CS5525-AS datasheet(21/30 Pages) CIRRUS

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CS5525 CS5526

DS202F5

sion. The user would then issue 8 SCLKs (with

SDI = logic 0) to clear the SDO flag. Upon the fall-

ing edge of the 8th SCLK, the SDO pin will present

the first bit (MSB) of the conversion word. 24

SCLKs (high, then low) are required to read the

conversion word from the port. The user must not

give an explicit command to read the conversion

data register when the PF bit is set to logic 1. The

data conversion word must be read before a new

command can be entered (if the SC command is

used with PF = 1).

If the CC (Continuous Conversion) command is is-

sued (CC = 1, CB =1, all other command bits = 0)

the SDO pin will go low at the completion of a con-

version. The user would then issue 8 SCLKs (with

SDI = logic 0) to clear the SDO flag. Upon the fall-

ing edge of the 8th SCLK, the SDO pin will present

the first bit (MSB) of the conversion word. 24

SCLKs (high, then low) are required to read the

conversion word from the port. The user must not

give an explicit command to read the conversion

data register when the PF bit is set to logic 1. When

operating in the continuous conversion mode, the

user need not read every conversion. If the user

does nothing after SDO falls, SDO will rise one

XIN clock cycle before the next conversion word is

available and then fall again to signal that another

conversion word is available. If the user begins to

clear the SDO flag and read the conversion data,

this action must be finished before the conversion

cycle which is occurring in the background is com-

plete if the user wants to be able to read the new

conversion data.

To exit the continuous conversion mode, issue any

valid command to the SDI input when the SDO flag

falls. If a CC command is issued to the converter

while it is performing a conversion, the filter will

restart a convolution cycle to perform a new con-

version.

Output Word Rate Selection

The WR2-WR0 bits of the configuration register

set the output conversion word rate of the convert-

ers as shown in Table 2. The word rates indicated

in the table assume a master clock of 32.768 kHz.

Upon reset the converters are set to operate with an

output word rate of 15.0 Sps.

Clock Generator

The CS5525/26 include a gate which can be con-

nected with an external crystal to provide the master

clock for the chips. They are designed to operate us-

ing a low-cost 32.768 kHz “tuning fork” type crys-

tal. The 32.768 kHz crystal should be connected as

shown in Figure 18. Lead lengths should be mini-

mized to reduce stray capacitance.

The converters will operate with an external

(CMOS compatible) clock with frequencies up to

three times the typical crystal frequency of 32.768

kHz. Figure 17 details the converter’s performance

at increased clock rates.

The 32.768 kHz crystal is normally specified as a

time-keeping crystal with tight specifications for

both initial frequency and for drift over temperature.

To maintain excellent frequency stability, these

crystals are specified only over limited operating

temperature ranges (i.e. -10 °C to +60 °C). However,

applications with the CS5525/26 don’t generally re-

quire such tight tolerances. When 32.768 kHz tuning

fork crystals are used, it is recommended that protec-

tion components, an external resistor and capacitor

as shown in Figure 18, be used.

Figure 17. High Speed Clock Performance

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