TS2007_11 Datasheet, PDF (22/29 Pages) STMicroelectronics – 3 W filter-free Class D audio power amplifer with 6-12 dB fixed gain select

Application information
4
Application information
TS2007
4.1
Differential configuration principle
The TS2007 is a monolithic fully-differential input/output class D power amplifier. The
TS2007 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 full-differential amplifier are:
● High PSRR (power supply rejection ratio)
● High common-mode noise rejection
● Virtually zero pop 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 thanks to common-mode feedback loop
4.2
Note:
Gain settings
In the flat region of the frequency-response curve (no input coupling capacitor or internal
feedback loop + load effect), the differential gain can be set to either 6 or 12 dB depending
on the logic level of the GS pin:
GS
Gain (dB)
Gain (V/V)
1
6 dB
2
0
12 dB
4
Between the GS pin and V_CC there is an internal 300 kΩ resistor. When the pin is floating
the gain is 6 dB.
4.3
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 2: Operating conditions on page 3), the
common-mode feedback loop can fulfill its role only within the defined range.
4.4
Low frequency response
If a low frequency bandwidth limitation is required, it is possible to use input coupling
capacitors. In the low frequency region, the input coupling capacitor C_in starts to have an
effect. C_in forms, with the input impedance Z_in, a first order high-pass filter with a -3 dB cutoff
frequency (see Table 5 to Table 9).
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Doc ID 13123 Rev 4