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CS5520-BSZ

16/20-bit bridge transducer A/D conveter

Cirrus Logic 

CS5516, CS5520

System Initialization

Whenever power is applied to the

CS5516/CS5520 A/D converters, the devices

must be reset to a known condition before

proper operation can occur. The internal reset is

applied after power is established and lasts for

approximately 100 ms. The RST pin can also be

used to establish a reset condition. The reset sig-

nal should remain low for at least one XIN clock

cycle to ensure adequate reset time. It is recom-

mended that the RST pin be used to reset the

converter if the power supplies rise very slowly

or with poor startup characteristics. The RST

signal can be generated by a microcontroller out-

put, or by use of an R-C circuit.

The reset function initializes the configuration

register and all five of the calibration registers;

and places the microcontroller in command

mode ready to accept a command from the serial

port. Whenever the device is reset the DRDY

pin will be set to a logic 1 and the on-chip regis-

ters are initialized to the following states:

Configuration

000000(H)

Calibration registers:

DAC

000000(H)

Gain

800000(H)

AIN Ratiometric Offset

000000(H)

AIN Non-ratiometric Offset 000000(H)

VREF Non-ratiometric Offset 000000(H)

1144

CALIBRATION

After the CS5516/20 is reset, the device is func-

tional and can perform measurements without

being calibrated. The converter will utilize the

initialized values of the calibration registers to

calculate output words.

The converter uses the two outputs (AIN &

VREF) of the dual channel converter along with

the contents of the calibration registers to com-

pute the conversion data word. The following

equation indicates the computation.

[[ ] ] R0 = R4

DAIN − R1

DVREF − R2

− R3

Where R0 is the output data, DAIN and DVREF

are the digital output words from the AIN and

VREF digital filter channels, and R1, R2, R3

and R4 are the contents of the following calibra-

tion registers:

R1 = AIN non-ratiometric offset

R2 = VREF non-ratiometric offset

R3 = AIN ratiometric offset

R4 = Gain

The computed output word, R0, is a two’s com-

plement number.

Calibration minimizes the errors in the converted

output data. If calibration has not been per-

formed, the measurements will include offset

and gain errors of the entire system.

The converter may be calibrated each time it is

powered up, or calibration words from a pre-

vious calibration may be uploaded into the

appropriate calibration registers from some type

of E2PROM by the system microcontroller.

The converter uses five different registers to

store specific calibration information. Each of

the calibration registers stores information perti-

nent to correcting a specific source of error

associated with either the converter or with the

input transducer and its wiring. The method by

DS74F21

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