ICL7139CPL 데이터 시트보기 (PDF) - Intersil
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ICL7139CPL Datasheet PDF : 13 Pages
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ICL7139, ICL7149
Integrator Capacitor, ClNT
As with all dual-slope integrating convertors, the integration
capacitor must have low dielectric absorption to reduce
linearity errors. Polypropylene capacitors add undetectable
errors at a reasonable cost, while polystyrene and
polycarbonate may be used in less critical applications. The
ICL7139 and ICL7149 are designed to use a 3.3nF
(0.0033µF) ClNT with an oscillator frequency of 120kHz and
an RlNTV of 10MΩ. With a 100kHz oscillator frequency (for
50Hz line frequency rejection), ClNT and RINTV affects the
voltage swing of the integrator. Voltage swing should be as
high as possible without saturating the integrator. Saturation
occurs when the integrator output is within 1V of either V+ or
V-. Integrator voltage swing should be about ±2V when using
standard component values. For different RlNTV and
oscillator frequencies the value of ClNT can be calculated
from:
CINT = (---I--n---t--e---g--(-r--Da----te-e--s---iT--r--ei-m--d---e--I--n)---t-×-e---g-(--Ir--na---t-t-eo---g-r--r-S-a---w-t-e---i-n-C---g--u-)--r--r--e---n----t--)
= -(--1---0----,-0----0---0-----x-----2-----x----O-----s---c---i-l--l-a---(-t-o-2---r-V--P--)--e----r--i-o---d----)----×----0----.-4----V----/--R----I--N-----T---V--
The ideal CAZ is a low leakage polypropylene or Teflon
capacitor. Other film capacitors such as polyester, polysty-
rene, and polycarbonate introduce negligible errors. If a few
seconds of settling time upon power-up is acceptable, the
CAZ may be a ceramic capacitor, provided it does not have
excessive leakage.
Ohm Measurement Resistors
Because the ICL7139 and ICL7149 use a ratiometric ohm
measurement technique, the accuracy of ohm reading is pri-
marily determined by the absolute accuracy of the
RKNOWN1 and RKNOWN2. These should normally be 10kΩ
and 1MΩ, with an absolute accuracy of at least 0.5%.
Current Sensing Resistors
The 0.1Ω and 9.9Ω current sensing resistors convert the
measured current to a voltage, which is then measured
using RlNT l. The two resistors must be closely matched, and
the ratio between RlNT l and these two resistors must be
accurate - normally 0.5%. The 0.1Ω resistor must be capa-
ble of handling the full scale current of 4A, which requires it
to dissipate 1.6W.
Continuity Beeper
Integrator Resistors
The normal values of the RlNT V and RlNT l resistors are
10MΩ and 1MΩ respectively. Though their absolute values
are not critical, unless the value of the current sensing resis-
tors are trimmed, their ratio should be 10:1, within 0.05%.
Some carbon composition resistors have a large voltage
coefficient which will cause linearity errors on the 400V scale.
Also, some carbon composition resistors are very noisy. The
class “A” output of the integrator begins to have nonlinearities
if required to sink more than 70µA (the sourcing limit is much
higher). Because RlNT V drives a virtual ground point, the
input impedance of the meter is equal to RlNT V.
Deintegration Resistor, RDElNT
Unlike most dual-slope A/D converters, the ICL7139 and
ICL7149 use different resistors for integration and deintegra-
tion. RDElNT should normally be the same value as RlNT V,
and have the same temperature coefficient. Slight errors in
matching may be corrected by trimming the reference voltage.
Autozero Capacitor, CAZ
The CAZ is charged to the integrator’s offset voltage during
the autozero phases, and subtracts that voltage from the
input signal during the integrate phases. The integrator thus
appears to have zero offset voltage. Minimum CAZ value is
determined by: 1) Circuit leakages; 2) CAZ self-discharge;
3) Charge injection from the internal autozero switches.
To avoid errors, the CAZ voltage change should be less than
1/10 of a count during the 10,000 count clock cycle integra-
tion period for the 400mV range. These requirements set a
lower limit of 0.047µF for CAZ but 0.1µF is the preferred
value. The upper limit on the value of CAZ is set by the time
constant of the autozero loop, and the 1 line cycle time
period allotted to autozero. CAZ may be several 10s of µF
before approaching this limit.
The Continuity Beeper output is designed to drive a piezo-
electric transducer at 2kHz (using a 120kHz crystal), with a
voltage output swing of V+ to V-. The beeper output off state
is at the V+ rail. When crystals with different frequencies are
used, the frequency needed to drive the transducer can be
calculated by dividing the crystal frequency by 60.
Display
The ICL7139 and ICL7149 use a custom, duplexed drive dis-
play with range, polarity, and low battery annunciators. With
a 3V peak display voltage, the RMS ON voltage will be
2.37V minimum; RMS OFF voltage will be 1.06V maximum.
Because the display voltage is not adjustable, the display
should have a 10% ON threshold of about 1.4V. Most display
manufacturers supply a graph that shows contrast versus
RMS drive voltage. This graph can be used to determine
what the contrast ratio will be when driven by the ICL7139
and ICL7149. Most display thresholds decrease with
increasing temperature. The threshold at the maximum
operating temperature should be checked to ensure that the
“off” segments will not be turned “on” at high temperatures.
Crystal
The ICL7139 and ICL7149 are designed to use a parallel
resonant 120kHz or 100kHz crystal with no additional exter-
nal components. The RS parameter should be less than
25kΩ to ensure oscillation. Initial frequency tolerance of the
crystal can be a relatively loose 0.05%.
Switches
Because the logic input draws only about 5µA, switches
driving these inputs should be rated for low current, or “dry”
operations. The switches on the external inputs must be able
to reliably switch low currents, and be able to handle
voltages in excess of 400VAC.
3-43
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