CS5560 datasheet(16/32 Pages) CIRRUS

16 / 32 page

CS5560

DS713A5

7/31/07

Calibration can be initiated in either of two ways. If CAL is high when RST transitions from low to high, a

calibration cycle will be performed. When calibration is performed, the offset and full-scale points of the

converter are calibrated. A calibration cycle takes 327,680 MCLK cycles. The RDY signal falls upon com-

pletion of reset and calibration sequence. If CAL is held low when RST transitions from low to high, no

calibration will be performed. Calibrations can be initiated any time the converter is idle by taking the CAL

input high. RDY will fall at the end of the calibration cycle. The CAL pin should be returned low when not

being used.

A calibration cycle calibrates the offset and full-scale points of the converter transfer function. When the

offset portion of the calibration is performed, the AIN+ and AIN- pins are disconnected from the input and

shorted internally. The offset of the converter is then measured and a correction factor is stored in the

offset calibration register. Then the voltage reference is internally connected to act as the input signal to

the converter and a gain calibration is performed. The gain correction results are placed in the gain cali-

bration register. The contents of the 24-bit offset and gain registers are used to map the conversion data

prior to its output from the converter. The offset and gain calibration registers can be read and written if

desired. To read or write the calibration registers inside of the converter, the converter must be idle, and

the serial port must be in the SEC mode (SMODE = VLR). Table 1 depicts the commands necessary to

read or write the calibration registers.

3.1.1 Offset Register

The offset register maps one for one with the conversion word when the gain register is set to 1 decimal.

After reset all bits are zero.

3.1.2 Gain Register

The gain register spans from 0 to (8 - 2-21). After reset, bit D22 is 1, all others are 0. This results in a dec-

imal gain value of 1.000....000.

Table 1. Offset & Gain Calibration Register Read/Write Commands

Read Command

Write Command

Offset Register

0x40

0xC0

Gain Register

0x20

0XA0

MSB

D22

D21

D20

D19

D18

D17

D16

D15

D14

D13

D12

Sign

2-2

2-12

000000000000

D11

D10

LSB

2-11

2-24

000000000000

MSB

D23

D22

D21

D20

D19

D18

D17

D16

D15

D14

D13

2-1

2-2

2-3

2-4

2-5

2-6

2-7

2-8

2-9

001000000000

D12

D11

D10

D9D8D7D6D5D4D3D2

LSB

2-10

2-11

2-12

2-13

2-14

2-15

2-16

2-17

2-18

2-19

2-20

2-21

000000000000

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