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LM2876 数据表(PDF) 7 Page - National Semiconductor (TI) |
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LM2876 数据表(HTML) 7 Page - National Semiconductor (TI) |
7 / 22 page External Components Description (Figures 1, 2) Components Functional Description 1. R IN Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals. 2. R A Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal. 3. C A Provides bias filtering. 4. C Provides AC coupling at the input and output of the amplifier for single supply operation. 5. R B Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load upon power-down of the system due to the low input impedance of the circuitry when the under-voltage circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V. 6. C C (Note 15) Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of the output transistor. The capacitor also suppresses external electromagnetic switching noise created from fluorescent lamps. 7. Ri Inverting input resistance to provide AC Gain in conjunction with R f1. 8. Ci (Note 15) Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at: f c = 1/(2 πRi Ci) 9. R f1 Feedback resistance to provide AC Gain in conjunction with Ri. 10. R f2 (Note 15) At higher frequencies feedback resistance works with C f to provide lower AC Gain in conjunction with Rf1 and Ri. A high frequency pole (lowpass roll-off) exists at: f c =[Rf1 Rf2 (s + 1/Rf2Cf)]/[(Rf1 +Rf2)(s + 1/Cf(Rf1 +Rf2))] 11. C f (Note 15) Compensation capacitor that works with R f1 and Rf2 to reduce the AC Gain at higher frequencies. 12. R M Mute resistance set up to allow 0.5 mA to be drawn from pin 8 to turn the muting function off. → R M is calculated using: RM ≤ (|V EE| − 2.6V)/I8 where I8 ≥ 0.5 mA. Refer to the Mute Attenuation vs Mute Current curves in the Typical Performance Characteristics section. 13. C M Mute capacitance set up to create a large time constant for turn-on and turn-off muting. 14. R SN (Note 15) Works with C SN to stabilize the output stage by creating a pole that eliminates high frequency oscillations. 15. C SN (Note 15) Works with R SN to stabilize the output stage by creating a pole that eliminates high frequency oscillations. f c = 1/(2 πR SNCSN) 16. L (Note 15) Provides high impedance at high frequecies so that R may decouple a highly capacitive load and reduce the Q of the series resonant circuit due to capacitive load. Also provides a low impedance at low frequencies to short out R and pass audio signals to the load. 17. R (Note 15) 18. C S Provides power supply filtering and bypassing. 19. S1 Mute switch that mutes the music going into the amplifier when opened. Note 15: Optional components dependent upon specific design requirements. Refer to the Application Information section for more information. OPTIONAL EXTERNAL COMPONENT INTERACTION Although the optional external components have specific desired functions that are designed to reduce the bandwidth and eliminate unwanted high frequency oscillations they may cause certain undesirable effects when they interact. Inter- action may occur for components whose reactances are in close proximity to one another. One example would be the coupling capacitor, C C, and the compensation capacitor, Cf. These two components act as low impedances to certain frequencies which will couple signals from the input to the output. Please take careful note of basic amplifier compo- nent functionality when designing in these components. The optional external components shown in Figure 2 and described above are applicable in both single and split volt- age supply configurations. www.national.com 7 |
类似零件编号 - LM2876_00 |
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类似说明 - LM2876_00 |
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