深圳市芯美电子科技有限公司 LM4990 2 Watt Audio Power Amplifier with Selectable Shutdown Logic Level General Description Key Specifications The LM4990 is an audio power amplifier primarily designed for demanding applications in mobile phones and other portable communication device applications. It is capable of delivering 1.25 watts of continuous average power to an 8Ω BTL load and 2 watts of continuous average power (LD and MH only) to a 4Ω BTL load with less than 1% distortion (THD+N+N) from a 5VDC power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4990 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 LM4990 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 pin to be driven in a likewise manner to enable shutdown. The LM4990 contains advanced pop & click circuitry which eliminates noise which would otherwise occur during turn-on and turn-off transitions. The LM4990 is unity-gain stable and can be configured by external gain-setting resistors. j Improved PSRR at 217Hz & 1KHz j Power Output at 5.0V, 1% THD+N, 4Ω (LD and MH only) 62dB 2W (typ) j Power Output at 5.0V, 1% THD+N, 8Ω 1.25W (typ) j Power Output at 3.0V, 1% THD+N, 4Ω 600mW (typ) j Power Output at 3.0V, 1% THD+N, 8Ω 425mW (typ) j Shutdown Current 0.1µA (typ) Features n Available in space-saving packages: LLP, Exposed-DAP TSSOP, MSOP, and ITL n Ultra low current shutdown mode n Improved pop & click circuitry eliminates noise during turn-on and turn-off transitions n 2.2 - 5.5V operation n No output coupling capacitors, snubber networks or bootstrap capacitors required n Unity-gain stable n External gain configuration capability n User selectable shutdown High or Low logic Level Applications n Mobile Phones n PDAs n Portable electronic devices Connection Diagrams Mini Small Outline (MSOP) Package MSOP Marking 20051071 200510B9 Top View Order Number LM4990MM See NS Package Number MUA08A Top View Z - Plant Code X - Date Code TT - Die Traceability G - Boomer Family A5 - LM4990MM Boomer ® is a registered trademark of National Semiconductor Corporation. © 2004 National Semiconductor Corporation DS200510 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 2 Watt Audio Power Amplifier with Selectable Shutdown Logic Level October 2004 LM4990 深圳市芯美电子科技有限公司 Connection Diagrams (Continued) LLP Package LLP Marking 200510B4 Top View Z - Plant Code XY - Date Code TT - Die Traceability Bottom Line - Part Number 200510B3 Top View Order Number LM4990LD See NS Package Number LDA10B Exposed-DAP TSSOP Package 20051096 Top View Order Number LM4990MH See NS Package Number MXF10A 9 Bump micro SMD 9 Bump micro SMD Marking 200510C1 Top View X — Date Code T — Die Traceability G — Boomer Family D2 — LM4990ITL 200510C0 Top View Order Number LM4990ITL, LM4990ITLX See NS Package Number TLA09ZZA www.national.com 2 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 LD MH MM ITL Shutdown Mode Selectable Selectable Low Low Typical Power Output at 5V, 1% THD+N 2W (RL = 4Ω) 2W (RL = 4Ω) 1.25W (RL = 8Ω) 1.25W (RL = 8Ω) . A SD_MODE select pin determines the Shutdown Mode for the LD and MH packages, whether it is an Asserted High or an Asserted Low device, to activate shutdown. . The SD_MODE select pin is not available with the MM and ITL packaged devices. Shutdown occurs only with a low assertion. Typical Application 20051001 Note: MM and ITL packaged devices are active low only; Shutdown Mode pin is internally tied to GND. FIGURE 1. Typical Audio Amplifier Application Circuit (LD and MH) 200510C4 FIGURE 2. Typical Audio Amplifier Application Circuit (ITL and MM) 3 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 Package LM4990 深圳市芯美电子科技有限公司 Absolute Maximum Ratings (Note 2) θJA (MSOP) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. θJA (9 Bump micro SMD) (Note 15) Supply Voltage (Note 11) 6.0V Storage Temperature 63˚C/W (Note 13) θJC (LLP) 12˚C/W (Note 13) See AN-1187 "Leadless Leadframe Package (LLP)." −0.3V to VDD +0.3V Power Dissipation (Notes 3, 12) 180˚C/W θJA (LLP) Soldering Information −65˚C to +150˚C Input Voltage 190˚C/W Internally Limited ESD Susceptibility (Note 4) 2000V ESD Susceptibility (Note 5) 200V Junction Temperature Operating Ratings Temperature Range 150˚C TMIN ≤ TA ≤ TMAX Thermal Resistance θJC (MSOP) −40˚C ≤ TA ≤ 85˚C 2.2V ≤ VDD ≤ 5.5V Supply Voltage 56˚C/W Electrical Characteristics VDD = 5V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. LM4990 Symbol Parameter Conditions VIN = 0V, Io = 0A, No Load IDD Quiescent Power Supply Current ISD Shutdown Current VSD = VSD VSDIH Shutdown Voltage Input High VSD VSDIL Shutdown Voltage Input Low VSDIH Shutdown Voltage Input High VSDIL Shutdown Voltage Input Low VSD VOS Output Offset Voltage ROUT Po TWU VIN = 0V, Io = 0A, 8Ω Load Mode (Note 8) (Notes 7, 9) 3 7 mA (max) 4 10 mA (max) 0.1 2.0 µA (max) MODE V VSD MODE = VDD 1.3 V VSD MODE = GND 1.5 V MODE = GND 1.3 V 7 8.5 THD+N = 1% (max); f = 1kHz Wake-up time THD+N+N Total Harmonic Distortion+Noise Po = 0.5Wrms; f = 1kHz PSRR Vripple = 200mV sine p-p Input terminated with 10Ω Power Supply Rejection Ratio (Note 6) 1.5 THD+N = 1% (max); f = 1kHz (4Ω) (Notes 13, 14) Limit = VDD Resistor Output to GND (Note 10) Output Power (8Ω) Units (Limits) Typical 1.25 50 mV (max) 9.7 kΩ (max) 7.0 kΩ (min) 0.9 W (min) 2 W 100 ms 0.2 % 60 (f = 217Hz) 64 (f = 1kHz) 55 dB (min) Electrical Characteristics VDD = 3V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. LM4990 Symbol Parameter Conditions (Note 6) (Notes 7, 9) Units (Limits) 2 7 mA (max) VIN = 0V, Io = 0A, 8Ω Load 3 9 mA (max) 0.1 2.0 µA (max) Quiescent Power Supply Current ISD Shutdown Current VSD = VSD VSDIH Shutdown Voltage Input High VSD VSDIL Shutdown Voltage Input Low VSD VSDIH Shutdown Voltage Input High VSD VSDIL Shutdown Voltage Input Low VSD VOS Output Offset Voltage Mode (Note 8) MODE = VDD 1.1 V MODE = VDD 0.9 V MODE = GND 1.3 V MODE = GND 1.0 7 Resistor Output to GND (Note 10) www.national.com Limit VIN = 0V, Io = 0A, No Load IDD ROUT Typical 8.5 V 50 mV (max) 9.7 kΩ (max) 7.0 kΩ (min) 4 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 LM4990 Electrical Characteristics VDD = 3V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. (Continued) LM4990 Symbol Po TWU Parameter Conditions Output Power (8Ω) (4Ω) Typical Limit (Note 6) (Notes 7, 9) THD+N = 1% (max); f = 1kHz 425 mW THD+N = 1% (max); f = 1kHz 600 mW 75 ms % Wake-up time THD+N+N Total Harmonic Distortion+Noise Po = 0.25Wrms; f = 1kHz 0.1 PSRR Vripple = 200mV sine p-p Input terminated with 10Ω 62 (f = 217Hz) 68 (f = 1kHz) Power Supply Rejection Ratio Units (Limits) 55 dB (min) Electrical Characteristics VDD = 2.6V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. LM4990 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 9) Units (Limits) VIN = 0V, Io = 0A, No Load 2.0 mA IDD Quiescent Power Supply Current VIN = 0V, Io = 0A, 8Ω Load 3.0 mA ISD Shutdown Current VSD = VSD 0.1 µA VSDIH Shutdown Voltage Input High VSD MODE = VDD 1.0 V VSDIL Shutdown Voltage Input Low VSD MODE = VDD 0.9 V VSDIH Shutdown Voltage Input High VSD MODE = GND 1.2 V VSDIL Shutdown Voltage Input Low VSD MODE = GND 1.0 V VOS Output Offset Voltage ROUT Po Mode (Note 8) 5 Resistor Output to GND (Note 10) 8.5 50 mV (max) 9.7 kΩ (max) 7.0 kΩ (min) Output Power ( 8Ω ) THD+N = 1% (max); f = 1kHz 300 ( 4Ω ) THD+N = 1% (max); f = 1kHz 400 70 ms THD+N+N Total Harmonic Distortion+Noise Po = 0.15Wrms; f = 1kHz 0.1 % PSRR Vripple = 200mV sine p-p Input terminated with 10Ω 51 (f = 217Hz) 51 (f = 1kHz) dB TWU Wake-up time Power Supply Rejection Ratio mW Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 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 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 is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. 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 LM4990, see power derating curves for additional information. Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Note 5: Machine Model, 220pF – 240pF discharged through all pins. Note 6: Typicals are measured at 25˚C and represent the parametric norm. Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 8: For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. Note 9: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 10: RROUT is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the two 20kΩ resistors. Note 11: If the product is in Shutdown mode and VDD exceeds 6V (to a max of 8V VDD), then most of the excess current will flow through the ESD protection circuits. If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is enabled when VDD is greater than 5.5V and less than 6.5V, no damage will occur, although operation life will be reduced. Operation above 6.5V with no current limit will result in permanent damage. Note 12: Maximum power dissipation in the device (PDMAX) occurs at an output power level significantly below full output power. PDMAX can be calculated using Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs. 5 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 深圳市芯美电子科技有限公司 Electrical Characteristics VDD = 2.6V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. (Continued) Note 13: The Exposed-DAP of the LDA10B package should be electrically connected to GND or an electrically isolated copper area. the LM4990LD demo board has the Exposed-DAP connected to GND with a PCB area of 86.7mils x 585mils (2.02mm x 14.86mm) on the copper top layer and 550mils x 710mils (13.97mm x 18.03mm) on the copper bottom layer. Note 14: The thermal performance of the LLP and exposed-DAP TSSOP packages when used with the exposed-DAP connected to a thermal plane is sufficient for driving 4Ω loads. The MSOP and ITL packages do not have the thermal performance necessary for driving 4Ω loads with a 5V supply and is not recommended for this application. Note 15: All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. All bumps must be connected to achieve specified thermal resistance. External Components Description See (Figure 1) Components Functional Description 1. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high pass filter with Ci at fC= 1/(2π RiCi). 2. Ci Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a highpass filter with Ri at fc = 1/(2π RiCi). 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 the closed-loop gain in conjunction with Ri. 4. 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. 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. Typical Performance Characteristics LD and MH Specific Characteristics THD+N+N vs Output Power VDD = 5V, RL = 4Ω, and f = 1 kHz THD+N+N vs Frequency VDD = 5V, RL = 4Ω, and PO = 1W 20051030 www.national.com 20051031 6 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 THD+N+N vs Frequency VDD = 5V, RL = 8Ω, and PO = 500mW THD+N+N vs Frequency VDD = 3V, RL = 4Ω, and PO = 500mW 20051032 20051033 THD+N+N vs Frequency VDD = 2.6V, RL = 4Ω, and PO = 150mW THD+N+N vs Frequency VDD = 3V, RL = 8Ω, and PO = 250mW 20051034 20051083 THD+N+N vs Output Power VDD = 2.6V, RL = 8Ω, and PO = 150mW THD+N+N vs Output Power VDD = 5V, RL = 8Ω, and f = 1kHz 20051084 20051085 7 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 Typical Performance Characteristics LM4990 深圳市芯美电子科技有限公司 Typical Performance Characteristics (Continued) THD+N+N vs Output Power VDD = 3V, RL = 4Ω, and f = 1kHz THD+N+N vs Output Power VDD = 3V, RL = 8Ω, and f = 1kHz 20051002 20051003 THD+N+N vs Output Power VDD = 2.6V, RL = 8Ω, and f = 1kHz THD+N+N vs Output Power VDD = 2.6V, RL = 4Ω, and f = 1kHz 20051004 20051005 Power Supply Rejection Ratio (PSRR) vs Frequency VDD = 5V, RL = 8Ω, input 10Ω terminated Power Supply Rejection Ratio (PSRR) vs Frequency VDD = 5V, RL = 8Ω, input floating 20051006 www.national.com 20051007 8 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 (Continued) Power Supply Rejection Ratio (PSRR) vs Frequency VDD = 3V, RL = 8Ω, input 10Ω terminated Power Supply Rejection Ratio (PSRR) vs Frequency VDD = 3V, RL = 8Ω, input floating 20051086 20051087 Power Supply Rejection Ratio (PSRR) vs Frequency VDD = 2.6V, RL = 8Ω, Input Floating Power Supply Rejection Ratio (PSRR) vs Frequency VDD = 2.6V, RL = 8Ω, input 10Ω terminated 20051088 20051089 Noise Floor, 5V, 8Ω 80kHz Bandwidth, Input to GND Open Loop Frequency Response, 5V 20051092 20051095 9 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 Typical Performance Characteristics LM4990 深圳市芯美电子科技有限公司 Typical Performance Characteristics (Continued) Power Dissipation vs Output Power, VDD = 5V Power Dissipation vs Output Power, VDD = 3V 200510B5 200510B6 Shutdown Hysteresis Voltage VDD = 5V, SD Mode = VDD Power Dissipation vs Output Power, VDD = 2.6V 200510B7 200510A0 Shutdown Hysteresis Voltage VDD = 5V, SD Mode = GND Shutdown Hysteresis Voltage VDD = 3V, SD Mode = VDD 200510A1 www.national.com 200510A2 10 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 LM4990 Typical Performance Characteristics (Continued) Shutdown Hysteresis Voltage VDD = 3V, SD Mode = GND Shutdown Hysteresis Voltage VDD = 2.6V, SD Mode = VDD 200510A3 200510A4 Shutdown Hysteresis Voltage VDD = 2.6V, SD Mode = GND Output Power vs Supply Voltage, RL = 4Ω 200510A5 200510B8 Output Power vs Supply Voltage, RL = 8Ω Output Power vs Supply Voltage, RL = 16Ω 200510A6 200510A7 11 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 深圳市芯美电子科技有限公司 Typical Performance Characteristics (Continued) Output Power vs Supply Voltage, RL = 32Ω Frequency Response vs Input Capacitor Size 200510A8 20051054 www.national.com 12 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4990 has two internal operational amplifiers. The first amplifier’s gain is externally configurable, while the second amplifier is internally fixed in a unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier’s gain is fixed by the two internal 20kΩ resistors. Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of phase by 180˚. Consequently, the differential gain for the IC is POWER SUPPLY BYPASSING As with any amplifier, 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. Typical applications employ a 5V regulator with 10µF tantalum or electrolytic capacitor and a ceramic bypass capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the LM4990. The selection of a bypass capacitor, especially CB, is dependent upon PSRR requirements, click and pop performance (as explained in the section, Proper Selection of External Components), system cost, and size constraints. AVD= 2 *(Rf/Ri) By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as “bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output power is possible as 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 clipped. In order to choose an amplifier’s closed-loop gain without causing excessive clipping, please refer to the Audio Power Amplifier Design section. A bridge configuration, such as the one used in LM4990, also creates a second advantage over single-ended amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load. This eliminates the need for an output coupling capacitor which is required in a single supply, single-ended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased internal IC power dissipation and also possible loudspeaker damage. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4990 contains shutdown circuitry that is used to turn off the amplifier’s bias circuitry. In addition, the LM4990 contains a Shutdown Mode pin (LD and MH packages only), 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 LM4990 as either a "shutdown-high" device or a "shutdown-low" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown pin to the same state as the Shutdown Mode pin. For simplicity’s sake, this is called "shutdown same", as the LM4990 enters shutdown mode whenever the two pins are in the same logic state. The MM package lacks this Shutdown Mode feature, and is permanently fixed as a ‘shutdown-low’ device. 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 may be 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. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. Since the LM4990 has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1. PDMAX = 4*(VDD)2/(2π2RL) 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 guarantees that the shutdown pin will not float, thus preventing unwanted state changes. (1) It is critical that the maximum junction temperature TJMAX of 150˚C is not exceeded. TJMAX can be determined from the power derating curves by using PDMAX and the PC board foil area. By adding copper foil, the thermal resistance of the application can be reduced from the free air value of θJA, resulting in higher PDMAX values without thermal shutdown protection circuitry being activated. Additional copper foil can be added to any of the leads connected to the LM4990. It is PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers is critical to optimize device and system performance. While the LM4990 is tolerant of 13 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 especially effective when connected to VDD, GND, and the output pins. Refer to the application information on the LM4990 reference design board for an example of good heat sinking. If TJMAX still exceeds 150˚C, then additional changes must be made. These changes can include reduced supply voltage, higher load impedance, or reduced ambient temperature. Internal power dissipation is a function of output power. Refer to the Typical Performance Characteristics curves for power dissipation information for different output powers and output loading. Application Information LM4990 深圳市芯美电子科技有限公司 Application Information AUDIO POWER AMPLIFIER DESIGN (Continued) A 1W/8Ω Audio Amplifier external component combinations, consideration to component values must be used to maximize overall system quality. Given: Power Output The LM4990 is unity-gain stable which gives the designer maximum system flexibility. The LM4990 should be used in low gain configurations to minimize THD+N+N values, and maximize 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 1Vrms 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. 1Wrms Load Impedance 8Ω Input Level 1Vrms Input Impedance 20kΩ 100Hz–20kHz ± 0.25dB Bandwidth A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating from the Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be easily found. Besides gain, one of the major considerations is the closedloop bandwidth of the amplifier. To a large extent, the bandwidth is dictated by the choice of external components shown in Figure 1. The input coupling capacitor, Ci, forms a first order high pass filter which limits low frequency response. This value should be chosen based on needed frequency response for a few distinct reasons. 5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4990 to reproduce peaks in excess of 1W without producing audible distortion. 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. Selection of Input Capacitor Size Large input 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 100Hz to 150Hz. Thus, using a large input capacitor may not increase actual 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 capacitor size, 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 LM4990 turns on. The slower the LM4990’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing CB equal to 1.0µF along with a small value of Ci (in the range of 0.1µF to 0.39µF), should produce a virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 0.1µF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 1.0µF is recommended in all but the most cost sensitive designs. Once the power dissipation equations have been addressed, the required differential gain can be determined from Equation 2. (2) Rf/Ri = AVD/2 From Equation 2, the minimum AVD is 2.83; use AVD = 3. Since the desired input impedance was 20kΩ, and with a AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results in an allocation of Ri = 20kΩ and Rf = 30kΩ. The final design step is to address the bandwidth requirements which must be stated as a pair of −3dB frequency points. Five times away from a −3dB point is 0.17dB down from passband response which is better than the required ± 0.25dB specified. fL = 100Hz/5 = 20Hz fH = 20kHz * 5 = 100kHz As stated in the External Components section, Ri in conjunction with Ci create a highpass filter. Ci ≥ 1/(2π*20kΩ*20Hz) = 0.397µF; use 0.39µF The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain, AVD. With a AVD = 3 and fH = 100kHz, the resulting GBWP = 300kHz which is much smaller than the LM4990 GBWP of 2.5MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential gain, the LM4990 can still be used without running into bandwidth limitations. www.national.com 14 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 LM4990 Application Information (Continued) 20051024 FIGURE 3. HIGHER GAIN AUDIO AMPLIFIER The LM4990 is unity-gain stable and requires no external components besides gain-setting resistors, an input coupling capacitor, and proper supply bypassing in the typical application. However, if a closed-loop differential gain of greater than 10 is required, a feedback capacitor (C4) may be needed as shown in Figure 2 to bandwidth limit the amplifier. This feedback capacitor creates a low pass filter that elimi- nates possible high frequency oscillations. Care should be taken when calculating the -3dB frequency in that an incorrect combination of R3 and C4 will cause rolloff before 20kHz. A typical combination of feedback resistor and capacitor that will not produce audio band high frequency rolloff is R3 = 20kΩ and C4 = 25pf. These components result in a -3dB point of approximately 320kHz. 15 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 深圳市芯美电子科技有限公司 Application Information (Continued) 20051029 FIGURE 4. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4990 20051025 FIGURE 5. REFERENCE DESIGN BOARD SCHEMATIC www.national.com 16 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 LM4990 Physical Dimensions inches (millimeters) unless otherwise noted MSOP Order Number LM4990MM NS Package Number MUA08A Exposed-DAP TSSOP Order Number LM4990MH NS Package Number MXF10A 17 www.national.com 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 深圳市芯美电子科技有限公司 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) LLP Order Number LM4990LD NS Package Number LDA10B 9–Bump micro SMD Order Number LM4990ITL, LM4990ITLX NS Package Number TLA09ZZA X1 = 1.463 ± 0.03 X2 = 1.463 ± 0.03 X3 = 0.600 ± 0.075 www.national.com 18 联系电话：１５９９９６４４５７９ ８３１５１７１５ 深圳市芯美电子科技有限公司 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 联系电话：１５９９９６４４５７９ ８３１５１７１５ LM4990 2 Watt Audio Power Amplifier with Selectable Shutdown Logic Level Notes