LM4898ITLBD

LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 LM4898 1 Watt Fully Differential Audio Power Amplifier With Shutdown Select Check for Samples: LM4898, LM4898MMBD FEATURES DESCRIPTION • • The LM4898 is a fully differential audio power amplifier primarily designed for demanding applications in mobile phones and other portable communication device applications. It is capable of delivering 1 watt of continuous average power to an 8Ω BTL load with less than 1% distortion (THD+N) from a 5VDC power supply. 1 2 • • • • • • Fully Differential Amplification Available in Space-Saving Packages DSBGA, VSSOP, and WSON Ultra Low Current Shutdown Mode Can Drive Capacitive Loads up to 500pF Improved Pop and Click Circuitry Eliminates Noises During Turn-On and Turn-Off Transitions 2.4 - 5.5V Operation No Output Coupling Capacitors, Snubber Networks or Bootstrap Capacitors Required Shutdown High or Low Selectivity APPLICATIONS • • • Mobile Phones PDAs Portable Electronic Devices KEY SPECIFICATIONS • • • • Improved PSRR at 217Hz: 83 dB(typ) Power Output at 5.0V, 1% THD: 1.0 W(typ) Power Output at 3.3V, 1% THD: 400 mW(typ) Shutdown Current: 0.1µA(typ) Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4898 does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement. The LM4898 features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by either logic high or low depending on mode selection. Driving the shutdown mode pin either high or low enables the shutdown select pin to be driven in a likewise manner to enable Shutdown. Additionally, the LM4898 features an internal thermal shutdown protection mechanism. The LM4898 contains advanced pop and click circuitry which virtually eliminates noises which would otherwise occur during turn-on and turn-off transitions. Connection Diagrams Top View Figure 1. VSSOP Package See Package Number DGS0010A Top View Top View Figure 2. WSON Package See Package Number NGZ0010B Figure 3. 9 Bump DSBGA Package See Package Number YZR0009AAA 1 2 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. All 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 © 2003–2013, Texas Instruments Incorporated LM4898, LM4898MMBD SNAS216E – MAY 2003 – REVISED APRIL 2013 www.ti.com Typical Application Figure 4. Typical Audio Amplifier Application Circuit 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. Absolute Maximum Ratings (1) (2) Supply Voltage 6.0V −65°C to +150°C Storage Temperature −0.3V to VDD +0.3V Input Voltage Power Dissipation (3) Internally Limited ESD Susceptibility (4) 2000V ESD Susceptibility (5) 200V Junction Temperature Thermal Resistance 150°C θJC (WSON) 12°C/W θJA (WSON) 63°C/W θJA (DSBGA) 220°C/W θJC (VSSOP) 56°C/W θJA (VSSOP) 190°C/W For Soldering Information, see AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009). (1) (2) (3) (4) (5) 2 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not ensure specific performance limits. Electrical Characteristics VDD = 3V 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 specified 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, 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. Human body model, 100pF discharged through a 1.5kΩ resistor. Machine Model, 220pF–240pF discharged through all pins. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 Operating Ratings TMIN ≤ TA ≤ TMAX Temperature Range −40°C ≤ TA ≤ 85°C 2.4V ≤ VDD ≤ 5.5V Supply Voltage Electrical Characteristics VDD = 5V (1) (2) (3) The following specifications apply for VDD = 5V, 8Ω load, and AV = 1V/V, unless otherwise specified. Limits apply for TA = 25°C. Parameter IDD Test Conditions Quiescent Power Supply Current LM4898 Typ (4) Limit (5) VIN = 0V, no load 3 6 VIN = 0V, RL = 8 Ω 5 10 0.1 1 ISD Shutdown Current VSDMODE = VSHUTDOWN = GND Po Output Power THD = 1% (max); f = 1 kHz LM4898LD, RL= 4Ω (6) 1.4 Units (Limits) mA (max) µA (max) W (min) LM4898, RL= 8Ω 1 0.05 % 83 dB (min) THD+N Total Harmonic Distortion+Noise Po = 0.4 Wrms; f = 1kHz PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p f = 217Hz f = 1kHz (7) f = 217Hz f = 1kHz (7) (8) (8) 0.9 90 83 71 83 71 CMRR Common_Mode Rejection Ratio f = 217Hz VCM = 200mVDD VOS Output Offset VIN = 0V VSDIH Shutdown Voltage Input High SD Mode = GND VSDIL Shutdown Voltage Input Low SD Mode = GND 0.7 V VSDIH Shutdown Voltage Input High SD Mode = VDD 0.9 V VSDIL Shutdown Voltage Input Low SD Mode = VDD 0.7 V (1) (2) (3) (4) (5) (6) (7) (8) 50 dB 2 mV 0.9 V 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 VDD = 3V 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 specified for parameters where no limit is given, however, the typical value is a good indication of device performance. For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. Typicals are measured at 25°C and represent the parametric norm. Datasheet min/max specification limits are specified by design, test, or statistical analysis. When driving 4Ω loads from a 5V supply, the LM4898LD must be mounted to a circuit board with the exposed-DAP area soldered down to a 1sq. in plane of 1oz. copper. Unterminated input. 10Ω terminated input. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD Submit Documentation Feedback 3 LM4898, LM4898MMBD SNAS216E – MAY 2003 – REVISED APRIL 2013 www.ti.com Electrical Characteristics VDD = 3V (1) (2) (3) The following specifications apply for VDD = 3V, 8Ω load and AV = 1V/V, unless otherwise specified. Limits apply for TA = 25°C. Parameter IDD LM4898 Test Conditions Quiescent Power Supply Current Typ (4) Limit (5) Units (Limits) 2.5 5 .5 mA (max) 4 9 1 VIN = 0V, no load VIN = 0V, RL = 8 Ω ISD Shutdown Current VSDMODE = VSHUTDOWN = GND 0.1 Po Output Power THD = 1% (max); f = 1kHz LM4898, RL = 8Ω 0.35 W THD+N Total Harmonic Distortion+Noise Po = 0.25Wrms; f = 1kHz 0.03 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p 83 dB f = 217Hz f = 1kHz f = 217Hz f = 1kHz (6) (6) µA (max) 84 (7) 83 (7) 83 CMRR Common-Mode Rejection Ratio f = 217Hz VCM = 200mVPP 50 dB VOS Output Offset VIN = 0V 2 mV VSDIH Shutdown Voltage Input High SD Mode = GND 0.8 V VSDIL Shutdown Voltage Input Low SD Mode = GND 0.6 V VSDIH Shutdown Voltage Input High SD Mode = VDD 0.8 V VSDIL Shutdown Voltage Input Low SD Mode = VDD 0.6 V (1) (2) (3) (4) (5) (6) (7) 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 VDD = 3V 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 specified for parameters where no limit is given, however, the typical value is a good indication of device performance. For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. Typicals are measured at 25°C and represent the parametric norm. Datasheet min/max specification limits are specified by design, test, or statistical analysis. Unterminated input. 10Ω terminated input. External Components Description (See Figure 4) Components 4 Functional Description 1. CS Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for information concerning proper placement and selection of the supply bypass capacitor. 2. 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. 3. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. 4. Rf Feedback resistance which sets the closed-loop gain in conjunction with Ri. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 Typical Performance Characteristics NGZ0010B Specific Characteristics THD+N vs Output Power VDD = 5V, RL = 4Ω THD+N vs Frequency VDD = 5V, RL = 4Ω, PO = 1W 10 10 20kHz 1 THD+N (%) THD+N (%) 1 1kHz 0.1 0.1 20Hz 0.01 0.01 0.001 10m 100m 1 3 0.001 20 OUTPUT POWER (W) 100 1k Figure 5. Figure 6. LM4898 Power Dissipation vs Output Power LM4898 Power Derating Curve Figure 7. Figure 8. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD 10k 20k FREQUENCY (Hz) Submit Documentation Feedback 5 LM4898, LM4898MMBD SNAS216E – MAY 2003 – REVISED APRIL 2013 www.ti.com Typical Performance Characteristics Non-NGZ0010B Specific Characteristics THD+N vs Frequency VDD = 3V, RL = 8Ω, PO = 275mW 10 10 1 1 THD+N (%) THD+N (%) THD+N vs Frequency VDD = 5V, RL = 8Ω, PO = 400mW 0.1 0.01 0.1 0.01 0.001 20 100 1k 0.001 20 10k 20k 100 Figure 10. THD+N vs Frequency VDD = 3V, RL = 4Ω, PO = 225mW THD+N vs Frequency VDD = 2.6V, RL = 8Ω, PO = 150mW 10 10 1 1 0.1 0.1 0.01 0.001 20 100 1k 0.001 20 10k 20k 100 FREQUENCY (Hz) 1k 10k 20k FREQUENCY (Hz) Figure 11. Figure 12. THD+N vs Frequency VDD = 2.6V, RL = 4Ω, PO = 150mW THD+N vs Output Power VDD = 5V, RL = 8Ω 10 10 1 1 THD+N (%) THD+N (%) 10k 20k Figure 9. 0.01 0.1 0.01 0.001 20 20kHz 1kHz 0.1 20Hz 0.01 100 1k 10k 20k 0.001 10m FREQUENCY (Hz) Submit Documentation Feedback 100m 1 2 OUTPUT POWER (W) Figure 13. 6 1k FREQUENCY (Hz) THD+N (%) THD+N (%) FREQUENCY (Hz) Figure 14. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 Typical Performance Characteristics Non-NGZ0010B Specific Characteristics (continued) THD+N vs Output Power VDD = 3V, RL = 8Ω THD+N vs Output Power VDD = 3V, RL = 4Ω 10 10 20kHz 20kHz 1 THD+N (%) THD+N (%) 1 1kHz 0.1 1kHz 0.1 20Hz 20Hz 0.01 0.001 10m 0.01 100m 0.001 10m 1 100m OUTPUT POWER (W) Figure 15. Figure 16. THD+N vs Output Power VDD = 2.6V, RL = 8Ω THD+N vs Output Power VDD = 2.6V, RL = 4Ω 10 10 20kHz 20kHz 1 THD+N (%) 1 THD+N (%) 1 OUTPUT POWER (W) 1kHz 0.1 1kHz 0.1 20Hz 0.01 20Hz 0.001 10m 0.01 100m 0.001 10m 1 100m 1 OUTPUT POWER (W) Figure 17. Figure 18. PSRR vs Frequency VDD = 5V, RL = 8Ω, Input 10Ω Terminated PSRR vs Frequency VDD = 3V, RL = 8Ω, Input 10Ω Terminated 0 0 -10 -10 -20 -20 -30 -30 PSRR (dB) PSRR (dB) OUTPUT POWER (W) -40 -50 -60 -40 -50 -60 -70 -70 -80 -80 -90 -90 -100 20 -100 20 100 1k 10k 100 FREQUENCY (Hz) 100 1k 10k 100 FREQUENCY (Hz) Figure 19. Figure 20. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD Submit Documentation Feedback 7 LM4898, LM4898MMBD SNAS216E – MAY 2003 – REVISED APRIL 2013 www.ti.com Typical Performance Characteristics Non-NGZ0010B Specific Characteristics (continued) Output Power vs Supply Voltage RL = 4Ω 2 2 1.8 1.8 1.6 1.6 OUTPUT POWER (W) OUTPUT POWER (W) Output Power vs Supply Voltage RL = 8Ω 1.4 1.2 10% THD+N 1 800m 1% THD+N 600m 1.4 1.2 1 600m 400m 400m 200m 200m 0 2.2 2.5 3 3.5 4 4.5 5 5.5 10% THD+N 800m 1% THD+N 0 2.2 SUPPLY VOLTAGE (V) 8 2.5 3 3.5 4 SUPPLY VOLTAGE (V) Figure 21. Figure 22. Power Dissipation vs Output Power Power Dissipation vs Output Power Figure 23. Figure 24. Power Dissipation vs Output Power Output Power vs Load Resistance Figure 25. Figure 26. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 Typical Performance Characteristics Non-NGZ0010B Specific Characteristics (continued) Supply Current vs Shutdown Voltage Shutdown Low Supply Current vs Shutdown Voltage Shutdown High Figure 27. Figure 28. Clipping (Dropout) Voltage vs Supply Voltage Open Loop Frequency Response Figure 29. Figure 30. Power Derating Curve Noise Floor OUTPUT NOISE VOLTAGE (V) 100u Vo1 + Vo2 10u 1u Shutdown On 100n 20 100 1k 10k 20k FREQUENCY (Hz) Figure 31. Figure 32. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD Submit Documentation Feedback 9 LM4898, LM4898MMBD SNAS216E – MAY 2003 – REVISED APRIL 2013 www.ti.com Typical Performance Characteristics Non-NGZ0010B Specific Characteristics (continued) CMRR vs Frequency VDD = 3V, RL = 8Ω, 200mVpp 0 0 -10 -10 -20 -20 -30 -30 CMRR (dB) CMRR (dB) CMRR vs Frequency VDD = 5V, RL = 8Ω, 200mVpp -40 -50 -60 -40 -50 -60 -70 -70 -80 -80 -90 -90 -100 20 100 1k 10k -100 20 100 100 Figure 34. PSRR vs Common Mode Voltage VDD = 5V PSRR vs Common Mode Voltage VDD = 3V, RL = 8Ω, 217Hz, 200mVpp 0 0 -10 -20 -20 -30 -30 -40 -50 -60 -40 -50 -60 -70 -70 -80 -80 -90 -90 -100 -100 1 2 3 4 DC COMMON-MODE VOLTAGE (V) 5 0 0.6 Submit Documentation Feedback 1.2 1.8 2.4 3 DC COMMON-MODE VOLTAGE (V) Figure 35. 10 100 FREQUENCY (Hz) -10 0 10k Figure 33. PSRR (dB) PSRR (dB) FREQUENCY (Hz) 1k Figure 36. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 APPLICATION INFORMATION DIFFERENTIAL AMPLIFIER EXPLANATION The LM4898 is a fully differential audio amplifier that features differential input and output stages. Internally this is accomplished by two circuits: a differential amplifier and a common mode feedback amplifier that adjusts the output voltages so that the average value remains VDD/2. When setting the differential gain, the amplifier can be considered to have two "halves". Each half uses an input and feedback resistor (Ri1 and Rf1) to set its respective closed-loop gain (see Figure 4). With Ri1 = Ri2 and Rf1 = Rf2, the gain is set at -Rf/Ri for each half. This results in a differential gain of AVD = -Rf/Ri (1) It is extremely important to match the input resistors to each other, as well as the feedback resistors to each other for best amplifier performance. See the PROPER SELECTION OF EXTERNAL COMPONENTS section for more information. A differential amplifier works in a manner where the difference between the two input signals is amplified. In most applications, this would require input signals that are 180° out of phase with each other. The LM4898 can be used, however, as a single ended input amplifier while still retaining its fully differential benefits. In fact, completely unrelated signals may be placed on the input pins. The LM4898 simply amplifies the difference between them. All of these applications, either single-ended or fully differential, provide what is known as a "bridged mode" output (bridge-tied-load, BTL). This results in output signals at Vo1 and Vo2 that are 180° out of phase with respect to each other. Bridged mode operation is different from the single-ended amplifier configuration that connects the load between the amplifier output and ground. A bridged amplifier design has distinct advantages over the single-ended configuration: it provides differential drive to the load, thus doubling maximum possible output swing for a specific supply voltage. Four times the output power is possible compared with a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier’s closed-loop gain without causing excess clipping, please refer to the AUDIO POWER AMPLIFIER DESIGN. A bridged configuration, such as the one used in the LM4898, also creates a second advantage over singleended amplifiers. Since the differential outputs, Vo1 and Vo2,are biased at half-supply, no net DC voltage exists across the load. This assumes that the input resistor pair and the feedback resistor pair are properly matched (see PROPER SELECTION OF EXTERNAL COMPONENTS). BTL configuration eliminates the output coupling capacitor required in single supply, single-ended amplifier configurations. If an output coupling capacitor is not used in a single-ended output configuration, the half-supply bias across the load would result in both increased internal IC power dissipation as well as permanent loudspeaker damage. Further advantages of bridged mode operation specific to fully differential amplifiers like the LM4898 include increased power supply rejection ratio, common-mode noise reduction, and click and pop reduction. EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS The LM4898’s exposed-DAP (die attach paddle) package (NGZ0010B) provides a low thermal resistance between the die and the PCB to which the part is mounted and soldered. This 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 1.4W 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 LM4898’s high power performance and activate unwanted, though necessary, thermal shutdown protection. The NGZ0010B 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 4 (2x2) vias. The via diameter should be 0.012in - 0.013in with a 0.050in pitch. Ensure efficient thermal conductivity by plating through and solder-filling the vias. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD Submit Documentation Feedback 11 LM4898, LM4898MMBD SNAS216E – MAY 2003 – REVISED APRIL 2013 www.ti.com 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 LM4898 should be 5in2 (min) for the same supply voltage and load resistance. The last two area recommendations apply for 25°C ambient temperature. In all circumstances and conditions, the junction temperature must be held below 150°C to prevent activating the LM4898’s thermal shutdown protection. The LM4898’s power derating curve in the TYPICAL PERFORMANCE CHARACTERISTICS shows the maximum power dissipation versus temperature. Further detailed and specific information concerning PCB layout, fabrication, and mounting an WSON package is available from Texas Instruments package Engineering Group under application note AN-1187 (SNOA401). 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 1.4W to1.37W. 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. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or single-ended. Equation 2 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 /(2π2RL) Single-Ended (2) However, a direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation versus a single-ended amplifier operating at the same conditions. PDMAX = 4*(VDD)2/(2π2RL) Bridge Mode (3) Since the LM4898 has bridged outputs, the maximum internal power dissipation is 4 times that of a single-ended amplifier. Even with this substantial increase in power dissipation, the LM4898 does not require additional heatsinking under most operating conditions and output loading. From Equation 3, assuming a 5V power supply and an 8. load,the maximum power dissipation point is 625mW. The maximum power dissipation point obtained from Equation 3 must not be greater than the power dissipation results from Equation 4: PDMAX = (TJMAX - TA)/θJA (4) The LM4898’s θJA in an DGS0010A package is 190°C/W. Depending on the ambient temperature, TA, of the system surroundings, Equation 4 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 3 is greater than that of Equation 4, then either the supply voltage must be decreased, the load impedance increased, the ambient temperature reduced, or theθJA reduced with heatsinking. In many cases, larger traces near the output, VDD, and GND pins can be used to lower the θJA. The larger areas of copper provide a form of heatsinking allowing higher power dissipation. For the typical application of a 5V power supply, with an 8Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 30°C provided that device operation is around the maximum power dissipation point. Recall that internal power dissipation is a function of output power. If typical operation is not around the maximum power dissipation point, the LM4898 can operate at higher ambient temperatures. Refer to the TYPICAL PERFORMANCE CHARACTERISTICS curves for power dissipation information. 12 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM4898 LM4898MMBD LM4898, LM4898MMBD www.ti.com SNAS216E – MAY 2003 – REVISED APRIL 2013 POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection ratio (PSRR). The capacitor location on both the bypass and power supply pins should be as close to the device as possible. A larger half-supply bypass capacitor improves PSRR because it increases half-supply stability. Typical applications employ a 5V regulator with 10µF and0.1µF bypass capacitors that increase supply stability. This, however, does not eliminate the need for bypassing the supply nodes of the LM4898. Although the LM4898 will operate without the bypass capacitor CB, the PSRR may decrease. A 1µF capacitor is recommended for CB. This value maximizes PSRR performance. Lesser values may be used, but PSRR decreases at frequencies below 1kHz. The issue of CB selection is thus dependant upon desired PSRR and click and pop performance as explained in the PROPER SELECTION OF EXTERNAL COMPONENTS. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4898 contains shutdown circuitry that is used to turn off the amplifier’s bias circuitry. In addition, the LM4898 contains a Shutdown Mode pin, allowing the designer to designate whether the part will be driven into shutdown with a high level logic signal or a low level logic signal. This allows the designer maximum flexibility in device use, as the Shutdown Mode pin may simply be tied permanently to either VDD or GND to set the LM4898 as either a "shutdown-high" device or a "shutdownlow" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown Select pin to the same state as the Shutdown Mode pin. For simplicity’s sake, this is called "shutdown same", as the LM4898 enters shutdown mode whenever the two pins are in the same logic state. The trigger point for either shutdown high or shutdown low is shown as a typical value in the Supply Current vs. Shutdown Voltage graphs in the TYPICAL PERFORMANCE CHARACTERISTICS section. It is best to switch between ground and supply for maximum performance. While the device may be disabled with shutdown voltages in between ground and supply, the idle current maybe greater than the typical value of 0.1µA. In either case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which provides a quick, smooth transition to shutdown. Another solution is to use a single-throw switch in conjunction with an external pull-up resistor (or pull-down, depending on shutdown high or low application). This scheme ensures that the shutdown pin will not float, thus preventing unwanted state changes. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers is critical when optimizing device and system performance. Although the LM4898 is tolerant to a variety of external component combinations, consideration of component values must be made when maximizing overall system quality. The LM4898 is unity-gain stable, giving the designer maximum system flexibility. The LM4898 should be used in low closed-loop gain configurations to minimize THD+N values and maximize signal to noise ratio. Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1Vrms are available from sources such as audio codecs. Please refer to the AUDIO POWER AMPLIFIER DESIGN section for a more complete explanation of proper gain selection. When used in its typical application as a fully differential power amplifier the LM4898 does not require input coupling capacitors for input sources with DC common-mode voltages of less than VDD. Exact allowable input common-mode voltage levels are actually a function of VDD, Ri, and Rf and may be determined by Equation 5: VCMi