TPA2001D2
1-W FILTERLESS STEREO CLASS-D AUDIO POWER AMPLIFIER
SLOS292A – MARCH 2000 – REVISED APRIL 2000
APPLICATION INFORMATION
Table 2. Gain Settings
GAIN0
0
0
1
1
GAIN1
0
1
0
1
AMPLIFIER GAIN
(dB)
TYP
8
12
17.5
23.5
INPUT IMPEDANCE
(kΩ)
TYP
104
74
44
24
input resistance
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. As a result, if a single capacitor is used in the input high pass filter, the –3 dB
or cut-off frequency will also change by over 6 times. If an additional resistor is connected from the input pin
of the amplifier to ground, as shown in the figure below, the variation of the cut-off frequency will be much
reduced.
ZF
Ci
Input
Signal
R
IN
ZI
The –3 dB frequency can be calculated using equation 4:
f
–3 dB
+
1
2p C
i
R
ø
Z
I
(4)
If the filter must be more accurate, the value of the capacitor should be increased while value of the resistor to
ground should be decreased. In addition, the order of the filter could be increased.
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 5.
–3 dB
f
c(highpass)
+
1
2
p
Z
I
C
i
(5)
fc
8
POST OFFICE BOX 655303
•
DALLAS, TEXAS 75265
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