LM4883 Dual 2.1W Audio Amplifier Plus Stereo Headphone Function General Description Key Specifications The LM4883 is a dual bridge-connected audio power amplifier which, when connected to a 5V supply, will deliver 2.1W to a 4Ω load (Note 1) or 2.4W to a 3Ω load (Note 2) with less than 1.0% THD+N. In addition, the headphone input pin allows the amplifiers to operate in single-ended mode when driving stereo headphones. A MUX control pin allows selection between the two stereo sets of amplifier inputs. The MUX control can also be used to select two different closedloop responses. Boomer audio power amplifiers were designed specifically to provide high quality output power from a surface mount package while requiring few external components. To simplify audio system design, the LM4883SQ combines dual bridge speaker amplifiers and stereo headphone amplifiers on one chip. The LM4883SQ features an internally controlled, low-power consumption shutdown mode, a stereo headphone amplifier mode, and thermal shutdown protection. It also utilizes circuitry to reduce “clicks and pops” during device turn-on. Note 1: An LM4883SQ that has been properly mounted to a circuit board will deliver 2.1W into 4Ω. See the Application Information sections for further information concerning the LM4883SQ. Note 2: An LM4883SQ that has been properly mounted to a circuit board and forced-air cooled will deliver 2.4W into 3Ω. j PO at 1% THD+N RL = 3Ω 2.4W (typ) RL = 4Ω 2.1W (typ) RL = 8Ω 1.3W (typ) j Single-ended mode THD+N 0.01% (typ) at 75mW into 32Ω (5V, 1kHz) j Shutdown current 0.04µA (typ) j Supply voltage range 2.4V to 5.5V j PSRR at 217Hz 85dB (typ) Features n n n n n Input mux control and two separate inputs per channel Stereo headphone amplifier mode Improved “click and pop” suppression circuitry Thermal shutdown protection circuitry PCB area-saving SQ package Applications n Multimedia monitors n Portable and desktop computers n Portable audio systems Connection Diagrams LM4883SQ LM4883SQ Top Mark 200887C6 Top View U = Fab Code Z = Assembly Plant Code XY = Date Code TT = Die Traceability 200887A3 Top View Order Number LM4883SQ See NS Package Number SQA24B Boomer ® is a registered trademark of National Semiconductor Corporation. © 2004 National Semiconductor Corporation DS200887 www.national.com LM4883 Dual 2.1W Audio Amplifier Plus Stereo Headphone Function November 2004 LM4883 Typical Application 200887A1 FIGURE 1. Typical Audio Amplifier Application Circuit External Components Description (Refer to Figure 1) Components Functional Description 1. R1, 4, 5, 6 The inverting input resistance R1, along with R3, set the closed-loop gain. R1, along with C1, form a high pass filter with fc = 1/(2πR1C1). 2. C1, 2, 3, 4 The input coupling capacitor blocks DC voltage at the amplifier’s input terminals. C1, along with R1, create a highpass filter with fc = 1/(2πR1C1). Refer to the section, SELECTING PROPER EXTERNAL COMPONENTS, for an explanation of determining the value of C1. 3. R2, 3, 7, 8 The feedback resistance, along with R1 sets the closed-loop gain. 4. C6 The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING section for information about properly placing, and selecting the value of, this capacitor. 5. C5 The capacitor, C5, filters the half-supply voltage present on the BYPASS pin. Refer to the SELECTING PROPER EXTERNAL COMPONENTS section for information concerning proper placement and selecting C5’s value. www.national.com 2 Small Outline Package If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Storage Temperature Input Voltage 215˚C Infrared (15 sec.) 220˚C Thermal Resistance 6.0V θJC (typ) — SQA24B 3˚C/W −65˚C to +150˚C θJA (typ) — SQA24B 42˚C/W −0.3V to VDD +0.3V Power Dissipation (Note 4) Internally limited ESD Susceptibility (Note 5) 2000V ESD Susceptibility (Note 6) 200V Junction Temperature Vapor Phase (60 sec.) Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ 85˚C 2.4V ≤ VDD ≤ 5.5V Supply Voltage 150˚C Solder Information Electrical Characteristics (5V) (Notes 3, 7, 13) The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C. Symbol VDD IDD Parameter Conditions LM4883 Typical Limit (Note 8) (Note 9) Supply Voltage Quiescent Power Supply Current Units (Limits) 2.4 V (min) 5.5 V (max) mA (max) VIN = 0V, IO = 0A (Note 10) , HP-IN = 0V 6 10 VIN = 0V, IO = 0A (Note 10) , HP-IN = 4V 3.0 6 mA (min) VDD applied to the SHUTDOWN pin 0.04 2 µA (max) ISD Shutdown Current VIH Headphone High Input Voltage 3.7 4 V (min) VIL Headphone Low Input Voltage 2.6 0.8 V (max) VIHSD Shutdown High Input Voltage 0.7VDD V (min) VILSD Shutdown Low Input Voltage 0.3VDD V (max) TWU Turn On Time 1µF Bypass Cap (C5) 140 ms Electrical Characteristics for Bridged-Mode Operation (5V) (Notes 3, 7, 13) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25˚C. Symbol VOS Parameter Output Offset Voltage Conditions VIN = 0V LM4883 Typical Limit (Note 8) (Note 9) 5 45 Units (Limits) mV (max) THD+N = 1%, f = 1kHz (Note 12) PO Output Power (Note 11) LM4883SQ, RL = 3Ω 2.4 LM4883SQ, RL = 4Ω 2.1 LM4883SQ, RL = 8Ω 1.3 W W 1.0 W (min) THD+N = 10%, f = 1kHz (Note 12) LM4883SQ, RL = 3Ω 3.0 W LM4883SQ, RL = 4Ω 2.5 W LM4883SQ, RL = 8Ω 1.7 W LM4883SQ, RL = 4Ω, PO = 1W 0.10 % LM4883SQ, RL = 8Ω, PO = .4W 0.06 % 1kHz, AVD = 2 THD+N Total Harmonic Distortion+Noise 3 www.national.com LM4883 Absolute Maximum Ratings (Note 3) LM4883 Electrical Characteristics for Bridged-Mode Operation (5V) (Notes 3, 7, 13) (Continued) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25˚C. Symbol PSRR Parameter Power Supply Rejection Ratio Conditions LM4883 Typical Limit (Note 8) (Note 9) Units (Limits) Input Floating, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 85 dB Input Floating, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 80 dB Input grounded, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 65 dB Input grounded, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 70 dB XTALK Channel Separation f = 1kHz, CB = 1.0µF 82 dB VNO Output Noise Voltage 1kHz, A-weighted 21 µV Electrical Characteristics for Single-Ended Operation (5V) (Notes 3, 7, 13) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25˚C. Symbol PO THD+N PSRR Parameter Output Power Total Harmonic Distortion+Noise Power Supply Rejection Ratio Conditions LM4883 Units (Limits) Typical Limit (Note 8) (Note 9) THD+N = 0.5%, f = 1 kHz, RL = 32Ω 90 75 THD+N = 1%, f = 1 kHz, RL = 8Ω 325 mW THD+N = 10%, f = 1 kHz, RL = 8Ω 400 mW 0.015 % Input Floating, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 70 dB Input Floating, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 72 dB Input grounded, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 65 dB Input grounded, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 70 dB PO = 20mW, 1kHz, RL = 32Ω mW (min) XTALK Channel Separation f = 1kHz, CB = 1.0µF 80 dB VNO Output Noise Voltage 1kHz, A-weighted 11 µV www.national.com 4 LM4883 Electrical Characteristics (3V) (Notes 3, 7, 13) The following specifications apply for VDD = 3V unless otherwise noted. Limits apply for TA = 25˚C. Symbol IDD Parameter Quiescent Power Supply Current Conditions LM4883 Typical Limit (Note 8) (Note 9) Units (Limits) VIN = 0V, IO = 0A (Note 10) , HP-IN = 0V 4.5 mA VIN = 0V, IO = 0A (Note 10) , HP-IN = 4V 2.5 mA VDD applied to the SHUTDOWN pin 0.01 µA V ISD Shutdown Current VIH Headphone High Input Voltage 2.2 VIL Headphone Low Input Voltage 1.5 VIHSD Shutdown High Input Voltage VILSD Shutdown Low Input Voltage TWU Turn On Time 1µF Bypass Cap (C5) V 0.7VDD V (min) 0.3VDD V (max) 140 ms Electrical Characteristics for Bridged-Mode Operation (3V) (Notes 3, 7, 13) The following specifications apply for VDD = 3V unless otherwise specified. Limits apply for TA = 25˚C. Symbol VOS Parameter Output Offset Voltage Conditions VIN = 0V LM4883 Typical Limit (Note 8) (Note 9) Units (Limits) 5 mV LM4883SQ, RL = 3Ω .82 W LM4883SQ, RL = 4Ω .70 W LM4883SQ, RL = 8Ω .43 W LM4883SQ, RL = 3Ω 1.0 W LM4883SQ, RL = 4Ω .85 W LM4883SQ, RL = 8Ω .53 W LM4883SQ, RL = 4Ω, PO = 280mW 0.1 % LM4883SQ, RL = 8Ω, PO = 200mW 0.05 % Input Floating, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 90 dB Input Floating, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 80 dB Input grounded, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 65 dB Input grounded, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 73 dB THD+N = 1%, f = 1kHz (Note 12) PO Output Power (Note 11) THD+N = 10%, f = 1kHz (Note 12) 1kHz THD+N PSRR Total Harmonic Distortion+Noise Power Supply Rejection Ratio XTALK Channel Separation f = 1kHz, CB = 1.0µF 85 dB VNO Output Noise Voltage 1kHz, A-weighted 21 µV 5 www.national.com LM4883 Electrical Characteristics for Single-Ended Operation (3V) (Notes 3, 7, 13) The following specifications apply for VDD = 3V unless otherwise specified. Limits apply for TA = 25˚C. Symbol PO THD+N PSRR Parameter Output Power Total Harmonic Distortion+Noise Power Supply Rejection Ratio Conditions LM4883 Typical Limit (Note 8) (Note 9) Units (Limits) THD+N = 0.5%, f = 1 kHz, RL = 32Ω 35 mW THD+N = 1%, f = 1 kHz, RL = 8Ω 125 mW THD+N = 10%, f = 1 kHz, RL = 8Ω 150 mW PO = 35mW, 20Hz ≤ f ≤ 20kHz, RL = 32Ω .015 % Input Floating, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 71 dB Input Floating, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 8Ω 79 dB Input grounded, 217Hz Vripple = 200mVp-p CB = 1µF, RL = 32Ω 65 dB Input grounded, 1kHz Vripple = 200mVp-p CB = 1µF, RL = 32Ω 72 dB XTALK Channel Separation f = 1kHz, CB = 1.0µF 80 dB VNO Output Noise Voltage 1kHz, A-weighted 11 µV Note 3: 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 operates within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given. The typical value however, is a good indication of device performance. Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θ JA, and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX − T A)/θJA. For the LM4883SQ, TJMAX = 150˚C. Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 6: Machine model, 220 pF–240 pF discharged through all pins. Note 7: All voltages are measured with respect to the ground (GND) pins, unless otherwise specified. Note 8: Typicals are specified at 25˚C and represent the parametric norm. Note 9: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 10: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier. Note 11: Output power is measured at the device terminals. Note 12: When driving 3Ω or 4Ω loads and operating on a 5V supply, the LM4883SQ must be mounted to a circuit board that has a minimum of 2.5in2 of exposed, uninterrupted copper area connected to the SQ package’s exposed DAP. Note 13: All measurements taken from Applications Diagram (Figure 3). www.national.com 6 LM4883 Typical Performance Characteristics THD+N vs Output Power 5V, 8Ω, BTL at 1kHz THD+N vs Output Power 5V, 4Ω, BTL at 1kHz 200887B6 200887B5 THD+N vs Output Power 5V, 3Ω, BTL at 1kHz THD+N vs Output Power 5V, 32Ω, BTL at 1kHz 200887B4 200887B8 THD+N vs Output Power 5V, 8Ω, SE at 1kHz THD+N vs Output Power 5V, 32Ω, SE at 1kHz 200887B7 200887B9 7 www.national.com LM4883 Typical Performance Characteristics (Continued) THD+N vs Output Power 3V, 8Ω, BTL at 1kHz THD+N vs Output Power 3V, 4Ω, BTL at 1kHz 20088780 20088779 THD+N vs Output Power 3V, 3Ω, BTL at 1kHz THD+N vs Output Power 3V, 32Ω, BTL at 1kHz 20088778 20088782 THD+N vs Output Power 3V, 8Ω, SE at 1kHz THD+N vs Output Power 3V, 32Ω, SE at 1kHz 20088781 www.national.com 20088783 8 LM4883 Typical Performance Characteristics (Continued) THD+N vs Frequency 5V, 8Ω, BTL at 400mW THD+N vs Frequency 5V, 4Ω, BTL at 1W 20088776 20088775 THD+N vs Frequency 5V, 32Ω, SE at 75mW THD+N vs Frequency 3V, 8Ω, BTL at 150mW 20088777 20088773 THD+N vs Frequency 3V, 4Ω, BTL at 250mW THD+N vs Frequency 3V, 32Ω, SE at 25mW 20088772 20088774 9 www.national.com LM4883 Typical Performance Characteristics (Continued) PSRR 5V, 8Ω, BTL, Input Unterminated PSRR 5V, 8Ω, BTL, Input Terminated 20088767 20088768 PSRR 5V, 32Ω, SE, Input Unterminated PSRR 5V, 32Ω, SE, Input Terminated 20088769 20088771 PSRR 3V, 8Ω, BTL, Input Unterminated PSRR 3V, 8Ω, BTL, Input Terminated 20088763 www.national.com 20088764 10 LM4883 Typical Performance Characteristics (Continued) PSRR 3V, 32Ω, SE, Input Unterminated PSRR 3V, 32Ω, SE, Input Terminated 20088765 20088766 Frequency Response 5V, 8Ω, BTL Frequency Response 3V, 8Ω, BTL 20088759 20088761 Frequency Response 5V, 32Ω, SE Frequency Response 3V, 32Ω, SE 20088762 20088760 11 www.national.com LM4883 Typical Performance Characteristics (Continued) Crosstalk 5V, 8Ω, BTL Crosstalk 3V, 8Ω, BTL 20088749 20088735 Crosstalk 3V, 32Ω, SE Dropout Voltage vs Supply Voltage 20088737 200887C0 Output Power vs Supply Voltage Open Loop Frequency Response 200887C2 www.national.com 200887C1 12 LM4883 Typical Performance Characteristics (Continued) Power Dissipation vs Output Power Power Dissipation vs Output Power 200887C4 200887C5 Power Dissipation vs Output Power Single Channel, f = 1kHz, THD+N ≤ 1.0%, BW < 80kHz Power Derating Curve 200887C7 200887C8 13 www.national.com LM4883 allows rapid heat transfer from the die to the surrounding PCB copper traces, ground plane and, finally, surrounding air. The result is a low voltage audio power amplifier that produces 2.1W at ≤ 1% THD with a 4Ω load. This high power is achieved through careful consideration of necessary thermal design. Failing to optimize thermal design may compromise the LM4883SQ’s high power performance and activate unwanted, though necessary, thermal shutdown protection. The SQ package must have its DAP soldered to a copper pad on the PCB. The DAP’s PCB copper pad is connected to a large plane of continuous unbroken copper. This plane forms a thermal mass and heat sink and radiation area. Place the heat sink area on either outside plane in the case of a two-sided PCB, or on an inner layer of a board with more than two layers. Connect the DAP copper pad to the inner layer or backside copper heat sink area with 6 (3x2) SQ vias. The via diameter should be 0.012in–0.013in with a 1.27mm pitch. Ensure efficient thermal conductivity by platingthrough and solder-filling the vias. Best thermal performance is achieved with the largest practical copper heat sink area. If the heatsink and amplifier share the same PCB layer, a nominal 2.5in2 (min) area is necessary for 5V operation with a 4Ω load. Heatsink areas not placed on the same PCB layer as the LM4883SQ should be 5in2 (min) for the same supply voltage and load resistance. The last two area recommendations apply for 25˚C ambient temperature. Increase the area to compensate for ambient temperatures above 25˚C. In all circumstances and conditions, the junction temperature must be held below 150˚C to prevent activating the LM4883SQ’s thermal shutdown protection. The LM4883SQ’s power de-rating curve in the Typical Performance Characteristics shows the maximum power dissipation versus temperature. Example PCB layouts for the exposed-Dap SQ package is shown in the Demonstration Board Layout section. Further detailed and specific information concerning PCB layout, fabrication, and mounting an SQ package is available from National Semiconductor’s AN1187. Application Information STEREO-INPUT MULTIPLEXER (STEREO MUX) Typical LM4883 applications use the MUX to switch between two stereo input signals. Each stereo channel’s gain can be tailored to produce the required output signal level. Choosing the input and feedback resistor ratio sets a MUX channel’s gain. Another configuration uses the MUX to select two different gains or frequency compensated gains to amplify a single pair of stereo input signals. Figure 2 shows two different feedback networks, Network 1 and Network 2. Network 1 produces increasing gain as the input signal’s frequency decreases. This can be used to compensate a small, fullrange speaker’s low frequency response roll-off. Network 2 sets the gain for an alternate load such as headphones. Connecting the MUX CTRL and HP-IN pins together applies the same control voltage to the MUX pins when connecting and disconnecting headphones using the headphone jack shown in Figure 3 or Figure 4. Simultaneously applying the control voltage automatically selects the amplifier (headphone or bridge loads) and switches the gain (MUX channel selection). Alternatively, leave the control pins independently accessible. This allows a user to select bass boost as needed. This alternative user-selectable bass-boost scheme requires connecting equal ratio resistor feedback networks to each MUX input channel. The value of the resistor in the RC network is chosen to give a gain that is necessary to achieve the desired bass-boost. Switching between the MUX channels may change the input signal source or the feedback resistor network. During the channel switching transition, the average voltage level present on the internal amplifier’s input may change. This change can slew at a rate that may produce audible voltage transients or clicks in the amplifier’s output signal. Using the MUX to select between two vastly dissimilar gains is a typical transient-producing situation. As the MUX is switched, an audible click may occur as the gain suddenly changes. PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω LOADS Power dissipated by a load is a function of the voltage swing across the load and the load’s impedance. As load impedance decreases, load dissipation becomes increasingly dependent on the interconnect (PCB trace and wire) resistance between the amplifier output pins and the load’s connections. Residual trace resistance causes a voltage drop, which results in power dissipated in the trace and not in the load as desired. For example, 0.1Ω trace resistance reduces the output power dissipated by a 4Ω load from 2.1W to 2.0W. This problem of decreased load dissipation is exacerbated as load impedance decreases. Therefore, to maintain the highest load dissipation and widest output voltage swing, PCB traces that connect the output pins to a load must be as wide as possible. Poor power supply regulation adversely affects maximum output power. A poorly regulated supply’s output voltage decreases with increasing load current. Reduced supply voltage causes decreased headroom, output signal clipping, and reduced output power. Even with tightly regulated supplies, trace resistance creates the same effects as poor supply regulation. Therefore, making the power supply traces as wide as possible helps maintain full output voltage swing. 20088770 FIGURE 2. Input MUX Example EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS The LM4883’s SQ exposed-DAP (die attach paddle) package provides a low thermal resistance between the die and the PCB to which the part is mounted and soldered. This www.national.com 14 LM4883 Application Information (Continued) 200887A4 * Refer to the section Selecting Proper External Components, for a detailed discussion of C5 size. FIGURE 3. Typical Audio Amplifier Application Circuit BRIDGE CONFIGURATION EXPLANATION As shown in Figure 3, the LM4883 consists of two pairs of operational amplifiers, forming a two-channel (channel A and channel B) stereo amplifier. External feedback resistors R3,2,7,8 and input resistors R1,4,5,6 set the closed-loop gain of Amp A (-out) and Amp B (-out) whereas two internal 20kΩ resistors set Amp A’s (+out) and Amp B’s (+out) gain at 1. The LM4883 drives a load, such as a speaker, connected between the two amplifier outputs, −OUTA and +OUTA. Figure 3 shows that Amp A’s (-out) output serves as Amp A’s (+out) input. This results in both amplifiers producing signals identical in magnitude, but 180˚ out of phase. Taking advantage of this phase difference, a load is placed between −OUTA and +OUTA and driven differentially (commonly referred to as “bridge mode”). This results in a differential gain of (1) AVD = 2 * (Rf/R i) or AVD = 2 * (R3/R1) Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a single amplifier’s output and ground. For a given supply voltage, bridge mode has a distinct advantage over the single-ended configuration: its differential output doubles the voltage swing across the load. This produces four times the output power when compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or that the output signal is not clipped. To ensure minimum output signal clipping when choosing an amplifier’s closed-loop gain, refer to the Audio Power Amplifier Design section. Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by biasing channel A’s and channel B’s outputs at half-supply. This eliminates the coupling capacitor that single supply, singleended amplifiers require. Eliminating an output coupling capacitor in a single-ended configuration forces a single-supply amplifier’s half-supply bias voltage across the load. This increases internal IC power dissipation and may permanently damage loads such as speakers. POWER DISSIPATION Power dissipation is a major concern when designing a successful single-ended or bridged amplifier. Equation (2) states the maximum power dissipation point for a singleended amplifier operating at a given supply voltage and driving a specified output load. (2) PDMAX = (VDD)2/(2π2RL) Single-Ended However, a direct consequence of the increased power delivered to the load by a bridge amplifier is higher internal power dissipation for the same conditions. The LM4883 has two operational amplifiers per channel. The maximum internal power dissipation per channel operating in the bridge mode is four times that of a single-ended amplifier. From Equation (3), assuming a 5V power supply and a 4Ω load, the maximum single channel power dissipation is 1.27W or 2.54W for stereo operation. (3) PDMAX = 4 * (VDD)2/(2π2RL) Bridge Mode The LM4883SQ’s power dissipation is twice that given by Equation (2) or Equation (3) when operating in the singleended mode or bridge mode, respectively. Twice the maximum power dissipation point given by Equation (3) must not exceed the power dissipation given by Equation (4): (4) PDMAX' = (TJMAX − TA)/θJA The LM4883’s TJMAX = 150˚C. In the SQ package soldered to a DAP pad that expands to a copper area of 5in2 on a 15 www.national.com LM4883 Application Information use a 10 µF in parallel with a 0.1 µF filter capacitor to stabilize the regulator’s output, reduce noise on the supply line, and improve the supply’s transient response. However, their presence does not eliminate the need for a local 1.0 µF tantalum bypass capacitance connected between the LM4883’s supply pins and ground. Do not substitute a ceramic capacitor for the tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors between the LM4883SQ’s power supply pin and ground as short as possible. Connecting a 1µF capacitor, C5, between the BYPASS pin and ground improves the internal bias voltage’s stability and improves the amplifier’s PSRR. The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however, increases turn-on time and can compromise amplifier’s click and pop performance. The selection of bypass capacitor values, especially C5, depends on desired PSRR requirements, click and pop performance (as explained in the section, Selecting Proper External Components), system cost, and size constraints. (Continued) PCB, the LM4883SQ’s θJA is 20˚C/W. At any given ambient temperature TA, use Equation (4) to find the maximum internal power dissipation supported by the IC packaging. Rearranging Equation (4) and substituting PDMAX for PDMAX' results in Equation (5). This equation gives the maximum ambient temperature that still allows maximum stereo power dissipation without violating the LM4883’s maximum junction temperature. (5) TA = TJMAX – 2*PDMAX θJA For a typical application with a 5V power supply and an 4Ω load, the maximum ambient temperature that allows maximum stereo power dissipation without exceeding the maximum junction temperature is approximately 99˚C for the SQ package. (6) TJMAX = PDMAX θJA + TA Equation (6) gives the maximum junction temperature TJMAX. If the result violates the LM4883’s 150˚C, reduce the maximum junction temperature by reducing the power supply voltage or increasing the load resistance. Further allowance should be made for increased ambient temperatures. The above examples assume that a device is a surface mount part operating around the maximum power dissipation point. Since internal power dissipation is a function of output power, higher ambient temperatures are allowed as output power or duty cycle decreases. If the result of Equation (2) is greater than that of Equation (3), then decrease the supply voltage, increase the load impedance, or reduce the ambient temperature. If these measures are insufficient, a heat sink can be added to reduce θJA. The heat sink can be created using additional copper area around the package, with connections to the ground pin(s), supply pin and amplifier output pins. External, solder attached SMT heatsinks such as the Thermalloy 7106D can also improve power dissipation. When adding a heat sink, the θJA is the sum of θJC, θCS, and θSA. (θJC is the junction-to-case thermal impedance, θCS is the case-to-sink thermal impedance, and θSA is the sink-to-ambient thermal impedance.) Refer to the Typical Performance Characteristics curves for power dissipation information at lower output power levels. MICRO-POWER SHUTDOWN The voltage applied to the SHUTDOWN pin controls the LM4883’s shutdown function. Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active, the LM4883’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The logic threshold is typically VDD/2. The low 0.04 µA typical shutdown current is achieved by applying a voltage that is as near as VDD as possible to the SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. Table 1 shows the logic signal levels that activate and deactivate micro-power shutdown and headphone amplifier operation. There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an external 10kΩ pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier operation by closing the switch. Opening the switch connects the SHUTDOWN pin to VDD through the pull-up resistor, activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or a microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the pull up resistor. POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. Applications that employ a 5V regulator typically TABLE 1. Logic Level Truth Table for SHUTDOWN, HP-IN, and MUX Operation SHUTDOWN PIN HP-INPIN MUX CHANNEL SELECT PIN OPERATIONAL MODE (MUX INPUT CHANNEL #) Logic Low Logic Low Logic Low Logic Low Bridged Amplifiers (1) Logic Low Logic High Bridged Amplifiers (2) Logic Low Logic High Logic Low Single-Ended Amplifiers (1) Logic Low Logic High Logic High Single-Ended Amplifiers (2) Logic High X X Micro-Power Shutdown HP-IN FUNCTION Applying a voltage between 4V and VDD to the LM4883’s HP-IN headphone control pin turns off Amp A (+out) and Amp B (+out) muting a bridged-connected load. Quiescent current consumption is reduced when the IC is in this single-ended mode. www.national.com Figure 4 shows the implementation of the LM4883’s headphone control function. With no headphones connected to the headphone jack, the R9-R10 voltage divider sets the voltage applied to the HP-IN pin (pin 20) at approximately 50mV. This 50mV enables Amp A (+out) and Amp B (+out) 16 achieve minimum THD+N and maximum signal-to-noise ratio. These parameters are compromised as the closed-loop gain increases. However, low gain demands input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal sources such as audio CODECs have outputs of 1VRMS (2.83VP-P). Please refer to the Audio Power Amplifier Design section for more information on selecting the proper gain. (Continued) placing the LM4883 in bridged mode operation. The output coupling capacitor blocks the amplifier’s half supply DC voltage, protecting the headphones. The HP-IN threshold is set at 4V. While the LM4883 operates in bridged mode, the DC potential across the load is essentially 0V. Therefore, even in an ideal situation, the output swing cannot cause a false single-ended trigger. Connecting headphones to the headphone jack disconnects the headphone jack contact pin from −OUTA and allows R1 to pull the HP Sense pin up to VDD. This enables the headphone function, turns off Amp A (+out) and Amp B (+out) which mutes the bridged speaker. The amplifier then drives the headphones, whose impedance is in parallel with resistors R11 and R12. These resistors have negligible effect on the LM4883’s output drive capability since the typical impedance of headphones is 32Ω. Input Capacitor Value Selection Amplifying the lowest audio frequencies requires high value input coupling capacitors (C1–4) in Figures 1, 3. A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases, however, the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 150 Hz. Applications using speakers with this limited frequency response reap little improvement by using large input capacitor. Figure 4 also shows the suggested headphone jack electrical connections. The jack is designed to mate with a threewire plug. The plug’s tip and ring should each carry one of the two stereo output signals, whereas the sleeve should carry the ground return. A headphone jack with one control pin contact is sufficient to drive the HP-IN pin when connecting headphones. A microprocessor or a switch can replace the headphone jack contact pin. When a microprocessor or switch applies a voltage greater than 4V to the HP-IN pin, a bridge-connected speaker is muted and Amp A (-out) and Amp B (-out) drive a pair of headphones. Besides effecting system cost and size, C1–4 have an effect on the LM4883’s click and pop performance. When the supply voltage is first applied, a transient (pop) is created as the charge on the input capacitor changes from zero to a quiescent state. The magnitude of the pop is directly proportional to the input capacitor’s size. Higher value capacitors need more time to reach a quiescent DC voltage (usually VDD/2) when charged with a fixed current. The amplifier’s output charges the input capacitor through the feedback resistors, R2,3,7,and 8. Thus, pops can be minimized by selecting an input capacitor value that is no higher than necessary to meet the desired −3dB frequency. A shown in Figure 3, the input resistors (R1,4,5, and 6) and the input capacitors, C1–4 produce a −3dB high pass filter cutoff frequency that is found using Equation (7). (7) As an example when using a speaker with a low frequency limit of 150Hz, C1, using Equation (7) is 0.053µF. The .33µF C1 shown in Figure 3 allows the LM4883 to drive high efficiency, full range speaker whose response extends below 30Hz. Bypass Capacitor Value Selection Besides minimizing the input capacitor size, careful consideration should be paid to value of C5, the capacitor connected to the BYPASS pin. Since C5 determines how fast the LM4883 settles to quiescent operation, its value is critical when minimizing turn-on pops. The slower the LM4883’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing C5 equal to 1.0 µF along with a small value of C1 (in the range of 0.1 µF to 0.39 µF), produces a click-less and pop-less shutdown function. As discussed above, choosing C1 no larger than necessary for the desired bandwith helps minimize clicks and pops. 20088724 FIGURE 4. Headphone Circuit SELECTING PROPER EXTERNAL COMPONENTS Optimizing the LM4883’s performance requires properly selecting external components. Though the LM4883 operates well when using external components with wide tolerances, best performance is achieved by optimizing component values. The LM4883 is unity-gain stable, giving a designer maximum design flexibility. The gain should be set to no more than a given application requires. This allows the amplifier to OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE The LM4883 contains circuitry that minimizes turn-on and shutdown transients or “clicks and pop”. For this discussion, turn-on refers to either applying the power supply voltage or when the shutdown mode is deactivated. While the power supply is ramping to its final value, the LM4883’s internal amplifiers are configured as unity gain buffers. An internal 17 www.national.com LM4883 Application Information LM4883 Application Information Typical Performance Characteristics curves, must be added to the result obtained by Equation (8). The result in Equation (9). (Continued) current source changes the voltage of the BYPASS pin in a controlled, linear manner. Ideally, the input and outputs track the voltage applied to the BYPASS pin. The gain of the internal amplifiers remains unity until the voltage on the bypass pin reaches 1/2 VDD . As soon as the voltage on the bypass pin is stable, the device becomes fully operational. Although the BYPASS pin current cannot be modified, changing the size of C5 alters the device’s turn-on time and the magnitude of “clicks and pops”. Increasing the value of C5 reduces the magnitude of turn-on pops. However, this presents a tradeoff: as the size of C5 increases, the turn-on time increases. There is a linear relationship between the size of C5 and the turn-on time. Here are some typical turn-on times for various values of C5: C5 (8) (9) VDD ≥ (VOUTPEAK + (VODTOP + VODBOT)) The Output Power vs Supply Voltage graph for an 8Ω load indicates a minimum supply voltage of 4.6V. This is easily met by the commonly used 5V supply voltage. The additional voltage creates the benefit of headroom, allowing the LM4883 to produce peak output power in excess of 1W without clipping or other audible distortion. The choice of supply voltage must also not create a situation that violates maximum power dissipation as explained above in the Power Dissipation section. TON 0.01µF 30ms 0.1µF 40ms 0.22µF 60ms 0.47µF 80ms 1.0µF 140 ms After satisfying the LM4883’s power dissipation requirements, the minimum differential gain needed to achieve 1W dissipation in an 8Ω load is found using Equation (10). (10) Thus, a minimum gain of 2.83 allows the LM4883’s to reach full output swing and maintain low noise and THD+N performance. For this example, let AVD = 3. The amplifier’s overall gain is set using the input (R1) and feedback (R3) resistors. With the desired input impedance set at 20kΩ, the feedback resistor is found using Equation (11). (11) R3/R1 = AVD/2 The value of Rf is 30kΩ. In order eliminate “clicks and pops”, all capacitors must be discharged before turn-on. Rapidly switching VDD may not allow the capacitors to fully discharge, which may cause “clicks and pops”. In a single-ended configuration, the output is coupled to the load by C7,8. These capacitors usually have a high value. C7,8 discharges through internal 20kΩ resistors. Depending on the size of C7,8, the discharge time constant can be relatively large. To reduce transients in single-ended mode, an external 1kΩ–5kΩ resistor can be placed in parallel with the internal 20kΩ resistor. The tradeoff for using this resistor is increased quiescent current. The last step in this design example is setting the amplifier’s −3dB frequency bandwidth. To achieve the desired ± 0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth limit. The gain variation for both response limits is 0.17dB, well within the ± 0.25dB desired limit. The results are an fL = 100Hz/5 = 20Hz and an fH = 20kHz*5 = 100kHz. As mentioned in the External Components section, R1 and C1 create a highpass filter that sets the amplifier’s lower bandpass frequency limit. Find the coupling capacitor’s value using Equation (12). (12) C1 ≥ 1/(2πR1fL) The result is 1/(2π*20kΩ*20Hz) = 0.398µF. Use a 0.39µF capacitor, the closest standard value. The product of the desired high frequency cutoff (100kHz in this example) and the differential gain, AVD, determines the upper passband response limit. With AVD = 3 and fH = 100kHz, the closed-loop gain bandwidth product (GBWP) is 300kHz. This is less than the LM4883’s 3.5MHz GBWP. With this margin, the amplifier can be used in designs that require more differential gain while avoiding performance-restricting bandwidth limitations. NO LOAD STABILITY The LM4883 may exhibit low level oscillation when the load resistance is greater than 10kΩ. This oscillation only occurs as the output signal swings near the supply voltages. Prevent this oscillation by connecting a 5kΩ between the output pins and ground. AUDIO POWER AMPLIFIER DESIGN Audio Amplifier Design: Driving 1W into an 8Ω Load The following are the desired operational parameters: Power Output: Load Impedance: Input Level: Input Impedance: Bandwidth: 1WRMS 8Ω 1Vrms 20kΩ 100Hz−20kHz ± 0.25dB The design begins by specifying the minimum supply voltage necessary to obtain the specified output power. One way to find the minimum supply voltage is to use the Output Power vs Supply Voltage curve in the Typical Performance Characteristics section. Another way, using Equation (8), is to calculate the peak output voltage necessary to achieve the desired output power for a given load impedance. To account for the amplifier’s dropout voltage, two additional voltages, based on the Dropout Voltage vs Supply Voltage in the www.national.com 18 These circuit boards are easy to use. Apply 5V and ground to the board’s VDD and GND pads, respectively. Connect the speakers between the board’s −OUTA and +OUTA and OUTB and +OUTB pads. (Continued) RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT Figures 5 through 7 show the recommended two-layer PC board layout that is optimized for the 24-pin SQ package. These circuits are designed for use with an external 5V supply and 8Ω, 4Ω, 3Ω speakers. 19 www.national.com LM4883 Application Information LM4883 Demonstration Board Layout 20088727 FIGURE 5. Top Layer 20088725 FIGURE 6. Bottom Layer www.national.com 20 LM4883 Demonstration Board Layout (Continued) 20088726 FIGURE 7. Silkscreen 21 www.national.com LM4883 Bill of Materials Analog Audio LM4883SQ Eval Board Assembly Part Number: 551012279–001 Revision: A Item Part Number Part Description Qty 1 551012279–001 LM4883SQ Eval Board PCB etch 001 1 Ref Designator Remark 2 IC LM4883SQ 1 U1 3 Tant Cap 0.33µF 50V 10% 4 C1–C4 4 Tant Cap 1µF 16V 10% Size = A 3216 2 C5, C6 5 Tant Cap 100µF 16V 10% Size = D 7343 2 C7, C8 6 Res 1kΩ 1/8W 1% 0805 2 R11, R12 7 Res 20kΩ 1/8W 1% 0805 8 R1–R8 8 Res 100kΩ 1/8W 1% 0805 2 R9, R10 9 RCA Jack 4 –A, –A2, –B, –B2 Mouser # 16PJ097 10 Banana Jack, Black 3 –OutA,– OutB, GND Mouser # ME164–6218 11 Banana Jack, Red 3 +OutA,+ OutB, VDD Mouser # ME164–6219 12 Jumper Header 3 x 1 2 SD, MUX www.national.com 22 inches (millimeters) unless otherwise noted LLP Package Order Number LM4883SQ NS Package Number SQA24B National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. National Semiconductor Americas Customer Support Center Email: [email protected] Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: [email protected] National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: [email protected] Tel: 81-3-5639-7560 LM4883 Dual 2.1W Audio Amplifier Plus Stereo Headphone Function Physical Dimensions