LM4666 Filterless High Efficiency Stereo 1.2W Switching Audio Amplifier General Description Key Specifications The LM4666 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 LM4666 processes analog inputs with a delta-sigma modulation technique that lowers output noise and THD when compared to conventional pulse width modulators. The LM4666 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 2.8V to 5.5V. The LM4666 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 79%, reaching 84% at 450mW output power. The LM4666 features a low-power consumption shutdown mode. Shutdown may be enabled by driving the Shutdown pin to a logic low (GND). The LM4666 has fixed selectable gain of either 6dB or 12dB. The LM4666 has short circuit protection against a short from the outputs to VDD or GND. j Efficiency at 3V, 100mW into 8Ω transducer 79% (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 85% (typ) 7.0mA (typ) j Total shutdown power supply current 0.02µA (typ) j Single supply range 2.8V 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: 6ms (typ) Minimum external components "Click and pop" suppression circuitry Micro-power shutdown mode Short circuit protection Available in space-saving SDA package Applications n Mobile phones n PDAs n Portable electronic devices Typical Application 200558E6 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2004 National Semiconductor Corporation DS200558 www.national.com LM4666 Filterless High Efficiency Stereo 1.2W Switching Audio Amplifier May 2004 LM4666 Connection Diagrams SDA Package 200558I8 Top View Order Number LM4666SDA See NS Package Number SDA14A SDA Marking 200558I9 Top View Z — Plant Code XY — Date Code TT — Die Traceability L4666 — LM4666 www.national.com 2 Junction Temperature (TJ) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Thermal Resistance Supply Voltage (Note1) Soldering Information 6.0V Storage Temperature −65˚C to +150˚C Voltage at Any Input Pin θJA (SDA) 63˚C/W θJC (SDA) 12˚C/W See AN-1112 "microSMD Wafers Level Chip Scale Package." VDD + 0.3V ≥ V ≥ GND - 0.3V Power Dissipation (Note 3) 150˚C Internally Limited ESD Susceptibility, pins 4, 7, 11, 14 (Note 4) Operating Ratings (Notes 1, 2) 1kV Temperature Range ESD Susceptibility, all other pins (Note 4) 2.0kV ESD Susceptibility (Note 5) TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ 85˚C 2.8V ≤ VDD ≤ 5.5V Supply Voltage 200V 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. LM4666 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) 15 16 mA mA ISD Shutdown Current 0.02 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 6 ms 1.2 W % Po Output Power THD = 1% (max), f = 1kHz, 22kHz BW THD+N Total Harmonic Distortion+Noise PO = 100mWRMS/Channel, fIN = 1kHz, 22kHz BW, Both channels in phase 0.65 XTALK Channel Separation PO = 100mWRMS, f = 1kHz RIN PSRR Differential Input Resistance Power Supply Rejection Ratio 57 dB Select = VDD 90 kΩ Select = GND 60 kΩ VRipple = 100mVRMS sine wave, fRIPPLE = 217Hz Inputs terminated to AC GND 60 dB VRipple = 100mVRMS sine wave, fRIPPLE = 217Hz POUT = 10mW,1kHz 65 dB 48 dB VGain VGain CMRR Common Mode Rejection Ratio VRipple = 100mVRMS, fRipple = 217Hz, Input referred 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 LM4666 Absolute Maximum Ratings (Notes 1, 2) LM4666 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. LM4666 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 6.5 7.0 10 mA (max) VSD = GND (Note 9) µA (max) ISD Shutdown Current 0.02 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 5.25 6.75 dB (min) dB (max) AV Closed Loop Gain VGain Select = GND 12 11.25 12.75 dB (min) dB (max) VOS Output Offset Voltage 10 35 mV (max) TWU Wake-up Time 6 Po Output Power THD = 1% (max); f = 1kHz, 22kHz BW THD+N Total Harmonic Distortion+Noise PO = 100mWRMS/Channel, fIN = 1kHz, 22kHz BW, Both channels in phase 0.65 XTALK Channel Separation PO = 100mWRMS, f = 1kHz RIN PSRR Differential Input Resistance Power Supply Rejection Ratio 450 ms 400 mW (min) % 57 dB Select = VDD 90 kΩ Select = GND 60 kΩ Vripple = 100mVRMS sine wave, fRIPPLE = 217Hz, Inputs terminated to AC GND 60 dB VRipple = 100mVRMS sine wave, fRIPPLE = 217Hz, POUT = 10mW,1kHz 65 dB 48 dB VGain VGain CMRR Common Mode Rejection Ratio VRipple = 100mVRMS, fRipple = 217Hz, Input referred 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 LM4666, TJMAX = 150˚C. The typical θJA is 63˚C/W and the typical θJC is 12˚C/W for the SDA 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. Note 10: The performance graphs were taken using the Audio Precision AUX–0025 Switching Amplifier Measurement Filter in series with the LC filter on the demo board. www.national.com 4 LM4666 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. Typical Performance Characteristics (Note 10) THD+N vs Frequency VDD = 3V, RL = 15µH + 8Ω + 15µH POUT = 100mW/Channel, 30kHz BW THD+N vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH POUT = 100mW/Channel, 30kHz BW 20055827 20055826 THD+N vs Output Power/Channel VDD = 5V, RL = 15µH + 8Ω + 15µH f = 1kHz, 22kHz BW THD+N vs Frequency VDD = 3V, RL = 15µH + 4Ω + 15µH POUT = 100mW/Channel, 30kHz BW 20055825 20055830 5 www.national.com LM4666 Typical Performance Characteristics (Note 10) THD+N vs Output Power/Channel VDD = 3V, RL = 15µH + 4Ω + 15µH f = 1kHz, 22kHz BW (Continued) THD+N vs Output Power/Channel VDD = 3V, RL = 15µH + 8Ω + 15µH f = 1kHz, 22kHz BW 20055828 20055829 CMRR vs Frequency VDD = 3V, RL = 15µH + 8Ω + 15µH VCM = 100mVRMS Sine Wave, 30kHz BW CMRR vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH VCM = 100mVRMS Sine Wave, 30kHz BW 20055811 20055810 PSRR vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH VRipple = 100mVRMS Sine Wave, 22kHz BW PSRR vs Frequency VDD = 3V, RL = 15µH + 8Ω + 15µH VRipple = 100mVRMS Sine Wave, 22kHz BW 20055819 20055818 www.national.com 6 VDD (Note 10) Efficiency and Power Dissipation vs Output Power = 5V, RL = 15µH + 8Ω + 15µH, f = 1kHz, THD ≤ 1% VDD (Continued) Efficiency and Power Dissipation vs Output Power = 3V, RL = 15µH + 8Ω + 15µH, f = 1kHz, THD ≤ 1% 20055814 VDD 20055813 Gain Select Threshold VDD = 3V Efficiency and Power Dissipation vs Output Power = 3V, RL = 15µH + 4Ω + 15µH, f = 1kHz, THD ≤ 1% 200558H6 20055812 Gain Select Threshold vs Supply Voltage RL = 15µH + 8Ω + 15µH Gain Select Threshold VDD = 5V 200558H1 20055815 7 www.national.com LM4666 Typical Performance Characteristics LM4666 Typical Performance Characteristics (Note 10) Output Power/Channel vs Supply Voltage RL = 15µH + 8Ω + 15µH, f = 1kHz 22kHz BW (Continued) Output Power/Channel vs Supply Voltage RL = 15µH + 4Ω + 15µH, f = 1kHz 22kHz BW 20055816 20055817 Shutdown Threshold VDD = 3V Shutdown Threshold VDD = 5V 20055821 20055822 Supply Current vs Shutdown Voltage RL = 15µH + 8Ω + 15µH Shutdown Threshold vs Supply Voltage RL = 15µH + 8Ω + 15µH 20055820 www.national.com 20055823 8 (Note 10) LM4666 Typical Performance Characteristics (Continued) Supply Current vs Supply Voltage RL = 15µH + 8Ω + 15µH 20055824 9 www.national.com LM4666 Application Information GENERAL AMPLIFIER FUNCTION the improved common mode rejection ratio (CMRR) over 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 LM4666 consist of two, BTL connected, output signals that pulse momentarily from near ground potential to VDD on each channel. The two outputs on a given channel can pulse independently with the exception that they both may never pulse simultaneously as this would result in zero volts across the BTL connected 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 LM4666 can achieve much higher efficiencies than class AB amplifiers while maintaining acceptable THD performance. The short (160ns) drive pulses emitted at the LM4666 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. 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 LM4666 and the load results is lower output power and decreased efficiency. Higher trace resistance between the supply and the LM4666 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. As the distance from the LM4666 and the speakers increase the amount of EMI radiation will increase since the output wires or traces acting as antenna become more efficient with length. What is acceptable EMI is highly application specific. Ferrite chip inductors placed close to the LM4666 may be needed to reduce EMI radiation. The value of the ferrite chip is very application specific. 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 LM4666 and in the transducer load. The amount of power dissipation in the LM4666 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 LM4666 dissipates only a fraction of the excess power requiring no additional PCB area or copper plane to act as a heat sink. 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 (CS) location should be as close as possible to the LM4666. 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 LM4666. 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 LM4666 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 LM4666 also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The LM4666 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 LM4666 simply amplifies the difference between the signals. A major benefit of a differential amplifier is www.national.com SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4666 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 LM4666 may be disabled with shutdown voltages in between ground and supply, the idle current will be greater than the 10 With only a 0.5V difference, an additional 8.3µA of current will be drawn while in the shutdown state. (Continued) typical value. Increased THD may also be observed with voltages less than VDD on the Shutdown pin when in PLAY mode. GAIN SELECTION FUNCTION The LM4666 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 permanently 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 LM4666 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. The LM4666 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 LM4666 will enter the shutdown state when the Shutdown pin is left floating or if not floating, when 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) 11 www.national.com LM4666 Application Information LM4666 Application Information (Continued) CIRCUIT CONFIGURATIONS 20055803 FIGURE 2. Single-Ended input with low gain selection configuration 20055802 FIGURE 3. Differential input with low gain selection configuration www.national.com 12 LM4666 Application Information (Continued) REFERENCE DESIGN BOARD SCHEMATIC 20055801 FIGURE 4. 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. 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. 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. The AUX-0025 Switching Amplifier Measurement Filter from Audio Precision may be used instead of the on board measurement filter. The AUX-0025 filter should be connected to the high current direct outputs on the evaluation board and in series with the measurement equipment. Attaching oscilloscope probes on the outputs of the AUX-0025 filter will display the audio waveforms. The AUX-0025 filter may also be connected to the on board filter without any adverse effects. 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 the signal needs to be single-ended, use an audio 13 www.national.com LM4666 Application Information (Continued) LM4666 SDA BOARD ARTWORK Composite View Silk Screen 20055808 20055805 Top Layer Internal Layer 1, GND 20055809 20055806 Internal Layer 2, VDD Bottom Layer 20055807 www.national.com 20055804 14 inches (millimeters) unless otherwise noted LLP Package Order NumberLM4666SD NS Package Number SDA14A 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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