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

(VAIN-) is the voltage between AIN+ and AIN-, f is either 256 or

32,768, and C is 32 pF. A typical input current for the higher ranges is

1.2 µA/V.

8) When reading the conversion data I get all zeroes no matter what the ana-

log signal is. Please explain why.

A: Check the voltage between pins 19 and 20 (VREF+ and VREF-). If it is

zero, the converter will compute all zeros because the digital output word

represents the ratio of the input signal to the voltage reference.

9) Is calibration required to use the converter?

A: When the CS5525/26 is reset, the registers are set to known values. If the

signal to be measured by the converter is within the nominal range, the

converter can perform conversions without the need for calibrations.

Errors in the system remain present when calibration is not performed,

however, this may be acceptable if the errors are insignificant to the mea-

surement or if the errors are removed by some other means, such as soft-

ware and registers in the microcontroller.

10) How often do I need to recalibrate?

A: To answer this question one must ask: 1) What accuracy is required from

the A/D converter? 2) What effects will temperature changes have upon

the entire circuit, including components outside the A/D? To obtain opti-

mum calibration accuracy, a calibration should be performed approxi-

mately one minute after power is applied to allow the chip to reach

thermal equilibrium.

A higher accuracy measurement requirement will generally require cali-

brations more often, because, after the initial calibration has been per-

formed, the converter is subject to some drift if the operating temperature

changes. Typical offset drift and gain drift are given in the data sheet

tables. The observed drift in the application circuit may be considerably

greater due to parasitic thermocouple effects and gain drift caused by the

limited tempco tracking of the external resistors. Once an estimate of

drift is determined for the entire application circuit (drift will usually be

dominated by error sources external to the converter), an assessment of

PI202PP3 JAN ‘98

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