LM390 1W Battery Operated Audio Power Amplifier General Description The LM390 Power Audio Amplifier is optimized for 6V, 7.5V, 9V operation into low impedance loads. The gain is internally set at 20 to keep the external part count low, but the addition of an external resistor and capacitor between pins 2 and 6 wil increase the gain to any value up to 200. The inputs are ground referenced while the output is automatically biased to one half the supply voltage. Y Y Y Y Applications Y Y Y Features Y Y Y Y Y Y Battery operation 1W output power Minimum external parts Excellent supply rejection Ground referenced input Self-centering output quiescent voltage Variable voltage gain Low distortion Fourteen pin dual-in-line package Y Y Y Y Y AM-FM radio amplifiers Portable tape player amplifiers Intercoms TV sound systems Lamp drivers Line drivers Ultrasonic drivers Small servo drivers Power converters Equivalent Schematic and Connection Diagrams Dual-In-Line Package TL/H/7848 – 2 Order Number LM390N See NS Package Number N14A TL/H/7848 – 1 C1995 National Semiconductor Corporation TL/H/7848 RRD-B30M115/Printed in U. S. A. LM390 1W Battery Operated Audio Power Amplifier April 1995 Absolute Maximum Ratings Operating Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Supply Voltage Package Dissipation 14-Pin DIP (Note 1) Input Voltage Storage Temperature 10V 8.3W g 0.4V 0§ C to a 70§ C Junction Temperature 150§ C Lead Temperature (Soldering, 10 sec.) Thermal Resistance iJC iJA 260§ C 30§ C/W 79§ C/W b 65§ C to a 150§ C Electrical Characteristics TA e 25§ C, (Figure 1) Symbol VS Parameter Conditions Operating Supply Voltage Min Typ 4 Units 9 V 20 mA 30 dB dB IQ Quiescent Current VS e 6V, VIN e 0 POUT Output Power VS e 6V, RL e 4X, THD e 10% 0.8 1.0 AV Voltage Gain VS e 6V, f e 1 kHz 10 mF from Pin 2 to 6 23 26 46 BW Bandwidth VS e 6V, Pins 2 and 6 Open 300 THD Total Harmonic Distortion VS e 6V, RL e 4X, POUT e 500 mW f e 1 kHz, Pins 2 and 6 Open 0.2 PSRR Power Supply Rejection Ratio VS e 6V, f e 1 kHz, CBYPASS e 10 mF, Pins 2 and 6 Open, Referred to Output (Note 2) 50 dB 50 kX 250 nA RIN Input Resistance IBIAS Input Bias Current 10 Max 10 VS e 6V, Pins 7 and 8 Open W kHz 1 % Note 1: Pins 3, 4, 5, 10, 11, 12 at 25§ C. Above 25§ C case, derate at 15§ C/W junction to case, or 85§ C/W junction to ambient. Note 2: If load and bypass capacitor are returned to VS (Figure 2) , rather than ground (Figure 1) , PSRR is typically 30 dB. Typical Performance Characteristics Maximum Device Dissipation vs Ambient Temperature Quiescent Supply Current vs Supply Voltage Power Supply Rejection Ratio (Referred to the Output) vs Frequency Peak-to-Peak Output Voltage Swing vs Supply Voltage Voltage Gain vs Frequency Distortion vs Frequency TL/H/7848 – 5 2 Typical Performance Characteristics Distortion vs Output Power (Continued) Device Dissipation vs Output Power 4X Load Device Dissipation vs Output Power 8X Load TL/H/7848 – 6 Application Hints bypass the unused input, preventing degradation of gain and possible instabilities. This is done with a 0.1 mF capacitor or a short to ground depending on the dc source resistance on the driven input. Gain Control To make the LM390 a more versatile amplifier, two pins (2 and 6) are provided for gain control. With pins 2 and 6 open, the 1.35 kX resistor sets the gain at 20 (26 dB). If a capacitor is put from pin 2 to 6, bypassing the 1.35 kX resistor, the gain will go up to 200 (46 dB). If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. A low frequency pole in the gain response is caused by the capacitor working against the external resistor in series with the 150X internal resistor. If the capacitor is eliminated and a resistor connects pin 2 to 6 then the output dc level may shift due to the additional dc gain. Gain control can also be done by capacitively coupling a resistor (or FET) from pin 6 to ground, as in Figure 7 . Additional external components can be placed in parallel with the internal feedback resistors to tailor the gain and frequency response for individual applications. For example, we can compensate poor speaker bass response by frequency shaping the feedback path. This is done with a series RC from pin 6 to 13 (paralleling the internal 15 kX resistor). For 6 dB effective bass boost: R j 15 kX, the lowest value for good stable operation is R e 10 kX if pin 2 is open. If pins 2 and 6 are bypassed then R as low as 2 kX can be used. This restriction is because the amplifier is only compensated for closed-loop gains greater than 9 V/V. Bootstrapping The base of the output transistor of the LM390 is brought out to pin 9 for Bootstrapping. The output stage of the amplifier during positive swing is shown in Figure 3 with its external circuitry. R1 a R2 set the amount of base current available to the output transistor. The maximum output current divided by beta is the value required for the current in R1 and R2: (R1 a R2) e bO (VS/2) b VBE IO MAX Good design values are VBE e 0.7V and bO e 100. Example 0.8 watt into 4X load with VS e 6V. 2 PO e 632 mA IO MAX e RL (6/2) b 0.7 e 364X (R1 a R2) e 100 0.632 0 # J To keep the current in R2 constant during positive swing capacitor CB is added. As the output swings positive CB lifts R1 and R2 above the supply, maintaining a constant voltage across R2. To minimize the value of CB, R1 e R2. The pole due to CB and R1 and R2 is usually set equal to the pole due to the output coupling capacitor and the load. This gives: Input Biasing The schematic shows that both inputs are biased to ground with a 50 kX resistor. The base current of the input transistors is about 250 nA, so the inputs are at about 12.5 mV when left open. If the dc source resistance driving the LM390 is higher than 250 kX it will contribute very little additional offset (about 2.5 mV at the input, 50 mV at the output). If the dc source resistance is less than 10 kX, then shorting the unused input to ground will keep the offset low (about 2.5 mV at the input 50 mV at the output). For dc source resistances between these values we can eliminate excess offset by putting a resistor from the unused input to ground, equal in value to the dc source resistance. Of course all offset problems are eliminated if the input is capacitively coupled. When using the LM390 with higher gains (bypassing the 1.35 kX resistor between pins 2 and 6) it is necessary to 4Cc C j c bO 25 Example: for 100 Hz pole and RL e 4X; Cc e 400 mF and CB e 16 mF, if R1 is made a diode and R2 increased to give the same current, CB can be decreased by about a factor of 4, as in Figure 4 . For reduced component count the load can replace R1. The value of (R1 a R2) is the same, so R2 is increased. Now CB is both the coupling and the bootstrapping capacitor (see Figure 2 ). CB j 3 Typical Applications TL/H/7848 – 4 TL/H/7848 – 3 FIGURE 2. Load Returned to Supply (Amplifier with Gain e 20) FIGURE 1. Load Returned to Ground (Amplifier with Gain e 20) TL/H/7848 – 7 FIGURE 3 TL/H/7848 – 8 FIGURE 4. Amplifier with Gain e 200 and Minimum CB FIGURE 5. 2.5W Bridge Amplifier 4 TL/H/7848 – 9 Typical Applications (Continued) TL/H/7848 – 11 TL/H/7848 – 10 FIGURE 6(b). Frequency Response with Bass Boost FIGURE 6(a). Amplifier with Bass Boost FIGURE 7. Intercom TL/H/7848 – 12 TL/H/7848 – 13 FIGURE 8. AM Radio Power Amplifier Note 1: Twist supply lead and supply ground very tightly. Note 4: R1C1 band limits input signals. Note 2: Twist speaker lead and ground very tightly. Note 5: All components must be spaced very close to IC. Note 3: Ferrite bead is Ferroxcube K5-001-001/3B with 3 turns of wire. 5 LM390 1W Battery Operated Audio Power Amplifier Physical Dimensions inches (millimeters) Molded Dual-In-Line Package (N) Order Number LM390N See NS Package Number N14A 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. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. 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