TS4974_07 Datasheet, PDF (16/25 Pages) STMicroelectronics – 1W differential audio power amplifier with up/down digital volume control pins

Application information
4
Application information
TS4974
4.1
Differential configuration principle
The TS4974 is a monolithic full-differential input/ output power amplifier with a digital volume
control. It has an internal gain range of -33 dB up to +12 dB, by steps of 3dB (see
Section 4.9: Volume setting on page 20), which offers better performance in terms of noise
immunity and PSRR.
The advantages of a full-differential amplifier are:
● Very high PSRR (power supply rejection ratio).
● High common mode noise rejection.
● Virtually zero pop without additional circuitry, giving a faster start-up time compared to
conventional single-ended input amplifiers.
● Easier interfacing with differential output audio DAC.
In theory, the filtering of the internal bias by an external bypass capacitor is not necessary.
But, to reach maximum performance in all tolerance situations, it is better to keep this
option.
4.2
Note:
Low frequency response
The input coupling capacitors block the DC part of the input signal at the amplifier inputs.
Input capacitors C_in and input impedance Z_in forms a first-order, high pass filter with -3 dB
cut-off frequency.
F_CL
=
2×
1
π × R_in
× C_in
(Hz)
Differential input impedance of 60 kΩ is a typical value, and there is tolerance around this
value.
From Figure 39 you can easily establish the C_in value required for a cut-off frequency of
-3 dB.
Figure 39. -3dB lower cut-off frequency vs. input capacitance
100
All gain setting
Tamb=25°C
Minimum Input
Impedance
Typical Input
Impedance
10
Maximum Input
Impedance
0.1
0.5
1
Input Capacitor Cin (μF)
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