LM4670 Filterless High Efficiency 3W Switching Audio Amplifier General Description Key Specifications The LM4670 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 external component count, simplifies circuit design, and reduces board area. The LM4670 processes analog inputs with a deltasigma modulation technique that lowers output noise and THD when compared to conventional pulse width modulators. The LM4670 is designed to meet the demands of mobile phones and other portable communication devices. Operating on a single 5V supply, it is capable of driving a 4Ω speaker load at a continuous average output of 2.3W with less than 1% THD+N. Its flexible power supply requirements allow operation from 2.4V to 5.5V. The LM4670 has high efficiency with speaker loads compared to a typical Class AB amplifier. With a 3.6V supply driving an 8Ω speaker, the IC’s efficiency for a 100mW power level is 77%, reaching 88% at 600mW output power. The LM4670 features a low-power consumption shutdown mode. Shutdown may be enabled by driving the Shutdown pin to a logic low (GND). The gain of the LM4670 is externally configurable which allows independent gain control from multiple sources by summing the signals. j Efficiency at 3.6V, 100mW into 8Ω speaker 77% (typ) j Efficiency at 3.6V, 600mW into 8Ω speaker 88% (typ) j Efficiency at 5V, 1W into 8Ω speaker j Quiescent current, 3.6V supply 87% (typ) 4.8mA (typ) j Total shutdown power supply current 0.01µA (typ) j Single supply range 2.4V to 5.5V Features n n n n n n n n No output filter required for inductive loads Externally configurable gain Very fast turn on time: 1.35ms (typ) Minimum external components "Click and pop" suppression circuitry Micro-power shutdown mode Short circuit protection Available in space-saving microSMD and LLP packages Applications n Mobile phones n PDAs n Portable electronic devices Typical Application 20089901 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2006 National Semiconductor Corporation DS200899 www.national.com LM4670 Filterless High Efficiency 3W Switching Audio Amplifier July 2006 LM4670 Connection Diagrams 9 Bump micro SMD Package micro SMD Marking 200899C6 Top View X — Date Code T — Die Traceability G — Boomer Family E6 – LM4670ITL 20089936 Top View Order Number LM4670ITL, LM4670ITLX See NS Package Number TLA09ZZA Leadless Leadframe Package (LLP) LLP Marking 20089949 Top View Order Number LM4670SD See NS Package Number SDA08A Contact NSC Sales Office for Availability www.national.com 20089951 Top View Z — Plant Code XY — Date Code TT — Die Traceability L4670 — LM4670 2 θJA (micro SMD) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Soldering Information Supply Voltage (Note 1) θJA (LLP) 73˚C/W See AN-1112 "microSMD Wafers Level Chip Scale Package." 6.0V Storage Temperature 220˚C/W −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) 2.0kV ESD Susceptibility (Note 5) 200V Junction Temperature (TJMAX) Operating Ratings (Note 1) (Note 2) Temperature Range TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ 85˚C 2.4V ≤ VDD ≤ 5.5V Supply Voltage (Note 12) 150˚C Thermal Resistance Electrical Characteristics (Notes 1, 2) The following specifications apply for AV = 2V/V (RI = 150kΩ), RL = 15µH + 8Ω + 15µH unless otherwise specified. Limits apply for TA = 25˚C. LM4670 Symbol |VOS| Parameter Differential Output Offset Voltage Conditions Typical Limit (Note 6) (Notes 7, 8) VI = 0V, AV = 2V/V, VDD = 2.4V to 5.0V 25 Units (Limits) mV (max) VDD = 2.4V to 5.0V, Input Referred 64 dB CMRRGSM GSM Common Mode Rejection Ratio VDD = 2.4V to 5.0V VIC = VDD/2 to 0.5V, VIC = VDD/2 to VDD – 0.8V, Input Referred 80 dB |IIH| Logic High Input Current VDD = 5.0V, VI = 5.8V 20 100 |IIL| Logic Low Input Current VDD = 5.0V, VI = –0.3V 1 5 µA (max) VIN = 0V, No Load, VDD = 5.0V 7.0 10 mA (max) VIN = 0V, No Load, VDD = 3.6V 4.8 VIN = 0V, No Load, VDD = 2.4V 3.8 5 mA (max) VSHUTDOWN = 0V VDD = 2.4V to 5.0V 0.01 1 µA (max) 1.0 1.4 V (min) 0.8 0.4 V (max) 270kΩ/RI 330kΩ/RI V/V (min) V/V (max) PSRRGSM GSM Power Supply Rejection Ratio IDD Quiescent Power Supply Current ISD Shutdown Current (Note 9) VSDIH Shutdown voltage input high VSDIL Shutdown voltage input low ROSD Output Impedance AV Gain RSD Resistance from Shutdown Pin to GND PO Output Power (Notes 11,12) VSHUTDOWN = 0.4V mA > 100 300kΩ/RI µA (max) kΩ 300 kΩ RL = 15µH + 4Ω + 15µH, THD = 10% (max) f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V 3.0 1.5 675 W W mW RL = 15µH + 4Ω + 15µH, THD+N = 1% (max) f = 1kHz, 22kHz BW VDD = 5V, VDD = 3.6V, VDD = 2.5V, 2.3 1.2 550 W W mW 3 www.national.com LM4670 Absolute Maximum Ratings (Notes 1, 2) LM4670 Electrical Characteristics (Notes 1, 2) The following specifications apply for AV = 2V/V (RI = 150kΩ), RL = 15µH + 8Ω + 15µH unless otherwise specified. Limits apply for TA = 25˚C. (Continued) LM4670 Symbol PO THD+N PSRR SNR eOUT Parameter Output Power (Note 11) Conditions Typical Limit (Note 6) (Notes 7, 8) RL = 15µH + 8Ω + 15µH, THD = 10% (max) f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V 1.65 850 400 RL = 15µH + 8Ω + 15µH, THD+N = 1% (max) f = 1kHz, 22kHz BW VDD = 5V, VDD = 3.6V, VDD = 2.5V, 1.35 680 325 Units (Limits) W mW mW 600 W mW (min) mW VDD = 5V, PO = 1WRMS, f = 1kHz 0.35 % VDD = 3.6V, PO = 0.5WRMS, f = 1kHz 0.30 % VDD = 3.6V, PO = 0.5WRMS, f = 5kHz 0.30 % VDD = 3.6V, PO = 0.5WRMS, f = 10kHz 0.30 % VDD = 3.6V, VRipple = 200mVPP Sine, fRipple = 217Hz Inputs to AC GND, CI = 0.1µ, Input Referred 68 dB VDD = 3.6V, VRipple = 200mVPP Sine, fRipple = 1kHz Inputs to AC GND, CI = 0.1µF Input Referred 65 dB VDD = 3.6V, VRipple = 200mVPP Sine, fRipple = 217Hz fIN = 1kHz, PO = 10mWRMS Input Referred 62 dB Signal to Noise Ratio VDD = 5V, PO = 1WRMS 93 dB 85 µVRMS Output Noise VDD = 3.6V, f = 20Hz – 20kHz Inputs to AC GND, CI = 0.1µF No Weighting, Input Referred VDD = 3.6V, Inputs to AC GND CI = 0.1µF, A Weighted Input Referred 65 µVRMS 80 dB Total Harmonic Distortion + Noise Power Supply Rejection Ratio CMRR Common Mode Rejection Ratio VDD = 3.6V, VRipple = 1VPP Sine fRipple = 217Hz, Input Referred TWU Wake-up Time VDD = 3.6V 1.35 ms TSD Shutdown Time VDD = 3.6V 0.01 ms www.national.com 4 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 LM4670, TJMAX = 150˚C. The typical θJA is 220˚C/W for the microSMD package and 64˚C/W for the LLP 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. 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 board. Note 11: Typical output power numbers are for the LM4670 in the ITL (µSMD) package. In the LLP (SDA) package, the output power will be lower due to higher resistance seen from the IC output pad to PCB trace. The difference increases with lower impedance loads. Note 12: The maximum operating voltage for the LM4670 in the SDA (LLP) package when driving 4Ω loads to greater than 10% THD+N is 5.0V. 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. RI Gain setting resistor. Differential gain is set by the equation AV = 2 * 150kΩ / Ri(V/V). 5 www.national.com LM4670 Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. LM4670 Typical Performance Characteristics (Note 10) THD+N vs Frequency VDD = 3.6V, RL = 15µH + 4Ω + 15µH POUT = 750mW, 22kHz BW THD+N vs Frequency VDD = 2.5V, RL = 15µH + 4Ω + 15µH POUT = 375mW, 22kHz BW 20089941 20089943 THD+N vs Frequency VDD = 2.5V, RL = 15µH + 8Ω + 15µH POUT = 200mW, 22kHz BW THD+N vs Frequency VDD = 5V, RL = 15µH + 4Ω + 15µH POUT = 1.5W, 22kHz BW 20089945 20089942 THD+N vs Frequency VDD = 5V, RL = 15µH + 8Ω + 15µH POUT = 1W, 22kHz BW THD+N vs Frequency VDD = 3.6V, RL = 15µH + 8Ω + 15µH POUT = 500mW, 22kHz BW 20089944 www.national.com 20089946 6 (Note 10) THD+N vs Output Power RL = 15µH + 4Ω + 15µH f = 1kHz, 22kHz BW LM4670 Typical Performance Characteristics (Continued) THD+N vs Output Power RL = 15µH + 8Ω + 15µH f = 1kHz, 22kHz BW 20089947 20089948 PSRR vs Frequency VDD = 3.6V, RL = 15µH + 8Ω + 15µH VCM = 200mVP-P Sine Wave, 22kHz BW CMRR vs Frequency VDD = 3.6V, RL = 15µH + 8Ω + 15µH VCM = 1VP-P Sine Wave, 22kHz BW 20089910 20089940 Efficiency and Power Dissipation vs Output Power RL = 15µH + 8Ω + 15µH, f = 1kHz, THD < 1% Efficiency and Power Dissipation vs Output Power RL = 15µH + 4Ω + 15µH, f = 1kHz, THD < 2% 20089911 20089912 7 www.national.com LM4670 Typical Performance Characteristics (Note 10) Output Power vs Supply Voltage RL = 15µH + 4Ω + 15µH, f = 1kHz, 22kHz BW Output Power vs Supply Voltage RL = 15µH + 8Ω + 15µH, f = 1kHz, 22kHz BW 20089914 20089915 Supply Current (RMS) vs Output Power RL = 15µH + 8Ω + 15µH, f = 1kHz Supply Current (RMS) vs Output Power RL = 15µH + 4Ω + 15µH, f = 1kHz 20089919 20089920 Shutdwon Threshold vs Supply Voltage RL = 15µH + 8Ω + 15µH Shutdwon Threshold RL = 15µH + 8Ω + 15µH 20089918 www.national.com (Continued) 200899H5 8 (Note 10) Supply Current vs Shutdown Voltage RL = 15µH + 8Ω + 15µH LM4670 Typical Performance Characteristics (Continued) Supply Current vs Supply Voltage RL = 15µH + 8Ω + 15µH 20089938 20089922 Differential Gain vs Supply Voltage RL = 15µH + 8Ω + 15µH, Ri = 150kΩ, f = 1kHz Supply Current vs Supply Voltage RL = Different µH loads 20089939 20089913 9 www.national.com LM4670 Application Information 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 LM4670 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 350ns. 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 LM4670 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 LM4670 and the load results is lower output power and decreased efficiency. Higher trace resistance between the supply and the LM4670 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 use of power and ground planes will give the best THD+N performance. While reducing trace resistance, the use of power planes also creates parasite capacitors that help to filter the power supply line. The rising and falling edges are necessarily short in relation to the minimum pulse width (350ns), having approximately 16ns 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 LM4670 and the speaker 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 LM4670 may be needed to reduce EMI radiation. The value of the ferrite chip is very application specific. The short (350ns) drive pulses emitted at the LM4670 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 LM4670 and in the transducer load. The amount of power dissipation in the LM4670 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 LM4670 dissipates only a fraction of the excess power requiring no additional PCB area or copper plane to act as a heat sink. 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 LM4670 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 LM4670 also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The LM4670 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 LM4670 simply amplifies the difference between the signals. A major benefit of a differential amplifier is the improved common mode rejection ratio (CMRR) over www.national.com 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 LM4670. 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 LM4670. A 1µF tantalum capacitor is recommended. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4670 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 10 capacitor coupled to ground (See Figures 5 – 7). Setting the high-pass filter point above the power supply noise frequencies, 217Hz in a GSM phone, for example, will filter out this noise so it is not amplified and heard on the output. Capacitors with a tolerance of 10% or better are recommended for impedance matching. (Continued) current usage while in the shutdown state. While the LM4670 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. DIFFERENTIAL CIRCUIT CONFIGURATIONS The LM4670 can be used in many different circuit configurations. The simplest and best performing is the DC coupled, differential input configuration shown in Figure 2. Equation (2) above is used to determine the value of the Ri resistors for a desired gain. The LM4670 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 LM4670 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) / 300kΩ Input capacitors can be used in a differential configuration as shown in Figure 3. Equation (3) above is used to determine the value of the Ci capacitors for a desired frequency response due to the high-pass filter created by Ci and Ri. Equation (2) above is used to determine the value of the Ri resistors for a desired gain The LM4670 can be used to amplify more than one audio source. Figure 4 shows a dual differential input configuration. The gain for each input can be independently set for maximum design flexibility using the Ri resistors for each input and Equation (2). Input capacitors can be used with one or more sources as well to have different frequency responses depending on the source or if a DC voltage needs to be blocked from a source. (1) With only a 0.5V difference, an additional 1.7µA of current will be drawn while in the shutdown state. PROPER SELECTION OF EXTERNAL COMPONENTS The gain of the LM4670 is set by the external resistors, Ri in Figure 1, The Gain is given by Equation (2) below. Best THD+N performance is achieved with a gain of 2V/V (6dB). AV = 2 * 150 kΩ / Ri (V/V) SINGLE-ENDED CIRCUIT CONFIGURATIONS The LM4670 can also be used with single-ended sources but input capacitors will be needed to block any DC at the input terminals. Figure 5 shows the typical single-ended application configuration. The equations for Gain, Equation (2), and frequency response, Equation (3), hold for the single-ended configuration as shown in Figure 5. When using more than one single-ended source as shown in Figure 6, the impedance seen from each input terminal should be equal. To find the correct values for Ci3 and Ri3 connected to the +IN input pin the equivalent impedance of all the single-ended sources are calculated. The singleended sources are in parallel to each other. The equivalent capacitor and resistor, Ci3 and Ri3, are found by calculating the parallel combination of all Civalues and then all Ri values. Equations (4) and (5) below are for any number of single-ended sources. (2) It is recommended that resistors with 1% tolerance or better be used to set the gain of the LM4670. The Ri resistors should be placed close to the input pins of the LM4670. Keeping the input traces close to each other and of the same length in a high noise environment will aid in noise rejection due to the good CMRR of the LM4670. Noise coupled onto input traces which are physically close to each other will be common mode and easily rejected by the LM4670. Input capacitors may be needed for some applications or when the source is single-ended (see Figures 3, 5). Input capacitors are needed to block any DC voltage at the source so that the DC voltage seen between the input terminals of the LM4670 is 0V. Input capacitors create a high-pass filter with the input resistors, Ri. The –3dB point of the high-pass filter is found using Equation (3) below. fC = 1 / (2πRi Ci ) (Hz) Ci3 = Ci1 + Ci2 + Cin ... (F) (4) Ri3 = 1 / (1/Ri1 + 1/Ri2 + 1/Rin ...) (Ω) (5) (3) The LM4670 may also use a combination of single-ended and differential sources. A typical application with one singleended source and one differential source is shown in Figure 7. Using the principle of superposition, the external component values can be determined with the above equations corresponding to the configuration. The input capacitors may also be used to remove low audio frequencies. Small speakers cannot reproduce low bass frequencies so filtering may be desired . When the LM4670 is using a single-ended source, power supply noise on the ground is seen as an input signal by the +IN input pin that is 11 www.national.com LM4670 Application Information LM4670 Application Information (Continued) 20089903 FIGURE 2. Differential input configuration 20089904 FIGURE 3. Differential input configuration with input capacitors www.national.com 12 LM4670 Application Information (Continued) 20089905 FIGURE 4. Dual differential input configuration 20089906 FIGURE 5. Single-ended input configuration 13 www.national.com LM4670 Application Information (Continued) 20089907 FIGURE 6. Dual single-ended input configuration 20089908 FIGURE 7. Dual input with a single-ended input and a differential input www.national.com 14 LM4670 Application Information (Continued) REFERENCE DESIGN BOARD SCHEMATIC 20089909 FIGURE 8. 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 350ns width is questionable necessitating the on board measurement filter. When in doubt or when the signal needs to be single-ended, 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 -0.25dB (3%). 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. 15 www.national.com LM4670 Application Information (Continued) LM4670 micro SMD BOARD ARTWORK Composite View Silk Screen 20089935 20089932 Top Layer Internal Layer 1, GND 20089937 20089933 Internal Layer 2, VDD Bottom Layer 20089934 www.national.com 20089931 16 LM4670 Application Information (Continued) LM4670 SDA BOARD ARTWORK Composite View Silk Screen 20089956 20089953 Top Layer Internal Layer 1, GND 20089957 20089954 Internal Layer 2, VDD Bottom Layer 20089955 20089952 17 www.national.com LM4670 Revision History Rev Date Description 1.0 12/15/04 Initial WEB of the D/S (TL pkg). 1.1 7/06/05 Re-released D/S to the WEB (added the SD package). 1.2 7/13/06 Edited Note 9, then re-released D/S to the WEB. www.national.com 18 LM4670 Physical Dimensions inches (millimeters) unless otherwise noted 9 Bump micro SMD Order Number LM4670ITL, LM4670ITLX NS Package Number TLA09ZZA X1 = 1.463 X2 = 1.463 X3 = 0.600 LLP Order Number LM4670SD NS Package Number SDA08A 19 www.national.com LM4670 Filterless High Efficiency 3W Switching Audio Amplifier Notes 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. 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