Datasheet

C
i
IN
Z
i
Z
f
Input
Signal
f +
1
2p Z
i
C
i
f
c
+
1
2p Z
i
C
i
−3 dB
f
c
C
i
+
1
2p Z
i
f
c
TPA3001D1
SLOS398E –DECEMBER 2002–REVISED AUGUST 2010 www.ti.com
Table 1. Gain Settings
AMPLIFIER GAIN INPUT IMPEDANCE
(dB) (kΩ)
GAIN1 GAIN0
TYP TYP
0 0 12 241
0 1 18 168
1 0 23.6 104
1 1 36 33
INPUT RESISTANCE
Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest
value to over six times that value. As a result, if a single capacitor is used in the input high-pass filter, the –3-dB
or cutoff frequency also changes by over six times.
The –3-dB frequency can be calculated using Equation 5. Use Table 1 for Z
I
values.
(5)
INPUT CAPACITOR, C
I
In the typical application, an input capacitor (C
I
) is required to allow the amplifier to bias the input signal to the
proper dc level for optimum operation. In this case, C
I
and the input impedance of the amplifier (Z
I
) form a
high-pass filter with the corner frequency determined in Equation 6.
(6)
The value of C
I
is important, as it directly affects the bass (low frequency) performance of the circuit. Consider
the example where Z
I
is 241 kΩ and the specification calls for a flat bass response down to 20 Hz. Equation 6 is
reconfigured as Equation 7.
(7)
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