ICL7129RCPL datasheet(10/11 Pages) INTERSIL

10 / 11 page

3-40

A single polarity power supply can be used to power the

ICL7129 in applications where battery operation is not

appropriate or convenient only if the power supply is isolated

from system ground. Measurements must be made with

respect to COMMON or some other voltage within its input

common-mode range.

Voltage References

The COMMON output of the ICL7129 has a temperature

coefﬁcient of

±80ppm/oC typically. This voltage is only suit-

able as a reference voltage for applications where ambient

temperature variations are expected to be minimal. When

the ICL7129 is used in most environments, other voltage ref-

erences should be considered. The diagram in the Typical

Application Schematic and Figure 15 show the ICL8069

1.2V band-gap voltage source used as the reference for the

ICL7129, and the COMMON output as its pre-regulator. The

reference voltage for the ICL7129 is set to 1.000V for both

2V and 200mV full-scale operation.

Multiple Integration A/D Converter

Equations

Oscillator Frequency

fOSC = 0.45/RC

COSC > 50pF; ROSC > 50kΩ

fOSC (Typ) = 120kHz

fOSC = 120kHz Crystal (Recommended)

Oscillator Period

tOSC = 1/fOSC

Integration Clock Period

tCLOCK = 2*tOSC

Integration Period

tINT(2V) = 1000*tCLOCK

(Range = 1)

tINT(200mV) = 10,000*tCLOCK (Range = 0)

60/50Hz Rejection Criterion

tINT/t60Hz or tINT/t50Hz = Integer

Optimum Integration Current

IINT = 13µA

Full Scale Analog Input Voltage

VINFS (Typ) = 200mV or 2V

Integrate Resistor

RINT = VINFS/IINT

RINT (Typ) = 150kΩ

Integrate Capacitor

Integrator Output Voltage Swing

VINT Maximum Swing:

(V- + 0.5V) < VINT < (V+ - 0.7V)

Display Count

(2V Range)

(200mV Range)

Minimum VREF: 500mV

Common Mode Input Voltage

(V- + 1V) < VIN < (V+ - 0.5V)

Auto Zero Capacitor: CAZ not used

Reference Capacitor: 0.1

µF < CREF < 1µF

VCOM

Biased Between V+ and V-.

VCOM ≅ V+ -2.9V

Regulation lost when V+ to V- <

≅ 6.4V.

If VCOM is externally pulled down to (V+ to V-)/2, the

VCOM circuit will turn off.

Power Supply: Single 9V

V+ - V- = 9V

Digital supply is generated internally

VGND ≅ V+ - 4.5V

Display: Triplexed LCD

Continuity Output On if

VINHI to VINLO < 200mV

Conversion Cycle (In Both Ranges)

tCYC = tCLOCK x 30,000

INT

() I

INT

()

INT

----------------------------------

INT

() I

INT

()

INT

----------------------------------

COUNT

10 000

REF

-----------------

Range = 1

()

COUNT

10 000

REF

-----------------------

Range = 0

()

REST X10

DE2 REST X10

DE3

DE1

DE-INTEGRATE

ZERO-INTEGRATE

INT1

INTEGRATE

ZERO-INTEGRATE

AND LATCH

INTEGRATOR

RESIDUE

VOLTAGE

2000

CLOCKS

1000 CLOCKS

10,000 CLOCKS

NOTE: Shaded area greatly expanded

in time and amplitude.

1000 CLOCKS

ICL7129

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