CS5525-AS datasheet(20/29 Pages) CIRRUS

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CS5525 CS5526

DS202F3

the input signal can be reduced to the point in

which the gain register reaches its upper limit of 2.0

(decimal) [FFFFFF Hex] (this is most likely to oc-

cur with an input signal approximately 1/2 the

nominal range). Alternatively, the input signal can

be increased to a point in which the modulator

reaches its one’s density upper limit of 80% (this is

most likely to occur with an input signal approxi-

mately 1.5 times the nominal range). Also, for full

scale inputs larger than the nominal full scale value

of the range selected, there is some voltage at

which the various internal circuits may saturate due

to limited amplifier headroom (this is most likely to

occur on the 100 mV range setting when NBV = -

1.8 V).

Analog Output Latch Pins

The A3-A0 pins of the converters mimic the D23-

D20 bits of the configuration register. A3-A0 can

be used to control multiplexers and other logic

functions outside the converter. The outputs can

sink or source at least 1 mA, but it is recommended

to limit drive currents to less than 2 0

µA to reduce

self-heating of the chip. These outputs are powered

from VA+, hence, their output voltage for a logic 1

will be limited to the VA+ voltage.

Serial Port Interface

The CS5525/26 serial interface consist of four pins,

SCLK, SDO, SDI, and CS. The CS pin must be

held low (logic 0) before SCLK transitions can be

recognized by the port logic. The SDO output will

be held at high impedance any time CS is a logic 1.

If the CS pin is tied low, the port can function as a

three wire interface.

The SCLK input is designed with a Schmitt-trigger

input to allow an optoisolator with slower rise and

fall times to directly drive the pin.

The SDO output is capable of sinking or sourcing

up to 5 mA to directly drive an optoisolator LED.

SDO will have less than a 400 mV loss in the drive

voltage when sinking or sourcin g 5mA.

Serial Port Initialization

The serial port is initialized to the command mode

whenever a power-on reset is performed inside the

converter, when the port initialization sequence is

completed, or whenever a command byte, data

word sequence is completed. The port initialization

sequence involves clocking 15 (or more) bytes of

all 1's, followed by one byte with the following bit

contents (11111110). This sequence places the

chips in the command mode where it waits for a

valid command.

Performing Conversions (With PF bit = 0)

Setting the SC (Single Conversion) bit of the com-

mand word to a logic 1 with the CB bit = 1, all other

command bits = 0, the CS5525/CS5526 will per-

form one conversion. At the completion of the con-

version the DF (Done Flag) bit of the configuration

the configuration register to determine if the DF bit

is set. If DF has been set, a command can be issued

to read the conversion data register to obtain the

conversion data word. The DF bit of the configu-

ration register will be cleared to logic 0 when the

data register, the gain register, the offset register, or

the set-up registers are read. Reading only the con-

figuration register will not clear the DF flag bit.

If an SC command is issued to the converters while

they are performing a conversion, the filter will re-

start a convolution cycle to perform a new conver-

sion.

Performing Conversions (With PF bit = 1)

Setting the PF bit of the configuration register to a

logic 1 enables the SDO output pin to behave as a

flag signal whenever conversions are completed.

This eliminates the need for the user to read the DF

flag bit of the configuration register to determine if

the conversion data word is available.

If the SC (Single Conversion) command is issued

(SC = 1, CB= 1, all other command bits = 0) the

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

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