CS3511 Datasheet, PDF (12/26 Pages) Cirrus Logic – Stereo 10 W High-efficiency Class-D Audio Power Amplifier

4. APPLICATIONS
CS3511
4.1 CS3511 Input Stage
The input stage of the CS3511 is configured as a differential receiver to maximize common-mode rejection
in typical audio circuits. To maximize this benefit, the INx+ and INx- pins should be driven with differential
signals from sources that have the same output impedance. Also, the signals should be routed parallel to
one another from their source to the analog inputs of the CS3511.
In some instances, there will be a necessity to drive the CS3511 with a single-ended input signal. In this
case, the unused input should be AC coupled to ground using the same value of C_I implemented for the
driven channel. Either input, INx+ or INx-, can be used for the signal input. To minimize the effects of ground
noise in the system, C_I should be terminated at the ground connection through a resistor, R_I. Please refer
to Figure 3. The value of the resistor should match the output impedance of the audio source.
Audio Source
CS3511
Z_OUT
C_I
C_I
R_I = Z_OUT
INx+
INx-
Figure 3. CS3511 Input Stage
4.2 Dynamic DC Offset Calibration
Abrupt changes in DC output offset level are a known cause of audible turn-on and turn-off pops. Typically,
when a system turns on (begins switching), the potential across the speaker changes abruptly from 0 V to
the steady-state DC offset voltage of the system. Similarly, when the system turns off, the potential changes
abruptly from the steady-state DC offset voltage to 0 V. These abrupt changes are heard as a pop.
The CS3511 employs a patented method for reducing this pop. Immediately before the outputs begin to
switch, a calibration circuit dynamically minimizes the amplifier’s internal offsets. With these offsets at a min-
imum, the outputs begin to switch and the CS3511 begins to slowly ramp the DC output offset potential to
the steady-state DC offset voltage. This ramp is slow enough to keep the speaker movement in the subsonic
range. During turn-off, this procedure is reversed. The static DC offset voltage is ramped down to a dynam-
ically minimized DC offset level before output switching is stopped.
Dynamic offset cancellation requires equal impedances on the positive and negative inputs. If a single-end-
ed audio source with a 600 Ω output impedance is connected to the IN1+ (through a DC blocking capacitor),
IN1- must be terminated to ground with a 600 Ω resistor (also through a DC blocking capacitor. (See
Figure 3).
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DS845PP2