TS4962_10 Datasheet, PDF (30/44 Pages) STMicroelectronics – 2.8 W filter-free mono class D audio power amplifier

Application information
4
Application information
TS4962
4.1
Differential configuration principle
The TS4962 is a monolithic, fully differential input/output class D power amplifier. The
TS4962 also includes a common-mode feedback loop that controls the output bias value to
average it at V_CC/2 for any DC common-mode input voltage. This allows the device to
always have a maximum output voltage swing, and by consequence, maximize the output
power. Moreover, as the load is connected differentially compared to a single-ended
topology, the output is four times higher for the same power supply voltage.
The advantages of a fully differential amplifier are:
● 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.
● no input coupling capacitors required because of common-mode feedback loop.
The main disadvantage is that, since the differential function is directly linked to the external
resistor mismatching, particular attention should be paid to this mismatching in order to
obtain the best performance from the amplifier.
4.2
Gain in typical application schematic
Typical differential applications are shown in Figure 1 on page 6.
In the flat region of the frequency-response curve (no input coupling capacitor effect), the
differential gain is expressed by the relation:
A_Vdiff
=
-^O-----^u---^t--⁺----–-----^O-----^u----^t-^-
In⁺ – In^-
=
3_----0_---0_--
R_in
with R_in expressed in kΩ.
Due to the tolerance of the internal 150 kΩ feedback resistor, the differential gain is in the
range (no tolerance on R_in):
-²---⁷---³--
R_in
≤
A_Vdiff
≤
3_----2_---7_--
R_in
30/44
Doc ID 10968 Rev 8