LM4667 Filterless High Efficiency 1.3W Switching Audio Amplifier General Description Key Specifications The LM4667 is a fully integrated single-supply high efficiency switching audio amplifier. It features an innovative modulator that eliminates the LC output filter used with typical switching amplifiers. Eliminating the output filter reduces parts count, simplifies circuit design, and reduces board area. The LM4667 processes analog inputs with a delta-sigma modulation technique that lowers output noise and THD when compared to conventional pulse width modulators. The LM4667 is designed to meet the demands of mobile phones and other portable communication devices. Operating on a single 3V supply, it is capable of driving 8Ω transducer loads at a continuous average output of 450mW with less than 1%THD+N. Its flexible power supply requirements allow operation from 2.7V to 5.5V. The LM4667 has high efficiency with an 8Ω transducer load compared to a typical Class AB amplifier. With a 3V supply, the IC’s efficiency for a 100mW power level is 74%, reaching 84% at 450mW output power. The LM4667 features a low-power consumption shutdown mode. Shutdown may be enabled by driving the Shutdown pin to a logic low (GND). The LM4667 has fixed selectable gain of either 6dB or 12dB. The LM4667 has short circuit protection against a short from the outputs to VDD, GND, or across the outputs. j Efficiency at 3V, 100mW into 8Ω transducer 74% (typ) j Efficiency at 3V, 450mW into 8Ω transducer 84% (typ) j Efficiency at 5V, 1W into 8Ω transducer j Total quiescent power supply current 86% (typ) 3.5mA (typ) j Total shutdown power supply current 0.01µA (typ) j Single supply range 2.7V to 5.5V Features n n n n n n n n No output filter required for inductive transducers Selectable gain of 6dB or 12dB Very fast turn on time: 5ms (typ) Minimum external components "Click and pop" suppression circuitry Micro-power shutdown mode Short circuit protection Available in space-saving micro SMD and MSOP packages Applications n Mobile phones n PDAs n Portable electronic devices Typical Application 200405G5 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2004 National Semiconductor Corporation DS200405 www.national.com LM4667 Filterless High Efficiency 1.3W Switching Audio Amplifier September 2004 LM4667 Connection Diagrams 9 Bump micro SMD Package micro SMD Marking 200405C6 Top View X — Date Code T — Die Traceability G — Boomer Family B4– LM4667ITL 20040536 Top View Order Number LM4667ITL, LM4667ITLX See NS Package Number TLA09AAA Mini Small Outline (MSOP) Package MSOP Marking 200405H8 Top View G — Boomer Family A6 — LM4667MM 200405I4 Top View Order Number LM4667MM See NS Package Number MUB10A www.national.com 2 θJA (micro SMD) 220˚C/W If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. θJA (MSOP ) 190˚C/W θJC (MSOP) 56˚C/W Supply Voltage (Note1) Soldering Information 6.0V Storage Temperature See AN-1112 "microSMD Wafers Level Chip Scale Package." −65˚C to +150˚C Voltage at Any Input Pin VDD + 0.3V ≥ V ≥ GND - 0.3V Power Dissipation (Note 3) Internally Limited ESD Susceptibility (Note 4) 7.0kV ESD Susceptibility (Note 5) 250V Junction Temperature (TJ) 150˚C Operating Ratings (Note 2) Temperature Range TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ 85˚C 2.7V ≤ VDD ≤ 5.5V Supply Voltage Thermal Resistance Electrical Characteristics VDD = 5V (Notes 1, 2) The following specifications apply for VDD = 5V and RL = 15µH + 8Ω + 15µH unless otherwise specified. Limits apply for TA = 25˚C. LM4667 Symbol Parameter Conditions IDD Quiescent Power Supply Current VIN = 0V, No Load VIN = 0V, RL = 15µH + 8Ω + 15µH VSD = GND (Note 9) Typical Limit (Note 6) (Notes 7, 8) Units (Limits) 8 9 mA mA ISD Shutdown Current 0.01 µA VSDIH Shutdown Voltage Input High 1.2 V VSDIL Shutdown Voltage Input Low 1.1 V VGSIH Gain Select Input High 1.2 V VGSIL Gain Select Input Low 1.1 V AV Closed Loop Gain VGain Select = VDD 6 dB AV Closed Loop Gain VGain Select = GND 12 dB VOS Output Offset Voltage 10 mV TWU Wake-up Time 5 ms W Po Output Power THD = 2% (max), f = 1kHz 1.3 THD+N Total Harmonic Distortion+Noise PO = 100mWRMS; fIN = 1kHz 0.8 % 90 kΩ RIN PSRR Differential Input Resistance Power Supply Rejection Ratio VGain Select = VDD VGain Select = GND 60 kΩ VRipple = 100mVRMS sine wave Inputs terminated to GND 55 (f = 217Hz) dB VRipple = 100mVRMS sine wave POUT = 10mW,1kHz 65 (f = 217Hz) dB 41 dB CMRR Common Mode Rejection Ratio VRipple = 100mVRMS, fRipple = 217Hz SNR Signal to Noise Ratio PO = 1WRMS; A-Weighted Filter 83 dB eOUT Output Noise A-Weighted filter, Vin = 0V 200 µV 3 www.national.com LM4667 Absolute Maximum Ratings (Notes 1, 2) LM4667 Electrical Characteristics VDD = 3V (Notes 1, 2) The following specifications apply for VDD = 3V and RL = 15µH + 8Ω + 15µH unless otherwise specified. Limits apply for TA = 25˚C. LM4667 Symbol Parameter Conditions Typical Limit Units (Limits) (Note 6) (Notes 7, 8) IDD Quiescent Power Supply Current VIN = 0V, No Load VIN = 0V, RL = 15µH + 8Ω + 15µH 3.50 3.75 5.0 mA (max) VSD = GND (Note 9) µA (max) ISD Shutdown Current 0.01 2.0 VSDIH Shutdown Voltage Input High 1.0 1.4 V (min) VSDIL Shutdown Voltage Input Low 0.8 0.4 V (max) VGSIH Gain Select Input High 1.0 1.4 V (min) VGSIL Gain Select Input Low 0.8 0.4 V (max) AV Closed Loop Gain VGain Select = VDD 6 5.5 6.5 dB (min) dB (max) AV Closed Loop Gain VGain Select = GND 12 11.5 12.5 dB (min) dB (max) VOS Output Offset Voltage 10 25 mV (max) TWU Wake-up Time 5 Po Output Power THD = 1% (max); f = 1kHz 450 425 mW (min) THD+N Total Harmonic Distortion+Noise PO = 100mWRMS; fIN = 1kHz 0.35 % 90 kΩ RIN Differential Input Resistance VGain Select = VDD VGain Select ms = GND 60 kΩ Vripple = 100mVRMS sine wave Inputs terminated to GND 56 (f = 217Hz) dB VRipple = 100mVRMS sine wave POUT = 10mW,1kHz 65 (f = 217Hz) dB PSRR Power Supply Rejection Ratio CMRR Common Mode Rejection Ratio VRipple = 100mVRMS, fRipple = 217Hz 41 dB SNR Signal to Noise Ratio PO = 400mWRMS, A-Weighted Filter 83 dB eOUT Output Noise A-Weighted filter, Vin = 0V 125 µV 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 LM4667, TJMAX = 150˚C. The typical θJA is 220˚C/W for the microSMD package and 190˚C/W for the MSOP package. 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 the parametric norm. Note 7: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 9: Shutdown current is measured in a normal room environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. The Shutdown pin should be driven as close as possible to GND for minimal shutdown current and to VDD for the best THD performance in PLAY mode. See the Application Information section under SHUTDOWN FUNCTION for more information. External Components Description (Figure 1) Components Functional Description 1. 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. 2. CI Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. www.national.com 4 LM4667 Typical Performance Characteristics THD+N vs Frequency VDD = 3V, RL = 15µH + 8Ω + 15µH POUT = 100mW, 30kHz BW THD+N vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH POUT = 100mW, 30kHz BW 200405D5 200405D6 THD+N vs Power Out VDD = 5V, RL = 15µH + 8Ω + 15µH f = 1kHz, 22kHz BW THD+N vs Frequency VDD = 3V, RL = 15µH + 4Ω + 15µH POUT = 300mW, 30kHz BW 200405D7 200405D8 THD+N vs Power Out VDD = 3V, RL = 15µH + 8Ω + 15µH f = 1kHz, 22kHz BW THD+N vs Power Out VDD = 3V, RL = 15µH + 4Ω + 15µH f = 1kHz, 22kHz BW 200405D9 200405E0 5 www.national.com LM4667 Typical Performance Characteristics (Continued) CMRR vs Frequency VDD = 3V, RL = 15µH + 8Ω + 15µH VCM = 300mVRMS Sine Wave, 30kHz BW CMRR vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH VCM = 300mVRMS Sine Wave, 30kHz BW 200405E1 200405E2 PSRR vs Frequency VDD = 3V, RL = 15µH + 8Ω + 15µH VRipple = 100mVRMS Sine Wave, 22kHz BW PSRR vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH VRipple = 100mVRMS Sine Wave, 22kHz BW 200405E3 VDD 200405E4 Efficiency and Power Dissipation vs Output Power = 5V, RL = 15µH + 8Ω + 15µH, f = 1kHz, THD < 2% VDD 200405E5 www.national.com Efficiency and Power Dissipation vs Output Power = 3V, RL = 15µH + 8Ω + 15µH, f = 1kHz, THD < 1% 200405E6 6 VDD LM4667 Typical Performance Characteristics (Continued) Gain Select Threshold VDD = 3V Efficiency and Power Dissipation vs Output Power = 3V, RL = 15µH + 4Ω + 15µH, f = 1kHz, THD < 1% 200405E7 200405H6 Gain Select Threshold vs Supply Voltage RL = 15µH + 8Ω + 15µH Gain Select Threshold VDD = 5V 200405H1 200405H2 Output Power vs Supply Voltage RL = 15µH + 8Ω + 15µH, f = 1kHz Output Power vs Supply Voltage RL = 15µH + 4Ω + 15µH, f = 1kHz 200405F3 200405F4 7 www.national.com LM4667 Typical Performance Characteristics (Continued) Output Power vs Supply Voltage RL = 15µH + 16Ω + 15µH, f = 1kHz Shutdown Threshold VDD = 5V 200405F5 200405H4 Shutdown Threshold vs Supply Voltage RL = 15µH + 8Ω + 15µH Shutdown Threshold VDD = 3V 200405H3 200405H5 Supply Current vs Supply Voltage RL = 15µH + 8Ω + 15µH Supply Current vs Shutdown Voltage RL = 15µH + 8Ω + 15µH 200405H0 www.national.com 200405G0 8 GENERAL AMPLIFIER FUNCTION single input amplifiers. The common-mode rejection characteristic of the differential amplifier reduces sensitivity to ground offset related noise injection, especially important in high noise applications. The output signals generated by the LM4667 consist of two, BTL connected, output signals that pulse momentarily from near ground potential to VDD. The two outputs can pulse independently with the exception that they both may never pulse simultaneously as this would result in zero volts across the BTL load. The minimum width of each pulse is approximately 160ns. However, pulses on the same output can occur sequentially, in which case they are concatenated and appear as a single wider pulse to achieve an effective 100% duty cycle. This results in maximum audio output power for a given supply voltage and load impedance. The LM4667 can achieve much higher efficiencies than class AB amplifiers while maintaining acceptable THD performance. PCB LAYOUT CONSIDERATIONS As output power increases, interconnect resistance (PCB traces and wires) between the amplifier, load and power supply create a voltage drop. The voltage loss on the traces between the LM4667 and the load results is lower output power and decreased efficiency. Higher trace resistance between the supply and the LM4667 has the same effect as a poorly regulated supply, increase ripple on the supply line also reducing the peak output power. The effects of residual trace resistance increases as output current increases due to higher output power, decreased load impedance or both. To maintain the highest output voltage swing and corresponding peak output power, the PCB traces that connect the output pins to the load and the supply pins to the power supply should be as wide as possible to minimize trace resistance. The rising and falling edges are necessarily short in relation to the minimum pulse width (160ns), having approximately 2ns rise and fall times, typical, depending on parasitic output capacitance. The inductive nature of the transducer load can also result in overshoot on one or both edges, clamped by the parasitic diodes to GND and VDD in each case. From an EMI standpoint, this is an aggressive waveform that can radiate or conduct to other components in the system and cause interference. It is essential to keep the power and output traces short and well shielded if possible. Use of ground planes, beads, and micro-strip layout techniques are all useful in preventing unwanted interference. The short (160ns) drive pulses emitted at the LM4667 outputs means that good efficiency can be obtained with minimal load inductance. The typical transducer load on an audio amplifier is quite reactive (inductive). For this reason, the load can act as it’s own filter, so to speak. This "filter-less" switching amplifier/transducer load combination is much more attractive economically due to savings in board space and external component cost by eliminating the need for a filter. POWER DISSIPATION AND EFFICIENCY In general terms, efficiency is considered to be the ratio of useful work output divided by the total energy required to produce it with the difference being the power dissipated, typically, in the IC. The key here is “useful” work. For audio systems, the energy delivered in the audible bands is considered useful including the distortion products of the input signal. Sub-sonic (DC) and super-sonic components ( > 22kHz) are not useful. The difference between the power flowing from the power supply and the audio band power being transduced is dissipated in the LM4667 and in the transducer load. The amount of power dissipation in the LM4667 is very low. This is because the ON resistance of the switches used to form the output waveforms is typically less than 0.25Ω. This leaves only the transducer load as a potential "sink" for the small excess of input power over audio band output power. The LM4667 dissipates only a fraction of the excess power requiring no additional PCB area or copper plane to act as a heat sink. As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection ratio (PSRR). The capacitor (CS) location should be as close as possible to the LM4667. Typical applications employ a voltage regulator with a 10µF and a 0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing on the supply pin of the LM4667. A 1µF tantalum capacitor is recommended. DIFFERENTIAL AMPLIFIER EXPLANATION As logic supply voltages continue to shrink, designers are increasingly turning to differential analog signal handling to preserve signal to noise ratios with restricted voltage swing. The LM4667 is a fully differential amplifier that features differential input and output stages. A differential amplifier amplifies the difference between the two input signals. Traditional audio power amplifiers have typically offered only single-ended inputs resulting in a 6dB reduction in signal to noise ratio relative to differential inputs. The LM4667 also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The LM4667 can be used, however, as a single ended input amplifier while still retaining it’s fully differential benefits. In fact, completely unrelated signals may be placed on the input pins. The LM4667 simply amplifies the difference between the signals. A major benefit of a differential amplifier is the improved common mode rejection ratio (CMRR) over SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4667 contains shutdown circuitry that reduces current draw to less than 0.01µA. The trigger point for shutdown is shown as a typical value in the Electrical Characteristics Tables and in the Shutdown Hysteresis Voltage graphs found in the Typical Performance Characteristics section. It is best to switch between ground and supply for minimum current usage while in the shutdown state. While the LM4667 may be disabled with shutdown voltages in between ground and supply, the idle current will be greater than the typical 0.01µA value. Increased THD may also be observed with voltages less than VDD on the Shutdown pin when in PLAY mode. The LM4667 has an internal resistor connected between GND and Shutdown pins. The purpose of this resistor is to eliminate any unwanted state changes when the Shutdown pin is floating. The LM4667 will enter the shutdown state when the Shutdown pin is left floating or if not floating, when POWER SUPPLY BYPASSING 9 www.national.com LM4667 Application Information LM4667 Application Information manently connected to VDD or driven to a logic high level. For a differential gain of 12dB, the Gain Select pin should be permanently connected to GND or driven to a logic low level. The gain of the LM4667 can be switched while the amplifier is in PLAY mode driving a load with a signal without damage to the IC. The voltage on the Gain Select pin should be switched quickly between GND (logic low) and VDD (logic high) to eliminate any possible audible artifacts from appearing at the output. For typical threshold voltages for the Gain Select function, refer to the Gain Threshold Voltages graph in the Typical Performance Characteristics section. (Continued) the shutdown voltage has crossed the threshold. To minimize the supply current while in the shutdown state, the Shutdown pin should be driven to GND or left floating. If the Shutdown pin is not driven to GND, the amount of additional resistor current due to the internal shutdown resistor can be found by Equation (1) below. (VSD - GND) / 60kΩ (1) With only a 0.5V difference, an additional 8.3µA of current will be drawn while in the shutdown state. GAIN SELECTION FUNCTION The LM4667 has fixed selectable gain to minimize external components, increase flexibility and simplify design. For a differential gain of 6dB, the Gain Select pin should be per- www.national.com 10 LM4667 Application Information (Continued) SINGLE-ENDED CIRCUIT CONFIGURATIONS 200405C8 FIGURE 2. Single-Ended Input with low gain selection configuration 200405C9 FIGURE 3. Single-Ended Input with high gain selection configuration 11 www.national.com LM4667 Application Information (Continued) REFERENCE DESIGN BOARD SCHEMATIC 200405C7 FIGURE 4. In addition to the minimal parts required for the application circuit, a measurement filter is provided on the evaluation circuit board so that conventional audio measurements can be conveniently made without additional equipment. This is a balanced input / grounded differential output low pass filter with a 3dB frequency of approximately 35kHz and an on board termination resistor of 300Ω (see schematic). Note that the capacitive load elements are returned to ground. This is not optimal for common mode rejection purposes, but due to the independent pulse format at each output there is a significant amount of high frequency common mode component on the outputs. The grounded capacitive filter elements attenuate this component at the board to reduce the high frequency CMRR requirement placed on the analysis instruments. The commonly used Audio Precision analyzer is differential, but its ability to accurately reject fast pulses of 160nS width is questionable necessitating the on board measurement filter. When in doubt or when the signal needs to be singleended, use an audio signal transformer to convert the differential output to a single ended output. Depending on the audio transformer’s characteristics, there may be some attenuation of the audio signal which needs to be taken into account for correct measurement of performance. Measurements made at the output of the measurement filter suffer attenuation relative to the primary, unfiltered outputs even at audio frequencies. This is due to the resistance of the inductors interacting with the termination resistor (300Ω) and is typically about -0.35dB (4%). In other words, the voltage levels (and corresponding power levels) indicated through the measurement filter are slightly lower than those that actually occur at the load placed on the unfiltered outputs. This small loss in the filter for measurement gives a lower output power reading than what is really occurring on the unfiltered outputs and its load. Even with the grounded filter the audio signal is still differential, necessitating a differential input on any analysis instrument connected to it. Most lab instruments that feature BNC connectors on their inputs are NOT differential responding because the ring of the BNC is usually grounded. www.national.com 12 LM4667 Application Information (Continued) LM4667 micro SMD BOARD ARTWORK Composite View Silk Screen 200405G7 200405G6 Top Layer Bottom Layer 200405G8 200405D1 13 www.national.com LM4667 Application Information (Continued) LM4667 MSOP BOARD ARTWORK Composite View Silk Screen 200405I1 200405I2 Top Layer Bottom Layer 200405I3 www.national.com 200405I0 14 LM4667 Physical Dimensions inches (millimeters) unless otherwise noted 9 Bump micro SMD Order Number LM4667ITL, LM4667ITLX NS Package Number TLA09AAA X1 = 1.514 X2 = 1.514 X3 = 0.600 Mini Small Outline (MSOP) Order Number LM4667MM NS Package Number MUB10A 15 www.national.com LM4667 Filterless High Efficiency 1.3W Switching Audio 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. 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. 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