CS42448 datasheet(26/64 Pages) CIRRUS

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DS648F2

CS42448

4.2.3

High-Pass Filter and DC Offset Calibration

The high-pass filter continuously subtracts a measure of the DC offset from the output of the decimation

filter. If the high-pass filter is disabled during normal operation, the current value of the DC offset for the

corresponding channel is frozen and this DC offset will continue to be subtracted from the conversion re-

sult. This feature makes it possible to perform a system DC offset calibration by:

1. Running the CS42448 with the high-pass filter enabled until the filter settles. See the Digital Filter

Characteristics for filter settling time.

Disabling the high-pass filter and freezing the stored DC offset.The high-pass filter for ADC1/ADC2 can

be enabled and disabled.

The high pass filter for ADC3 can be independently enabled and dis-

abled. The high-pass filters are controlled using the HPF_FREEZE bit in the register “ADC Control & DAC

De-Emphasis (Address 05h)” on page 45.

4.3

Analog Outputs

4.3.1

Initialization

The initialization and Power-Down sequence flow chart is shown in Figure 12 on page 27. The CS42448

enters a power-down state upon initial power-up. The interpolation and decimation filters, delta-sigma

modulators and control port registers are reset. The internal voltage reference, multi-bit digital-to-analog

and analog-to-digital converters and switched-capacitor low-pass filters are powered down.

The device remains in the power-down state until the RST pin is brought high. The control port is acces-

sible once RST is high, and the desired register settings can be loaded per the interface descriptions in

the “Control Port Description and Timing” on page 35.

Once MCLK is valid, VQ will ramp up to VA/2, and the internal voltage references, FILT+_ADC and

FILT+_DAC, will begin powering up to normal operation. Power is applied to the D/A converters and

switched-capacitor filters, and the analog outputs are clamped to the quiescent voltage, VQ. Once LRCK is

valid, MCLK occurrences are counted over one LRCK period to determine the MCLK/LRCK frequency ra-

tio. After an approximate 2000 sample period delay, normal operation begins.

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