planes are available. Some additional guidelines to be observed (all designators are referencing Figure 1): 1. Keep the path between L1, D1, and Co extremely short. Parasitic trace inductance in series with D1 and Co will increase noise and ringing. 2. The feedback components R1, R2 and Cf1 must be kept close to the FB pin to prevent noise injection on the FB pin trace. 3. Since the external components of the boost converter are switching, L1 and D1 should be kept away from the input traces to prevent the noise from injecting into the input. 4. The power supply bypass capacitors, Cs1 and Cs2 should be placed as close to the LM48520 device as possible. GROUNDING GUIDELINES There are three grounds on the LM48520, GND, SW_GND, and PGND. When laying out the PCB, it is critical to connect the grounds as close to the device as possible. The simplest way to do that is to place vias close to the GND, SW_GND, and PGND bumps and connect the GND, SW_GND, and PGND vias using a single ground plane in an inner layer of the PCB. combining all terms, we can develop an expression which allows the maximum available load current to be calculated: ILOAD(max) = (1–DC)x(ISW(max)–DC(VIN-VSW))/fL (9) The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-OFF switching losses of the FET and diode. DESIGN PARAMETERS VSW AND ISW The value of the FET "ON" voltage (referred to as VSW in equations 4 thru 7) is dependent on load current. A good approximation can be obtained by multiplying the "ON Resistance" of the FET times the average inductor current. FET on resistance increases at VIN values below 5V, since the internal N-FET has less gate voltage in this input voltage range (see Typical Performance Characteristics curves). Above VIN = 5V, the FET gate voltage is internally clamped to 5V. The maximum peak switch current the device can deliver is dependent on duty cycle. For higher duty cycles, see Typical Performance Characteristics curves. INDUCTOR SUPPLIERS The recommended inductor for the LM48520 is the NR8040T6R8N from Taiyo Yuden. When selecting an induc- 13 www.national.com LM48520 Output Speaker Protection Function The LM48520’s output voltage limiter can be used to set a minimum and maximum output voltage swing magnitude. The voltage applied to the VLimit pin controls the limit on the output voltage level. The output level is determined by the following equation: Vout clipped = 8/3 * (PV1 — 2 * Vlimit) or Vout clipped = 1/2 * (PV1 — 3/8 * Vout clipped) Where, Vout clipped = the desired output level measured in Vpk, PV1 = Boost output voltage, and Vlimit is the voltage applied the the Vlimit pin on the LM48520. To disable the limiter, set Vlimit = 0V. Figure 2 provides an example of how the output voltage limiter functions with VDD = 3.3V, AV = 6dB, PV1 = 5V, Vlimit = 2V, RL = 8Ω, VIN = 2VP. 20198729 FIGURE 2. Soft Clipping vs No Clipping www.national.com 14 LM48520 Revision History Rev 1.0 1.01 1.02 Date 02/27/08 03/07/08 03/12/08 Initial release. Added the Soft clipping vs No clipping curve. Text edits. Description 15 www.national.com LM48520 Physical Dimensions inches (millimeters) unless otherwise noted micro SMD Package Order Number LM48520TL NS Package Number TLA25AAA X1 = 2.49mm, X2 = 2.49mm, X3 = 0.6mm, www.national.com 16 LM48520 Notes 17 www.national.com LM48520 Boosted Stereo Class D Audio Power Amplifier with Output Speaker Protection and Spread Spectrum Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers Audio Clock Conditioners Data Converters Displays Ethernet Interface LVDS Power Management Switching Regulators LDOs LED Lighting PowerWise Serial Digital Interface (SDI) Temperature Sensors Wireless (PLL/VCO) www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/displays www.national.com/ethernet www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/powerwise www.national.com/sdi www.national.com/tempsensors www.national.com/wireless WEBENCH Analog University App Notes Distributors Green Compliance Packaging Design Support www.national.com/webench www.national.com/AU www.national.com/appnotes www.national.com/contacts www.national.com/quality/green www.national.com/packaging www.national.com/quality www.national.com/refdesigns www.national.com/feedback Quality and Reliability Reference Designs Feedback THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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