LM4881 www.ti.com LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 Dual 200 mW Headphone Amplifier with Shutdown Mode Check for Samples: LM4881 FEATURES DESCRIPTION * * * * * The LM4881 is a dual audio power amplifier capable of delivering 200mW of continuous average power into an 8 load with 0.1% THD+N from a 5V power supply. 1 23 VSSOP Surface Mount Packaging Unity-gain Stable External Gain Configuration Capability Thermal Shutdown Protection Circuitry No Bootstrap Capacitors, or Snubber Circuits are Necessary APPLICATIONS * * * Headphone Amplifier Personal Computers Microphone Preamplifier KEY SPECIFICATIONS * * * * * THD+N at 1kHz at 125mW Continuous Average Output Power into 8 0.1% (max) THD+N at 1kHz at 75mW Continuous 0.02% (typ) Output Power at 10% THD+N at 1kHz into 8 300 mW (typ) Shutdown Current 0.7A (typ) Supply Voltage Range 2.7V to 5.5 V BoomerTM audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components using surface mount packaging. Since the LM4881 does not require bootstrap capacitors or snubber networks, it is optimally suited for low-power portable systems. The LM4881 features an externally controlled, low power consumption shutdown mode which is virtually clickless and popless, as well as an internal thermal shutdown protection mechanism. The unity-gain stable LM4881 can be configured by external gain-setting resistors. 1 2 3 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. Boomer is a trademark of Texas Instruments. All other trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 1997-2013, Texas Instruments Incorporated LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com Typical Application *Refer to Application Information for information concerning proper selection of the input and output coupling capacitors. Figure 1. Typical Audio Amplifier Application Circuit Connection Diagrams Figure 2. VSSOP Package Top View See Package Number DGK0008A Figure 3. SOIC and PDIP Package Top View See Package Number D0008A, or P0008E These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 2 Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 LM4881 www.ti.com SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 Absolute Maximum Ratings (1) (2) Supply Voltage 6.0V -65C to +150C Storage Temperature -0.3V to VDD + 0.3V Input Voltage Power Dissipation (3) Internally limited (4) 2000V ESD Susceptibility ESD Susceptibility (5) 200V Junction Temperature 150C Soldering Information Small Outline Package Vapor Phase (60 seconds) 215C Infrared (15 seconds) Thermal Resistance (1) (2) (3) (4) (5) 220C JC (VSSOP) 56C/W JA (VSSOP) 210C/W JC (SOIC) 35C/W JA (SOIC) 170C/W JC (PDIP) 37C/W JA (PDIP) 107C/W 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, JA, and the ambient temperature TA. The maximum allowable power dissipation is P DMAX = (TJMAX - TA) / JA. For the LM4881, TJMAX = 150C, and the typical junctionto-ambient thermal resistance, when board mounted, is 210C/W for the VSSOP Package and 107C/W for package P0008E. Human body model, 100 pF discharged through a 1.5 k resistor. Machine Model, 220 pF-240 pF discharged through all pins. Operating Ratings Temperature Range TMIN TA TMAX -40C T A 85C 2.7V VDD 5.5V Supply Voltage Electrical Characteristics (1) (2) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25C. Symbol Parameter Conditions LM4881 Typ (3) Limit (4) VDD Power Supply Voltage IDD Quiescent Current VIN = 0V, IO = 0A 3.6 ISD Shutdown Current VPIN1 = VDD 0.7 5 A (max) VOS Offset Voltage VIN = 0V 5 50 mV (max) (1) (2) (3) (4) 2.7 Units (Limits) V (min) 5.5 V (max) 6.0 mA (max) All voltages are measured with respect to the ground pin, unless otherwise specified. 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. Typicals are measured at 25C and represent the parametric norm. Limits are specified to TI's AOQL (Average Outgoing Quality Level). Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 3 LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com Electrical Characteristics(1)(2) (continued) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25C. Symbol Parameter Conditions LM4881 Typ PO Output Power (3) Limit (4) Units (Limits) THD = 0.1% (max); f = 1 kHz; RL = 8 200 RL = 16 150 125 mW (min) mW RL = 32 85 mW RL = 8 300 mW RL = 16 200 mW RL = 32 110 mW RL = 16, P O = 120 mWrms; 0.025 % R L = 32, PO = 75 mWrms; f = 1 kHz 0.02 % CB = 1.0 F, VRIPPLE = 200 mVrms, f = 120Hz 50 dB mA THD + N = 10%; f = 1 kHz; THD+N Total Harmonic Distortion + Noise PSRR IDD Quiescent Current VIN = 0V, IO = 0A 1.1 ISD Shutdown Current VPIN1 = VDD 0.7 A VOS Offset Voltage VIN = 0V 5 mV PO Output Power THD = 1% (max); f = 1 kHz; RL = 8 70 mW RL= 16 65 mW RL = 32 30 mW RL = 8 95 mW RL = 16 65 mW RL = 32 35 mW RL = 16, P O = 60 mWrms; 0.2 % RL = 32, PO = 25 mWrms; f = 1 kHz 0.03 % CB = 1.0 F, VRIPPLE = 200 mVrms, f = 100 Hz 50 dB THD + N = 10%; f = 1 kHz; THD+N Total Harmonic Distortion + Noise PSRR Power Supply Rejection Ratio External Components Description (Figure 1) Components 4 Functional Description 1. Ri Inverting input resistance which sets the closed-loop gain in conjuction with Rf. This resistor also forms a high pass filter with Ci at fc = 1 / (2R iCi). 2. Ci Input coupling capacitor which blocks the DC voltage at the amplifier's input terminals. Also creates a highpass filter with Ri at fc = 1 / (2RiC i). Refer to the section, Proper Selection of External Components, for an explanation of how to determine the value of Ci. 3. Rf Feedback resistance which sets closed-loop gain in conjuction with Ri. 4. CS Supply bypass capacitor which provides power supply filtering. Refer to the Application Information section for proper placement and selection of the supply bypass capacitor. 5. CB Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External Components, for information concerning proper placement and selection of CB. 6. CO Output coupling capacitor which blocks the DC voltage at the amplifier's output. Forms a high pass filter with RL at fO = 1/(2RLCO) Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 LM4881 www.ti.com SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 Typical Performance Characteristics THD+N vs Frequency THD+N vs Frequency Figure 4. Figure 5. THD+N vs Frequency THD+N vs Frequency Figure 6. Figure 7. THD+N vs Frequency THD+N vs Frequency Figure 8. Figure 9. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 5 LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com Typical Performance Characteristics (continued) 6 THD+N vs Output Power THD+N vs Output Power Figure 10. Figure 11. THD+N vs Output Power THD+N vs Output Power Figure 12. Figure 13. THD+N vs Output Power THD+N vs Output Power Figure 14. Figure 15. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 LM4881 www.ti.com SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 Typical Performance Characteristics (continued) Output Power vs Supply Voltage Output Power vs Supply Voltage Figure 16. Figure 17. Output Power vs Supply Voltage Power Dissipation vs Output Power Figure 18. Figure 19. Output Power vs Load Resistance Output Power vs Load Resistance Figure 20. Figure 21. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 7 LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com Typical Performance Characteristics (continued) Power Dissipation vs Output Power Clipping Voltage vs Supply Voltage Figure 22. Figure 23. Clipping Voltage vs Supply Voltage 8 Channel Separation Figure 24. Figure 25. Output Attenuation in Shutdown Mode Supply Current vs Supply Voltage Figure 26. Figure 27. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 LM4881 www.ti.com SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 Typical Performance Characteristics (continued) Power Supply Rejection Ratio Open Loop Frequency Response Figure 28. Figure 29. Noise Floor Frequency Response vs Output Capacitor Size Figure 30. Figure 31. Frequency Response vs Output Capacitor Size Frequency Response vs Output Capacitor Size Figure 32. Figure 33. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 9 LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com Typical Performance Characteristics (continued) Typical Application Frequency Response Typical Application Frequency Response Figure 34. Figure 35. Power Derating Curve Figure 36. 10 Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 LM4881 www.ti.com SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 APPLICATION INFORMATION SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4881 contains a shutdown pin to externally turn off the amplifier's bias circuitry. This shutdown feature turns the amplifier off when a logic high is placed on the shutdown pin. The trigger point between a logic low and logic high level is typically half supply. It is best to switch between ground and supply to provide maximum device performance. By switching the shutdown pin to the VDD, the LM4881 supply current draw will be minimized in idle mode. While the device will be disabled with shutdown pin voltages less than VDD, the idle current may be greater than the typical value of 0.7 A. In either case, the shutdown pin should be tied to a definite voltage because leaving the pin floating may result in an unwanted shutdown condition. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry which provides a quick, smooth transition into shutdown. Another solution is to use a singlepole, single-throw switch in conjunction with an external pull-up resistor. When the switch is closed, the shutdown pin is connected to ground and enables the amplifier. If the switch is open, then the external pull-up resistor will disable the LM4881. This scheme ensures that the shutdown pin will not float which will prevent unwanted state changes. POWER DISSIPATION Power dissipation is a major concern when using any power amplifier and must be thoroughly understood to ensure a successful design. Equation 1 states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a specified output load. PDMAX = (VDD) 2 / (22RL) (1) Since the LM4881 has two operational amplifiers in one package, the maximum internal power dissipation point is twice that of the number which results from Equation 1. Even with the large internal power dissipation, the LM4881 does not require heat sinking over a large range of ambient temperature. From Equation 1, assuming a 5V power supply and an 8 load, the maximum power dissipation point is 158 mW per amplifier. Thus the maximum package dissipation point is 317 mW. The maximum power dissipation point obtained must not be greater than the power dissipation that results from Equation 2: PDMAX = (TJMAX - TA) / JA (2) For package DGK0008A, JA = 230C/W, and for package D0008A, JA = 170C/W, and for package P0008E, JA = 107C/W. TJMAX = 150C for the LM4881. Depending on the ambient temperature, TA, of the system surroundings, Equation 2 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 1 is greater than that of Equation 2, then either the supply voltage must be decreased, the load impedance increased or TA reduced. For the typical application of a 5V power supply, with an 8 load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 96C provided that device operation is around the maximum power dissipation point. Power dissipation is a function of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient temperature may be increased accordingly. Refer to the Typical Performance Characteristics curves for power dissipation information for lower output powers. POWER SUPPLY BYPASSING As with any power amplifer, proper supply bypassing is critical for low noise performance and high power supply rejection. The capacitor location on both the bypass and power supply pins should be as close to the device as possible. As displayed in the Typical Performance Characteristics section, the effect of a larger half supply bypass capacitor is improved low frequency PSRR due to increased half-supply stability. Typical applications employ a 5V regulator with 10 F and a 0.1 F bypass capacitors which aid in supply stability, but do not eliminate the need for bypassing the supply nodes of the LM4881. The selection of bypass capacitors, especially CB, is thus dependent upon desired low frequency PSRR, click and pop performance as explained in Proper Selection of External Components system cost, and size constraints. PROPER SELECTION OF EXTERNAL COMPONENTS Selection of external components when using integrated power amplifiers is critical to optimize device and system performance. While the LM4881 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 11 LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com The LM4881 is unity gain stable and this gives a designer maximum system flexibility. The LM4881 should be used in low gain configurations to minimize THD+N values, and maximum the signal-to-noise ratio. Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1 Vrms are available from sources such as audio codecs. Please refer to the section, Audio Power Amplifier Design, for a more complete explanation of proper gain selection. Besides gain, one of the major considerations is the closed loop bandwidth of the amplifier. To a large extent, the bandwidth is dicated by the choice of external components shown in Figure 1. Both the input coupling capacitor, Ci, and the output coupling capacitor, Co, form first order high pass filters which limit low frequency response. These values should be chosen based on needed frequency response for a few distinct reasons. Selection of Input and Output Capacitor Size Large input and output capacitors are both expensive and space hungry for portable designs. Clearly a certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 150 Hz. Thus using large input and output capacitors may not increase system performance. In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally 1/2 VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable. Thus, by minimizing the capacitor size based on necessary low frequency response, turn on pops can be minimized. Besides minimizing the input and output capacitor sizes, careful consideration should be paid to the bypass capacitor value. Bypass capacitor CB is the most critical component to minimize turn on pops since it determines how fast the LM4881 turns on. The slower the LM4881's outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn on pop. Thus choosing CB equal to 1.0 F along with a small value of Ci (in the range of 0.1 F to 0.39 F), the shutdown function should be virtually clickless and popless. While the device will function properly, (no oscillations or motorboating), with C B equal to 0.1 F, the device will be much more susceptible to turn on clicks and pops. Thus, a value of CB equal to 0.1 F or larger is recommended in all but the most cost sensitive designs. AUDIO POWER AMPLIFIER DESIGN Design a Dual 200mW/8 Audio Amplifier Given: Power Output 200 mWrms Load Impedance 8 Input Level 1 Vrms (max) Input Impedance 20 k Bandwidth 100 Hz-20 kHz 0.50 dB A designer must first determine the needed supply rail to obtain the specified output power. Calculating the required supply rail involves knowing two parameters, VOPEAK and also the dropout voltage. The latter is typically 530 mV and can be found from the graphs in the Typical Performance Characteristics. VOPEAK can be determined from Equation 3. (3) For 200 mW of output power into an 8 load, the required VOPEAK is 1.79 volts. A minimum supply rail of 2.32V results from adding VOPEAK and VOD. Since 5V is a standard supply voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4881 to reproduce peaks in excess of 200 mW without clipping the signal. At this time, the designer must make sure that the power supply choice along with the output impedance does not violate the conditions explained in the Power Dissipation section. Remember that the maximum power dissipation point from Equation 1 must be multiplied by two since there are two independent amplifiers inside the package. 12 Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 LM4881 www.ti.com SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 Once the power dissipation equations have been addressed, the required gain can be determined from Equation 4. (4) (5) AV = Rf/Ri From Equation 4, the minimum gain is: AV = 1.26 Since the desired input impedance was 20 k, and with a gain of 1.26, a value of 27 k is designated for Rf, assuming 5% tolerance resistors. This combination results in a nominal gain of 1.35. The final design step is to address the bandwidth requirements which must be stated as a pair of -3 dB frequency points. Five times away from a -3 dB point is 0.17 dB down from passband response assuming a single pole roll-off. As stated in the External Components Description section, both Ri in conjunction with C i, and Co with RL, create first order highpass filters. Thus to obtain the desired frequency low response of 100 Hz within 0.5 dB, both poles must be taken into consideration. The combination of two single order filters at the same frequency forms a second order response. This results in a signal which is down 0.34 dB at five times away from the single order filter -3 dB point. Thus, a frequency of 20 Hz is used in the following equations to ensure that the response is better than 0.5 dB down at 100 Hz. Ci 1 / (2 * 20 k * 20 Hz) = 0.397 F; use 0.39 F. Co 1 / (2 * 8 * 20 Hz) = 995 F; use 1000 F. (6) (7) The high frequency pole is determined by the product of the desired high frequency pole, fH, and the closed-loop gain, A V. With a closed-loop gain of 1.35 and fH = 100 kHz, the resulting GBWP = 135 kHz which is much smaller than the LM4881 GBWP of 18 MHz. This figure displays that if a designer has a need to design an amplifier with a higher gain, the LM4881 can still be used without running into bandwidth limitations. Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 13 LM4881 SNAS001D - SEPTEMBER 1997 - REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision C (May 2013) to Revision D * 14 Page Changed layout of National Data Sheet to TI format .......................................................................................................... 13 Submit Documentation Feedback Copyright (c) 1997-2013, Texas Instruments Incorporated Product Folder Links: LM4881 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 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