LM4702

LM4702 Overture ® Stereo High Fidelity 200 Volt* Driver with Mute September 2005 LM4702 Overture ® Audio Power Amplifier Series Stereo High Fidelity 200 Volt* Driver with Mute General Description The LM4702 is a high fidelity audio power amplifier driver designed for demanding consumer and pro-audio applications. Amplifier output power may be scaled by changing the supply voltage and number of output devices. The LM4702 is capable of delivering in excess of 300 watts per channel single ended into an 8 ohm load in the presence of 10% high line headroom and 20% supply regulation. The LM4702 includes thermal shut down circuitry that activates when the die temperature exceeds 150˚C. The LM4702’s mute function, when activated, mutes the input drive signal and forces the amplifier output to a quiescent state. The LM4702 is available in 3 grades that span a wide range of applications and performance levels. The LM4702C is targeted at high volume applications. The LM4702B (in development) includes a higher voltage rating along with the tighter specifications. The LM4702A (in development) is the premium part with the highest voltage rating, fully specified with limits over voltage and temperature, and is offered in a military 883 compliant TO-3 package. * Tentative Max Operating voltage for the LM4702A, LM4702B (in development) Key Specifications j Wide operating voltage range LM4702A (in development) LM4702B (in development) LM4702C j Equivalent Noise j PSRR j THD ± 20V to ± 85V ± 20V to ± 80V ± 20V to ± 75V 3µV 110dB (typ) 0.001% Features n n n n n Very high voltage operation Scalable output power Minimum external components External compensation Thermal Shutdown and Mute Applications n n n n AV receivers Audiophile power amps Pro Audio High voltage industrial applications Typical Application and Connection Diagrams 20158302 Plastic Package — 15 Lead TO-220 (for LM4702; LM4702B, in development) 20158320 Metal Can — 15 Lead TO-3 (for LM4702A, in development) 20158319 FIGURE 1. Typical Audio Amplifier Application Circuit SPiKe™ Protection and Overture™ are trademarks of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS201583 www.national.com LM4702 Typical Application and Connection Diagrams (Continued) 20158319 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM4702 Connection Diagram Plastic Package (For B and C) (Note 13) 20158301 Top View Order Number LM4702T(B & C) See NS Package Number TA15A 3 www.national.com LM4702 Absolute Maximum Ratings 2) (Notes 1, Storage Temperature Thermal Resistance θJA θJC -40˚C to +150˚C 30˚C/W 1˚C/W If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage |V+| + |V-| Differential Input Voltage Common Mode Input Range Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature (TJMAX) (Note 9) Soldering Information T Package (10 seconds) 260˚C 200V +/-6V 0.4 Vee to 0.4 Vcc 4W 1.5kV 200V 150˚C Operating Ratings (Notes 1, 2) Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage |V+| + |V-| LM4702A (in development) LM4702B (in development) LM4702C +/-20V ≤ VTOTAL ≤ +/-85V +/-20V ≤ VTOTAL ≤ +/-80V +/-20V ≤ VTOTAL ≤ +/-75V −20˚C ≤ TA ≤ +75˚C Electrical Characteristics (LM4702C) Vcc = +75V, Vee = –75V Symbol Parameter Conditions Typical ICC THD+N RS Av Av open Vom Vnoise IOUT Imute XTALK SR VOS IB PSRR Total Quiescent Power Supply Current Total Harmonic Distortion + Noise Input Bias Resistor Closed Loop Voltage Gain Open Loop Gain Output Voltage Swing Output Noise Output Current Current into Mute Pin Channel Separation (Note 11) Slew Rate Input Offset Voltage Input Bias Current Power Supply Rejection Ratio Vin = 1mVrms, f = 1KHz, C = 30pF THD = 0.05%, Freq = 20Hz to 20KHz Rs = 10kΩ, LPF = 30kHz, Av = 30dB A-weighted Current from Source to Sink Pins To put part in “play” mode f = 1kHz @ Av = 30dB VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted VCM = 0V, IO = 0mA VCM = 0V, IO = 0mA Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 93 51 150 90 5.5 1.5 85 15 10 500 110 VCM = 0V, VO = 0V, IO = 0A No load, AV = 30dB VOUT = 14VRMS @ 1kHz 25 0.005 50 (Notes 1, 2) The following specifications apply for IMUTE = 1.5mA, unless otherwise specified. Limits apply for TA = 25˚C. LM4702 Limit 30 (Note 6) (Notes 7, 8) mA (max) % 100 26 kΩ (max) dB (min) dB Vrms (min) 300 3 10 1 2 µV (max) µV mA(min) mA (max) mA(min) mA (max) dB V/µs 35 95 mV (max) nA dB (min) Units (Limits) Electrical Characteristics (LM4702C) Vcc = +50V, Vee = –50V Symbol Parameter Conditions Typical ICC THD+N RS Total Quiescent Power Supply Current Total Harmonic Distortion + Noise Input Bias Resistor VCM = 0V, VO = 0V, IO = 0A No load, AV = 30dB VOUT = 10VRMS @ 1kHz 22 0.005 50 (Notes 1, 2) The following specifications apply for IMUTE = 1.5mA, unless otherwise specified. Limits apply for TA = 25˚C. LM4702 Limit 30 (Note 6) (Notes 7, 8) mA (max) % 100 kΩ (max) Units (Limits) www.national.com 4 LM4702 Electrical Characteristics (LM4702C) Vcc = +50V, Vee = –50V Symbol Parameter Conditions (Notes 1, 2) (Continued) The following specifications apply for IMUTE = 1.5mA, unless otherwise specified. Limits apply for TA = 25˚C. LM4702 Typical Av Av open Vom Vnoise IOUT Imute XTALK SR VOS IB PSRR Closed Loop Voltage Gain Open Loop Gain Output Voltage Swing Output Noise Output Current Current into Mute Pin Channel Separation (Note 11) Slew Rate Input Offset Voltage Input Bias Current Power Supply Rejection Ratio Vin = 1mVrms, f = 1KHz, C = 30pF THD = 0.05%, Freq = 20Hz to 20KHz Rs = 10kΩ, LPF = 30kHz, Av = 30dB A-weighted Outputs Shorted To put part in “play” mode f = 1kHz at Av = 30dB VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted VCM = 0V, IO = 0mA VCM = 0V, IO = 0mA Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 93 33 150 90 5.2 1.5 85 15 10 500 110 95 35 3 10 1 2 300 Limit 26 (Note 6) (Notes 7, 8) dB (min) dB Vrms (min) µV (max) µV mA(min) mA (max) mA(min) mA (max) dB V/µs mV (max) nA dB (min) Units (Limits) Electrical Characteristics (LM4702B) Vcc = +80V, Vee = –80V (Pre-release information) (Notes 1, 2) The following specifications apply for IMUTE = 1.5mA, unless otherwise specified. Limits apply for TA = 25˚C. Symbol Parameter Conditions LM4702 Typical ICC THD+N RS Av Av open Vom Vnoise Total Quiescent Power Supply Current Total Harmonic Distortion + Noise Input Bias Resistor Closed Loop Voltage Gain Open Loop Gain Output Voltage Swing Output Noise Vin = 1mVrms, f = 1KHz, C = 30pF THD = 0.05%, Freq = 20Hz to 20KHz Rs = 10kΩ, LPF = 30kHz, Av = 30dB A-weighted Outputs Shorted To put part in “play” mode f = 1kHz at Av = 30dB VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted VCM = 0V, IO = 0mA VCM = 0V, IO = 0mA Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 93 54 150 90 5.5 1.5 85 17 7 350 110 TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD VCM = 0V, VO = 0V, IO = 0A No load, AV = 30dB VOUT = 20VRMS @ 1kHz 27 0.003 50 Limit TBD TBD TBD TBD (Note 6) (Notes 7, 8) mA (max) % (max) kΩ (max) dB (min) dB Vrms (min) µV (max) mA(min) mA (max) mA(min) mA (max) dB (min) V/µs (min) mV (max) nA (max) dB (min) Units (Limits) IOUT Imute XTALK SR VOS IB PSRR Output Current Current into Mute Pin Channel Separation (Note 11) Slew Rate Input Offset Voltage Input Bias Current Power Supply Rejection Ratio 5 www.national.com LM4702 Electrical Characteristics (LM4702A) Vcc = +85V, Vee = –85V (Pre-release information) (Notes 1, 2) The following specifications apply for IMUTE = 1.5mA, unless otherwise specified. Limits apply for TA = 25˚C. Symbol Parameter Conditions LM4702 Typical ICC THD+N RS Av Av open Vom Vnoise Total Quiescent Power Supply Current Total Harmonic Distortion + Noise Input Bias Resistor Closed Loop Voltage Gain Open Loop Gain Output Voltage Swing Output Noise Vin = 1mVrms, f = 1KHz, C = 30pF THD = 0.05%, Freq = 20Hz to 20KHz Rs = 10kΩ, LPF = 30kHz, Av = 30dB A-weighted Outputs Shorted To put part in “play” mode f = 1kHz at Av = 30dB VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted VCM = 0V, IO = 0mA VCM = 0V, IO = 0mA Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 93 57 100 80 5.5 1.5 90 TBD 5 150 110 TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD VCM = 0V, VO = 0V, IO = 0A No load, AV = 30dB VOUT = 20VRMS @ 1kHz 27 0.001 50 Limit TBD TBD TBD TBD (Note 6) (Notes 7, 8) mA (max) % (max) kΩ (max) dB (min) dB Vrms (min) µV (max) mA(min) mA (max) mA(min) mA (max) dB (min) V/µs (min) mV (max) nA (max) dB (min) Units (Limits) IOUT Imute XTALK SR VOS IB PSRR Output Current Current into Mute Pin Channel Separation (Note 11) Slew Rate Input Offset Voltage Input Bias Current Power Supply Rejection Ratio Note 1: All voltages are measured with respect to the ground pins, 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 condition 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’s performance. Note 3: The maximum power dissipation must be de-rated at elevated temperatures and is dictated by TJMAX, θJC, and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX -TA)/θJC or the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4702, TJMAX = 150˚C and the typical θJC is 1˚C/W. Refer to the Thermal Considerations section for more information. Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Note 5: Machine Model: a 220pF - 240pF discharged through all pins. Note 6: Typical specifications are measured 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: The maximum operating junction temperature is 150˚C. Note 10: PCB layout will affect cross talk. It is recommended that input and output traces be separated by as much distance as possible. Return ground traces from outputs should be independent back to a single ground point and use as wide of traces as possible. Note 11: The TA15A is a non-isolated package. The package’s metal back and any heat sink to which it is mounted are connected to the Vee potential when using only thermal compound. If a mica washer is used in addition to thermal compound, θCS (case to sink) is increased, but the heat sink will be electrically isolated from Vee. www.national.com 6 LM4702 Typical Performance Characteristics for LM4702C THD+N vs Output Voltage VDD = ± 50V, f = 1kHz, outputs shorted THD+N vs Output Voltage VDD = ± 75V, f = 1kHz, outputs shorted 20158308 20158338 THD+N vs Frequency VDD = ± 50V, VOUT = 10Vrms, outputs shorted THD+N vs Frequency VDD = ± 75V, VOUT = 14Vrms, outputs shorted 20158310 20158339 Crosstalk vs Frequency VDD = ± 50V Crosstalk vs Frequency VDD = ± 75V 20158335 20158336 7 www.national.com LM4702 Typical Performance Characteristics for LM4702C +PSRR vs Frequency VDD = ± 50V, RS = 1kΩ, Ripple on VCC (Continued) −PSRR vs Frequency VDD = ± 50V, RS = 1kΩ, Ripple on Vee 20158331 20158333 +PSRR vs Frequency VDD = ± 75V, RS = 1kΩ, Ripple on VCC −PSRR vs Frequency VDD = ± 75V, RS = 1kΩ, Ripple on Vee 20158332 20158334 Open Loop and Phase Upper-Phase, Lower-Gain 20158337 www.national.com 8 LM4702 Test Circuit 20158303 FIGURE 1. 9 www.national.com LM4702 Application Information MUTE FUNCTION The mute function of the LM4702 is controlled by the amount of current that flows into the mute pin. If there is less than 1mA of current flowing into the mute pin, the part will be in mute. This can be achieved by shorting the mute pin to ground or by floating the mute pin. If there is between 1mA and 2mA of current flowing into the mute pin, the part will be in “play” mode. This can be done by connecting a power supply (Vmute) to the mute pin through a resistor (Rm). The current into the mute pin can be determined by the equation Imute = (Vmute – 2.9) / Rm. For example, if a 5V power supply is connected through a 1.4k resistor to the mute pin, then the mute current will be 1.5mA, at the center of the specified range. It is also possible to use Vcc as the power supply for the mute pin, though Rm will have to be recalculated accordingly. It is not recommended to flow more than 2mA of current into the mute pin because damage to the LM4702 may occur. It is highly recommended to switch between mute and “play” modes rapidly. This is accomplished most easily through using a toggle switch that alternatively connects the mute pin through a resistor to either ground or the mute pin power supply. Slowly increasing the mute current may result in undesired voltages on the outputs of the LM4702, which can damage an attached speaker. THERMAL PROTECTION The LM4702 has a sophisticated thermal protection scheme to prevent long-term thermal stress of the device. When the temperature on the die exceeds 150˚C, the LM4702 shuts down. It starts operating again when the die temperature drops to about 145˚C, but if the temperature again begins to rise, shutdown will occur again above 150˚C. Therefore, the device is allowed to heat up to a relatively high temperature if the fault condition is temporary, but a sustained fault will cause the device to cycle in a Schmitt Trigger fashion between the thermal shutdown temperature limits of 150˚C and 145˚C. This greatly reduces the stress imposed on the IC by thermal cycling, which in turn improves its reliability under sustained fault conditions. Since the die temperature is directly dependent upon the heat sink used, the heat sink should be chosen so that thermal shutdown is not activated during normal operation. Using the best heat sink possible within the cost and space constraints of the system will improve the long-term reliability of any power semiconductor device, as discussed in the Determining the Correct Heat Sink section. POWER DISSIPATION AND HEAT SINKING When in “play” mode, the LM4702 draws a constant amount of current, regardless of the input signal amplitude. Consequently, the power dissipation is constant for a given supply voltage and can be computed with the equation PDMAX = Icc * (Vcc – Vee). For a quick calculation of PDMAX, approximate the current to be 25mA and multiply it by the total supply voltage (the current varies slightly from this value over the operating range). DETERMINING THE CORRECT HEAT SINK The choice of a heat sink for a high-power audio amplifier is made entirely to keep the die temperature at a level such that the thermal protection circuitry is not activated under normal circumstances. The thermal resistance from the die to the outside air, θJA (junction to ambient), is a combination of three thermal resistances, θJC (junction to case), θCS (case to sink), and θSA (sink to ambient). The thermal resistance, θJC (junction to case), of the LM4702T is 0.8˚C/W. Using Thermalloy Thermacote thermal compound, the thermal resistance, θCS (case to sink), is about 0.2˚C/W. Since convection heat flow (power dissipation) is analogous to current flow, thermal resistance is analogous to electrical resistance, and temperature drops are analogous to voltage drops, the power dissipation out of the LM4702 is equal to the following: (1) PDMAX = (TJMAX−TAMB) / θJA where TJMAX = 150˚C, TAMB is the system ambient temperature and θJA = θJC + θCS + θSA. 20158355 Once the maximum package power dissipation has been calculated using equation 2, the maximum thermal resistance, θSA, (heat sink to ambient) in ˚C/W for a heat sink can be calculated. This calculation is made using equation 4 which is derived by solving for θSA in equation 3. θSA = [(TJMAX−TAMB)−PDMAX(θJC +θCS)] / PDMAX (2) Again it must be noted that the value of θSA is dependent upon the system designer’s amplifier requirements. If the ambient temperature that the audio amplifier is to be working under is higher than 25˚C, then the thermal resistance for the heat sink, given all other things are equal, will need to be smaller. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components is required to meet the design targets of an application. The choice of external component values that will affect gain and low frequency response are discussed below. The gain of each amplifier is set by resistors Rf and Ri for the non-inverting configuration shown in Figure 1. The gain is found by Equation (3) below: (3) AV = 1 + Rf / Ri (V/V) For best noise performance, lower values of resistors are used. A value of 1kΩ is commonly used for Ri and then setting the value of Rf for the desired gain. For the LM4702 the gain should be set no lower than 26dB. Gain settings below 26dB may experience instability. The combination of Ri with Ci (see Figure 1) creates a high pass filter. The low frequency response is determined by these two components. The -3dB point can be found from Equation (4) shown below: (4) fi = 1 / (2πRiCi) (Hz) If an input coupling capacitor is used to block DC from the inputs as shown in Figure 5, there will be another high pass filter created with the combination of CIN and RIN. When using a input coupling capacitor RIN is needed to set the DC www.national.com 10 LM4702 Application Information (Continued) bias point on the amplifier’s input terminal. The resulting -3dB frequency response due to the combination of CIN and RIN can be found from Equation (5) shown below: fIN = 1 / (2πRINCIN) (Hz) (5) With large values of RIN oscillations may be observed on the outputs when the inputs are left floating. Decreasing the value of RIN or not letting the inputs float will remove the oscillations. If the value of RIN is decreased then the value of CIN will need to increase in order to maintain the same -3dB frequency response. AVOIDING THERMAL RUNAWAY WHEN USING BIPOLAR OUTPUT STAGES When using a bipolar output stage with the LM4702 (as in Figure 1), the designer must beware of thermal runaway. Thermal runaway is a result of the temperature dependence of Vbe (an inherent property of the transistor). As temperature increases, Vbe decreases. In practice, current flowing through a bipolar transistor heats up the transistor, which lowers the Vbe. This in turn increases the current again, and the cycle repeats. If the system is not designed properly, this positive feedback mechanism can destroy the bipolar transistors used in the output stage. One of the recommended methods of preventing thermal runaway is to use a heat sink on the bipolar output transistors. This will keep the temperature of the transistors lower. A second recommended method is to use emitter degeneration resistors (see Re1, Re2, Re3, Re4 in Figure 1). As current increases, the voltage across the emitter degeneration resistor also increases, which decreases the voltage across the base and emitter. This mechanism helps to limit the current and counteracts thermal runaway. A third recommended method is to use a “Vbe multiplier” to bias the bipolar output stage (see Figure 1). The Vbe multiplier consists of a bipolar transistor (Qmult, see Figure 1) and two resistors, one from the base to the collector (Rb2, Rb4, see Figure 1) and one from the base to the emitter (Rb1, Rb3, see Figure 1). The voltage from the collector to the emitter (also the bias voltage of the output stage) is Vbias = Vbe(1+Rb2/Rb1), which is why this circuit is called the Vbe multiplier. When Vbe multiplier transistor (Qmult, see Figure 1) is mounted to the same heat sink as the bipolar output transistors, its temperature will track that of the output transistors. Its Vbe is dependent upon temperature as well, and so it will draw more current as the output transistors heat it up. This will limit the base current into the output transistors, which counteracts thermal runaway. 11 www.national.com LM4702 LM4702 Demo Board Artwork Top Overlay 20158330 Top Layer 20158329 www.national.com 12 LM4702 LM4702 Demo Board Artwork (Continued) Bottom Layer 20158328 13 www.national.com LM4702 Revision History Rev 1.0 Date 8/18/05 Description Input corrected data under the Typical and Limit columns on all the 4 EC tables (per Kevin H.). Changed limits back on LM4702A/B/C to ± 85V/80V/75V respectively (under Key Spec...) First WEB released of the datasheet. Due to miscommunication with the ASSY plant (EM), the datasheet needs to be taken off the WEB for now (per Robin Simpson). Taken out Limits on Vom (under the +75V and +50V.. LM4702C EC tables), then released D/S to the WEB (per Robin Simpson). Changed TM to R ( Overture R) in the doc title (per Kevin C), Naomi Mitchell called Kevin about it. Re-released D/S to the WEB with Overture “R”. 1.1 8/22/05 1.2 1.3 8/31/05 9/2/05 1.4 9/09/05 1.5 9/14/05 1.6 9/15/05 www.national.com 14 LM4702 Overture ® Stereo High Fidelity 200 Volt* Driver with Mute Physical Dimensions inches (millimeters) unless otherwise noted Non-Isolated TO-220 15-Lead Package Order Number LM4702T(B&C) NS Package Number TA15A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. 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