TS4998 STMicroelectronics, TS4998 Datasheet - Page 20

• Manufacturer Part Number: TS4998
• Description: 2 X 1w Differential Input Stereo Audio Amplifier
• Manufacturer: STMicroelectronics

Application information
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4.1
4.2
4.3
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Application information
General description
The TS4998 integrates two monolithic full-differential input/output power amplifiers with two
selectable standby pins dedicated for each channel. The gain of each channel is set by
external input resistors.
Differential configuration principle
The TS4998 also includes a common mode feedback loop that controls the output bias
value to average it at V
output voltage swing, and therefore, to maximize the output power. Moreover, as the load is
connected differentially instead of single-ended, output power is four times higher for the
same power supply voltage.
The advantages of a full-differential amplifier are:
●
●
●
●
●
In theory, the filtering of the internal bias by an external bypass capacitor is not necessary.
However, to reach maximum performance in all tolerance situations, it is recommended to
keep this option.
The only constraint is that the differential function is directly linked to external resistor
mismatching, therefore you must pay particular attention to this mismatching in order to
obtain the best performance from the amplifier.
Gain in typical application schematic
A typical differential application is shown in
The value of the differential gain of each amplifier is dependent on the values of external
input resistors R
region of the frequency-response curve (no C
is expressed by the relation given in
Equation 1
where R
feedback resistors).
High PSRR (power supply rejection ratio),
High common mode noise rejection,
Virtually no pops&clicks without additional circuitry, giving a faster startup time
compared to conventional single-ended input amplifiers,
Easier interfacing with differential output audio DAC,
No input coupling capacitors required due to common mode feedback loop.
IN
= R
IN1
IN1
= R
to R
IN2
CC
IN4
= R
/2 for any DC common mode input voltage. This allows maximum
and of integrated feedback resistors with fixed value. In the flat
IN3
A
V
diff
= R
=
IN4
Equation
----------------------------------------------------- -
Diff
expressed in kΩ and R
input+
V
O+
Figure 1 on page
IN
1.
–
–
V
Diff
effect), the differential gain of each channel
O-
input-
=
R
------------- -
R
feed
3.
IN
feed
=
= 50kΩ (value of internal
50kΩ
------------- -
R
IN
TS4998