CS5503-BP データシートの表示（PDF） - Cirrus Logic
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CS5503-BP Datasheet PDF : 54 Pages
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CS5501 CS5503
CS5501/CS5503
equation which defines settling time, an equation
for the maximum acceptable source resistance is
derived
Rsmax
=
CLKIN(20pF+CEXT
)
−64
ln
Ve
+
Ve
20pF(100mv)
( 20pF+CEXT )
This equation assumes that the offset voltage of
the buffer is 100 mV, which is the worst case.
The value of Ve is the maximum error voltage
which is acceptable.
For a maximum error voltage (Ve) of 10 µV in
the CS5501 (1/4LSB at 16-bits) and 600 nV in
the CS5503 (1/4LSB at 20-bits), the above equa-
tion indicates that when operating from a
4.096 MHz CLKIN, source resistances up to
84 kΩ in the CS5501 or 64 kΩ in the CS5503 are
acceptable in the absence of external capacitance
(CEXT = 0). If higher input source resistances
are desired the master clock rate can be reduced
to yield a longer settling time for the 64 cycle pe-
riod.
10
160
5
80
0
0
-5
-80
-10
-160
drift. Charge injection in the analog switches and
leakage currents at the sampling node are the pri-
mary sources of offset voltage drift in the
converter. Figure 12 indicates the typical offset
drift due to temperature changes experienced after
calibration at 25 °C. Drift is relatively flat up to
about 75 °C. Above 75 °C leakage current be-
comes the dominant source of offset drift.
Leakage currents approximately double with each
10 °C of temperature increase. Therefore the off-
set drift due to leakage current increases as the
temperature increases. The value of the voltage on
the sample capacitor is updated at a rate deter-
mined by the master clock, therefore the amount
of offset drift which occurs will be proportional to
the elapsed time between samples. In conclusion,
the offset drift increases with temperature and is
inversely proportional to the CLKIN rate. To
minimize offset drift with increased temperature,
higher CLKIN rates are desirable. At temperatures
above 100 °C, a CLKIN rate above 1 MHz is rec-
ommended. The effects of offset drift due to
temperature changes can be eliminated by recali-
brating the CS5501/CS5503 whenever the
temperature has changed.
Gain drift within the converter depends predomi-
nately upon the temperature tracking of internal
capacitors. Gain drift is not affected by leakage
currents, therefore gain drift is significantly less
than comparable offset errors due to temperature
increases. The typical gain drift over the specified
temperature range is less than 2.5 LSBs for the
CS5501 and less than 40 LSBs for the CS5503 .
-15
-240
-20
-55 -35 -15
5 25 45 65 85
Temperature in Deg. C.
-320
105 125
Figure 12. Typical Self-Cal Bipolar Offset vs. Tem-
perature After Calibration at 25 °C
Analog Input Drift Considerations
The CS5501/CS5503 analog input uses chopper-
stabilization techniques to minimize input offset
Measurement errors due to offset drift or gain
drift can be eliminated at any time by recalibrat-
ing the converter. Using the system calibration
mode can also minimize offset and gain errors in
the signal conditioning circuitry. The
CS5501/CS5503 can be recalibrated at any tem-
perature to remove the effects of these errors.
Linearity and differential non linearity are not sig-
nificantly affected by temperature changes.
2222
DS31F54
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