TS4995 Datasheet, PDF (17/26 Pages) STMicroelectronics – 1.2 W fully differential audio power amplifier with selectable standby and 6 dB fixed gain

TS4995
4
Application information
Application information
4.1
Differential configuration principle
The TS4995 is a monolithic full-differential input/ output power amplifier with fixed +6 dB
gain. The TS4995 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 maximum
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:
● Very high PSRR (power supply rejection ratio)
● High common mode noise rejection
● Virtually no pop and click 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 due to common mode feedback loop
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.
4.2
Common mode feedback loop limitations
As explained previously, the common mode feedback loop allows the output DC bias voltage
to be averaged at V_CC/2 for any DC common mode bias input voltage.
Due to the V_IC limitation of the input stage (see Table 4 on page 5), the common mode
feedback loop can fulfil its role only within the defined range.
4.3
Note:
Low frequency response
The input coupling capacitors block the DC part of the input signal at the amplifier inputs. C_in
and R_in form a first-order high pass filter with -3 dB cut-off frequency.
F_CL
=
2×
1
π × R_in
× C_in
(Hz)
The input impedance for the TS4995 is typically 20kΩ and there is tolerance around this
value.
From Figure 56, you can easily establish the C_in value required for a -3 dB cut-off frequency.
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