LM4915 Pseudo-Differential Mono Headphone Amplifier with Fixed 6dB Gain General Description Key Specifications The LM4915 is a pseudo-differential audio power amplifier primarily designed for demanding applications in mobile phones and other portable audio device applications with mono headphones. It is capable of delivering 90 miliwatts of continuous average power to a 32Ω BTL load with less than 1% distortion (THD+N) from a 3VDC power supply. n n n n Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4915 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 LM4915 features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by driving the shutdown pin low. Additionally, the LM4915 features an internal thermal shutdown protection mechanism. The LM4915 contains advanced pop & click circuitry which virtually eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4915 has an internally fixed gain of 6dB. Improved PSRR at 217Hz and 1kHz 75dB (typ) Power Output at 5.0V & 1% THD into 32Ω 280mW (typ) Power Output at 3.0V & 1% THD into 32Ω 90mW (typ) Output Noise, A-weighted 20µV (typ) Features Pseudo-differential amplification Internal gain-setting resistors Available in space-saving LLP package Ultra low current shutdown mode Can drive capacitive loads up to 500pF Improved pop & click circuitry virtually eliminates noises during turn-on and turn-off transitions n 2.2 - 5.5V operation n No output coupling capacitors, snubber networks, bootstrap capacitors or gain-setting resistors required n Ultra low noise n n n n n n Applications n Mobile phones n PDAs n Portable electronics devices Typical Application 200482B4 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2003 National Semiconductor Corporation DS200482 www.national.com LM4915 Pseudo-Differential Mono Headphone Amplifier with Fixed 6dB Gain May 2003 LM4915 Connection Diagrams LQ Package 200482B5 Top View Order Number LM4915LQ See NS Package Number LQB08A 8 Pin LQ Marking 200482E7 X - Date Code TT - Die Traceability G - Boomer A5 - LM4915LQ www.national.com 2 Junction Temperature (Note 2) Thermal Resistance If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage 150˚C θJC (LQ) 57˚C/W θJA (LQ) 140˚C/W 6.0V Storage Temperature −65˚C to +150˚C Operating Ratings -0.3V to VDD + 0.3V Input Voltage Temperature Range Power Dissipation (Note 3) Internally Limited ESD Susceptibility (Note 4) 2000V TMIN ≤ TA ≤ TMAX 200V Supply Voltage (VDD) ESD Susceptibility (Note 5) −40˚C ≤ TA ≤ +85˚C 2.2V ≤ VCC ≤ 5.5V Electrical Characteristics VDD = 5V (Notes 1, 2, 8) The following specifications apply for VDD = 5V, RL = 16Ω unless otherwise specified. Limits apply to TA = 25˚C. Symbol Parameter Conditions IDD Quiescent Power Supply Current VIN = 0V, IO = 0A VSHUTDOWN = GND LM4915 Units (Limits) Typ (Note 6) Limit (Note 7) 2 3.5 mA (max) 0.1 Note 9 µA(max) ISD Shutdown Current VSDIH Shutdown Voltage Input High 1.8 V VSDIL Shutdown Voltage Input Low 0.4 V PO Output Power THD = 1% (max); f = 1kHz RL = 16 RL = 32 400 280 VNO Output Noise Voltage BW = 20Hz to 20kHz, A-weighted 20 PSRR Power Supply Rejection Ratio VRIPPLE = 200mV sine p-p 75 VOS Output Offset Voltage VIN = 0V 2 375 250 mW µV dB 20 mV (max) Electrical Characteristics VDD = 3.0V (Notes 1, 2, 8) The following specifications apply for VDD = 3.0V, RL = 16Ω unless otherwise specified. Limits apply to TA = 25˚C. Symbol Parameter Conditions LM4915 Typ (Note 6) Limit (Note 7) Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, IO = 0A 1.5 2.5 mA (max) ISD Shutdown Current VSHUTDOWN = GND 0.1 Note 9 µA(max) VSDIH Shutdown Voltage Input High VSDIL Shutdown Voltage Input Low PO Output Power 1.8 V 0.4 V THD = 1% (max); f = 1kHz RL = 16 RL = 32 125 90 VNO Output Noise Voltage BW = 20Hz to 20kHz, A-weighted 20 PSRR Power Supply Rejection Ratio VRIPPLE = 200mV sine p-p 70 VOS Output Offset Voltage VIN = 0V 2 100 80 mW (min) µV dB 20 mV (max) Note 1: All voltages are measured with respect to the GND 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 LM4915, see power derating curves for more 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: Datasheet min/max specifications are guaranteed by design, test, or statistical analysis. 3 www.national.com LM4915 Absolute Maximum Ratings LM4915 Electrical Characteristics VDD = 3.0V (Notes 1, 2, 8) (Continued) Note 9: See ISD distribution values shown in the ISD Distribution curve, VDD = 5V and V = 3V, shown in the Typical Performance Characteristics section. External Components Description Components (Figure 1) Functional Description 1. CB Bypass pin capacitor that provides half-supply filtering. Refer to the section Proper Selection of External Components for information concerning proper placement and selection of CB. 2. Ci Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a high-pass filter with the internal input resistance Ri. For the LM4915, Ri = 20kΩ, thus creating a high-pass filter fc = 1/(2πRiCi). Refer to the section Proper Selection of External Components for an explanantion of how to determine the value of Ci. Typical Performance Characteristics THD+N vs Frequency VDD = 5V, RL = 32Ω THD+N vs Frequency VDD = 5V, RL = 16Ω 200482C6 200482C7 THD+N vs Frequency VDD = 3V, RL = 32Ω, PO = 80mW THD+N vs Frequency VDD = 3V, RL = 16Ω, PO = 100mW 200482C4 www.national.com 200482C5 4 LM4915 Typical Performance Characteristics (Continued) THD+N vs Frequency VDD = 2.6V, RL = 16Ω, PO = 50mW THD+N vs Frequency VDD = 2.6V, RL = 32Ω, PO = 40mW 200482C2 200482C3 THD+N vs Output Power VDD = 5V, RL = 32Ω THD+N vs Output Power VDD = 5V, RL = 16Ω 200482D2 200482D3 THD+N vs Output Power VDD = 3V, RL = 32Ω THD+N vs Output Power VDD = 3V, RL = 16Ω 200482D0 200482D1 5 www.national.com LM4915 Typical Performance Characteristics (Continued) THD+N vs Output Power VDD = 2.6V, RL = 16Ω THD+N vs Output Power VDD = 2.6V, RL = 32Ω 200482C8 200482C9 PSRR vs Frequency VDD = 5V, RL = 32Ω, PO = 250mW Input 10Ω Terminated PSRR vs Frequency VDD = 5V, RL = 16Ω, PO = 375mW Input 10Ω Terminated 200482C0 200482C1 PSRR vs Frequency VDD = 3V, RL = 32Ω Input 10Ω Terminated PSRR vs Frequency VDD = 3V, RL = 16Ω Input 10Ω Terminated 200482B8 www.national.com 200482B9 6 LM4915 Typical Performance Characteristics (Continued) PSRR vs Frequency VDD = 2.6V, RL = 16Ω Input 10Ω Terminated PSRR vs Frequency VDD = 2.6V, RL = 32Ω Input 10Ω Terminated 200482B6 200482B7 Output Power vs Supply Voltage RL = 16Ω Output Power vs Load Resistance VDD = 2.6V, RL = 32Ω 200482D9 200482E5 Power Dissipation vs Output Power VDD = 5V Output Power vs Supply Voltage RL = 32Ω 200482E4 200482E1 7 www.national.com LM4915 Typical Performance Characteristics (Continued) Power Dissipation vs Output Power VDD = 3V Frequency Response vs Input Capacitor Size 200482E0 200482E6 Noise Floor Shutdown Hysterisis Voltage VDD = 5V 200482E8 200482D8 ISD Distribution VDD = 5V Shutdown Hysterisis Voltage VDD = 3V 200482E9 200482F0 www.national.com 8 LM4915 Typical Performance Characteristics (Continued) ISD Distribution VDD = 3V 200482F1 figuration, the half-supply bias across the load would result in both increased internal IC power dissipation as well as permanent loudspeaker damage. Application Information DIFFERENTIAL AMPLIFIER EXPLANATION The LM4915 is a pseudo-differential audio amplifier that features a fixed gain of 6dB. Internally this is accomplished by two separate sets of inverting amplifiers, each set to a gain of 2. The LM4915 features precisely matched internal gain-setting resistors set to Ri = 20kΩ and Rf = 40kΩ, thus eliminating the need for external resistors and fixing the differential gain at AVD = 6dB. 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 LM4915 works in a pseudo-differential manner, so DC offset normally cancelled by a fully differential amplifier needs to be blocked by input coupling capacitors for the LM4915 to amplify the difference between the inputs. The LM4915 provides 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. A bridged configuration, such as the one used in the LM4915, 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. BTL configuration eliminates the output coupling capacitor required in singlesupply, single-ended amplifier configurations. If an output coupling capacitor is not used in a single-ended output con- POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifer, whether the amplifier is bridged or single-ended. 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 / (2π2RL) Single-Ended (1) 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 (2) Since the LM4915 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 LM4915 does not require additional heatsinking under most operating conditions and output loading. From Equation 2, assuming a 5V power supply and an 16Ω load, the maximum power dissipation point is 316mW. The maximum power dissipation point obtained from Equation 2 must not be greater than the power dissipation results from Equation 3: PDMAX = (TJMAX - TA) / θJA (3) The LM4915’s θJA in an LQB08A package is 140˚C/W. Depending on the ambient temperature, TA , of the system surroundings, Equation 3 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 2 is greater than that of Equation 3, 9 www.national.com LM4915 Application Information The switch and resistor guarantee that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the pull-up resistor. (Continued) then either the supply voltage must be decreased, the load impedance increased, the ambient temperature reduced, or the θJA 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 a 16Ω load power dissipation is not an issue. Recall that internal power dissipation is a function of output power. If typical operation is not around the maximum power dissipation point, the LM4915 can operate at higher ambient temperatures. Refer to the Typical Performance Characteristics curves for power dissipation information. 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 LM4915 is tolerant of external component combinations, and requires minimal external components, consideration to component values must be used to maximize overall system quality. The input coupling capacitor, Ci, forms a first order high pass filter which limits low frequency response given by fc = 1/(2πRiCi). Ri is internally set to 20kΩ. This value should be chosen based on needed frequency response for a few distinct reasons. 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. 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 affected 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 LM4915 turns on. The slower the LM4915’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing CB equal to 4.7µF along with a small value of CI (in the range of 0.1µF to 0.47µF), should produce a virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 1.0µF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 4.7µF is recommended in all but the most cost sensitive designs. Typical applications employ a 5V regulator with 10µF and 0.1µF bypass capacitors that increase supply stability. This, however, does not eliminate the need for bypassing the supply nodes of the LM4915. A 1µF capacitor is recommended for CS. A 4.7µF capacitor is recommended for CB. This value coupled with small input capacitors (0.1µF to 0.47µF) gives virtually zero click and pop with outstanding PSRR performance. MICRO POWER SHUTDOWN The voltage applied to the SHUTDOWN pin controls the LM4915’s shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHUTDOWN pin. When active, the LM4915’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The trigger point is 0.4V for a logic-low level, and 1.8V for a logic-high level. The low 0.1µA (typ) shutdown current is achieved by applying a voltage that is as near as ground as possible to the SHUTDOWN pin. A voltage that is higher than ground may increase the shutdown current. There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100k. pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier operation by opening the switch. Closing the switch connects the SHUTDOWN pin to ground, activating micro-power shutdown. www.national.com 10 inches (millimeters) unless otherwise noted Order Number LM4915LQ NS Package Number LQB08A 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. 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 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. 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