CS5525(1998) Просмотр технического описания (PDF) - Cirrus Logic

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CS5525
(Rev.:1998)

16-Bit/20-Bit ∆Σ Multi-Range ADC with 4-Bit Latch

Cirrus Logic 

CS5525 CS5526

FAQs

how it affects measurement accuracy as temperature changes can be

made. Once the amount of drift is known, you can determine if a new cal-

ibration is required. A good rule of thumb is to recalibrate the converter

(or system) with every ten degrees of ambient temperature change.

11) What do the numbers in the calibration registers actually mean?

A: There are two internal read/write calibration registers in the CS5525/26

(offset, and gain). One LSB in the offset register is 2-24 proportion of the

input span (bipolar span is 2 times the unipolar span). The MSB in the

offset register determines if the offset that is to be trimmed is either posi-

tive or negative. The converter can typically trim ±50% of the input span.

The gain register spans from 0 to (2 - 2-23). The decimal equivalent

meaning of the gain register is:

D = b020+ b12-1 + b22-2 + b32-3 + ... + bN2-N

where the binary numbers have a value of either zero or one. After a gain

calibration has been performed, the numeric value in the gain register

should not exceed the range of 0.5 to 2.0 (decimal) [400000(Hex) to

FFFFFF(Hex)].

12) How can the gain be calibrated if a full-scale signal is not available?

A: The CS5525/26 can be gain calibrated with some input signal other than

full scale. For example, when the converter is reset, the gain register’s

calibration word is 1.0 (decimal). If a signal representing ten percent of

full scale reads three percent less than it should, the value in the gain reg-

ister can be scaled up by three percent. Gain accuracy can be improved if

output words are averaged while using this technique. Use caution when

a calibration signal less than full scale is being used. If the transfer func-

tion of the transducer being used to generate the ten percent signal hap-

pens to have a major nonlinearity at the point at which calibration is

being performed, it will cause the rest of the transfer function to be incor-

rect.

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?

6

PI202PP3 JAN ‘98

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