March 16, 2010 Ground-Referenced, Ultra Low Noise, Stereo Headphone Amplifier General Description Key Specifications The LM48861 is a single supply, ground-referenced stereo headphone amplifier. Part of National's PowerWise® product family, the LM48861 consumes only 3mW of power, yet still provides great audio performance. The ground-referenced architecture eliminates the larger DC blocking capacitors required by traditional headphone amplifier's saving board space and reducing cost. The LM48861 features common-mode sensing that corrects for any differences between the amplifier ground and the potential at the headphone return terminal, minimizing noise created by any ground mismatches. The LM48861 delivers 22mW/channel into a 32Ω load with <1% THD+N with a 1.8V supply. Power supply requirements allow operation from 1.2V to 2.8V. High power supply rejection ratio (PSRR), 83dB at 217Hz, allows the device to operate in noisy environments without additional power supply conditioning. A low power shutdown mode reduces supply current consumption to 0.01µA. Superior click and pop suppression eliminates audible transients on power-up/down and during shutdown. The LM48861 is available in an ultra-small 12-bump, 0.4mm pitch, micro SMD package (1.215mm x 1.615mm). ■ Output Power/channel at VDD = 1.5V, THD+N = 1% RL = 16Ω RL = 32Ω 12mW (typ) 13mW (typ) ■ Output Power/channel at VDD = 1.8V, THD+N = 1% RL = 16Ω RL = 32Ω 24mW (typ) 22mW (typ) ■ Quiescent Power Supply Current at 1.5V ■ PSRR at 217Hz ■ Shutdown Current 2mA (typ) 83dB (typ) 0.01μA (typ) Features ■ Ground referenced outputs – eliminates output coupling ■ ■ ■ ■ ■ ■ ■ capacitors Common-mode sensing Advanced click-and-pop suppression Low supply current Minimum external components Micro-power shutdown ESD protection of 8kV HBM contact Available in space-saving 12-bump microSMD package Applications ■ Mobile Phones ■ Portable electronic devices ■ MP3 Players Boomer® is a registered trademark of National Semiconductor Corporation. © 2010 National Semiconductor Corporation 300541 www.national.com LM48861 PowerWise® Ground-Referenced, Ultra Low Noise, Stereo Headphone Amplifier LM48861 LM48861 Typical Application 300541a9 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM48861 Connection Diagrams TM Package 1.215mm x 1.615mm x 0.6mm 12 – Bump TM Marking 300541h5 Top View X = Date code V = Lot traceability G = Boomer K3 = LM48861TM 300541a8 Top View Order Number LM48861TM See NS Package Number TMD12AAA Ordering Information Order Number Package LM48861TM 12 Bump microSMD 0.4mm Pitch Package DWG # Transport Media MSL Level Green Status TMD12AAA 250 and 3000 units on tape and reel 1 RoHS/no Sb/Br Bump Description Bump Name A1 CPP Description A2 PGND A3 CPN Charge Pump Flying Capacitor Negative Terminal B1 VDD Positive Power Supply B2 SHDN Active Low Shutdown Charge Pump Flying Capacitor Positive Terminal Power Ground B3 CPVSS Charge Pump Output C1 OUTL Left Channel Output C2 VSS Negative Power Supply C3 INL Left Channel Input D1 OUTR Right Channel Output D2 COM Ground reference for inputs and HP D3 INR Right Channel Input 3 www.national.com LM48861 ESD Susceptibility (Machine Model) (Note 5) Junction Temperature Thermal Resistance Absolute Maximum Ratings (Note 1, Note 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Ratings (HBM) (Note 4) ESD Ratings (OUTL, OUTR) (Note 4) 200V 150°C θJA (TM) 70°C/W (typ) Operating Ratings 3V −65°C to +150°C -0.3V to VDD + 0.3V Internally Limited 2000V Temperature Range TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ +85°C 1.2V ≤ VDD ≤ 2.8V Supply Voltage (VDD) 8000V Electrical Characteristics VDD = 1.5V (Note 1, Note 2) The following specifications apply for VDD = 1.5V, AV = –1V/V, RL = 32kΩ, f = 1kHz, unless otherwise specified. Limits apply for TA = 25°C. LM48861 Symbol IDD Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) Quiescent Power Supply Current VIN = 0V, Both channels enabled 2 2.8 mA (max) ISD Shutdown Current Shutdown Enabled VSHDN = GND 0.01 1.5 µA (max) VOS Output Offset Voltage VIN = 0V, RL = 32Ω Both channels enabled 0.5 1.5 mV (max) VIH Shutdown Input Voltage High 1.4 V(min) VIL Shutdown Input Voltage Low 0.4 V(max) TWU Wake Up Time PO Output Power 500 700 μs (max) THD+N = 1% RL = 32Ω, f = 1kHz, Both channels in phase and active VDD = 1.5V VDD = 1.8V 13 22 12 20 mW (min) mW (min) THD+N = 1% RL = 16Ω, f = 1kHz, Both channels in phase and active VDD = 1.5V VDD = 1.8V 12 24 mW mW RL = 10kΩ, f = 1kHz VLINE-OUT THD+N Output Voltage to Line Out VDD = 1.5V, THD+N = 1%, RL = 10kΩ 1.1 1 VRMS (min) VDD = 1.8V, THD+N = 1%, RL = 10kΩ 1.3 1.2 VRMS (min) PO = 8mW, f = 1kHz, RL = 32Ω 0.04 % 0.07 % 0.001 % Total Harmonic Distortion + Noise PO = 8mW, f = 1kHz, RL = 16Ω VOLIF = 900mVRMS, f = 1kHz, RL = 10kΩ VRIPPLE = 200mVP-P Sine, Inputs AC GND, C1 = C2 = 0.39μF PSRR Power Supply Rejection Ratio SNR Signal-to-Noise Ratio XTALK Crosstalk www.national.com fRIPPLE = 217Hz fRIPPLE = 1kHz fRIPPLE = 15kHz 83 77 57 dB dB dB RL = 32Ω, POUT = 8mW (A-weighted), f = 1kHz BW = 20Hz to 22kHz 102 dB RL = 32Ω, POUT = 5mW, f = 1kHz 93 dB 4 Parameter NOUT Output Noise C-P Click-Pop Conditions A-weighted, AV = 5.1dB R1 = R2 = 10kΩ, R3 = R4 = 18kΩ Inputs Grounded BW = <10Hz to >500kHz Typical (Note 6) Units (Limits) Limit (Note 7) 5 μV 79 dB Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum RatingsRatings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. Note 3: Maximum allowable power dissipation is PDMAX = (TJMAX - TA) / θJA or the number given in Absolute Maximum Ratings, whichever is lower. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. 5 www.national.com LM48861 LM48861 Symbol LM48861 Typical Performance Characteristics THD+N vs Frequency VDD = 1.5V, RL = 16Ω, PO = 8mW THD+N vs Frequency VDD = 1.5V, RL = 32Ω, PO = 8mW 300541b3 300541b2 THD+N vs Frequency VDD = 1.8V, RL = 16Ω, PO = 18mW THD+N vs Frequency VDD = 1.8V, RL = 32Ω, PO = 20mW 300541b5 300541b4 THD+N vs Output Power VDD = 1.5V & 1.8V, RL = 16Ω, f = 1kHz THD+N vs Output Power VDD = 1.5V & 1.8V, RL = 32Ω, f = 1kHz 300541d1 www.national.com 300541d2 6 LM48861 Power Dissipation vs Output Power RL = 16Ω, f = 1kHz Power Dissipation vs Output Power RL = 32Ω, f = 1kHz 300541h2 300541h3 PSRR vs Frequency VDD = 1.5V, VRIPPLE = 200mVP-P, RL = 32Ω Output Power vs Supply Voltage RL = 16Ω, f = 1kHz 300541c8 30054102 Output Power vs Supply Voltage RL = 32Ω, f = 1kHz Supply Current vs Supply Voltage No Load 300541d0 30054103 7 www.national.com LM48861 Shutdown Current vs Supply Voltage No Load Crosstalk vs Frequency VDD = 1.5V, POUT = 5mW, RL = 32Ω 300541c9 www.national.com 300541c7 8 voltage to the SHDN pin. Driving the SHDN pin with active circuitry eliminates the pull-up resistor. GENERAL AMPLIFIER FUNCTION The LM48861 headphone amplifier features National’s ground referenced architecture that eliminates the large DCblocking capacitors required at the outputs of traditional headphone amplifiers. A low-noise inverting charge pump creates a negative supply (CPVSS) from the positive supply voltage (VDD). The headphone amplifiers operate from these bipolar supplies, with the amplifier outputs biased about GND, instead of a nominal DC voltage (typically VDD/2), like traditional amplifiers. Because there is no DC component to the headphone output signals, the large DC-blocking capacitors (typically 220μF) are not necessary, conserving board space and system cost, while improving frequency response. POWER DISSIPATION Power dissipation is a major concern when using any power amplifier, especially one in mobile devices. In the LM48861, the power dissipation comes from the charge pump and two operational amplifiers. Refer to the Power Dissipation vs Output Power curve in the Typical Performance Characteristics section of the datasheet to find the power dissipation associated the output power level of the LM48861. The power dissipation should not exceed the maximum power dissipation point of the micro SMD package given in equation 1. PDMAX = (TJMAX - TA) / (θJA) COMMON MODE SENSE The LM48861 features a ground (common mode) sensing feature. In noisy applications, or where the headphone jack is used as a line out to other devices, noise pick up and ground imbalance can degrade audio quality. The LM48861 COM input senses and corrects any noise at the headphone return, or any ground imbalance between the headphone return and device ground, improving audio reproduction. Connect COM directly to the headphone return terminal of the headphone jack (Figure 2). No additional external components are required. Connect COM to GND if the common-mode sense feature is not in use. (1) For the LM48861TM micro SMD package, θJA = 70°C/W. TJMAX = 150°C, and TA is the ambient temperature of the system surroundings. PROPER SELECTION OF EXTERNAL COMPONENTS Power Supply Bypassing/Filtering Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass capacitors as close to the supply pins as possible. Place a 1μF ceramic capacitor from VDD to GND. Additional bulk capacitance may be added as required. Charge Pump Capacitor Selection Use low ESR ceramic capacitors (less than 100mΩ) for optimum performance. Charge Pump Flying Capacitor (C5) The flying capacitor (C5) affects the load regulation and output impedance of the charge pump. A C5 value that is too low results in a loss of current drive, leading to a loss of amplifier headroom. A higher valued C5 improves load regulation and lowers charge pump output impedance to an extent. Above 2.2μF, the RDS(ON) of the charge pump switches and the ESR of C5 and C6 dominate the output impedance. A lower value capacitor can be used in systems with low maximum output power requirements. 30054101 FIGURE 2. MICRO POWER SHUTDOWN The voltage applied to the shutdown (SHDN) pin controls the LM48861’s shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHDN pin. When active, the LM48861’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The trigger point is 0.4V (max) for a logic-low level, and 1.4V (min) 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 SHDN 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 100kΩ pull-up resistor between the SHDN pin and GND. Connect the switch between the SHDN pin and VDD. Select normal amplifier operation by closing the switch. Opening the switch connects the SHDN pin to ground, activating micro-power shutdown. The switch and resistor guarantee that the SHDN 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 Charge Pump Hold Capacitor (C6) The value and ESR of the hold capacitor (C6) directly affects the ripple on CPVSS. Increasing the value of C6 reduces output ripple. Decreasing the ESR of C6 reduces both output ripple and charge pump output impedance. A lower value capacitor can be used in systems with low maximum output power requirements. Power Supply Bypassing /Filtering Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass capacitors as close to the device as possible. Typical applications employ a voltage regulator with 10µF and 0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing of the LM48861 supply pins. A 1µF capacitor is recommended. Input Capacitor Selection The LM48861 requires input coupling capacitors. Input capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of the audio source and the bias voltage of the LM48861. The input capacitors create a high-pass filter with the input resistors RIN. 9 www.national.com LM48861 Application Information LM48861 The -3dB point of the high-pass filter is found using Equation (2) below. f = 1 / 2πRINCIN PCB Layout Guidelines Minimize trace impedance of the power, ground and all output traces for optimum performance. Voltage loss due to trace resistance between the LM48861 and the load results in decreased output power and efficiency. Trace resistance between the power supply and ground has the same effect as a poorly regulated supply, increased ripple and reduced peak output power. Use wide traces for power supply inputs and amplifier outputs to minimize losses due to trace resistance, as well as route heat away from the device. Proper grounding improves audio performance, minimizes crosstalk between channels and prevents switching noise from interfering with the audio signal. Use of power and ground planes is recommended. As described in the Common Mode Sense section, the LM48861 features a ground sensing feature. On the PCB layout, connect the COM pin (pin D2) directly to the headphone jack ground and also to the left and right input grounds. This will help correct any noise or any ground imbalance between the headphone return, input, and the device ground, therefore improving audio reproduction. The charge pump capacitors and traces connecting the capacitor to the device should be kept away from the input and output traces to avoid any switching noise injected into the input or output. (2) Where the value of RIN is selected based on the gain-setting resistor selection. In relation to Figure 1, RIN = R1 = R2, CIN = C1 = C2. The input capacitors can also be used to remove low frequency content from the audio signal. Small speakers can not reproduce, and may even be damaged by low frequencies. High-pass filtering the audio signal helps protect the speakers. When the LM48861 is using a single-ended source, power supply noise on the ground is seen as an input signal. Setting the high-pass filter point above the power supply noise frequencies, 217Hz in a GSM phone, for example, filters out the noise such that it is not amplified and heard on the output. Capacitors with a tolerance of 10% or better are recommended for impedance matching and improved CMRR and PSRR. www.national.com 10 LM48861 Demo Board Schematic and Layout 30054199 FIGURE 4: Top Solder Mask 30054110 FIGURE 3: Top Silkscreen Layer 30054106 FIGURE 5: Bottom Solder Mask 30054109 FIGURE 6: Top Layer 11 www.national.com LM48861 30054108 30054107 FIGURE 8: Layer 3 FIGURE 7: Layer 2 30054105 FIGURE 10: Bottom Silkscreen 30054104 FIGURE 9: Bottom Layer www.national.com 12 LM48861 Revision History Rev Date 1.0 06/11/08 Initial release. Description 1.01 02/08/10 Input text edits. 13 www.national.com LM48861 Physical Dimensions inches (millimeters) unless otherwise noted TM Package Order Number LM48861TM NS Package Number TMD12AAA X1 = 1.215mm, X2 = 1.615mm, X3 = 0.6mm www.national.com 14 LM48861 Notes 15 www.national.com LM48861 PowerWise® Ground-Referenced, Ultra Low Noise, Stereo Headphone Amplifier Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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