TPA2001D2

1-W FILTERLESS STEREO CLASS-D AUDIO POWER AMPLIFIER

SLOS292A – MARCH 2000 – REVISED APRIL 2000

8

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

Table 2. Gain Settings

GAIN0

GAIN1

AMPLIFIER GAIN

(dB)

INPUT IMPEDANCE

(k

Ω)

GAIN0

GAIN1

TYP

TYP

0

0

8

104

0

1

12

74

1

0

17.5

44

1

1

23.5

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.

Ci

R

IN

ZI

ZF

Input

Signal

The –3 dB frequency can be calculated using equation 4:

(4)

f

–3 dB +

1

2

p C

i R ø ZI

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, Ci

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.

f

c(highpass) +

1

2

pZ

I

C

i

–3 dB

fc

(5)