CRD4525-D1(2008) データシートの表示（PDF） - Cirrus Logic

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CRD4525-D1
(Rev.:2008)

30 W Digital Audio Amplifier with Integrated ADC

Cirrus Logic 

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 Table 11

below.

Supplied XTAL or

SYS_CLK Frequency

18.432 MHz

24.576 MHz

27.000 MHz

PWM Switch Rate

329.143 kHz

341.300 kHz

375 kHz

Quantization Levels

56

72

72

Table 11. PWM Output Switching Rates and Quantization Levels

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

Sample Rate Converters” on page 58.

Referenced Control

Register Location

FreqShift.............................. “AM Frequency Shifting (FreqShift)” on page 70

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 “Channel Mixer” on page 30, “2-Way Crossover & Sensitivity

Control” on page 42, and “Bass Management” on page 35 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.

DS726PP3

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