LM4981 Ground-Referenced, 80mW Stereo Headphone Amplifier with Digital Volume Control General Description Key Specifications The LM4981 is a stereo, ground-referenced, output capacitor-less headphone amplifier capable of delivering 83mW of continuous average power into a 16Ω load with less than 1% THD+N while operating from a single 3V supply. The LM4981 features a new circuit technology that utilizes a charge pump to generate a negative reference voltage. This allows the outputs to be biased about ground, thereby eliminating output-coupling capacitors typically used with normal single-ended loads. The LM4981 provides high quality audio reproduction with minimal external components. A ground referenced output eliminates the output coupling capacitors typically required to drive single-ended loads such as headphones. The ground reference architecture reduces components count, cost and board space consumption, making the LM4981 ideal for handheld MP3 players, mobile phones and other portable equipment where board space is at a premium. Eliminating the output capacitors also improves low frequency response. The LM4981 operates from a single 2.0V – 4.2V supply, and features a 2-wire, up/down volume control that sets the gain of the amplifier between -33dB to +12dB in 16 discrete steps. Selectable (active high/low) low power shutdown mode provides flexible shutdown control. Superior click and pop suppression eliminates audible transients during start-up and shutdown. The LM4981 features an Automatic Standby Mode circuitry (patent pending). In the absence of an input signal, after approximately 12 seconds, the LM4981 goes into low current standby mode. The LM4981 recovers into full power operating mode immediately after a signal is applied to either the left or right input pins. This feature saves power supply current in battery operated applications. j Improved PSRR at 217Hz 67dB (typ) j THD+N at 1kHz, 50mW into 32Ω SE (3V) j Single Supply Operation (VDD) j Power Output at VDD = 3V, RL = 16Ω, THD ≤ 1% j Shutdown Current 1.0% (typ) 2.0 to 4.2V 83mW (typ) 0.01µA (typ) Features Ground Referenced Outputs No Output Coupling Capacitors 16-Step Volume Control Auto-Standby Mode High PSRR Available in Space Saving LLP package Low Power Shutdown Mode Improved Click and Pop Suppression Eliminates Noises During Turn-on and Turn-off Transients n 2.0V to 4.2V Operation n 83mW Per Channel Into 16Ω n Selectable Shutdown Controls (Active High/Low) n n n n n n n n Applications n Portable MP3 Players n Mobile Phones n PDAs Boomer ® is a registered trademark of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS201473 www.national.com LM4981 Ground-Referenced, 80mW Stereo Headphone Amplifier with Digital Volume Control November 2005 LM4981 Connection Diagrams LLP Package 20147338 Top View Order Number LM4981SQ See NS Package Number SQA16A LLP Marking 20147321 Top View U = Plant Code ZX = Date Code X = Die Traceability Bottom Line = Part Number www.national.com 2 LM4981 Typical Application 20147337 FIGURE 1. Typical Audio Amplifier Application Circuit Pin Name Function 1 CPVDD Charge Pump Power Supply 2 CCP+ Positive Terminal- charge pump flying capacitor 3 PGND Power Ground 4 CCP- Negative Terminal- charge pump flying capacitor 5 VCP_OUT Charge Pump Output 6 CLOCK Clock 7 UP/DN Up / Down 8 INR Right Input 9 AVDD Positive Power Supply - Amplifier 10 OUT R Right Output 11 AVSS Negative Power Supply - Amplifier 12 OUT L Left Output 13 IN L Left Input 14 SGND Signal Ground 15 SD Shutdown 16 SD MODE Shutdown Mode Pin 3 www.national.com LM4981 Absolute Maximum Ratings (Note 2) ESD Susceptibility (Note 5) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Junction Temperature Supply Voltage Temperature Range −65˚C to +150˚C TMIN ≤ TA ≤ TMAX −0.3V to VDD +0.3V Input Voltage Power Dissipation(Note 3) −40˚C ≤ T A ≤ 85˚C 2.0V ≤ VCC ≤ 4.2V Supply Voltage (VDD) Internally Limited ESD Susceptibility (Note 4) 150˚C Operating Ratings 4.5V Storage Temperature 250V 2500V Electrical Characteristics VDD = 3V (Notes 1, 2) The following specifications apply for VDD = 3V, AV = 1V/V RL = 32Ω, f = 1kHz, unless otherwise specified. Limits apply to TA = 25˚C. Symbol Parameter IDD Quiescent Power Supply Current IDD Standby Power Supply Current Conditions VIN = 0V, RL = ∞ ISD Shutdown Current VSD = GND Logic Input Voltage High SHDN, SDM, CLOCK, U/D VIL Logic Input Voltage Low SHDN, SDM, CLOCK, U/D Wake Up Time VOS Output Offset Voltage PO THD+N PSRR ∈OS Output Power Total Harmonic Distortion Power Supply Rejection Ratio Output Noise www.national.com 10 Units (Limits) mA mA 3.5 µA 0.7VDD V 0.3VDD V Input Referred Maximum Gain 12 dB Input Referred Minimum Gain –33 dB 3 dB Step Size Error TWU 7 0.1 Volume Step Size Channel-to-Channel Volume Tracking Error Limit (Note 7) 2.3 VIH Digital Volume LM4981 Typical (Note 6) All gain settings ± 0.3 dB 0.15 dB 300 µs RL = 32Ω 1 THD+N = 1% (max); f = 1kHz, RL = 16Ω, one channel 83 mW THD+N = 1% (max); f = 1kHz, RL = 32Ω, one channel 75 mW THD+N = 1% (max); f = 1kHz, RL = 16Ω, (two channels in phase) 40 33 mW (min) THD+N = 1% (max); f = 1kHz, RL = 32Ω, (two channels in phase) 47 43 mW (min) PO = 60mW, f = 1kHz, RL = 16Ω single channel 0.03 PO = 50mW, f = 1kHz, RL = 32Ω single channel 0.02 5 mV % VRIPPLE = 200mVP-PSine, fRIPPLE = 1kHz, Inputs AC GND, Cl = 1µF 65 dB VRIPPLE = 200mVP-PSine, fRIPPLE = 10kHz, Inputs AC GND, Cl = 1µF 50 dB VRIPPLE = 200mVP-PSine, fRIPPLE = 217Hz 67 dB A-Weighted Filter 11 µV 4 (Continued) Note 1: All voltages are measured with respect to the GND pin unless other wise 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 LM4917, see power derating currents 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: Typical specifications are specified at +25˚C and represent parametric norm. Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). 5 www.national.com LM4981 Electrical Characteristics VDD = 3V (Notes 1, 2) LM4981 Typical Performance Characteristics THD+N vs Frequency VDD = 1.8V, RL = 32Ω, PO = 5mW THD+N vs Frequency VDD = 1.8V, RL = 16Ω, PO = 5mW 20147339 20147340 THD+N vs Frequency VDD = 3V, RL = 32Ω, PO = 50mW THD+N vs Frequency VDD = 3V, RL = 16Ω, PO = 50mW 20147341 20147342 THD+N vs Frequency VDD = 3.6V, RL = 32Ω, PO = 100mW THD+N vs Frequency VDD = 3.6V, RL = 16Ω, PO = 100mW 20147343 www.national.com 20147345 6 LM4981 Typical Performance Characteristics (Continued) THD+N vs Frequency VDD = 4.2V, RL = 16Ω, PO = 150mW THD+N vs Frequency VDD = 4.2V, RL = 32Ω, PO = 150mW 20147346 20147347 THD+N vs Output Power VDD = 1.8V, RL = 16Ω, f = 1kHz, two channels THD+N vs Output Power VDD = 1.8V, RL = 16Ω, f = 1kHz, one channel 20147348 20147349 THD+N vs Output Power VDD = 1.8V, RL = 32Ω, f = 1kHz, two channels THD+N vs Output Power VDD = 1.8V, RL = 32Ω, f = 1kHz, one channel 20147352 20147353 7 www.national.com LM4981 Typical Performance Characteristics (Continued) THD+N vs Output Power VDD = 3V, RL = 16Ω, f = 1kHz, one channel THD+N vs Output Power VDD = 3V, RL = 16Ω, f = 1kHz, two channels 20147355 20147354 THD+N vs Output Power VDD = 3V, RL = 32Ω, f = 1kHz, two channels THD+N vs Output Power VDD = 3V, RL = 32Ω, f = 1kHz, one channel 20147356 20147367 THD+N vs Output Power VDD = 3.6V, RL = 16Ω, f = 1kHz, two channels THD+N vs Output Power VDD = 3.6V, RL = 16Ω, f = 1kHz, one channel 20147368 www.national.com 20147369 8 (Continued) THD+N vs Output Power VDD = 3.6V, RL = 32Ω, f = 1kHz, one channel THD+N vs Output Power VDD = 3.6V, RL = 32Ω, f = 1kHz, two channels 20147370 20147371 THD+N vs Output Power VDD = 4.2V, RL = 16Ω, f = 1kHz, two channels THD+N vs Output Power VDD = 4.2V, RL = 16Ω, f = 1kHz, one channel 20147372 20147373 THD+N vs Output Power VDD = 4.2V, RL = 32Ω, f = 1kHz, two channels THD+N vs Output Power VDD = 4.2V, RL = 32Ω, f = 1kHz, one channel 20147374 20147375 9 www.national.com LM4981 Typical Performance Characteristics LM4981 Typical Performance Characteristics (Continued) Output Power vs Supply Voltage RL = 16Ω, f = 1kHz, one channel Output Power vs Supply Voltage RL = 16Ω, f = 1kHz, two channels 20147377 20147376 Output Power vs Supply Voltage RL = 32Ω, f = 1kHz, two channels Output Power vs Supply Voltage RL = 32Ω, f = 1kHz, one channel 20147378 20147379 Supply Current vs Supply Voltage Power Dissipation vs Output Power RL = 16Ω, VDD = 3V 20147381 20147380 www.national.com 10 LM4981 Typical Performance Characteristics (Continued) PSRR vs Frequency VDD = 3V, RL = 32Ω Vripple = 200mVp-p Power Dissipation vs Output Power RL = 32Ω, VDD = 3V 20147382 20147383 11 www.national.com LM4981 SUPPLY VOLTAGE SEQUENCING It is a good general practice to first apply the supply voltage to a CMOS device before any other signal or supply on other pins. This is also true for the LM4891 audio amplifier which is a CMOS device. Application Information DIGITAL VOLUME CONTROL The LM4981’s gain is controlled by the signals applied to the CLOCK and UP/DN inputs. An external clock is required to drive the CLOCK pin. At each rising edge of the clock signal, the gain will either increase or decrease by a 3dB step depending on the logic voltage level applied to the UP/DN pin. A logic high voltage level applied to the UP/DN pin causes the gain to increase by 3dB at each rising edge of the clock signal. Conversely, a logic low voltage level applied to the UP/DN pin causes the gain to decrease 3dB at each rising edge of the clock signal. For both the CLOCK and UP/DN inputs, the trigger point is 1.4V minimum for a logic high level, and 0.4V maximum for a logic low level. There are 16 discrete gain settings ranging from +12dB maximum to −33dB minimum. Upon device power on, the amplifier’s gain is set to a default value of 0dB. However, when coming out of shutdown mode, the LM4981 will revert back to its previous gain setting. Before applying any signal to the inputs or shutdown pins of the LM4891, it is important to apply a supply voltage to the VDD pins. After the device has been powered, signals may be applied to the shutdown pins (see MICRO POWER SHUTDOWN) and input pins. POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. Applications that employ a 3V power supply typically use a 4.7µF capacitor in parallel with a 0.1µF ceramic filter capacitor to stabilize the power supply’s output, reduce noise on the supply line, and improve the supply’s transient response. Keep the length of leads and traces that connect capacitors between the LM4981’s power supply pin and ground as short as possible. The LM4981’s CLOCK and UP/DN pins should be debounced in order to avoid unwanted state changes during transitions between VIL and VIH. This will ensure correct operation of the digital volume control. A microcontroller or microprocessor output is recommended to drive the CLOCK and UP/DN pins. 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) / (2π2RL) (1) Since the LM4981 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 LM4981 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 40mW per amplifier. Thus the maximum package dissipation point is 80mW. The maximum power dissipation point obtained must not be greater than the power dissipation predicted by Equation 2: 20147384 FIGURE 2. Timing Diagram ELIMINATING THE OUTPUT COUPLING CAPACITOR The LM4981 features a low noise inverting charge pump that generates an internal negative supply voltage. This allows the outputs of the LM4981 to be biased about GND instead of a nominal DC voltage, like traditional headphone amplifiers. Because there is no DC component, the large DC blocking capacitors (typically 220µF) are not necessary. The coupling capacitors are replaced by two, small ceramic charge pump capacitors, saving board space and cost. Eliminating the output coupling capacitors also improves low frequency response. In traditional headphone amplifiers, the headphone impedance and the output capacitor form a high pass filter that not only blocks the DC component of the output, but also attenuates low frequencies, impacting the bass response. Because the LM4981 does not require the output coupling capacitors, the low frequency response of the device is not degraded by external components. In addition to eliminating the output coupling capacitors, the ground referenced output nearly doubles the available dynamic range of the LM4981 when compared to a traditional headphone amplifier operating from the same supply voltage. www.national.com 2 PDMAX = (TJMAX − TA) / θJA (2) For a given 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. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4981 contains shutdown circuitry that is used to turn off the amplifier’s bias circuitry. In addition, the LM4981 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 LM4981 as either a "shutdown-high" device or a "shutdown-low" device, respectively. The device may then be placed into shutdown mode by toggling the Shut12 The LD package should have its DAP soldered to a copper pad on the PCB. The DAP’s PCB copper pad may be connected to a large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink, and radiation area However, since the LM4981 is designed for headphone applications, connecting a copper plane to the DAP’s PCB copper pad is not required. The DAP on the LM4981 should be connected to GND to ensure correct functionality. (Continued) down pin to the same state as the Shutdown Mode pin. For simplicity’s sake, this is called "shutdown same", as the LM4981 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 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. 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. SELECTING PROPER EXTERNAL COMPONENTS Optimizing the LM4981’s performance requires properly selecting external components. Though the LM4981 operates well when using external components with wide tolerances, best performance is achieved by optimizing component values Charge Pump Capacitor Selection Use low ESR (equivalent series resistance) ( < 100mΩ) ceramic capacitors with an X7R dielectric for best performance. Low ESR capacitors keep the charge pump output impedance to a minimum, extending the headroom on the negative supply. Higher ESR capacitors result in reduced output power from the audio amplifiers. Charge pump load regulation and output impedance are affected by the value of the flying capacitor (CC). A larger valued CC (up to 3.3uF) improves load regulation and minimizes charge pump output resistance. Beyond 3.3uF, the switch-on resistance dominates the output impedance for capacitor values above 2.2uF. The output ripple is affected by the value and ESR of the output capacitor (CSS). Larger capacitors reduce output ripple on the negative power supply. Lower ESR capacitors minimize the output ripple and reduce the output impedance of the charge pump. AUTOMATIC STANDBY MODE The LM4981 features Automatic Standby Mode circuitry (patent pending). In the absence of an input signal, after approximately 12 seconds, the LM4981 goes into low current standby mode. The LM4981 recovers into full power operating mode immediately after a signal, which is greater than the input threshold voltage, is applied to either the left or right input pins. The input threshold voltage is not a static value, as the supply voltage increases, the input threshold voltage decreases. This feature reduces power supply current consumption in battery operated applications. Please see also the graph entitled Representation of Automatic Standby Mode Behavior in the Typical Performance Characteristics section. To ensure correct operation of Automatic Standby Mode, proper layout techniques should be implemented. Separating PGND and SGND can help reduce noise entering the LM4981 in noisy environments. Auto Standby mode works best when output impedance of the audio source driving LM4981 is equal or less than 50 Ohms. While Automatic Standby Mode reduces power consumption very effectively during silent periods, maximum power saving is achieved by putting the device into shutdown when it is not in use. The LM4981 charge pump design is optimized for 2.2uF, low ESR, ceramic, flying, and output capacitors. Input Capacitor Value Selection Amplifying the lowest audio frequencies requires high value input coupling capacitors (CinA and CinB in Figure 1). A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases, however, the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 150Hz. Applications using speakers with this limited frequency response reap little improvement by using high value input and output capacitors. Besides affecting system cost and size, the input capacitor has an effect on the LM4981’s click and pop performance. The magnitude of the pop is directly proportional to the input capacitor’s size. Thus, pops can be minimized by selecting an input capacitor value that is no higher than necessary to meet the desired −3dB frequency. As shown in Figure 1, the internal input resistor, Ri and the input capacitor, Ci, produce a -3dB high pass filter cutoff frequency that is found using Equation (3). Conventional headphone amplifiers require output capacitors; Equation (3) can be used, along with the value of RL, to determine towards the value of output capacitor needed to produce a –3dB high pass filter cutoff frequency. OUTPUT TRANSIENT (’CLICK AND POPS’) ELIMINATED The LM4981 contains advanced circuitry that virtually eliminates output transients (’clicks and pops’). This circuitry prevents all traces of transients when the supply voltage is first applied or when the part resumes operation after coming out of shutdown mode. EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION The LM4981’s exposed-dap (die attach paddle) package (LD) 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 surrounding air. fi-3dB = 1 / 2πRiCi 13 (3) www.national.com LM4981 Application Information LM4981 Application Information types of capacitors (tantalum, electrolytic, ceramic) have unique performance characteristics and may affect overall system performance. (See the section entitled Charge Pump Capacitor Selection.) (Continued) Also, careful consideration must be taken in selecting a certain type of capacitor to be used in the system. Different 20147389 Demo Board Schematic FIGURE 3. www.national.com 14 LM4981 Application Information (Continued) LM4981 DEMO BOARD ARTWORK Top Layer 20147390 Mid Layer 1 20147391 15 www.national.com LM4981 Application Information (Continued) Mid Layer 2 20147392 Bottom Layer 20147393 www.national.com 16 LM4981 Revision History Rev Date Description 1.0 8/29/05 Added the Typ Perf curves. 1.1 9/02/05 Added the Apps Information section and more Typ Perf curves. 1.2 9/06/05 Added the LLP Marking and the table. 1.3 9/23/05 Input some text edits and also edited the Application ckt dg (pg 3). 1.4 11/9/05 Added the demo boards and Fig 3. 1.5 11/9/05 1st WEB released. 17 www.national.com LM4981 Ground-Referenced, 80mW Stereo Headphone Amplifier with Digital Volume Control Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM4981SQ NS Package Number NSQAL016 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 manufactures products and uses packing materials that 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. Leadfree products are RoHS compliant. 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