Cirrus Logic CS44800 - Manual (Page 75)

DS632F1 75
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 (C
PSR
)
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
7 6 5 4 3 2 1 0
DEC_OUTD23 DEC_OUTD22 DEC_OUTD21 DEC_OUTD20 DEC_OUTD19 DEC_OUTD18 DEC_OUTD17 DEC_OUTD16
7 6 5 4 3 2 1 0
DEC_OUTD15 DEC_OUTD14 DEC_OUTD13 DEC_OUTD12 DEC_OUTD11 DEC_OUTD10 DEC_OUTD09 DEC_OUTD08
7 6 5 4 3 2 1 0
DEC_OUTD07 DEC_OUTD06 DEC_OUTD05 DEC_OUTD04 DEC_OUTD03 DEC_OUTD02 DEC_OUTD01 DEC_OUTD00