ICL7109 Ver la hoja de datos (PDF) - Intersil
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ICL7109 Datasheet PDF : 25 Pages
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ICL7109
GND, the normal integrator output swing at full scale is ±4V.
Since the integrator output can go to 0.3V from either supply
without significantly affecting linearity, a 4V integrator output
swing allows 0.7V for variations in output swing due to com-
ponent value and oscillator tolerances. With ±5V supplies
and a common mode range of ±1V required, the component
values should be selected to provide ±3V integrator output
swing. Noise and roll-over will be slightly worse than in the
±4V case. For larger common mode voltage ranges, the inte-
grator output swing must be reduced further. This will
increase both noise and roll-over errors. To improve the per-
formance, supplies of ±6V may be used.
Integrating Resistor
Both the buffer amplifier and the integrator have a class A output
stage with 100µA of quiescent current. They supply 20µA of drive
current with negligible nonlinearity. The integrating resistor
should be large enough to remain in this very linear region over
the input voltage range, but small enough that undue leakage
requirements are not placed on the PC board. For 409.6mV full-
scale, 200kΩ is near optimum and similarly a 20kΩ for a
409.6mV scale. For other values of full scale voltage, RINT
should be chosen by the relation :
RINT = f--u----l-l---s---c--2-a--0-l--e-·µ----vA---o---l-t--a---g----e- .
with the integrating capacitor forms an R-C time constant
that determines the speed of recovery from overloads and
the error that exists at the end of an auto-zero cycle. For
409.6mV full scale where noise is very important and the
integrating resistor small, a value of CAZ twice CINT is opti-
mum. Similarly for 4.096V full scale where recovery is more
important than noise, a value of CAZ equal to half of CINT is
recommended.
For optimal rejection of stray pickup, the outer foil of CAZ
should be connected to the R-C summing junction and the
inner foil to pin 31. Similarly the outer foil of CINT should be
connected to pin 32 and the inner foil to the R-C summing
junction. Teflon, or equivalent, capacitors are recommended
above 85oC for their low leakage characteristics.
Reference Capacitor
A 1µF capacitor gives good results in most applications.
However, where a large reference common mode voltage
exists (i.e., the reference low is not at analog common) and
a 409.6mV scale is used, a large value is required to prevent
roll-over error. Generally 10µF will hold the roll-over error to
0.5 count in this instance. Again, Teflon, or equivalent
capacitors should be used for temperatures above 85oC for
their low leakage characteristics.
Integrating Capacitor
The integrating capacitor CINT should be selected to give the
maximum voltage swing that ensures tolerance build-up will
not saturate the integrator swing (approximately. 0.3V from
either supply). For the ICL7109 with ±5V supplies and analog
common connected to GND, a ±3.5V to ±4V integrator output
swing is nominal. For 71/2 conversions per second (61.72kHz
clock frequency) as provided by the crystal oscillator, nominal
values for CINT and CAZ are 0.15µF and 0.33µF, respec-
tively. If different clock frequencies are used, these values
should be changed to maintain the integrator output swing. In
general, the value CINT is given by:
CINT = i--n-(--t-2-e--0-g--4-r--8a----t-×o----r-c---ol--o-u--c-t--pk---u--p-t--e--v-r--oi--o-l--td-a---)-g-(--e-2---0-s---µw---A-i--n--)-g-- .
An additional requirement of the integrating capacitor is that
it have low dielectric absorption to prevent roll-over errors.
While other types of capacitors are adequate for this applica-
tion, polypropylene capacitors give undetectable errors at
The integrating capacitor should have a low dielectric
absorption to prevent roll-over errors. While other types may
be adequate for this application, polypropylene capacitors
give undetectable errors at reasonable cost up to 85oC.
Teflon™ capacitors are recommended for the military tem-
perature range. While their dielectric absorption characteris-
tics vary somewhat from unit to unit, selected devices should
give less than 0.5 count of error due to dielectric absorption.
Auto-Zero Capacitor
The size of the auto-zero capacitor has some influence on
the noise of the system: a smaller physical size and a larger
capacitance value lower the overall system noise. However,
CAZ cannot be increased without limits since it, in parallel
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