CS44800 datasheet(75/80 Pages) CIRRUS

75 / 80 page

DS632F1

CS44800

7.33.2

Decimator Scale (DEC_SCALE[18:0])

Default = 25868h

Function:

These bits are used to scale the power supply reading (Decimator Outd (addresses 3Bh, 3Ch, 3Dh)) dur-

ing the PSR feedback calibration sequence. DEC_SCALE[18:0] has 19-bit precision, formatted as signed

1.18 with decimal values from -1 to 1-2^(-18). The combination of shift and scale factors

(DEC_SCALE[18:0]*2^(DEC_SHIFT[2:0])) can be viewed as a floating point coefficient. The floating point

coefficient will be determined during the PSR feedback calibration sequence. See Decimator Shift

(DEC_SHIFT[2:0]) register description and “Recommended PSR Calibration Sequence” on page 44.

7.34

Decimator Outd (addresses 3Bh, 3Ch, 3Dh)

7.34.1

Decimator Outd (DEC_OUTD[23:0])

Default = 000000h (Read Only)

Function:

These bits reflect the real-time power supply value as measured by the external PSR feedback circuit.

DEC_OUTD[23:0] has 24-bit precision, formatted as signed 2.22 with decimal values from -4 to 4-2^(-22).

Calibration needs to be done to correlate the value of DEC_OUTD[23:0] with the real power supply value.

A quiet DC power supply without any ripple is treated as 1.0 with DEC_OUTD[23:0] calibrated at 400000h.

See “Recommended PSR Calibration Sequence” on page 44.

DEC_SCALE[18:0]

DEC_SHIFT[2:0]

Calculated Coefficient (CPSR)

20000h=0.5

001b=1

0.5*2^(1)=1

28851h=0.6331

010b=2

0.6331*2^(2)=2.5325

Table 18. Decimator Shift/Scale Coefficient Calculation Examples

432

DEC_OUTD23

DEC_OUTD22

DEC_OUTD21

DEC_OUTD20

DEC_OUTD19

DEC_OUTD18

DEC_OUTD17

DEC_OUTD16

765

DEC_OUTD15

DEC_OUTD14

DEC_OUTD13

DEC_OUTD12

DEC_OUTD11

DEC_OUTD10

DEC_OUTD09

DEC_OUTD08

765

DEC_OUTD07

DEC_OUTD06

DEC_OUTD05

DEC_OUTD04

DEC_OUTD03

DEC_OUTD02

DEC_OUTD01

DEC_OUTD00

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