TPA0112 Datasheet, PDF (21/34 Pages) Texas Instruments – 2-W STEREO AUDIO POWER AMPLIFIER WITH FOUR SELECTABLE GAIN SETTINGS

TPA0112
2-W STEREO AUDIO POWER AMPLIFIER
WITH FOUR SELECTABLE GAIN SETTINGS
SLOS204B – MAY 1999 – REVISED MARCH 2000
APPLICATION INFORMATION
gain setting via GAIN0 and GAIN1 inputs
The gain of the TPA0112 is set by two input terminals, GAIN0 and GAIN1.
Table 1. Gain Settings
GAIN0
0
0
1
1
X
GAIN1
0
1
0
1
X
SE/BTL
0
0
0
0
1
A_V
–2 V/V
–6 V/V
–12 V/V
–24 V/V
–1 V/V
The gains listed in Table 1 are realized by changing the taps on the input resistors inside the amplifier. This
causes the input impedance, Z_I, to be dependant on the gain setting. The actual gain settings are controlled
by ratios of resistors, so the actual gain distribution from part-to-part is quite good. However, the input
impedance will shift by 30% due to shifts in the actual resistance of the input impedance.
For design purposes, the input network (discussed in the next section) should be designed assuming an input
impedance of 10 kΩ, which is the absolute minimum input impedance of the TPA0112. At the higher gain
settings, the input impedance could increase as high as 115 kΩ.
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
C
Input
Signal
IN
ZI
R
The input impedance at each gain setting is given in the table below:
A_V
–24 V/V
–12 V/V
–6 V/V
–2 V/V
Z_I
14 kΩ
26 kΩ
45.5 kΩ
91 kΩ
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