CS5531-ASZ datasheet(32/50 Pages) CIRRUS

32 / 50 page

CS5531/32/33/34-AS

DS289F5

2.5.6. System Calibration

For the system calibration functions, the user must

supply the converter’s calibration signals which rep-

resent ground and full scale. When a system offset

calibration is performed, a ground-referenced signal

must be applied to the converters. Figure 13 illus-

trates system offset calibration.

As shown in Figure 14, 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 the System Calibration Specifications).

2.5.7. Calibration Tips

Calibration steps are performed at the output word

rate selected by the WR2-WR0 bits of the channel

setup registers. Due to limited register lengths in

the faster word-rate filters (240 Sps and higher),

channels that are used at these rates should also be

calibrated in one of these word rates, and channels

used in the lower word rates (120 Sps and lower)

should be calibrated at one of these lower rates.

Since higher word rates result in conversion words

with more peak-to-peak noise, calibration should

be performed at the lowest possible output word

rate for maximum accuracy. For the 7.5 Sps to 120

Sps word rate settings, calibrations can be per-

formed at 7.5 Sps, and for 240 Sps and higher, cal-

ibration can be performed at 240 Sps. To minimize

digital noise near the device, the user should wait

for each calibration step to be completed before

reading or writing to the serial port. Reading the

calibration registers and averaging multiple cali-

brations together can produce a more accurate cal-

ibration result. Note that accessing the ADC’s

serial port before a calibration has finished may re-

sult in the loss of synchronization between the mi-

AIN+

AIN-

1X GAIN

Figure 11. Self-calibration of Offset

AIN+

AIN-

OPEN

XGAIN

OPEN

CLOSED

VREF+

CLOSED

VREF-

Reference

Figure 12. Self-calibration of Gain

XGAIN

External

Connections

AIN+

AIN-

CM +

Figure 13. System Calibration of Offset

XGAIN

External

Connections

Full Scale +

AIN+

AIN-

CM +

Figure 14. System Calibration of Gain

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