LM831 Low Voltage Audio Power Amplifier General Description Features The LM831 is a dual audio power amplifier optimized for very low voltage operation. The LM831 has two independent amplifiers, giving stereo or higher power bridge (BTL) operation from two- or three-cell power supplies. The LM831 uses a patented compensation technique to reduce high-frequency radiation for optimum performance in AM radio applications. This compensation also results in lower distortion and less wide-band noise. The input is direct-coupled to the LM831, eliminating the usual coupling capacitor. Voltage gain is adjustable with a single resistor. Y Y Y Y Y Low voltage operation, 1.8V to 6.0V High power, 440 mW, 8X, BTL, 3V Low AM radiation Low noise Low THD Applications Y Y Y Y Portable tape recorders Portable radios Headphone stereo Portable speakers Typical Application Dual Amplifier with Minimum Parts TL/H/6754 – 1 AV e 46 dB,BW e 250 Hz to 35 kHz POUT e 220 mW/Ch,RL e 4X C1995 National Semiconductor Corporation TL/H/6754 RRD-B30M115/Printed in U. S. A. LM831 Low Voltage Audio Power Amplifier December 1994 Absolute Maximum Ratings Storage Temperature, Tstg Junction Temperature, Tj Lead Temp. (Soldering, 10 sec.), TL Thermal Resistance iJC (DIP) iJA (DIP) iJC (SO Package) iJA (SO Package) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Supply Voltage, VS Input Voltage, VIN Power Dissipation (Note 1), PD Operating Temperature (Note 1), Topr 7.5V g 0.4V 1.3W (M Package) 1.4W (N Package) b 40§ C to a 85§ C b 65§ C to a 150§ C a 150§ C a 260§ C 27§ C/W 75§ C/W 20§ C/W 95§ C/W Electrical Characteristics Unless otherwise specified, TA e 25§ C, VS e 3V, f e 1 kHz, test circuit is dual or BTL amplifier with minimum parts. Symbol Parameter Typ Tested Limit Unit (Limit) 3 3 1.8 6 V(Min) V(Max) VIN e 0, Dual Mode VIN e 0, BTL Mode 5 6 10 15 mA (Max) mA (Max) VIN e 0, BTL Mode 10 50 mV (Max) 25 15 35 k (Min) k (Max) VIN e 2.25 mVrms, f e 1 kHz, Dual Mode 46 44 48 dB (Min) dB (Max) Supply Rejection VS e 3V a 200 mVrms 46 30 dB (Min) Power Out VS e 3V, RL e 4X, 10% THD, Dual Mode 220 150 mW (Min) PODL Power Out Low, VS VS e 1.8V, RL e 4X, 10% THD, Dual Mode 45 10 mW (Min) POB Power Out VS e 3V, RL e 8X, 10% THD, BTL Mode 440 300 mW (Min) Power Out Low, VS VS e 1.8V, RL e 8X, 90 20 mW (Min) 52 40 dB (Min) 1 2 mA (Max) VS Operating Voltage IQ Supply Current VOS Output DC Offset RIN Input Resistance AV Voltage Gain PSRR POD POBL Conditions @ f e 1 kHz 10% THD, BTL Mode Sep Channel Separation IB Input Bias Current Referenced to VO e 200 mVrms En0 Output Noise Wide Band (250 E 35 kHz) 250 500 mV (Max) THD Distortion VS e 3V, PO e 50 mW, f e 1 kHz, Dual 0.25 1 % (Max) Note 1: For operation in ambient temperatures above 25§ C, the device must be derated based on a 150§ C maximum junction temperature and a thermal resistance of 98§ C/W junction to ambient for the M package or 90§ C/W junction to ambient for the N package. Connection Diagram Dual-In-Line Package TL/H/6754 – 2 Top View Order Number LM831M or N See NS Package Number M16B or N16E 2 Typical Performance Characteristics Supply Current vs Supply Voltage PSRR vs Supply Voltage Supply Current vs Temperature PSRR vs Supply Voltage DC Output vs Supply Voltage Separation vs Supply Voltage TL/H/6754 – 4 3 Typical Performance Characteristics (Continued) Separation vs Frequency Power Output vs Supply Voltage Gain vs Frequency Power Output vs Temperature Gain vs Frequency Bandwidth vs BW Capacitance TL/H/6754 – 5 4 Typical Performance Characteristics (Continued) Dual Mode, RL e 4X Distortion vs Frequency Dual Mode, RL e 8X Distortion vs Frequency Distortion vs Power Output (Note 2) Distortion vs Power Output (Note 2) Power Dissipation vs Power Output Power Dissipation vs Power Output TL/H/6754 – 6 5 Typical Performance Characteristics (Continued) BTL Mode, RL e 8X Distortion vs Frequency Device Dissipation vs Ambient Temperature Distortion vs Power Output (Note 2) Supply Current vs Power Output Power Dissipation vs Power Output Note 2: 1 kHz curve is measured with 400 Hz–30 kHz Filter. TL/H/6754 – 7 6 Typical Applications BTL Amplifier with Minimum Parts TL/H/6754 – 8 AV e 52 dB, BW e 250 Hz to 25 kHz POUT e 440 mW, RL e 8X BTL Amplifier for Hi-Fi Quality TL/H/6754 – 9 AV e 40 dB, BW e 20 Hz to 20 kHz POUT e 440 mW, RL e 8X (Dynamic Range Over 80 dB) 7 Typical Applications (Continued) Dual Amplifier for Hi-Fi Quality TL/H/6754 – 10 AV e 34 dB, BW e 50 Hz to 20 kHz POUT e 220 mW/Ch, RL e 4X (Dynamic Range Over 80 dB) Low-Cost Power Amplifier (No Bootstrap) TL/H/6754 – 11 POUT e 150 mW/Ch, BW e 300 Hz to 35 kHz BTL Mode is also possible *For 3-cell applications, the 120k resistor should be changed to 20K. 8 LM831 Circuit Description Refer to the external component diagram and equivalent schematic. The capacitor CNF on Pin 2 provides unity DC gain for maximum DC accuracy. Q2 provides voltage gain and the rest of the devices buffer the output load from Q2’s collector. Bootstrapping of Pin 5 by CBS allows maximum output swing and improved supply rejection. R5 is provided for bridge (BTL) operation. The power supply is applied to Pin 9 and is filtered by resistor R1 and capacitor CBY on Pin 16. This filtered voltage at Pin 16 is used to bias all of the LM831 circuits except the power output stage. Resistor R0 generates a biasing current that sets the output DC voltage for optimum output power for any given supply voltage. Feedback is provided to the input transistor Q1 emitter by R6 and R7. External Component Diagram TL/H/6754 – 12 9 LM831 Equivalent Schematic TL/H/6754 – 13 LM831 Circuit Description (Continued) 10 External Components (Refer to External Component Diagram) Component Min Max CO Required to stabilize output stage. Comments 0.33 mF 1 mF Cc Output coupling capacitors for Dual Mode. Sets a low-frequency pole in the frequency response. 1 fL e 2qCcRL 100 mF 10,000 mF CBS Bootstrap capacitors. Sets a low-frequency pole in the power BW. Recommended value is 1 CBS e 10 # 2q # fL # RL 22 mF or (short Pins 4 & 12 to 9) 470 mF CS Supply bypass. Larger values improve low-battery performance by reducing supply ripple. 47 mF 10,000 mF CBY Filters the supply for improved low-voltage operation. Also sets turn-on delay. 47 mF 470 mF CNF Sets a low-frequency response. Also affects turn-on delay. 1 fL e 2q # CNF # (RAV a 80) 10 mF 100 mF 0.1 mF 1 mF In BTL Mode, CNF on Pin 15 can be reduced without affecting the frequency response. However, the turn-on ‘‘POP‘‘ will be worsened. CBTL Used only in the Bridge Mode. Connects the output of the first amplifier to the inverting input of the other through an internal resistor. Sets a lowfrequency pole in one-half the frequency response. 1 fL e 2q # CBTL # 16k CBW Improves clipping waveform and sets the high-frequency bandwidth. Works with an internal 16k resistor. (This equation applies for RAV i 0. For 46 dB application, see BW–CBW curve.) 1 fH e 2q # CBW # 16k See table below RAV Used to reduce the gain and improve the distortion and signal to noise. If this is desired, CBW must also be used. See table below Typical AV CBW RAV Min Max Short Open 4700 pF 40 dB 82 100 pF 4700 pF 34 dB 240 270 pF 4700 pF 28 dB 560 500 pF 4700 pF 46 dB 11 Printed Circuit Layout for LM831N (Foil Side View) Refer to External Component Diagram TL/H/6754 – 14 Note: Power ground pattern should be as wide as possible. Supply bypass capacitor should be as close to the IC as possible. Output compensation capacitors should also be close to the IC. 12 Physical Dimensions inches (millimeters) Molded SO Package (M) Order Number LM831M NS Package Number M16B 13 LM831 Low Voltage Audio Power Amplifier Physical Dimensions inches (millimeters) (Continued) Molded Dual-In-Line Package (N) Order Number LM831N NS Package Number N16E 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 OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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