TPA2000D2PWPR datasheet(12/20 Pages) TI

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INPUT RESISTANCE

Input

Signal

*3 dB

2p C

I Z I

(4)

INPUT CAPACITOR, C

c(highpass) +

2 p Z

−3 dB

(5)

I +

2p Z

I fc

(6)

CI ≤ CBYP / 10

(7)

TPA2000D2

SLOS291F – MARCH 2000 – REVISED MARCH 2007

Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest

value to over 6 times that value.

The -3 dB frequency can be calculated using Equation 4:

In the typical application an input capacitor, CI, is required to allow the amplifier to bias the input signal to the

proper dc level for optimum operation. In this case, CI and the input impedance of the amplifier, ZI, form a

high-pass filter with the corner frequency determined in Equation 5.

The value of CI is important, as it directly affects the bass (low frequency) performance of the circuit. Consider

the example where ZI is 20 kΩ and the specification calls for a flat bass response down to 80 Hz. Equation 5 is

reconfigured as Equation 6.

In this example, CI is 0.1 µF, so one would likely choose a value in the range of 0.1 µF to 1 µF. If the gain is

known and is constant, use ZI from Table 1 to calculate CI. A further consideration for this capacitor is the

leakage path from the input source through the input network (CI) and the feedback network to the load. This

leakage current creates a dc offset voltage at the input to the amplifier that reduces useful headroom, especially

in high gain applications. For this reason a low-leakage tantalum or ceramic capacitor is the best choice. When

polarized capacitors are used, the positive side of the capacitor should face the amplifier input in most

applications as the dc level there is held at VDD/2, which is likely higher than the source dc level. Note that it is

important to confirm the capacitor polarity in the application.

CI should be 10 times smaller than the bypass capacitor to reduce clicking and popping noise from power on/off

and entering and leaving shutdown. After sizing CI for a given cutoff frequency, size the bypass capacitor up to

10 times that of the input capacitor.

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