DS726PP2
51
CS4525
6.1.9.2
PWM AM Frequency Shift
When using a PWM amplifier in a system containing an AM tuner, it is possible that the PWM switch rate
conflicts with the desired tuning frequency of the AM tuner. To overcome this effect, the CS4525 includes
a PWM switch rate shift feature.
The feature adjusts the PWM switching frequency and quantization levels to remove interference when
the desired tuning frequency of an AM tuner is positioned near a harmonic of the PWM switching rate.
This feature is enabled by setting the FreqShift bit in the Clock Config register. When this feature is en-
abled, the output switch rate is lowered and the quantization levels are increased as shown in
below.
The nominal PWM switching frequencies and quantization levels are discussed in
Sample Rate Converters” on page 58
.
6.1.10
Headphone Detection & Hardware Mute Input
The CS4525 includes a configurable HP_DETECT/MUTE input pin which can be used as a hardware
mute input or a headphone detection input. The function of this pin is set by the HP/Mute bit in the Clock
Config register.
When configured as a mute input pin, all PWM modulators and the AUX_SDOUT signal will be placed in
a mute state when the pin is active.
When configured as a headphone detect input pin and the HP_DETECT/MUTE input is active, the
PWM_SIG1 and PWM_SIG2 output pins can output audio from channel 1 and channel 2 respectively re-
gardless of the setting of the PWMDSel[1:0] bits. The OUT1 - OUT4 PWM driver outputs will mute by out-
putting a non-modulated 50% duty cycle signal. While the headphone detect input signal is active, the
channel mixing, 2-way crossover, and bass management features will all be disabled regardless of the
settings of the LChMix[1:0], En2Way, and BassMgr[2:0] bits, respectively. It should be noted that the right
channel’s channel mixing is not affected by the headphone detection input signal and will always output
as dictated by the RChMix[1:0] bits. See
,
“2-Way Crossover & Sensitivity
for more information.
When configured as a headphone detect input pin and the HP_DETECT/MUTE input is inactive, the
OUT1 - OUT4 driver outputs will output audio according to the channel mixer and bass manager bits’ set-
tings, and the PWM_SIG output pins will mute by outputting a non-modulated 50% duty cycle.
Supplied XTAL or
SYS_CLK Frequency
PWM Switch Rate
Quantization Levels
18.432 MHz
329.143 kHz
56
24.576 MHz
341.300 kHz
72
27.000 MHz
375 kHz
72
Table 11. PWM Output Switching Rates and Quantization Levels
Referenced Control
Register Location
FreqShift..............................
