LM4951ASD

LM4951A Wide Voltage Range 1.8 Watt Audio Amplifier With Short Circuit Protection September 5, 2008 LM4951A Wide Voltage Range 1.8 Watt Audio Amplifier With Short Circuit Protection General Description The LM4951A is an audio power amplifier designed for applications with supply voltages ranging from 2.7V up to 9V. The LM4951A is capable of delivering 1.8W continuous average power with less than 1% THD+N into a bridge connected 8Ω load when operating from a 7.5VDC power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4951A does not require bootstrap capacitors, or snubber circuits. The LM4951A features a low-power consumption active-low shutdown mode. Additionally, the LM4951A features an internal thermal shutdown protection mechanism and short circuit protection. The LM4951A contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4951A is unity-gain stable and can be configured by external gain-setting resistors. Features ■ Pop & click circuitry eliminates noise during turn-on and ■ ■ ■ ■ ■ ■ ■ turn-off transitions Wide supply voltage range: 2.7V to 9V Low current, active-low shutdown mode Low quiescent current Thermal shutdown protection Short circuit protection Unity-gain stable External gain configuration capability Applications ■ ■ ■ ■ ■ Portable devices Cell phones Laptop computers Computer speaker systems MP3 player speakers Key Specifications ■ Wide Voltage Range ■ Quiescent Power Supply Current (VDD = 7.5V) 2.5mA (typ) 1.8W (typ) 0.01µA (typ) 25ms (typ) 2.7V to 9V ■ Power Output BTL at 7.5V, 1% THD ■ Shutdown Current ■ Fast Turn on Time Boomer® is a registered trademark of National Semiconductor Corporation. © 2008 National Semiconductor Corporation 300578 www.national.com LM4951A Typical Application 300578f4 FIGURE 1. Typical Bridge-Tied-Load (BTL) Audio Amplifier Application Circuit www.national.com 2 LM4951A Connection Diagrams SD Package 30057829 Top View Order Number LM4951ASD See NS Package Number SDC10A SD Package Marking 30057831 Top View U = Fab site code Z = Assembly plant code XY = Date code TT = Die traceability 4951A = LM4951A SD = Package code Ordering Information Order Number LM4951ASD LM4951ASDX Package 10 Lead LLP 10 Lead LLP Package DWG # SDC10A SDC10A Transport Media 1000 units in Tape and Reel 4500 units in Tape and Reel MSL Level 1 1 Green Status RoH and no Sb/Br RoH and no Sb/Br Features 3 www.national.com LM4951A TABLE 1. Pin Name and Function Pin Number 1 Name Bypass Function ½ supply reference voltage bypass output. See sections POWER SUPPLY BYPASSING and SELECTING EXTERNAL COMPONENTS for more information. Shutdown control active low signal. A logic low voltage will put the LM4951A into Shutdown mode. Input capacitor charge to decrease turn on time. See section Selecting A Value for RC for more information. No connection to die. Pin can be connected to any potential. Single-ended signal input pin. Inverting output of amplifier. Ground connection. No connection to die. Pin can be connected to any potential. Power supply. Non-Inverting output of amplifier. No connect. Pin must be electrically isolated (floating) or connected to GND. Type Analog Output 2 3 4 5 6 7 8 9 10 Exposed DAP Shutdown CCHG NC VIN VOGND NC VDD VO+ NC Digital Input Analog Output No Connect Analog Input Analog Output Ground No Connect Power Analog Output No Connect www.national.com 4 LM4951A 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 Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Rating (Note 4) ESD Rating (Note 5) Junction Temperature (TJMAX) 9.5V −65°C to +150°C −0.3V to VDD + 0.3V Internally limited 2000V 200V 150°C Thermal Resistance  θJA (LLP) (Note 3) Soldering Information See AN-1187 'Leadless Leadframe Packaging (LLP).' 73°C/W Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage (Notes 1, 2) −40°C ≤ T A ≤ +85°C 2.7V ≤ VDD ≤ 9V Electrical Characteristics VDD = 7.5V Symbol IDD ISD VOS VSDIH VSDIL RPULLDOWN TWU TSD TSD PO Parameter Quiescent Power Supply Current Shutdown Current Output Offset Voltage Shutdown Voltage Input High Shutdown Voltage Input Low Pull-down Resistor on SD pin Wake-up Time Shutdown time Thermal Shutdown Temperature Output Power (Notes 1, 2) LM4951A Conditions Typical (Note 6) 2.5 0.01 5 Limit (Note 7) 4.5 5 30 1.2 0.4 75 45 35 10 170 150 190 1.5 0.5 The following specifications apply for VDD = 7.5V, AV-BTL = 6dB, RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C. Units (Limits) mA (max) µA (max) mV (max) V (min) V (max) kΩ (min) ms (max) ms (max) °C (min) °C (max) W (min) % (max) % µV 56 dB (min) VIN = 0V, IO = 0A, RL = 8Ω BTL VSD = GND (Note 8) CB = 1.0µF CB = 1.0µF 25 THD = 1% (max); f = 1kHz RL = 8Ω Mono BTL PO = 600mWRMS; f = 1kHz AV-BTL = 6dB PO = 600mWRMS; f = 1kHz AV-BTL = 26dB A-Weighted Filter, Ri = Rf = 20kΩ Input Referred (Note 9) VRIPPLE = 200mVp-p, f = 217Hz, CB = 1.0μF, Input Referred (Notes 1, 2) 1.8 0.07 0.35 10 66 THD+N Total Harmonic Distortion + Noise εOS PSRR Output Noise Power Supply Rejection Ratio Electrical Characteristics VDD = 3.3V Symbol IDD ISD VOS VSDIH VSDIL TWU TSD Parameter Quiescent Power Supply Current Shutdown Current Output Offset Voltage Shutdown Voltage Input High Shutdown Voltage Input Low Wake-up Time Shutdown time The following specifications apply for VDD = 3.3V, AV-BTL = 6dB, RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C. LM4951A Conditions VIN = 0V, IO = 0A, RL = 8Ω BTL VSHUTDOWN = GND (Note 8) Typical (Note 6) 2.5 0.01 3 Limit (Note 7) 4.5 2 30 1.2 0.4 CB = 1.0µF CB = 1.0µF 25 10 Units (Limits) mA (max) µA (max) mV (max) V (min) V (max) ms ms (max) 5 www.national.com LM4951A LM4951A Symbol Parameter Conditions THD = 1% (max); f = 1kHz RL = 8Ω Mono BTL PO = 100mWRMS = 1kHz AV-BTL = 6dB PO = 100mWRMS; f = 1kHz AV-BTL = 26dB A-Weighted Filter, Ri = Rf = 20kΩ Input Referred, (Note 9) VRIPPLE = 200mVp-p, f = 217Hz, CB = 1μF, Input Referred Typical (Note 6) 280 0.07 0.35 10 71 61 Limit (Note 7) 230 0.5 Units (Limits) mW (min) % (max) % µV dB (min) PO Output Power THD+N Total Harmonic Distortion + Noise εOS PSRR Output Noise Power Supply Rejection Ratio 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 s 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. For the LM4951A typical application (shown in Figure 1) with VDD = 7.5V, RL = 8Ω mono-BTL operation the max power dissipation is 1.42W. θJA = 73ºC/W. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25ºC, 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: Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to GND for minimum shutdown current. Note 9: Noise measurements are dependent on the absolute values of the closed loop gain setting resistors (input and feedback resistors). www.national.com 6 LM4951A Typical Performance Characteristics THD+N vs Frequency VDD = 3.3V, PO = 100mW, AV = 6dB THD+N vs Frequency VDD = 3.3V, PO = 100mW, AV = 26dB 300578f9 30057802 THD+N vs Frequency VDD = 5V, PO = 400mW, AV = 6dB THD+N vs Frequency VDD = 5V, PO = 400mW, AV = 26dB 30057803 30057804 THD+N vs Frequency VDD = 7.5V, PO = 600mW, AV = 6dB THD+N vs Frequency VDD = 7.5V, PO = 600mW, AV = 26dB 30057805 300578g0 7 www.national.com LM4951A THD+N vs Output Power VDD = 3.3V, f = 1kHz, AV = 6dB THD+N vs Output Power VDD = 3.3V, f = 1kHz, AV = 26dB 300578g1 30057808 THD+N vs Output Power VDD = 5V, f = 1kHz, AV = 6dB THD+N vs Output Power VDD = 5V, f = 1kHz, AV = 26dB 30057809 30057810 THD+N vs Output Power VDD = 7.5V, f = 1kHz, AV = 6dB THD+N vs Output Power VDD = 7.5V, f = 1kHz, AV = 26dB 30057811 30057812 www.national.com 8 LM4951A Power Supply Rejection vs Frequency VDD = 3.3V, AV = 6dB, VRIPPLE = 200mVP-P Input Terminated into 10Ω Power Supply Rejection vs Frequency VDD = 3.3V, AV = 26dB, VRIPPLE = 200mVP-P Input Terminated into 10Ω 30057813 30057814 Power Supply Rejection vs Frequency VDD = 5V, AV = 6dB, VRIPPLE = 200mVP-P Input Terminated into 10Ω Power Supply Rejection vs Frequency VDD = 5V, AV = 26dB, VRIPPLE = 200mVP-P Input Terminated into 10Ω 30057815 30057816 Power Supply Rejection vs Frequency VDD = 7.5V, AV = 6dB, VRIPPLE = 200mVP-P Input Terminated into 10Ω Power Supply Rejection vs Frequency VDD = 7.5V, AV = 26dB, VRIPPLE = 200mVP-P Input Terminated into 10Ω 30057817 30057818 9 www.national.com LM4951A Noise Floor VDD = 3.3V, AV = 6dB, Ri = Rf = 20kΩ BW < 80kHz, A-weighted Noise Floor VDD = 3V, AV = 26dB, Ri = 20kΩ, Rf = 200kΩ BW < 80kHz, A-weighted 30057819 30057820 Noise Floor VDD = 5V, AV = 6dB, Ri = Rf = 20kΩ BW < 80kHz, A-weighted Noise Floor VDD = 5V, AV = 26dB, Ri = 20kΩ, Rf = 200kΩ BW < 80kHz, A-weighted 30057821 30057822 Noise Floor VDD = 7.5V, AV = 6dB, Ri = Rf = 20kΩ BW < 80kHz, A-weighted Noise Floor VDD = 7.5V, AV = 26dB, Ri = 20kΩ, Rf = 200kΩ BW < 80kHz, A-weighted 30057823 30057824 www.national.com 10 LM4951A Power Dissipation vs Output Power VDD = 3.3V, RL = 8Ω, f = 1kHz Power Dissipation vs Output Power VDD = 7.5V, RL = 8Ω, f = 1kHz 30057825 30057826 Supply Current vs Supply Voltage RL = 8Ω, VIN = 0V, Rsource = 50Ω Clipping Voltage vs Supply Voltage RL = 8Ω, from top to bottom: Negative Voltage Swing; Positive Voltage Swing 30057827 300578e9 Output Power vs Supply Voltage RL = 8Ω, from top to bottom: THD+N = 10%, THD+N = 1% Output Power vs Load Resistance VDD = 3.3V, f = 1kHz from top to bottom: THD+N = 10%, THD+N = 1% 300578f0 300578f1 11 www.national.com LM4951A Output Power vs Load Resistance VDD = 7.5V, f = 1kHz from top to bottom: THD+N = 10%, THD+N = 1% Frequency Response vs Input Capacitor Size R L = 8Ω from top to bottom: Ci = 1.0µF, Ci = 0.39µF, Ci = 0.039µF 300578f2 300578f3 www.national.com 12 LM4951A Application Information BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4951A consists of two operational amplifiers that drive a speaker connected between their outputs. The value of input and feedback resistors determine the gain of each amplifier. External resistors Ri and Rf set the closed-loop gain of AMPA, whereas two 20kΩ internal resistors set AMPB's gain to -1. Figure 1 shows that AMPA's output serves as AMPB's 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 AMPA and AMPB and driven differentially (commonly referred to as "bridge-tied load"). This results in a differential, or BTL, gain of: AVD = 2(Rf / Ri) (V/V) (1) stereo power dissipation without violating the LM4951A's maximum junction temperature. TA = TJMAX - PDMAX-MONOBTLθJA (°C) (4) For a typical application with a 7.5V power supply and a BTL 8Ω load, the maximum ambient temperature that allows maximum stereo power dissipation without exceeding the maximum junction temperature is 46°C for the SD package. TJMAX = PDMAX-MONOBTLθJA + TA (°C) (5) 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 an advantage over the single-ended configuration: its differential output doubles the voltage swing across the load. Theoretically, 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 and that the output signal is not clipped. Under rare conditions, with unique combinations of high power supply voltage and high closed loop gain settings, the LM4951A may exhibit low frequency oscillations. Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by biasing AMP1's and AMP2's outputs at half-supply. This eliminates the coupling capacitor that single supply, single-ended amplifiers require. Eliminating an output coupling capacitor in a typical 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 The LM4951A's dissipation when driving a BTL load is given by Equation (2). For a 7.5V supply and a single 8Ω BTL load, the dissipation is 1.42W. PDMAX-MONOBTL = 4(VDD) 2 / 2π2RL (W) (2) Equation (5) gives the maximum junction temperature TJMAX. If the result violates the LM4951A's maximum junction temperature of 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 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. Further, ensure that speakers rated at a nominal 8Ω do not fall below 6Ω. 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 pins, supply pin and amplifier output pins. Refer to the Typical Performance Characteristics curves for power dissipation information at lower output power levels. 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 voltage regulator typically use a 10µF in parallel with a 0.1µF filter capacitors 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 1.0µF tantalum bypass capacitance connected between the LM4951A'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 LM4951A's power supply pin and ground as short as possible. Connecting a larger capacitor, CBYPASS, 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 the amplifier's click and pop performance. The selection of bypass capacitor values, especially CBYPASS, depends on desired PSRR requirements, click and pop performance, system cost, and size constraints. MICRO-POWER SHUTDOWN The LM4951A features an active-low micro-power shutdown mode. When active, the LM4951A's micro-power shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The low 0.01µA typical shutdown current is achieved by applying a voltage to the SHUTDOWN pin that The maximum power dissipation point given by Equation (2) must not exceed the power dissipation given by Equation (3): PDMAX = (TJMAX - TA) / θJA (3) The LM4951A's TJMAX = 150°C. In the SD package, the LM4951A's θJA is 73°C/W when the metal tab is soldered to a copper plane of at least 1in2. This plane can be split between the top and bottom layers of a two-sided PCB. Connect the two layers together under the tab with an array of vias. At any given ambient temperature TA, use Equation (3) to find the maximum internal power dissipation supported by the IC packaging. Rearranging Equation (3) and substituting PDMAX for PDMAX' results in Equation (4). This equation gives the maximum ambient temperature that still allows maximum 13 www.national.com LM4951A is as near to GND as possible. A voltage that is greater than GND may increase the shutdown current. SELECTING EXTERNAL COMPONENTS Input Capacitor Value Selection Two quantities determine the value of the input coupling capacitor: the lowest audio frequency that requires amplification and desired output transient suppression. As shown in Figure 1, the input resistor (Ri) and the input capacitor (Ci) create a high-pass filter. The cutoff frequency can be found using Equation (6). fc = 1/2πRiCi (Hz) (6) turn-on refers to either applying the power supply voltage or when the micro-power shutdown mode is deactivated. As the VDD/2 voltage present at the BYPASS pin ramps to its final value, the LM4951A's internal amplifiers are configured as unity gain buffers. An internal current source charges the capacitor connected between the BYPASS pin and GND in a controlled 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 VDD/2. As soon as the voltage on the bypass pin is stable, there is a delay to prevent undesirable output transients (“click and pops”). After this delay, the device becomes fully functional. THERMAL SHUTDOWN AND SHORT CIRCUIT PROTECTION The LM4951A has thermal shutdown and short circuit protection to fully protect the device. The thermal shutdown circuit is activated when the die temperature exceeds a safe temperature. The short circuit protection circuitry senses the output current. When the output current exceeds the threshold under a short condition, a short will be detected and the output deactivated until the short condition is removed. If the output current is lower than the threshold then a short will not be detected and the outputs will not be deactivated. Under such conditions the die temperature will increase and, if the condition persist to raise the die temperature to the thermal shutdown threshold, initiate a thermal shutdown response. Once the die cools the outputs will become active. RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT Figures 2–4 show the recommended two-layer PC board layout that is optimized for the SD10A. This circuit is designed for use with an external 7.5V supply 8Ω (min) speakers. As an example when using a speaker with a low frequency limit of 50Hz, Ci, using Equation (6) is 0.159µF with Ri set to 20kΩ. The values for Ci and Ri shown in Figure 1 allow the LM4951A to drive a high efficiency, full range speaker whose response extends down to 20Hz. Selecting Value A For RC The LM4951A is designed for very fast turn on time. The CCHG pin allows the input capacitor to charge quickly to improve click/pop performance. RC protects the CCHG pin from any over/under voltage conditions caused by excessive input signal or an active input signal when the device is in shutdown. The recommended value for RC is 1kΩ. If the input signal is less than VDD+0.3V and greater than -0.3V, and if the input signal is disabled when in shutdown mode, RC may be shorted out. OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE The LM4951A contains circuitry that eliminates turn-on and shutdown transients ("clicks and pops"). For this discussion, www.national.com 14 LM4951A Demonstration Board Circuit 30057830 FIGURE 2. Demo Board Circuit 15 www.national.com LM4951A Demonstration Board Layout 30057832 FIGURE 3. Top Silkscreen 300578f7 FIGURE 4. Top Layer 300578f6 FIGURE 5. Bottom Layer www.national.com 16 LM4951A Bill Of Materials TABLE 2. Bill Of Materials Designator RIN1 R1 RPULLUP R2 R4, R5 CIN1 CSUPPLY CBYPASS C1 0.100” 1x2 header, vertical mount U1 LM4951A, Mono, 1.8W, Audio Amplifier Value 20kΩ 200kΩ 100kΩ 1kΩ 0Ω 0.39μF 4.7μF 1μF Tolerance 1% 1% 1% 1% 1% 10% 10% 10% Part Description 1/8W, 0805 Resistor 1/8W, 0805 Resistor 1/8W, 0805 Resistor 1/8W, 0805 Resistor 1/8W, 0805 Resistor Ceramic Capacitor, 25V, Size 1206 16V Tantalum Capacitor, Size A 16V Tantalum Capacitor, Size A Not Used Input, Output, Vdd/GND Shutdown SDC10A package Comments 17 www.national.com LM4951A Revision History Rev 1.0 1.01 Date 08/13/08 09/05/08 Initial release. Text edits. Description www.national.com 18 LM4951A Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM4951ASD NS Package Number SDC10A 19 www.national.com LM4951A Wide Voltage Range 1.8 Watt Audio Amplifier With Short Circuit Protection 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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