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TPA721 Datasheet(PDF) 15 Page - Texas Instruments |
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TPA721 Datasheet(HTML) 15 Page - Texas Instruments |
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15 / 28 page  www.ti.com APPLICATION SCHEMATICS Audio Input Bias Control VDD 700 mW 6 5 7 VO+ VDD 1 2 4 BYPASS IN– VDD/2 CI CS 1 µF CB 2.2 µF SHUTDOWN VO– 8 GND From System Control 3 IN+ RI 10 k Ω RF 50 k Ω – + – + COMPONENT SELECTION Gain-Setting Resistors, RF and RI BTL gain + * 2 R F R I (5) Effective impedance + R F R I R F ) R I (6) TPA721 SLOS231E – NOVEMBER 1998 – REVISED JUNE 2004 Figure 26 is a schematic diagram of a typical handheld audio application circuit, configured for a gain of –10 V/V. Figure 26. TPA721 Application Circuit The following sections discuss the selection of the components used in Figure 26. The gain for each audio input of the TPA721 is set by resistors RF and RI according to Equation 5 for BTL mode. BTL mode operation brings about the factor 2 in the gain equation due to the inverting amplifier mirroring the voltage swing across the load. Given that the TPA721 is a MOS amplifier, the input impedance is high; consequently, input leakage currents are not generally a concern, although noise in the circuit increases as the value of RF increases. In addition, a certain range of RF values is required for proper startup operation of the amplifier. Taken together, it is recommended that the effective impedance seen by the inverting node of the amplifier be set between 5 k Ω and 20 kΩ. The effective impedance is calculated in Equation 6. As an example, consider an input resistance of 10 k Ω and a feedback resistor of 50 kΩ. The BTL gain of the amplifier would be –10 V/V, and the effective impedance at the inverting terminal would be 8.3 k Ω, which is well within the recommended range. For high-performance applications, metal film resistors are recommended because they tend to have lower noise levels than carbon resistors. For values of RF above 50 kΩ, the amplifier tends to become unstable due to a pole formed from RF and the inherent input capacitance of the MOS input structure. For this reason, a small compensation capacitor of approximately 5 pF should be placed in parallel with RF when RF is greater than 50 k Ω. This, in effect, creates a low-pass filter network with the cutoff frequency defined in Equation 7. 15 |
Similar Part No. - TPA721_16 |
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Similar Description - TPA721_16 |
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