LM48413

LM48413 Ultra Low EMI, Filterless, 1.2W Stereo Class D Audio Power Amplifier with E2S and National 3D Enhancement January 9, 2009 LM48413  Ultra Low EMI, Filterless, 1.2W Stereo Class D Audio Power Amplifier with E2S and National 3D Enhancement General Description The LM48413 is a single supply, high efficiency, 1.2W/channel, filterless switching audio amplifier. The LM48413 features National’s Enhanced Emissions Suppression (E2S) system - a unique patented ultra low EMI, spread spectrum, PWM architecture. It significantly reduces RF emission while preserving audio quality and efficiency. The E2S system improves battery life, reduces external component count, board area consumption, system cost and product design cycle time. The LM48413TL is available in a micro-SMD package, further saving space. The LM48413 is designed to meet the demands of mobile phones and other portable communication devices. Operating from a single 5V supply, the device is capable of delivering 1.2W/channel of continuous output power to a 8Ω load with less than 1% THD+N. Flexible power supply requirements allow operation from 2.4V to 5.5V. The wide band spread spectrum architecture of the LM48413 reduces EMI-radiated emissions due to the modulator frequency. The LM48413 features high efficiency compared with conventional Class AB amplifiers. The E2S system includes an advanced, patent-pending edge rate control (ERC) architecture that further reduce emissions by minimizing the high frequency components of the device output, while maintaining its high quality audio reproduction and high efficiency (η = 85% at VDD = 3.6V, PO = 500mW). The LM48413 also includes National’s 3D audio enhancement that improves stereo sound quality. In devices where the left and right speakers are in close proximity, 3D enhancement affects channel specialization, widening the perceived soundstage. Output short circuit protection prevents the device from being damaged during fault conditions. Superior click and pop suppression eliminates audible transients on power up/down and during shutdown. Shutdown control also provided to maximizes power savings. Key Specifications ■ Quiescent Power Supply Current at 3.6V supply 4mA (typ) 1.2W (typ) 0.03μA (typ) 80% (typ) 85% (typ) 86% (typ) ■ Power Output at VDD = 5V, RL = 8Ω, THD ≤ 1% ■ Shutdown current ■ Efficiency at 3.6V, 100mW into 8Ω ■ Efficiency at 3.6V, 500mW into 8Ω ■ Efficiency at 5V, 1W into 8Ω Features ■ E2S system reduces EMI preserving audio quality and ■ ■ ■ ■ ■ ■ ■ ■ efficiency Output Short Circuit Protection Stereo Class D operation No output filter required National 3D Enhancement Minimum external components Click and Pop suppression Micro-power shutdown Available in space-saving approximately 2mm x 2.2mm micro SMD package Applications ■ Mobile phones ■ PDAs ■ Laptops EMI Plot Using 6 inch Speaker Cables EMI Radiation vs Frequency VDD = 3V, RL = 15μH + 8Ω + 15μH 30063536 Boomer® is a registered trademark of National Semiconductor Corporation. © 2009 National Semiconductor Corporation 300635 www.national.com LM48413 Typical Application 30063541 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM48413 Connection Diagrams 30063539 Top View XY = 2 Digit date code TT = Die Traceability G = Boomer Family L2 = LM48413TL 30063538 Top View Order Number LM48413TL See NS Package Number TLA18CBA Ordering Information Order Number LM48413TL LM48413TLX Package 18 Bump micro SMD 18 Bump micro SMD Package DWG # TLA18CBA TLA18CBA Transport Media 250 units on tape and reel 3000 units on tape and reel MSL Level 1 1 Green Status RoHS & no Sb/Br RoHS & no Sb/Br 3 www.national.com LM48413 Bump Descriptions Bump A1 A3 A5 A7 B2 B4 B6 C1 C3 C5 C7 D2 D4 D6 E1 E3 E5 E7 Name INL3DEN OUTLA OUTLB INL+ 3DLGND 3DL+ 3DR+ VDD PGND INR+ 3DRPVDD INRSD OUTRA OUTRB Left Channel Inverting Input 3D Enable Input Left Channel Non-Inverting Output Left Channel Inverting Output Left Channel Non-Inverting Input Left Channel inverting 3D connection. Connect to 3DR- through C3D- and R3DGround Left Channel non-inverting 3D connection. Connect to 3DR+ through C3D+ and R3D+ Right Channel non-inverting 3D connection. Connect to 3DL+ through C3D+ and R3D+ Power Supply. Connect to PVDD supplying same voltage. Power Ground Right Channel Non-inverting Input Right Channel inverting 3D connection. Connect to 3DL- through C3D- and R3DAmplifier Power Supply Right Channel Inverting Input Connect to GND for disabling the device. Connect to VDD for normal operation. Right Channel Non-inverting Output Right Channel Inverting Output Description www.national.com 4 LM48413 Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Rating (Note 4) ESD Rating (Note 5) 6.0V −65°C to +150°C –0.3V to VDD + 0.3V Internally Limited 2000V 200V Junction Temperature Thermal Resistance  θJA 150°C 47°C/W (Notes 1, 2) −40°C ≤ TA ≤ 85°C Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage (VDD, PVDD) 2.4V ≤ VDD ≤ 5.5V Electrical Characteristics VDD = PVDD = 3.6V (Notes 1, 2) RL = 8Ω (Note 8), f = 1kHz, unless otherwise specified. Limits apply for TA = 25°C. Symbol VOS IDD ISD VIH VIL TWU AV RIN Parameter Differential Output Offset Voltage Quiescent Power Supply Current Shutdown Current Logic Input High Voltage Logic Input Low Voltage Wake-Up Time Gain Input Resistance THD ≤ 10%, f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V PO Output Power (Per Channel) VDD = 2.5V THD ≤ 1%, f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V PO = 500mW/Ch, f = 1kHz, 22kHz BW PO = 300mW/Ch, f = 1kHz, 22kHz BW VRIPPLE = 200mVP-P Sine, Inputs AC GND, CIN = 1μF, input referred fRIPPLE = 217Hz fRIPPLE = 1kHz VRIPPLE = 1VP-P fRIPPLE = 217Hz PO = 1W/Ch, f = 1kHz, RL = 8Ω, VDD = 5V PO = 500mW/Ch, f = 1kHz VDD = 5V, PO = 1W Input referred, A-Weighted Conditions VIN = 0, VDD = 2.4V to 5.0V VIN = 0, No Load, VSD = VDD, VDD = 3.6V VDD = 5V VSD = GND The following specifications apply for LM48413 Typical (Note 6) 3 4.3 5.2 0.03 5.5 7 1 1.4 0.4 4 24 20 1.5 720 320 1.2 600 260 0.03 0.03 600 23.5 24.5 Limit (Note 7) Units (Limits) mV mA (max) mA (max) μA (max) V (min) V (max) ms dB (min) dB (max) kΩ W mW (min) mW W mW mW % % THD+N Total Harmonic Distortion + Noise PSRR Power Supply Rejection Ratio 91 90 72 86 93 88 5 dB dB dB % dB dB μV CMRR η XTALK SNR εOS Common Mode Rejection Ratio Efficiency Crosstalk Signal-to-Noise Ratio Output Noise 5 www.national.com LM48413 Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditionsindicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. 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 number given in Absolute Maximum Ratings, whichever is lower. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. The ESD Machine Model rating of device bump E3 = 150V. Note 6: Typical values represent most likely parametric norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. Note 8: RL is a resistive load in series with two inductors to simulate an actual speaker load. For RL = 8Ω, the load is 15µH + 8Ω +15µH. www.national.com 6 LM48413 Typical Performance Characteristics THD+N vs Output Power/Channel f = 1kHz, RL = 8Ω, 22kHz BW THD+N vs Frequency VDD = 2.5V, POUT = 100mW/Ch RL = 8Ω, 22kHz BW 30063543 30063517 THD+N vs Frequency VDD = 3.6V, POUT = 250mW/Ch RL = 8Ω, 22kHz BW THD+N vs Frequency VDD = 5V, POUT = 375mW/Ch RL = 8Ω, 22kHz BW 30063521 30063519 Efficiency vs Output Power RL = 8Ω, f = 1kHz Power Dissipation vs Total Output Power RL = 8Ω, f = 1kHz 30063533 30063544 7 www.national.com LM48413 Output Power/Channel vs Supply Voltage RL = 8Ω, f = 1kHz, 22kHz BW PSRR and CMRR vs Frequency VDD = 3.6V, RL = 8Ω 30063537 30063542 Crosstalk vs Frequency VDD = 3.6V, PO = 500mW, RL = 8Ω Supply Current vs Supply Voltage No Load 30063531 30063529 EMI Radiation vs Frequency VDD = 3V, RL = 8Ω, 3 inch cables EMI Radiation vs Frequency VDD = 3V, RL = 8Ω, 6 inch cables 30063535 30063536 www.national.com 8 LM48413 EMI Radiation vs Frequency VDD = 3V, RL = 8Ω, 12 inch cables 30063534 9 www.national.com LM48413 Application Information GENERAL AMPLIFIER FUNCTION The LM48413 stereo Class D audio power amplifier features a filterless modulation scheme that reduces external component count, conserving board space and reducing system cost. The outputs of the device transition from PVDD to GND with a 390kHz switching frequency. With no signal applied, the outputs 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. When an input signal is applied, the duty cycle (pulse width) of the LM48413 output's change. For increasing output voltage, the duty cycle of one side of each output increases, while the duty cycle of the other side of each output decreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. SHUTDOWN FUNCTION The LM48413 features a low current shutdown mode. Set SD = GND to disable the amplifier and reduce supply current to 0.03μA. Switch SD between GND and VDD for minimum current consumption in shutdown. The LM48413 may be disabled with shutdown voltages in between GND and VDD, but the idle current will be greater than the typical value. The LM48413 shutdown input has an internal 300kΩ pull-down resistor. The purpose of this resistor is to eliminate any unwanted state changes when this pin is floating. To minimize shutdown current, it should be driven to GND or left floating. If it is not driven to GND, or floating, a small increase in shutdown supply current will be noticed. SPREAD SPECTRUM The LM48413 outputs are modulated in spread spectrum scheme eliminating the need for output filters, ferrite beads or chokes. During its operation, the switching frequency varies randomly by 30% about a 390kHz center frequency, reducing the wideband spectral content and improving EMI emissions radiated by the speaker and associated cables and traces. A fixed frequency class D exhibits large amounts of spectral energy at multiples of the switching frequency. The spread spectrum architecture of the LM48413 spreads the same energy over a larger bandwidth. The cycle-to-cycle variation of the switching period does not affect the audio reproduction, efficiency, or PSRR. ENHANCED EMISSIONS SUPPRESSION SYSTEM (E2S) The LM48413 features National’s patented E2S system that further reduces EMI, while maintaining high quality audio reproduction and efficiency. The advanced edge rate control (ERC) embedded within the E2S system works simultaneously with the spread spectrum already activated. The LM48413 ERC greatly reduces the high frequency components of the output square waves by controlling the output rise and fall times, slowing the transitions to reduce RF emissions, while maximizing THD+N and efficiency performance. DIFFERENTIAL AMPLIFIER EXPLANATION As logic supplies continue to shrink, system designers are increasingly turning to differential analog signal handling to preserve signal to noise ratios with restricted voltage swings. The LM48413 features two fully differential speaker amplifiers. 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 of SNR relative to differential inputs. The LM48413 also offers the possibility of DC input coupling which eliminates the input coupling capacitors. A major benefit of the fully differential amplifier is the improved common mode rejection ratio (CMRR) over single-ended input amplifiers. The increased CMRR of the differential amplifier reduces sensitivity to ground offset related noise injection, especially important in noisy systems. POWER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM48413 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 a Class AB amplifier. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET on-resistance, along with switching losses due to gate charge. PROPER SELECTION OF EXTERNAL COMPONENTS Power Supply Bypassing/Filtering Proper power supply bypassing is important for low noise performance and high PSRR. Place the 1μF supply bypass capacitor as close to the device as possible. Traditionally, a pair of bypass capacitors with typical value 0.1μF and 10μF are applied to the supply rail for increasing stability. Nevertheless, these capacitors do not eliminate the need for bypassing of the LM48413 supply pins. Input Capacitor Selection Input capacitors may be required for some applications, or when the audio source is single-ended. Input capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of the audio source and the bias voltage of the LM48413. The input capacitors create a highpass filter with the input resistance RIN. The -3dB point of the high-pass filter is found using Equation 1 below. f = 1 / 2πRINCIN (Hz) (1) The input capacitors can also be used to remove low frequency content from the audio signal. When the LM48413 is using a single-ended source, power supply noise on the ground is seen as an input signal. Setting the high-pass filter point above the power supply noise frequencies, 217Hz in a GSM phone, for example, filters out the noise such that it is not amplified and heard on the output. Capacitors with a tolerance of 10% or better are recommended for impedance matching and improved CMRR and PSRR. National 3D Enhancement The LM48413 features National’s 3D enhancement effect that widens the perceived soundstage of a stereo audio signal. The 3D enhancement increases the apparent stereo channel separation, improving audio reproduction whenever the left and right speakers are too close to one another. An external RC network shown in Figure 1 is required to enable the 3D effect. Because the LM48413 is a fully differential amplifier, there are two separate RC networks, one for each stereo input pair (INL+ and INR+, and INL- and INR-). Set 3DEN high to enable the 3D effect. Set 3DEN low to disable the 3D effect. www.national.com 10 LM48413 The 3D RC network acts as a high-pass filter. The amount of the 3D effect is set by the R3D resistor. Decreasing the value of R3D increases the 3D effect. The C3D capacitor sets the frequency at which the 3D effect occurs. Increasing the value of C3D decreases the low frequency cutoff point, extending the 3D effect over a wider bandwidth. The low frequency cutoff point is given by Equation 2: f3D(–3dB) = 1 / 2π(R3D)(C3D) (Hz) (2) 6dB whenever the 3D effect is enabled. The Equation (2) holds for both differential and single-end configuration. The recommended tolerance of the resistor value and capacitor value of the two RC networks are 5% and 10% respectively. Tolerance out of this range may affect the 3D gain and low frequency cut-off point too much. The desired sound quality of the 3D effect may not be obtained consequently. SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION The LM48413 is compatible with single-ended sources. When configured for single-ended inputs, input capacitors must be used to block and DC component at the input of the device. Figure 2 shows the typical single-ended applications circuit. Enabling the 3D effect increase the gain by a factor of (1 +40kΩ/R3D). Setting R3D to 40kΩ results in a gain increase of 30063525 FIGURE 2. Single-Ended Circuit Diagram 11 www.national.com LM48413 AUDIO AMPLIFIER GAIN The LM48413 has a fix gain value 24dB which is suitable for ordinary audio applications. To reduce the amplifier gain, insert two pairs of external input resistors with same value before the IC’s input signal pins. Figure 3 show the configuration of these input resistors and the amplifier’s internal gain setting. Accordingly, the overall amplifier gain is given by Equation 3: AV = 2 * (160k) / (20k + RIN ) (3) For example, if the gain to be set is 12dB, then AV is equal to 4. Thus, Equation (3) the input resistors' value RIN = [(2 * 160k)/4] –20k = 60kΩ. 30063528 FIGURE 3. Audio Amplifier Gain Setting www.national.com 12 LM48413 PCB LAYOUT GUIDELINES As output power increases, interconnect resistance (PCB traces and wires) between the amplifier, load and power supply create a voltage drop. The voltage loss due to the traces between the LM48413 and the load results in lower output power and decreased efficiency. Higher trace resistance between the supply and the LM48413 has the same effect as a poorly regulated supply, increasing ripple on the supply line, and reducing peak output power. The effects of residual trace resistance increases as output current increases due to higher output power, decreased load impedance or both. To maintain the highest output voltage swing and corresponding peak output power, the PCB traces that connect the output pins to the load and the supply pins to the power supply should be as wide as possible to minimize trace resistance. The use of power and ground planes will give the best THD +N performance. In addition to reducing trace resistance, the use of power planes creates parasitic capacitors that help to filter the power supply line. The inductive nature of the transducer load can also result in overshoot on one or both edges, clamped by the parasitic diodes to GND and VDD in each case. From an EMI standpoint, this is an aggressive waveform that can radiate or conduct to other components in the system and cause interference. It is essential to keep the power and output traces short and well shielded if possible. Use of ground planes beads and micros-strip layout techniques are all useful in preventing unwanted interference. As the distance from the LM48413 and the speaker increases, the amount of EMI radiation increases due to the output wires or traces acting as antennas. The EMI output spectrums of LM48413 evaluation board connected with different speaker cable lengths to an 8Ω load were measured (See Typical Performance Characteristics). Lengths from 3 inches to 12 inches are shown all fall within the limit of the FCC Class B requirement. THD+N MEASUREMENT Class D amplifiers, by design, switch their output power devices at a much higher frequency than the accepted audio range (20Hz – 22kHz). Alternately switching the output voltage between VDD and GND allows the LM48413 to operate at much higher efficiency. However, it also increases the outof-band noise. Since THD+N measurement is a bandwidth limited measurement, it can be significantly affected by outof-band noise, resulting in a higher than expected THD+N measurement. To achieve a more accurate measurement of THD+N, the test equipment’s input bandwidth must be limited. The input filter limits the out-of-band noise resulting in a more relevant THD+N value. A low-pass filter with a cut-off at 28kHz was used in addition to the internal filter of the THD+N measurement equipment (See Figure 4). In real applications, the output filters are not necessary since the speakers will act as low-pass filters blocking the remaining switching noise and smoothing the output signals. Instead of connecting the LM48413's BTL outputs to speakers during measurements, the 28kHz low-pass filter is used as shown in Figure 4. This measurement technique also applies to measurements such as PSRR, CMRR, and output power. 30063540 FIGURE 4. THD+N Measurement Test Setup 13 www.national.com LM48413 Bill Of Materials TABLE 1. LM48413 Demonstration Board Bill of Materials Item 1 2 3 4 5 6 7 8 9 Designator U1 R1, R2 Description Stereo Class-D Resistor (0603) GRM188R71C105KA01D C3216X741H105K 594D106X0025B2T Part Number LM48413TL Qty 1 2 4 4 1 3 2 2 ST-4EB100k 2 100kΩ Copal Electronics 4.7kΩ ± 5% 1µF ± 10%, 25V 1µF ± 10%, 25V 10µF ± 10%, 25V Value Recommended Supplier National Semiconductor Towa Murata TDK Vishay Ceramic Capacitor C1, C2, C3, C8 (0603) X7R C4, C5, C6, C7 C9 Ceramic Capacitor (1206) X7R Tantium Capacitor (1210) Header 3-pin Header 4-pin Potentiometer JP5, JP6, JP7 Header 2-pin JP1, JP2 JP3, JP4 R3, R4 www.national.com 14 LM48413 Demonstration Board Schematic 30063510 FIGURE 5. LM48413 Demonstration Board Schematic 15 www.national.com LM48413 Demonstration Board Layout 30063511 Top Silkscreen 30063515 Top Layer www.national.com 16 LM48413 30063513 Middle Layer 1 30063514 Middle Layer 2 17 www.national.com LM48413 30063512 Bottom Layer www.national.com 18 LM48413 Revision Table Rev 1.0 1.01 Date 11/19/08 01/08/09 Initial release. Text edits. Description 19 www.national.com LM48413 Physical Dimensions inches (millimeters) unless otherwise noted MicroSMD 18 Bump Package Order Number LM48413TL, LM48413TLX NS Package Number TLA18CBA X1 = 2.047mm ±0.030mm X2 = 2.250mm ±0.030mm X3 = 0.60mm ±0.075mm www.national.com 20 LM48413 Notes 21 www.national.com LM48413 Ultra Low EMI, Filterless, 1.2W Stereo Class D Audio Power Amplifier with E2S and National 3D Enhancement Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage Reference PowerWise® Solutions 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/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise www.national.com/sdi www.national.com/tempsensors www.national.com/wireless WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/AU Quality and Reliability Feedback/Support Design Made Easy Solutions Mil/Aero Solar Magic® Analog University® THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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