LME49724 High Performance, High Fidelity, Fully-Differential Audio Operational Amplifier RL = 600Ω General Description The LME49724 is an ultra-low distortion, low noise, high slew rate fully-differential operational amplifier optimized and fully specified for high performance, high fidelity applications. Combining advanced leading-edge process technology with state of the art circuit design, the LME49724 fully-differential audio operational amplifier delivers superior audio signal amplification for outstanding audio performance. The LME49724 combines extremely low voltage noise density (2.1nV/√Hz) with vanishingly low THD+N (0.00003%) to easily satisfy the most demanding audio applications. To ensure that the most challenging loads are driven without compromise, the LME49724 has a high slew rate of ±18V/μs and an output current capability of ±80mA. Further, dynamic range is maximized by an output stage that drives 600Ω loads to 52VP-P while operating on a ±15V supply voltage. The LME49724's outstanding CMRR (102dB), PSRR (125dB), and VOS (0.2mV) results in excellent operational amplifier DC performance. The LME49724 has a wide supply range of ±2.5V to ±18V. Over this supply range the LME49724’s input circuitry maintains excellent common-mode and power supply rejection, as well as maintaining its low input bias current. The LME49724 is unity gain stable. This Fully-Differential Audio Operational Amplifier achieves outstanding AC performance while driving complex loads with capacitive values as high as 100pF. Key Specifications ■ Power Supply Voltage Range ±2.5V to ±18V ■ THD+N (AV = 1, VOUT = 3VRMS, fIN = 1kHz) RL = 2kΩ © 2008 National Semiconductor Corporation ■ Input Noise Density ■ Slew Rate 0.00003% (typ) 2.1nV/√Hz (typ) ±18V/μs (typ) ■ Gain Bandwidth Product 50MHz (typ) ■ Open Loop Gain (RL = 600Ω) 125dB (typ) ■ Input Bias Current 60nA (typ) ■ Input Offset Voltage 0.2mV (typ) ■ DC Gain Linearity Error 0.000009% Features ■ ■ ■ ■ ■ Drives 600Ω loads with full output signal swing Optimized for superior audio signal fidelity Output short circuit protection PSRR and CMRR exceed 100dB (typ) Available in PSOP package Applications ■ ■ ■ ■ ■ ■ ■ ■ Ultra high quality audio amplification High fidelity preamplifiers and active filters Simple single-ended to differential conversion State of the art D-to-A converters State of the art A-to-D input amplifiers Professional Audio High fidelity equalization and crossover networks High performance line drivers and receivers 0.00003% (typ) 300442 www.national.com LME49724 High Performance, High Fidelity, Fully-Differential Audio Operational Amplifier November 12, 2008 LME49724 Typical Application 300442w9 FIGURE 1. Typical Application Circuit Connection Diagrams PSOP Marking 300442r6 Top View XY — Date Code TT — Die Traceability L49724 — LME49724 MR — Package Code 300442r4 Order Number LME49724MR See NS Package Number MRA08B Ordering Information Order Number Package Package DWG # LME49724MR 8 lead PSOP MRA08B www.national.com Transport Media 2 MSL Level Green Status Features Pin Name 1 VIN- 2 VOCM 3 VCC Pin Function Type Input pin Analog Input Sets the output DC voltage. Internally set by a resistor divider to the midpoint of the voltages on the VCC and VEE pins. Can be forced Analog Input externally to a different voltage (50kΩ input impedance). Positive power supply pin. Power Supply Analog Output 4 VOUT+ Output pin. Signal is inverted relative to VIN- where the feedback loop is connected. 5 VOUT- Output pin. Signal is inverted relative to VIN+ where the feedback loop is connected. Analog Output 6 VEE Negative power supply pin or ground for a single supply configuration. Power Supply Enables the LME49724 when the voltage is greater than 2.35V above the voltage on the VEE pin. Disable the LME49724 by connecting to the same voltage as on the VEE pin which will reduce current consumption to less than 0.3mA (typ). Analog Input Input pin Analog Input 7 ENABLE 8 VIN+ Exposed Pad Exposed pad for improved thermal performance. Connect to the same potential as the VEE pin or electrically isolate. 3 www.national.com LME49724 Pin Descriptions LME49724 Junction Temperature (TJMAX) Soldering Information Vapor Phase (60sec.) Infrared (60sec.) Thermal Resistance Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Power Supply Voltage (VS = VCC + |VEE |) Storage Temperature Input Voltage Output Short Circuit Power Dissipation (Note 3) ESD Rating (Note 4) ESD Rating (Note 5) (Notes 1, 2) 215°C 220°C θJA (MR) 38V −65°C to 150°C (VEE) – 0.7V to (VCC) + 0.7V Continuous Internally Limited 2000V 200V Electrical Characteristics 150°C 49.6°C/W Operating Ratings (Notes 1, 2) Temperature Range TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ +85°C ±2.5V ≤ VS ≤ ±18V Supply Voltage Range The following specifications apply for VS = ±15V, RL = 2kΩ, fIN = 1kHz, and TA = 25°C, unless otherwise specified. LME49724 Symbol Parameter Conditions Typical Limit (Note 6) (Note 7) Units (Limits) POWER SUPPLY VS ±2.5V ±18V V (min) V (max) 10 0.3 15 0.5 mA (max) mA (max) 125 95 dB (min) Operating Power Supply ICCQ Total Quiescent Current VO = 0V, IO = 0mA Enable = GND Enable = VEE PSRR Power Supply Rejection Ratio VS = ±5V to ±15V (Note 8) VENIH Enable High Input Voltage Device active, TA = 25°C (Note 9) VEE + 2.35 V VENIL Enable Low Input Voltage Device disabled, TA = 25°C (Note 9) VEE + 1.75 V DYNAMIC PERFORMANCE AV = 1, VOUT = 3VRMS THD+N Total Harmonic Distortion + Noise RL = 2kΩ 0.00003 0.00003 RL = 600Ω IMD Intermodulation Distortion GBWP Gain Bandwidth Product AV = 1, VOUT = 3VRMS Two-tone, 60Hz & 7kHz 4:1 0.00009 0.0005 50 % % (max) % 35 MHz (min) FPBW Full Power Bandwidth VOUT = 1VP-P, –3dB referenced to output magnitude at f = 1kHz SR Sew Rate RL = 2kΩ ±18 Settling time AV = –1, 10V step, CL = 100pF settling time to 0.1% 0.2 –10V < VOUT < 10V, RL = 600Ω 125 –10V < VOUT < 10V, RL = 2kΩ 125 dB –10V < VOUT < 10V, RL = 10kΩ 125 dB Equivalent Input Noise Voltage fBW = 20Hz to 20kHz 0.30 Equivalent Input Noise Density f = 1kHz f = 10Hz 2.1 3.7 tS AVOL Open-Loop Voltage Gain 13 MHz ±13 V/μs (min) μs 100 dB (min) NOISE eN 0.64 μVRMS (max) nV/√Hz (max) INPUT CHARACTERISTICS VOS Offset Voltage ±0.2 ΔVOS/ΔTemp Average Input Offset Voltage Drift vs –40°C ≤ TA ≤ 85°C Temperature 0.5 www.national.com 4 ±1 mV (max) μV/°C Symbol Parameter Conditions Typical Limit Units (Limits) (Note 6) (Note 7) IB Input Bias Current VCM = 0V 60 200 nA (max) IOS Input Offset Current VCM = 0V 10 65 nA (max) ΔIOS/ΔTemp Input Bias Current Drift vs Temperature –40°C ≤ TA ≤ 85°C 0.1 VIN-CM Common-Mode Input Voltage Range CMRR Common-Mode Rejection ZIN –10V < VCM < 10V Differential Input Impedance Common-Mode Input Impedance nA/°C ±14 VCC – 1.5 VEE + 1.5 V (min) V (min) 102 95 dB (min) 16 kΩ –10V < VCM < 10V 500 MΩ RL = 600Ω 52 RL = 2kΩ 52 VP-P RL = 10kΩ 53 VP-P 80 mA OUTPUT CHARACTERISTICS VOUTMAX Maximum Output Voltage Swing VP-P (min) 50 IOUT-CC Instantaneous Short Circuit Current ROUT Output Impedance fIN = 10kHz Closed-Loop Open-Loop 0.01 23 Ω Ω CLOAD Capacitive Load Drive Overshoot CL = 100pF 5 % Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. Note 3: 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. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. Note 8: PSRR is measured as follows: VOS is measured at two supply voltages, ±5V and ±15V. PSRR = | 20log(ΔVOS/ΔVS) |. Note 9: The ENABLE threshold voltage is determined by VBE voltages and will therefore vary with temperature. The typical values represent the most likely parametric norms at TA = +25°C. 5 www.national.com LME49724 LME49724 LME49724 Typical Performance Characteristics THD+N vs Frequency VS = ±2.5V, VO = 0.5VRMS, Differential Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW THD+N vs Frequency VS = ±2.5V, VO = 0.8VRMS, Differential Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW 300442s3 300442s4 THD+N vs Frequency VS = ±15V, VO = 3VRMS, Differential Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW THD+N vs Frequency VS = ±15V, VO = 10VRMS, Differential Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW 300442s5 300442s6 THD+N vs Frequency VS = ±18V, VO = 3VRMS, Differential Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW THD+N vs Frequency VS = ±18V, VO = 10VRMS, Differential Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW 300442s7 www.national.com 300442s8 6 THD+N vs Output Voltage VS = ±15V, RL = 600Ω, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442t1 300442t4 THD+N vs Output Voltage VS = ±18V, RL = 600Ω, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±2.5V, RL = 2kΩ, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442t7 300442s9 THD+N vs Output Voltage VS = ±15V, RL = 2kΩ, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±18V, RL = 2kΩ, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442t2 300442t5 7 www.national.com LME49724 THD+N vs Output Voltage VS = ±2.5V, RL = 600Ω, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW LME49724 THD+N vs Output Voltage VS = ±2.5V, RL = 10kΩ, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±15V, RL = 10kΩ, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442t0 300442t3 THD+N vs Output Voltage VS = ±18V, RL = 10kΩ, Differential Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Frequency VS = ±2.5V, VO = 0.5VRMS, Single-ended Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW 300442u8 300442t6 THD+N vs Frequency VS = ±15V, VO = 3VRMS, Single-ended Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW THD+N vs Frequency VS = ±2.5V, VO = 0.8VRMS, Single-ended Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW 300442u9 www.national.com 300442v0 8 THD+N vs Frequency VS = ±18V, VO = 3VRMS, Single-ended Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW 300442v1 300442v2 THD+N vs Frequency VS = ±18V, VO = 5VRMS, Single-ended Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW THD+N vs Output Voltage VS = ±2.5V, RL = 600Ω, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442v3 300442v6 THD+N vs Output Voltage VS = ±15V, RL = 600Ω, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±18V, RL = 600Ω, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442v9 300442w2 9 www.national.com LME49724 THD+N vs Frequency VS = ±15V, VO = 5VRMS, Single-ended Input RL = 600Ω, 2kΩ, 10kΩ, 80kHz BW LME49724 THD+N vs Output Voltage VS = ±2.5V, RL = 2kΩ, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±15V, RL = 2kΩ, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442v4 300442v7 THD+N vs Output Voltage VS = ±18V, RL = 2kΩ, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±2.5V, RL = 10kΩ, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442w0 300442v5 THD+N vs Output Voltage VS = ±15V, RL = 10kΩ, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW THD+N vs Output Voltage VS = ±18V, RL = 10kΩ, Single-ended Input f = 20Hz, 1kHz, 20kHz, 80kHz BW 300442v8 www.national.com 300442w1 10 LME49724 PSRR vs Frequency VS = ±2.5V, RL = 600Ω, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW PSRR vs Frequency VS = ±15V, RL = 600Ω, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW 300442u0 300442u3 PSRR vs Frequency VS = ±18V, RL = 600Ω, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW PSRR vs Frequency VS = ±2.5V, RL = 2kΩ, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW 300442u6 300442t8 PSRR vs Frequency VS = ±18V, RL = 2kΩ, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW PSRR vs Frequency VS = ±15V, RL = 2kΩ, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW 300442u1 300442u4 11 www.national.com LME49724 PSRR vs Frequency VS = ±2.5V, RL = 10kΩ, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW PSRR vs Frequency VS = ±15V, RL = 10kΩ, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW 300442t9 300442u2 PSRR vs Frequency VS = ±18V, RL = 10kΩ, Inputs to GND VRIPPLE = 200mVP-P, 80kHz BW CMRR vs Frequency VS = ±2.5V, VCMRR = 1VP-P RL = 600Ω, 2kΩ, 10kΩ 300442u5 300442y0 CMRR vs Frequency VS = ±18V, VCMRR = 1VP-P RL = 600Ω, 2kΩ, 10kΩ CMRR vs Frequency VS = ±15V, VCMRR = 1VP-P RL = 600Ω, 2kΩ, 10kΩ 300442x8 www.national.com 300442x9 12 LME49724 Output Voltage vs Load Resistance VS = ±2.5V, RL = 500Ω – 10kΩ THD+N ≤ 1%, 80kHz BW Output Voltage vs Load Resistance VS = ±15V, RL = 500Ω – 10kΩ THD+N ≤ 1%, 80kHz BW 300442w3 300442w4 Output Voltage vs Load Resistance VS = ±18V, RL = 500Ω – 10kΩ THD+N ≤ 1%, 80kHz BW Output Voltage vs Supply Voltage RL = 600Ω, 2kΩ, 10kΩ, THD+N ≤ 1% 80kHz BW 300442w6 300442w5 Supply Current vs Supply Voltage VIN = 0V, RL = No Load 300442u7 13 www.national.com LME49724 Application Information supply, drive the ENABLE pin to ground for standby mode and to VCC for active mode. GENERAL OPERATION The LME49724 is a fully differential amplifier with an integrated common-mode reference input (VOCM). Fully differential amplification provides increased noise immunity, high dynamic range, and reduced harmonic distortion products. Differential amplifiers typically have high CMRR providing improved immunity from noise. When input, output, and supply line trace pairs are routed together, noise pick up is common and easily rejected by the LME49724. CMRR performance is directly proportional to the tolerance and matching of the gain configuring resistors. With 0.1% tolerance resistors the worst case CMRR performance will be about 60dB (20LOG (0.001)). A differential output has a higher dynamic range than a singleended output because of the doubling of output voltage. The dynamic range is increased by 6dB as a result of the outputs being equal in magnitude but opposite in phase. As an example, a single-ended output with a 1VPP signal will be two 1VPP signals with a differential output. The increase is 20LOG (2) = 6dB. Differential amplifiers are ideal for low voltage applications because of the increase in signal amplitude relative to a single-ended amplifier and the resulting improvement in SNR. Differential amplifiers can also have reduced even order harmonics, all conditions equal, when compared to a singleended amplifier. The differential output causes even harmonics to cancel between the two inverted outputs leaving only the odd harmonics. In practice even harmonics do not cancel completely, however there still is a reduction in total harmonic distortion. FULLY DIFFERENTIAL OPERATION The LME49724 performs best in a fully differential configuration. The circuit shown in Figure 2 is the typical fully differential configuration. 300442r9 FIGURE 2. Fully Differential Configuration The closed-loop gain is shown in Equation 1 below. AV = RF / Ri OUTPUT COMMON-MODE VOLTAGE (VOCM pin) The output common-mode voltage is the DC voltage on each output. The output common-mode voltage is set by the VOCM pin. The VOCM pin can be driven by a low impedance source. If no voltage is applied to the VOCM pin, the DC common-mode output voltage will be set by the internal resistor divider to the midpoint of the voltages on the VCC and VEE pins. The input impedance of the VOCM pin is 50kΩ. The VOCM pin can be driven up to VCC - 1.5V and VEE + 1.5V. The VOCM pin should be bypassed to ground with a 0.1μF to 1μF capacitor. The VOCM pin should be connected to ground when the desired output common-mode voltage is ground reference. The value of the external capacitor has an effect on the PSRR performance of the LME49724. With the VOCM pin only bypassed with a low value capacitor, the PSRR performance of the LME49724 will be reduced, especially at low audio frequencies. For best PSRR performance, the VOCM pin should be connected to stable, clean reference. Increasing the value of the bypass capacitor on the VOCM pin will also improve PSRR performance. (1) SINGLE-ENDED TO DIFFERENTIAL CONVERSION For many applications, it is required to convert a single-ended signal to a differential signal. The LME49724 can be used for a high performance, simple single-to-differential converter. Figure 3 shows the typical single-to-differential converter circuit configuration. ENABLE FUNCTION The LME49724 can be placed into standby mode to reduce system current consumption by driving the ENABLE pin below VEE + 1.75V. The LME49724 is active when the voltage on the ENABLE pin is above VEE + 2.35V. The ENABLE pin should not be left floating. For best performance under all conditions, drive the ENABLE pin to the VEE pin voltage to enter standby mode and to ground for active operation when operating from split supplies. When operating from a single www.national.com (V/V) Where RF1 = RF2, Ri1 = Ri2. Using low value resistors will give the lowest noise performance. 300442s0 FIGURE 3. Single-Ended Input to Differential Output 14 SUPPLY BYPASSING The LME49724 should have its supply leads bypassed with low-inductance capacitors such as leadless surface mount (SMT) capacitors located as close as possible to the supply pins. It is recommended that a 10μF tantalum or electrolytic capacitor be placed in parallel with a 0.1μF ceramic or film type capacitor on each supply pin. These capacitors should be star routed with a dedicated ground return plane or large trace for best THD performance. Placing capacitors too far from the power supply pins, especially with thin connecting traces, can lead to excessive inductance, resulting in degraded high-frequency bypassing. Poor high-frequency bypassing can result in circuit instabilities. When using high bandwidth power supplies, the value and number of supply bypass capacitors should be reduced for optimal power supply performance. BALANCE CABLE DRIVER With high peak-to-peak differential output voltage and plenty of low distortion drive current, the LME49724 makes an excellent balanced cable driver. Combining the single-to-differential configuration with a balanced cable driver results in a high performance single-ended input to balanced line driver solution. Although the LME49724 can drive capacitive loads up to 100pF, cable loads exceeding 100pF can cause instability. For such applications, series resistors are needed on the outputs before the capacitive load. 300442s1 FIGURE 4. Single Supply Configuration ANALOG-TO-DIGITAL CONVERTER (ADC) APPLICATION Figure 5 is a typical fully differential application circuit for driving an analog-to-digital converter (ADC). The additional components of R5, R6, and C7 are optional components and are for stability and proper ADC sampling. ADC's commonly use switched capacitor circuitry at the input. When the ADC samples the signal the current momentarily increases and may disturb the signal integrity at the sample point causing a signal glitch. Component C7 is significantly larger than the input capacitance of a typical ADC and acts as a charge reservoir greatly reducing the effect of the signal sample by the ADC. Resistors R5 and R6 decouple the capacitive load, C7, for stability. The values shown are general values. Specific values should be optimized for the particular ADC loading requirements. The output reference voltage from the ADC can be used to drive the VOCM pin to set the common-mode DC voltage on the outputs of the LME49724. A buffer may be needed to drive the LME49724's VOCM pin if the ADC cannot drive the 50kΩ input impedance of the VOCM pin. In order to minimize circuit distortion when using capacitors in the signal path, the capacitors should be comprised of either NPO ceramic, polystyrene, polypropylene or mica composition. Other types of capacitors may provide a reduced distortion performance but for a cost improvement, so capacitor selection is dependent upon design requirements. The performance/cost tradeoff for a specific application is left up to the user. DRIVING A CAPACITIVE LOAD The LME49724 is a high speed op amp with excellent phase margin and stability. Capacitive loads up to 100pF will cause little change in the phase characteristics of the amplifiers and are therefore allowable. Capacitive loads greater than 100pF must be isolated from the output. The most straightforward way to do this is to put a resistor in series with the output. This resistor will also prevent excess power dissipation if the output is accidentally shorted. THERMAL PCB DESIGN The LME49724's high operating supply voltage along with its high output current capability can result in significant power dissipation. For this reason the LME49724 is provided in the exposed DAP MSOP (PSOP) package for improved thermal dissipation performance compared to other surface mount packages. The exposed pad is designed to be soldered to a copper plane on the PCB which then acts as a heat sink. The thermal plane can be on any layer by using multiple thermal vias under and outside the IC package. The vias under the IC should have solder mask openings for the entire pad under the IC on the top layer but cover the vias on the bottom layer. This method prevents solder from being pulled away from the thermal vias during the reflow process resulting in optimum thermal conductivity. Heat radiation from the PCB plane area is best accomplished when the thermal plane is on the top or bottom copper layers. The LME49724 should always be soldered down to a copper 15 www.national.com LME49724 pad on the PCB for both optimum thermal performance as well as mechanical stability. The exposed pad is for heat transfer and the thermal plane should either be electrically isolated or connected to the same potential as the VEE pin. For high frequency applications (f > 1MHz) or lower impedance loads, the pad should be connected to a plane that is connected to the VEE potential. SINGLE SUPPLY OPERATION The LME49724 can be operated from a single power supply, as shown in Figure 4. The supply voltage range is limited to a minimum of 5V and a maximum of 36V. The common-mode output DC voltage will be set to the midpoint of the supply voltage. The VOCM pin can be used to adjust the commonmode output DC voltage on the outputs, as described previously, if the supply voltage midpoint is not the desired DC voltage. LME49724 300442x7 * Value is application and converted dependent. FIGURE 5. Typical Analog-to-Digital Converter Circuit tered, the feedback available to correct distortion errors is reduced, which means that measurement resolution increases. To ensure minimum effects on distortion measurements, keep the value of R5 low. The distortion reading on the audio analyzer must be divided by a factor of (R3 + R4)/R5, where R1 = R2 and R3 = R4, to get the actual measured distortion of the device under test. The values used for the LME49724 measurements were R1, R2, R3, R4 = 1kΩ and R5 = 20Ω. This technique is verified by duplicating the measurements with high closed-loop gain and/or making the measurements at high frequencies. Doing so produces distortion components that are within the measurement equipment’s capabilities. DISTORTION MEASUREMENTS The vanishing low residual distortion produced by the LME49724 is below the capabilities of commercially available equipment. This makes distortion measurements more difficult than simply connecting a distortion meter to the amplifier’s inputs and outputs. The solution, however, is quite simple: an additional resistor. Adding this resistor extends the resolution of the distortion measurement equipment. The LME49724’s low residual distortion is an input referred internal error. As shown in Figure 6, adding a resistor connected between the amplifier’s inputs changes the amplifier’s noise gain. The result is that the error signal (distortion) is increased. Although the amplifier’s closed-loop gain is unal- www.national.com 16 LME49724 300442r5 FIGURE 6. THD+N and IMD Distortion Test Circuit PERFORMANCE VARIATIONS The LME49724 has excellent performance with little variation across different supply voltages, load impedances, and input configuration (single-ended or differential). Inspection of the THD+N vs Frequency and THD+N vs Output Voltage performance graphs reveals only minimal differences with different load values. Figures 7 and 8 below show the performance across different supply voltages with the same output signal level and load. Figure 7 has plots at ±5V, ±12V, ±15V, and ±18V with a 3VRMS output while Figure 8 has plots at ±12V, ±15V, and ±18V with a 10VRMS output. Both figures use a 600Ω load. The performance for each different supply voltage under the same conditions is so similar it is nearly impossible to discern the different plots lines. 300442x4 FIGURE 8. THD+N vs FREQUENCY with RL = 600Ω VOUT = 10VRMS, Differential Input, 80kHz BW VS = ±12V, ±15V, and ±18V Whether the input configuration is single-ended or differential has only a minimal affect on THD+N performance at higher audio frequencies or higher signal levels. For easy comparison, Figures 9 and 10 are a combination of the performance graphs found in the Typical Performance Characteristics section above. 300442x5 FIGURE 7. THD+N vs FREQUENCY with RL = 600Ω VOUT = 3VRMS, Differential Input, 80kHz BW VS = ±5V, ±12V, ±15V, and ±18V 17 www.national.com LME49724 VS = ±2.5V, ±15V, and ±18V, 80kHz BW 300442x3 FIGURE 9. THD+N vs FREQUENCY with RL = 10kΩ VOUT = 3VRMS, VS = ±15V, 80kHz BW Single-ended and Differential Input 300442x0 FIGURE 12. PSRR vs FREQUENCY with VS = ±15V RL = 600Ω, 2kΩ, and 10kΩ, 80kHz BW Although supply current may not be a critical specification for many applications, there is also no real variation in supply current with no load or with a 600Ω load. This is a result of the extremely low offset voltage, typically less than 1mV. Figure 13 shows the supply current under the two conditions with no real difference discernable. 300442x6 FIGURE 10. THD+N vs OUTPUT VOLTAGE with RL = 10kΩ f = 20Hz, 1kHz, 20kHz, VS = ±15V, 80kHz BW Single-ended and Differential Input Power Supply Rejection Ratio does not vary with load value nor supply voltage. For easy comparison, Figures 11 and 12 below are created by combining performance graphs found in the Typical Performance Characteristics section above. 300442x2 FIGURE 13. Supply Current vs Supply Voltage RL = No Load and 600Ω 300442x1 FIGURE 11. PSRR vs FREQUENCY with RL = 600Ω www.national.com 18 LME49724 Demo Board Schematic 300442w8 FIGURE 14. Demonstration Board Circuit 19 www.national.com LME49724 Build of Materials TABLE 1. Reference Demo Board Bill of Materials Designator Value Tolerance Part Description R1, R2, R3, R4 1kΩ 1% 1/8W, 0603 Resistor R5, R6 40.2Ω 1% 1/8W, 0603 Resistor C1, C2 1000pF 10% 0603, NPO Ceramic Capacitor, 50V C3, C4, C8, C9 0.1μF –20%, +80% 0603, Y5V Ceramic Capacitor, 25V C5, C6 10μF 20% Size C (6032), Tantalum Capacitor, 25V C7 2700pF 10% 0805, NPO Ceramic Capacitor, 50V Comment U1 LME49724MR J1, J2, J3, J4 SMA coaxial connector J5 0.100" 1x3 header, vertical mount VDD, VEE, GND 0.100" 1x2 header, vertical mount Inputs, Outputs, VOCM, Enable J6, J7, J8, J9, J10, J11 www.national.com 20 Inputs & Outputs LME49724 Revision History Rev Date 1.0 11/12/08 Description Initial release. 21 www.national.com LME49724 Physical Dimensions inches (millimeters) unless otherwise noted 8 – Lead PSOP Package Order Number LME49724MR NS Package Number MRA08B www.national.com 22 LME49724 Notes 23 www.national.com LME49724 High Performance, High Fidelity, Fully-Differential Audio Operational Amplifier Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage Reference www.national.com/vref Design Made Easy www.national.com/easy PowerWise® Solutions www.national.com/powerwise Solutions www.national.com/solutions Serial Digital Interface (SDI) www.national.com/sdi Mil/Aero www.national.com/milaero Temperature Sensors www.national.com/tempsensors Solar Magic® www.national.com/solarmagic Wireless (PLL/VCO) www.national.com/wireless Analog University® www.national.com/AU THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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