24

DS658F2

CS5345

4.2.2

Master Mode

As a clock master, LRCK and SCLK will operate as outputs. LRCK and SCLK are internally derived from

MCLK with LRCK equal to Fs and SCLK equal to 64 x Fs as shown in Figure 8.

4.2.3

Slave Mode

In Slave Mode, SCLK and LRCK operate as inputs. The Left/Right clock signal must be equal to the sam-

ple rate, Fs, and must be synchronously derived from the supplied master clock, MCLK.

The serial bit clock, SCLK, must be synchronously derived from the master clock, MCLK, and be equal to

128x, 64x, 48x or 32x Fs, depending on the desired speed mode. Refer to Table 3 for required clock ra-

tios.

4.3

High-Pass Filter and DC Offset Calibration

When using operational amplifiers in the input circuitry driving the CS5345, a small DC offset may be driven

into the A/D converter. The CS5345 includes a high-pass filter after the decimator to remove any DC offset

which could result in recording a DC level, possibly yielding clicks when switching between devices in a mul-

tichannel system.

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

filter. If the HPFFreeze bit (See “High-Pass Filter Freeze (Bit 1)” on page 32.) is set during normal operation,

the current value of the DC offset for the each channel is frozen and this DC offset will continue to be sub-

tracted from the conversion result. This feature makes it possible to perform a system DC offset calibration

by:

1. Running the CS5345 with the high-pass filter enabled until the filter settles. See the Digital Filter Char-

acteristics section for filter settling time.

2. Disabling the high-pass filter and freezing the stored DC offset.

A system calibration performed in this way will eliminate offsets anywhere in the signal path between the

calibration point and the CS5345.

Single-Speed

Double-Speed

Quad-Speed

SCLK/LRCK Ratio

32x, 48x, 64x, 128x

32x, 48x, 64x

32x, 48x, 64x

Table 3. Slave Mode Serial Bit Clock Ratios

÷256

÷128

÷64

÷4

÷2

÷1

00

01

10

00

01

10

LRCK

SCLK

000

001

010

÷1

÷1.5

÷2

011

100

÷3

÷4

MCLK

FM Bits

MCLK Freq Bits

Figure 8. Master Mode Clocking