LM4752 Stereo 11W Audio Power Amplifier General Description The LM4752 is a stereo audio amplifier capable of delivering 11W per channel of continuous average output power to a 4Ω load, or 7W per channel into 8Ω using a single 24V supply at 10% THD+N. The LM4752 is specifically designed for single supply operation and a low external component count. The gain and bias resistors are integrated on chip, resulting in a 11W stereo amplifier in a compact 7 pin TO220 package. High output power levels at both 20V and 24V supplies and low external component count offer high value for compact stereo and TV applications. A simple mute function can be implemented with the addition of a few external components. Key Specifications n Output power at 10% THD+N with 1kHz into 4Ω at VCC = 24V: 11W (typ) n Output power at 10% THD+N with 1kHz into 8Ω at VCC = 24V: 7W (typ) n Closed loop gain: 34dB (typ) n PO at 10% THD+N @ 1 kHz into 4Ω single-ended TO-263 package at VCC = 12V: 2.5W (typ) n PO at 10% THD+N @ 1kHz into 8Ω bridged TO-263 package at VCC = 12V: 5W (typ) Features n n n n n n n n n Drives 4Ω and 8Ω loads Internal gain resistors (AV = 34 dB) Minimum external component requirement Single supply operation Internal current limiting Internal thermal protection Compact 7-lead TO-220 package Low cost-per-watt Wide supply range 9V - 40V Applications n n n n Compact stereos Stereo TVs Mini component stereos Multimedia speakers Typical Application 10003901 FIGURE 1. Typical Audio Amplifier Application Circuit © 2004 National Semiconductor Corporation DS100039 www.national.com LM4752 Stereo 11W Audio Power Amplifier August 2000 LM4752 Connection Diagrams Plastic Package 10003902 Package Description Top View Order Number LM4752T Package Number TA07B 10003950 Package Description Top View Order Number LM4752TS Package Number TS07B www.national.com 2 Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Operating Ratings Supply Voltage Temperature Range TMIN ≤ TA ≤ TMAX 40V ± 0.7V Input Voltage Output Current ESD Susceptability (Note 4) 62.5W 2 kV Junction Temperature 150˚C Soldering Information T Package (10 sec) 250˚C −40˚C ≤ TA ≤ +85˚C Supply Voltage Internally Limited Power Dissipation (Note 3) −40˚C to 150˚C 9V to 32V θJC 2˚C/W θJA 79˚C/W Electrical Characteristics The following specifications apply to each channel with VCC = 24V, TA = 25˚C unless otherwise specified. LM4752 Symbol Itotal Po Parameter Conditions Total Quiescent Power Supply Current VINAC = 0V, Vo = 0V, RL = ∞ Output Power (Continuous f = 1 kHz, THD+N = 10%, RL = 8Ω Average per Channel) f = 1 kHz, THD+N = 10%, RL = 4Ω Units (Limits) Typical (Note 5) Limit (Note 6) 10.5 20 mA(max) 7 mA(min) 10 W(min) 7 W VCC = 20V, RL = 8Ω 4 W VCC = 20V, R 7 W f = 1 kHz, THD+N = 10%, RL = 4Ω VS = 12V, TO-263 Pkg. 2.5 W 0.08 % V L = 4Ω THD+N Total Harmonic Distortion plus Noise f = 1 kHz, Po = 1 W/ch, RL = 8Ω VOSW Output Swing RL = 8Ω, V RL = 4Ω, V CC = 20V 15 CC = 20V 14 V 55 dB 50 dB Xtalk Channel Separation See Figure 1 PSRR Power Supply Rejection Ratio See Figure 1 f = 1 kHz, Vo = 4 Vrms, RL = 8Ω VCC = 22V to 26V, R L = 8Ω VODV Differential DC Output Offset Voltage SR Slew Rate 2 RIN Input Impedance 83 kΩ PBW Power Bandwidth 3 dB BW at Po = 2.5W, RL = 8Ω 65 kHz A VCL Closed Loop Gain (Internally Set) RL = 8Ω 34 VINAC = 0V 0.09 ein Noise IHF-A Weighting Filter, RL = 8Ω Io Output Short Circuit Current Limit VIN = 0.5V, R 0.4 V(max) V/µs 33 dB(min) 35 dB(max) 0.2 mVrms Output Referred L = 2Ω 2 A(min) Note 1: All voltages are measured with respect to the GND pin (4), 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: For operating at case temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance of θJC = 2˚C/W (junction to case). Refer to the section Determining the Maximum Power Dissipation in the Application Information section for more information. Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 5: Typicals are measured at 25˚C and represent the parametric norm. Note 6: Limits are guarantees that all parts are tested in production to meet the stated values. Note 7: The TO-263 Package is not recommended for VS > 16V due to impractical heatsinking limitations. 3 www.national.com LM4752 Absolute Maximum Ratings (Note 2) LM4752 Test Circuit 10003936 FIGURE 2. Test Circuit www.national.com 4 LM4752 Typical Application with Mute 10003903 FIGURE 3. Application with Mute Function 5 www.national.com www.national.com 6 Equivalent Schematic Diagram 10003904 LM4752 LM4752 System Application Circuit 10003905 FIGURE 4. Circuit for External Components Description External Components Description Components Function Description 1, 2 Cs Provides power supply filtering and bypassing. 3, 4 Rsn Works with Csn to stabilize the output stage from high frequency oscillations. 5, 6 Csn Works with Rsn to stabilize the output stage from high frequency oscillations. 7 Cb Provides filtering for the internally generated half-supply bias generator. 8, 9 Ci Input AC coupling capacitor which blocks DC voltage at the amplifier’s input terminals. Also creates a high pass filter with fc =1/(2 • π • Rin • Cin). 10, 11 Co Output AC coupling capacitor which blocks DC voltage at the amplifier’s output terminal. Creates a high pass filter with fc =1/(2 • π • Rout • Cout). 12, 13 Ri Voltage control - limits the voltage level to the amplifier’s input terminals. 7 www.national.com LM4752 Typical Performance Characteristics THD+N vs Output Power THD+N vs Output Power 10003912 10003913 THD+N vs Output Power THD+N vs Output Power 10003914 10003906 THD+N vs Output Power THD+N vs Output Power 10003907 www.national.com 10003908 8 LM4752 Typical Performance Characteristics (Continued) THD+N vs Output Power THD+N vs Output Power 10003915 10003916 THD+N vs Output Power THD+N vs Output Power 10003917 10003909 THD+N vs Output Power THD+N vs Output Power 10003910 10003911 9 www.national.com LM4752 Typical Performance Characteristics (Continued) THD+N vs Output Power THD+N vs Output Power 10003938 10003939 THD+N vs Output Power THD+N vs Output Power 10003940 10003941 THD+N vs Output Power THD+N vs Output Power 10003942 www.national.com 10003943 10 LM4752 Typical Performance Characteristics (Continued) THD+N vs Output Power THD+N vs Output Power 10003944 10003945 THD+N vs Output Power THD+N vs Output Power 10003946 10003947 THD+N vs Output Power THD+N vs Output Power 10003948 10003949 11 www.national.com LM4752 Typical Performance Characteristics (Continued) Output Power vs Supply Voltage Output Power vs Supply Voltage 10003918 10003919 Frequency Response THD+N vs Frequency 10003921 10003920 THD+N vs Frequency Frequency Response 10003923 10003922 www.national.com 12 LM4752 Typical Performance Characteristics (Continued) Channel Separation PSRR vs Frequency 10003924 10003925 Supply Current vs Supply Voltage Power Derating Curve 10003926 10003927 Power Dissipation vs Output Power Power Dissipation vs Output Power 10003928 10003929 13 www.national.com LM4752 Typical Performance Characteristics (Continued) Power Dissipation vs Output Power Power Dissipation vs Output Power 10003951 10003952 pull-down time such that output “pops” and signal feedthroughs will be minimized. The pull-down timing is a function of a number of factors, including the external mute circuitry, the voltage used to activate the mute, the bias capacitor, the half-supply voltage, and internal resistances used in the half-supply generator. Table 1 shows a list of recommended values for the external mute circuitry. Application Information CAPACITOR SELECTION AND FREQUENCY RESPONSE With the LM4752, as in all single supply amplifiers, AC coupling capacitors are used to isolate the DC voltage present at the inputs (pins 2,6) and outputs (pins 1,7). As mentioned earlier in the External Components section these capacitors create high-pass filters with their corresponding input/output impedances. The Typical Application Circuit shown in Figure 1 shows input and output capacitors of 0.1 µF and 1,000 µF respectively. At the input, with an 83 kΩ typical input resistance, the result is a high pass 3 dB point occurring at 19 Hz. There is another high pass filter at 39.8 Hz created with the output load resistance of 4Ω. Careful selection of these components is necessary to ensure that the desired frequency response is obtained. The Frequency Response curves in the Typical Performance Characteristics section show how different output coupling capacitors affect the low frequency rolloff. TABLE 1. Values for Mute Circuit R1 5V 10 kΩ VS 20 kΩ VS 20 kΩ R2 C1 R3 CB VCC 10 kΩ 4.7 µF 360Ω 100 µF 21V–32V 1.2 kΩ 4.7 µF 180Ω 100 µF 15V–32V 910Ω 4.7 µF 180Ω 47 µF 22V–32V OPERATING IN BRIDGE-MODE Though designed for use as a single-ended amplifier, the LM4752 can be used to drive a load differentially (bridgemode). Due to the low pin count of the package, only the non-inverting inputs are available. An inverted signal must be provided to one of the inputs. This can easily be done with the use of an inexpensive op-amp configured as a standard inverting amplifier. An LF353 is a good low-cost choice. Care must be taken, however, for a bridge-mode amplifier must theoretically dissipate four times the power of a single-ended type. The load seen by each amplifier is effectively half that of the actual load being used, thus an amplifier designed to drive a 4Ω load in single-ended mode should drive an 8Ω load when operating in bridge-mode. APPLICATION CIRCUIT WITH MUTE With the addition of a few external components, a simple mute circuit can be implemented, such as the one shown in Figure 3. This circuit works by externally pulling down the half supply bias line (pin 5), effectively shutting down the input stage. When using an external circuit to pull down the bias, care must be taken to ensure that this line is not pulled down too quickly, or output “pops” or signal feedthrough may result. If the bias line is pulled down too quickly, currents induced in the internal bias resistors will cause a momentary DC voltage to appear across the inputs of each amplifier’s internal differential pair, resulting in an output DC shift towards V SUPPLY. An R-C timing circuit should be used to limit the www.national.com VMUTE 14 LM4752 Application Information (Continued) 10003930 FIGURE 5. Bridge-Mode Application 10003931 10003937 FIGURE 6. THD+N vs. POUT for Bridge-Mode Application PREVENTING OSCILLATIONS With the integration of the feedback and bias resistors onchip, the LM4752 fits into a very compact package. However, due to the close proximity of the non-inverting input pins to the corresponding output pins, the inputs should be AC terminated at all times. If the inputs are left floating, the amplifier will have a positive feedback path through high impedance coupling, resulting in a high frequency oscillation. In most applications, this termination is typically provided by the previous stage’s source impedance. If the application will require an external signal, the inputs should be terminated to ground with a resistance of 50 kΩ or less on the AC side of the input coupling capacitors. UNDERVOLTAGE SHUTDOWN If the power supply voltage drops below the minimum operating supply voltage, the internal under-voltage detection circuitry pulls down the half-supply bias line, shutting down the preamp section of the LM4752. Due to the wide operating supply range of the LM4752, the threshold is set to just under 9V. There may be certain applications where a higher 15 www.national.com LM4752 Application Information where: PDMAX = maximum power dissipation of the IC TJ(˚C) = junction temperature of the IC TA(˚C) = ambient temperature θJC(˚C/W) = junction-to-case thermal resistance of the IC (Continued) threshold voltage is desired. One example is a design requiring a high operating supply voltage, with large supply and bias capacitors, and there is little or no other circuitry connected to the main power supply rail. In this circuit, when the power is disconnected, the supply and bias capacitors will discharge at a slower rate, possibly resulting in audible output distortion as the decaying voltage begins to clip the output signal. An external circuit may be used to sense for the desired threshold, and pull the bias line (pin5) to ground to disable the input preamp. Figure 7 shows an example of such a circuit. When the voltage across the zener diode drops below its threshold, current flow into the base of Q1 is interrupted. Q2 then turns on, discharging the bias capacitor. This discharge rate is governed by several factors, including the bias capacitor value, the bias voltage, and the resistor at the emitter of Q2. An equation for approximating the value of the emitter discharge resistor, R, is given below: R = (0.7V) / (CB • (V S / 2) / 0.1s) θCS(˚C/W) = case-to-heatsink thermal resistance (typically 0.2 to 0.5 ˚C/W) θSA(˚C/W) = thermal resistance of heatsink When determining the proper heatsink, the above equation should be re-written as: θSA ≤ [ (TJ − TA) / PDMAX] − θ JC − θCS TO-263 Heatsinking Surface mount applications will be limited by the thermal dissipation properties of printed circuit board area. The TO263 package is not recommended for surface mount applications with VS > 16V due to limited printed circuit board area. There are TO-263 package enhancements, such as clip-on heatsinks and heatsinks with adhesives, that can be used to improve performance. Standard FR-4 single-sided copper clad will have an approximate Thermal resistance (θSA) ranging from: Note that this is only a linearized approximation based on a discharge time of 0.1s. The circuit should be evaluated and adjusted for each application. As mentioned earlier in the Application Circuit with Mute section, when using an external circuit to pull down the bias line, the rate of discharge will have an effect on the turn-off induced distortions. Please refer to the Application Circuit with Mute section for more information. 20–27˚C/W 16–23˚C/W (TA=28˚C, Sine wave testing, 1 oz. Copper) The above values for θSA vary widely due to dimensional proportions (i.e. variations in width and length will vary θSA). For audio applications, where peak power levels are short in duration, this part will perform satisfactory with less heatsinking/copper clad area. As with any high power design proper bench testing should be undertaken to assure the design can dissipate the required power. Proper bench testing requires attention to worst case ambient temperature and air flow. At high power dissipation levels the part will show a tendency to increase saturation voltages, thus limiting the undistorted power levels. Determining Maximum Power Dissipation For a single-ended class AB power amplifier, the theoretical maximum power dissipation point is a function of the supply voltage, V S, and the load resistance, RL and is given by the following equation: (single channel) PDMAX (W) = [VS 2 / (2 • π2 • RL) ] The above equation is for a single channel class-AB power amplifier. For dual amplifiers such as the LM4752, the equation for calculating the total maximum power dissipated is: (dual channel) PDMAX (W) = 2 • [V S2 / (2 • π2 • RL) ] or VS2 / (π 2 • RL) (Bridged Outputs) PDMAX (W) = 4[VS2 / (2π2 • RL)] 10003932 FIGURE 7. External Undervoltage Pull-Down THERMAL CONSIDERATIONS Heat Sinking Proper heatsinking is necessary to ensure that the amplifier will function correctly under all operating conditions. A heatsink that is too small will cause the die to heat excessively and will result in a degraded output signal as the internal thermal protection circuitry begins to operate. The choice of a heatsink for a given application is dictated by several factors: the maximum power the IC needs to dissipate, the worst-case ambient temperature of the circuit, the junction-to-case thermal resistance, and the maximum junction temperature of the IC. The heat flow approximation equation used in determining the correct heatsink maximum thermal resistance is given below: TJ–TA = P DMAX • (θJC + θCS + θ SA) www.national.com 1.5 x 1.5 in. sq. 2 x 2 in. sq. Heatsink Design Example Determine the system parameters: V 16 S = 24V Operating Supply Voltage RL = 4Ω Minimum load impedance TA = 55˚C Worst case ambient temperature PDMAX from PD vs PO Graph: (Continued) PDMAX ≈ 3.7W Calculating PDMAX: PDMAX = VCC2 / (π2RL) = (12V)2 / (π2(4Ω)) = 3.65W Device parameters from the datasheet: T J = 150˚C θJC = 2˚C/W Maximum junction temperature Junction-to-case thermal resistance Calculations: 2 • PDMAX = 2 • [V 2 S Calculating Heatsink Thermal Resistance: θSA < [(TJ − TA) / PDMAX] − θJC − θCS θSA < 100˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 24.8˚C/W / (2 • π2 • RL) ] = (24V)2 / (2 • π2 • 4Ω) = 14.6W Therefore the recommendation is to use 2.0 x 2.0 square inch of single-sided copper clad. Example 3: (Bridged Output) θSA ≤ [ (TJ − TA) / PDMAX] − θ JC − θCS = [ (150˚C − 55˚C) / 14.6W ] − 2˚C/W − 0.2˚C/W = 4.3˚C/W Conclusion: Choose a heatsink with θSA ≤ 4.3˚C/W. Given: TO-263 Heatsink Design Examples Example 1: (Stereo Single-Ended Output) Given: TA=30˚C TA=50˚C TJ=150˚C RL=8Ω VS=12V θJC=2˚C/W TJ=150˚C RL=4Ω VS=12V θJC=2˚C/W Calculating PDMAX: PDMAX = 4[VCC2 / (2π2RL)] = 4(12V)2 / (2π2(8Ω)) = 3.65W Calculating Heatsink Thermal Resistance: θSA < [(TJ − TA) / PDMAX] − θJC − θCS < θSA 100˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 24.8˚C/W Therefore the recommendation is to use 2.0 x 2.0 square inch of single-sided copper clad. PDMAX from PD vs PO Graph: PDMAX ≈ 3.7W Calculating PDMAX: PDMAX = VCC2 / (π2RL) = (12V)2 / π2(4Ω)) = 3.65W Calculating Heatsink Thermal Resistance: θSA < [(T J − TA) / PDMAX] − θJC − θCS θSA < 120˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 30.2˚C/W Therefore the recommendation is to use 1.5 x 1.5 square inch of single-sided copper clad. Example 2: (Stereo Single-Ended Output) Given: TA=50˚C TJ=150˚C RL=4Ω VS=12V θJC=2˚C/W Layout and Ground Returns Proper PC board layout is essential for good circuit performance. When laying out a PC board for an audio power amplifer, particular attention must be paid to the routing of the output signal ground returns relative to the input signal and bias capacitor grounds. To prevent any ground loops, the ground returns for the output signals should be routed separately and brought together at the supply ground. The input signal grounds and the bias capacitor ground line should also be routed separately. The 0.1 µF high frequency supply bypass capacitor should be placed as close as possible to the IC. 17 www.national.com LM4752 Application Information LM4752 Application Information (Continued) PC BOARD LAYOUT — COMPOSITE 10003933 www.national.com 18 LM4752 Application Information (Continued) PC BOARD LAYOUT — SILK SCREEN 10003934 19 www.national.com LM4752 Application Information (Continued) PC BOARD LAYOUT — SOLDER SIDE 10003935 www.national.com 20 LM4752 Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM4752T NS Package Number TA07B Order Number LM4752TS NS Package Number TS7B 21 www.national.com LM4752 Stereo 11W Audio Power 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. For the most current product information visit us at www.national.com. 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