TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C – JANUARY1998 – REVISED MARCH 2000
APPLICATION INFORMATION
component selection (continued)
As an example, consider an input resistance of 10 kΩ and a feedback resistor of 50 kΩ. The BTL gain of the
amplifier would be –10 V/V, and the effective impedance at the inverting terminal would be 8.3 kΩ, which is well
within the recommended range.
Forhighperformanceapplicationsmetalfilmresistorsarerecommendedbecausetheytendtohavelowernoise
levels than carbon resistors. For values of R above 50 kΩ the amplifier tends to become unstable due to a pole
F
formed from R and the inherent input capacitance of the MOS input structure. For this reason, a small
F
compensation capacitor, C , of approximately 5 pF should be placed in parallel with R when R is greater than
F
F
F
50 kΩ. This, in effect, creates a low-pass filter network with the cutoff frequency defined in equation 7.
–3 dB
1
2 R C
(7)
f
co(lowpass)
F F
f
co
For example, if R is 100 kΩ and C is 5 pF then f is 318 kHz, which is well outside of the audio range.
F
F
co
input capacitor, C
I
In the typical application an input capacitor, C , is required to allow the amplifier to bias the input signal to the
I
proper dc level for optimum operation. In this case, C and R form a high-pass filter with the corner frequency
I
I
determined in equation 8.
–3 dB
1
f
(8)
co(highpass)
2 R C
I
I
f
co
The value of C is important to consider as it directly affects the bass (low frequency) performance of the circuit.
I
Consider the example where R is 10 kΩ and the specification calls for a flat bass response down to 40 Hz.
I
Equation 8 is reconfigured as equation 9.
1
C
(9)
I
2 R f
co
I
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TI [ TEXAS INSTRUMENTS ]
