CS5460 datasheet(28/34 Pages) CIRRUS

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CS5460

DS279PP5

5.4 Voltage Reference

The CS5460 is specified for operation with a +2.5

V reference between the VREFIN and VA- pins.

The converter includes an internal 2.5 V reference

(60 ppm/°C drift) that can be used by connecting

the VREFOUT pin to the VREFIN pin of the de-

vice. If higher accuracy/stability is required, an ex-

ternal reference can be used.

5.5 Performing Calibrations

The CS5460 offers two DC calibration modes: sys-

tem offset and system gain. For system calibration

the user must supply the converter calibration sig-

nals which represent ground and full scale. The

user must provide the positive full scale point to

perform a system gain calibration and a ground

referenced signal when a system offset is per-

formed. The offset and gain signals must be within

the specified calibration limits for each specific

calibration step and channel. Since each converter

channel has its own offset and gain register asso-

ciated with it, system offset, or system gain can be

performed on either channel without the calibra-

tion results from one channel corrupting the other.

The Cycle Count register N, determines the number

of conversions averaged to obtain the calibration

results. The larger N, the higher the accuracy of the

calibration results. Once a calibration cycle is com-

plete, DRDY is set and the results are stored in ei-

ther the gain or offset register. Note that if

additional calibrations are performed, the latest cal-

ibration results will replace the effects from the

previous calibration. In any event, offset and gain

calibration steps take one cycle each to complete.

After the part is reset, the device is functional and

can perform measurements without being calibrat-

ed. The converters will utilize the initialized values

of the on-chip registers (Gain = 1.0, Offset = 0.0) to

calculate power information. Although the device

can be used without performing an offset or gain

calibration, any initial offset and gain errors in the

internal circuitry of the chip will remain.

5.5.1 System Calibration

For the system calibration functions, the user must

supply the converters calibration signals which repre-

sent ground and full scale. When a system offset cal-

ibration is performed, a ground reference signal must

be applied to the converters. Figure 12 illustrates sys-

tem offset calibration.

As shown in Figure 13, the user must input a signal

representing the positive full scale point to perform

a system gain calibration. In either case, the cali-

bration signals must be within the specified calibra-

tion limits for each specific calibration step (refer

to Full Scale DC Calibration Range).

XGAIN

External

Connections

AIN+

AIN-

CM +

Figure 12. System Calibration of Offset.

XGAIN

External

Connections

Full Scale +

AIN+

AIN-

CM +

Figure 13. System Calibration of Gain.

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