CS4525 datasheet(47/91 Pages) CIRRUS

47 / 91 page

DS726A1

CS4525

6.1.7.5

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

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 the PWM switching rate. This feature is

enabled by setting the FreqShift bit in the Clock Config register. When this feature is enabled, the output

switch rate is lowered and the quantization levels are increased as shown in Table 9 below.

The nominal PWM switching frequencies and quantization levels are discussed in “PWM Modulators and

Sample Rate Converters” on page 53.

6.1.8

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 will output audio from channel 1 and channel 2 respectively re-

gardless of the setting of the PWMDSel[1:0] bits; see “PWM_SIG Logic-Level Output Configurations” on

page 44 for more information. The OUT1 - OUT4 PWM driver outputs will mute by outputting a non-mod-

ulated 50% duty cycle signal. If the Ch1Mix[1:0] bits are configured for a mono mix on channel 1, the mix

will be disabled and channel 1 will be output on PWM_SIG1 while the headphone detect input signal is

active; see “Channel Mixer” on page 30 for more information. If the bass manager is enabled, it will be

automatically disabled while the headphone detect input signal is active; see “Bass Management” on

page 35 for more information.

When configured as a headphone detect input pin and the input is inactive, the OUT1 - OUT4 driver out-

puts will output audio according to the channel mixer and bass manager registers settings, and the

PWM_SIG output pins will mute by outputting a non-modulated 50% duty cycle.

In both configurations, the active logic input level is determined by the HP/MutePol bit.

Supplied XTAL or

SYS_CLK Frequency

PWM Switch Rate

Quantization Levels

18.432 MHz

329.143 kHz

24.576 MHz

341.300 kHz

27.000 MHz

375 kHz

Table 9. PWM Output Switching Rates and Quantization Levels

Referenced Control

FreqShift.............................. “AM Frequency Shifting (FreqShift)” on page 65

Referenced Control

HP/Mute .............................. “HP_Detect/Mute Pin Mode (HP/Mute)” on page 65

HP/MutePol ......................... “HP_Detect/Mute Pin Active Logic Level (HP/MutePol)” on page 65

PWMDSel[1:0]..................... “PWM Signals Output Data Select (PWMDSel[1:0])” on page 68

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