LM4808M

LM4808 Dual 105 mW Headphone Amplifier February 2000 LM4808 Dual 105 mW Headphone Amplifier General Description The LM4808 is a dual audio power amplifier capable of delivering 105 mW per channel of continuous average power into a 16Ω load with 0.1% (THD+N) from a 5V power supply. Boomer 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 LM4808 does not require bootstrap capacitors or snubber networks, it is optimally suited for low-power portable systems. The unity-gain stable LM4808 can be configured by external gain-setting resistors. Key Specifications n THD+N at 1 kHz at 105 mW continuous average output power into 16Ω n THD+N at 1 kHz at 70 mW continuous average output power into 32Ω n Output power at 0.1% THD+N at 1 kHz into 32Ω 0.1% (max) 0.1% (typ) 70 mW (typ) Features n n n n n SOP and MSOP surface mount packaging Switch on/off click suppression Excellent power supply ripple rejection Unity-gain stable Minimum external components Applications n Headphone Amplifier n Personal Computers n Microphone Preamplifier Typical Application Connection Diagram SOP & MSOP Package DS101276-2 Top View Order Number LM4808M, LM4808MM See NS Package Number M08A, MUA08A DS101276-1 *Refer to the Application Information Section for information concerning proper selection of the input and output coupling capacitors. FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2000 National Semiconductor Corporation DS101276 www.national.com LM4808 Absolute Maximum Ratings (Note 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Storage Temperature Input Voltage Power Dissipation (Note 4) ESD Susceptibility (Note 5) ESD Susceptibility (Note 6) Junction Temperature Soldering Information (Note 1) Small Outline Package Vapor Phase (60 seconds) 6.0V −65˚C to +150˚C −0.3V to VDD + 0.3V Internally limited 3500V 250V 150˚C Infrared (15 seconds) Thermal Resistance θJC (MSOP) θJA (MSOP) θJC (SOP) θJA (SOP) 220˚C 56˚C/W 210˚C/W 35˚C/W 170˚C/W Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage −40˚C ≤ T A ≤ 85˚C 2.0V ≤ VDD ≤ 5.5V Note 1: See AN-450 “Surface Mounting and their Effects on Product Reliability” for other methods of soldering surface mount devices. 215˚C Electrical Characteristics (Notes 2, 3) The following specifications apply for VDD = 5V unless otherwise specified, limits apply to TA = 25˚C. Symbol VDD IDD Ptot VOS Ibias VCM GV Io RO VO PSRR Crosstalk THD+N Parameter Supply Voltage Supply Current Total Power Dissipation Input Offset Voltage Input Bias Current Common Mode Voltage Open-Loop Voltage Gain Max Output Current Output Resistance Output Swing Power Supply Rejection Ratio Channel Separation Total Harmonic Distortion + Noise RL = 32Ω, 0.1% THD+N, Min RL = 32Ω, 0.1% THD+N, Max Cb = 1.0µF, Vripple = 100mVPP, f = 100Hz RL = 32Ω f = 1 kHz RL = 16Ω, VO =3.5VPP (at 0 dB) RL = 32Ω, VO =3.5VPP (at 0 dB) SNR fG Po Signal-to-Noise Ratio Unity Gain Frequency Output Power VO = 3.5Vpp (at 0 dB) Open Loop, RL = 5kΩ THD+N = 0.1%, f = 1 kHz RL = 16Ω RL = 32Ω THD+N = 10%, f = 1 kHz RL = 16Ω RL = 32Ω CI CL SR Input Capacitance Load Capacitance Slew Rate Unity Gain Inverting 3 150 90 3 200 mW mW pF pF V/µs 105 70 60 mW mW 0.05 66 0.05 66 105 5.5 % dB % dB dB MHz RL = 5kΩ THD+N < 0.1 % VIN = 0V, IO = 0A VIN = 0V, IO = 0A VIN = 0V 1.2 6 10 10 0 4.3 67 70 0.1 .3 4.7 89 75 Conditions LM4808 Typ (Note 7) Limit (Note 8) 2.0 5.5 3.0 16.5 50 V (min) V (max) mA (max) mW (max) mV (max) pA V V dB mA Ω V dB dB Units (Limits) www.national.com 2 LM4808 Electrical Characteristics (Notes 2, 3) The following specifications apply for VDD = 3.3V unless otherwise specified, limits apply to TA = 25˚C. Symbol IDD VOS Po Parameter Supply Current Input Offset Voltage Output Power Conditions VIN = 0V, IO = 0A VIN = 0V THD+N = 0.1%, f = 1 kHz RL = 16Ω RL = 32Ω THD+N = 10%, f = 1 kHz RL = 16Ω RL = 32Ω 56 38 mW mW 40 28 mW mW 1.0 7 Conditions Typ (Note 7) Limit (Note 8) mA (max) mV (max) Units (Limits) Electrical Characteristics (Notes 2, 3) The following specifications apply for VDD = 2.6V unless otherwise specified, limits apply to TA = 25˚C. Symbol IDD VOS Po Parameter Supply Current Input Offset Voltage Output Power Conditions VIN = 0V, IO = 0A VIN = 0V THD+N = 0.1%, f = 1 kHz RL = 16Ω RL = 32Ω THD+N = 10%, f = 1 kHz RL = 16Ω RL = 32Ω Note 2: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 3: 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 4: 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 P DMAX = (TJMAX − TA) / θJA. For the LM4808, TJMAX = 150˚C, and the typical junction-to-ambient thermal resistance, when board mounted, is 210˚C/W for the MSOP Package and 107˚C/W for package N08E. Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 6: Machine Model, 220 pF–240 pF discharged through all pins. Note 7: Typicals are measured at 25˚C and represent the parametric norm. Note 8: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Conditions Typ (Note 7) 0.9 5 20 16 31 22 Limit (Note 8) Units (Limits) mA (max) mV (max) mW mW mW mW 3 www.national.com LM4808 External Components Description Components 1. Ri 2. Ci 3. Rf 4. CS 5. CB 6. CO 7. RB (Figure 1) Functional Description 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 / (2πR iCi). Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a highpass filter with Ri at fc = 1 / (2πRiC i). Refer to the section, Proper Selection of External Components, for and explanation of how to determine the value of Ci. Feedback resistance which sets closed-loop gain in conjuction with Ri. Supply bypass capacitor which provides power supply filtering. Refer to the Application Information section for proper placement and selection of the supply bypass capacitor. 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. Output coupling capacitor which blocks the DC voltage at the amplifier’s output. Forms a high pass filter with RL at fO = 1/(2πRLCO) Resistor which forms a voltage divider that provides a half-supply DC voltage to the non-inverting input of the amplifier. Typical Performance Characteristics THD+N vs Frequency THD+N vs Frequency THD+N vs Frequency DS101276-3 DS101276-4 DS101276-5 THD+N vs Frequency THD+N vs Frequency THD+N vs Frequency DS101276-6 DS101276-7 DS101276-8 www.national.com 4 LM4808 Typical Performance Characteristics THD+N vs Frequency (Continued) THD+N vs Frequency THD+N vs Frequency DS101276-9 DS101276-10 DS101276-11 THD+N vs Frequency THD+N vs Output Power THD+N vs Output Power DS101276-12 DS101276-13 DS101276-14 THD+N vs Output Power THD+N vs Output Power THD+N vs Output Power DS101276-15 DS101276-16 DS101276-17 5 www.national.com LM4808 Typical Performance Characteristics THD+N vs Output Power (Continued) THD+N vs Output Power THD+N vs Output Power DS101276-18 DS101276-19 DS101276-20 THD+N vs Output Power Output Power vs Load Resistance Output Power vs Load Resistance DS101276-21 DS101276-22 DS101276-23 Output Power vs Load Resistance Output Power vs Supply Voltage Output Power vs Power Supply DS101276-24 DS101276-25 DS101276-26 www.national.com 6 LM4808 Typical Performance Characteristics Output Power vs Power Supply (Continued) Clipping Voltage vs Supply Voltage Power Dissipation vs Output Power DS101276-27 DS101276-28 DS101276-29 Power Dissipation vs Output Power Power Dissipation vs Output Power Channel Separation DS101276-30 DS101276-32 DS101276-31 Channel Separation Noise Floor Power Supply Rejection Ratio DS101276-33 DS101276-34 DS101276-35 7 www.national.com LM4808 Typical Performance Characteristics Open Loop Frequency Response (Continued) Open Loop Frequency Response Open Loop Frequency Response DS101276-50 DS101276-51 DS101276-38 Supply Current vs Supply Voltage Frequency Response vs Output Capacitor Size Frequency Response vs Output Capacitor Size DS101276-44 DS101276-45 DS101276-46 Frequency Response vs Output Capacitor Size Typical Application Frequency Response Typical Application Frequency Response DS101276-47 DS101276-48 DS101276-49 www.national.com 8 LM4808 Application Information 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 / (2π2RL) (1) Since the LM4808 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 LM4808 does not require heat sinking over a large range of ambient temperature. From Equation 1, assuming a 5V power supply and a 32Ω load, the maximum power dissipation point is 40 mW per amplifier. Thus the maximum package dissipation point is 80 mW. The maximum power dissipation point obtained must not be greater than the power dissipation that results from Equation 2: PDMAX = (TJMAX − TA) / θJA (2) For package MUA08A, θJA = 210˚C/W, and for package M08A, θJA = 170˚C/W. TJMAX = 150˚C for the LM4808. 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 a 32Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 131.6˚C 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 µF and a 0.1 µF bypass capacitors which aid in supply stability, but do not eliminate the need for bypassing the supply nodes of the LM4808. The selection of bypass capacitors, especially CB, is thus dependent upon desired low frequency PSRR, click and pop performance as explained in the section, Proper Selection of External Components section, 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 LM4808 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The LM4808 is unity gain stable and this gives a designer maximum system flexibility. The LM4808 should be used in 9 low gain configurations to minimize THD+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 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 value input and output capacitors are both expensive and space consuming 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 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 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 LM4808 turns on. The slower the LM4808’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn on pop. While the device will function properly, (no oscillations or motorboating), with CB equal to 1 µF, the device will be much more susceptible to turn on clicks and pops. Thus, a value of CB equal to 1 µF or larger is recommended in all but the most cost sensitive designs. AUDIO POWER AMPLIFIER DESIGN Design a Dual 70mW/32Ω Audio Amplifier Given: Power Output Load Impedance Input Level Input Impedance 70 mW 32Ω 1 Vrms (max) 20 kΩ 100 Hz–20 kHz ± 0.50 dB Bandwidth 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 300mV and can be found from the graphs in the Typical Performance Characteristics. VOPEAK can be determined from Equation 3. (3) www.national.com LM4808 Application Information (Continued) For 70 mW of output power into a 32Ω load, the required VOPEAK is 2.12 volts. A minimum supply rail of 2.42V 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 LM4808 to reproduce peaks in excess of 70 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. Once the power dissipation equations have been addressed, the required gain can be determined from Equation 4. (4) AV = Rf/Ri (5) From Equation 4, the minimum gain is: AV = 1.26 Since the desired input impedance was 20kΩ, and with a gain of 1.26, a value of 27kΩ 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 −3dB point is 0.17dB down from passband response assuming a single pole roll-off. As stated in the External Components 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 100Hz within ± 0.5dB, 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 0.34dB at five times away from the single order filter −3dB point. Thus, a frequency of 20Hz is used in the following equations to ensure that the response is better than 0.5dB down at 100Hz. Ci ≥ 1 / (2π * 20 kΩ * 20 Hz) = 0.397µF; use 0.39µF. Co ≥ 1 / (2π * 32Ω * 20 Hz) = 249µF; use 330µF. 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 = 100kHz, the resulting GBWP = 135kHz which is much smaller than the LM4808 GBWP of 900kHz. This figure displays that if a designer has a need to design an amplifier with a higher gain, the LM4808 can still be used without running into bandwidth limitations. www.national.com 10 LM4808 Application Information Silk Screen (Continued) Bottom Layer DS101276-42 DS101276-39 Drill Drawing Top Layer DS101276-43 DS101276-40 Solder Mask DS101276-41 11 www.national.com LM4808 Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM4808MM NS Package Number MUA08A Order Number LM4808M NS Package Number M08A www.national.com 12 LM4808 Dual 105 mW Headphone Amplifier Notes 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 Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com www.national.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com 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. National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 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.