CS5529(1997) Ver la hoja de datos (PDF) - Cirrus Logic

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CS5529
(Rev.:1997)

16-Bit, Programmable ∆Σ ADC with 6-Bit Latch

Cirrus Logic 

CS5529

FAQs

13) Why does the offset move when the CS5525/26 with a 2.5 V reference, is

calibrated several times? What can be done to prevent this?

A: The CS5526 is a 20-bit ADC with inherent Gaussian thermal and quanti-

zation noise associated with each conversion. Therefore, every time the

converter is calibrated, a different offset calibration output has a chance

of occurring. By averaging conversions, the peak-to-peak noise can be

reduced by a factor of 1/sqrt(n) (where n is the number of samples taken).

The offset register can be accessed after calibration, and the offset uncer-

tainty of a converter can almost be eliminated (to 1 code) by averaging.

The CS5525 (16-bits) always has 1 count of variability, even if averaged,

because the noise and calibration can occur at a boundary between two

codes. If the calibration code is on the boundary the random noise could

toggle the offset between the two codes.

14) Is a different calibration required for each gain getting?

A: For maximum accuracy, calibrations should be performed for offset and

gain for each gain setting. If a factory calibration is performed using a

system calibration, the offset and gain register contents can be read by

the system microcontroller and stored in EEPROM. These same calibra-

tion words can then be uploaded into the offset and gain registers of the

converter when power is re-applied to the system, or when the gain range

is changed.

15) What is the advantage of performing calibrations at lower output word

rates?

A: Calibrations are performed at the output word rate selected by the WR2-

WR0 bits of the configuration register. Since higher word rates result in

conversion words with more peak-to-peak noise, it is better to calibrate at

lower output word rates. To minimize the digital noise near the device,

the user should wait for each calibration step to be completed before

reading or writing to the serial port.

16) How can I get the best noise performance from the CS5525/26?

A: Use the bipolar mode or increase the reference voltage, since each of

these increase the size of the LSB.

PI246PP1 OCT ‘97

7

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