A21SP16 Datasheet, PDF (27/37 Pages) STMicroelectronics – Thermal shutdown protection

A21SP16
5
Application information
Application information
5.1
Differential configuration principle
The A21SP16 is a monolithic fully-differential input/output class D power amplifier. The
A21SP16 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, maximizes 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 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.
The main disadvantage is:
 As the differential function is directly linked to external resistor mismatching, paying
particular attention to this mismatching is mandatory in order to obtain the best
performance from the amplifier.
5.2
Gain in typical application schematic
Typical differential applications are shown in Figure 1 on page 4.
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----_I-^u--_n-^t--⁺⁺----––-----^OI--_n---^u_-----^t-^- = ³-_R---⁰--_i-⁰_n--
with R_in expressed in k
Due to the tolerance of the internal 150 k feedback resistor, the differential gain will be in
the range (no tolerance on R_in):
2_-R---7_--i-3_{n--  AVdiff } 3_-R---2_--i-7_n--
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