TPA0122

2-W STEREO AUDIO POWER AMPLIFIER

WITH FOUR SELECTABLE GAIN SETTINGS

SLOS247B – JUNE 1999 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

gain setting via GAIN0 and GAIN1 inputs

The gain of the TPA0122 is set by two input terminals, GAIN0 and GAIN1.

Table 1. Gain Settings

GAIN0

GAIN1

SE/BTL

0

0

0

–2 V/V

0

1

0

–6 V/V

1

0

0

–12 V/V

1

1

0

–24 V/V

X

X

1

–1 V/V

The gains listed in Table 1 are realized by changing the taps on the input resistors inside the amplifier. This

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 k

Ω, which is the absolute minimum input impedance of the TPA0122. At the higher gain

settings, the input impedance could increase as high as 115 k

Ω.

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.

C

R

IN

ZI

ZF

Input

Signal

The input resistance at each gain setting is given in the table below:

–24 V/V

14 k

Ω

–12 V/V

26 k

Ω

–6 V/V

45.5 k

Ω

–2 V/V

91 k

Ω