ICL7129_00 Datasheet, PDF (5/10 Pages) Intersil Corporation – 4½ Digit LCD, Single-Chip A/D Converter

ICL7129
PIN
SYMBOL
DESCRIPTION
PIN
SYMBOL
DESCRIPTION
37
RANGE
3µA pull-down for 200mV scale.
39
Pulled HIGH externally for 2V scale.
DP₁
Internal 3µA pull-down. When HI,
decimal point 1 will be on.
38
DP₂
Internal 3µA pull-down. When HI,
40
OSC2
Output of first clock inverter. Input of
decimal point 2 will be on.
second clock inverter.
C_REF
R_INT
C_INT
REF HI REF LO
BUFFER INT , IN
INT OUT
DE DE
IN HI
INT₁
DE-
COMMON
IN LO
DE+
INT₁, INT₂
-
+
DE+
BUFFER
Z1, X10
DE-
INT
REST, INT₂
X10
10
COMPARATOR 1
-
De⁺tailed D₁₀e₀ scrip⁺t^-ion ⁺_-
INTEGRATOR
TO DIGITAL
SECTION
COMPARATOR 2
FIGURE 1. ANALOG BLOCK DIAGRAM
ZERO-INTEGRATE
INT₁
DE₁
AND LATCH
INTEGRATE DE-INTEGRATE REST X10 DE₂ REST X10 DE₃ ZERO-INTEGRATE
NOTE: Shaded area greatly expanded
in time and amplitude.
1000 CLOCKS
10,000 CLOCKS
2000
CLOCKS
INTEGRATOR
RESIDUE
VOLTAGE
1000 CLOCKS
FIGURE 2. INTEGRATOR WAVEFORM FOR NEGATIVE INPUT VOLTAGE SHOWING SUCCESSIVE INTEGRATION PHASES AND
RESIDUE VOLTAGE
COMMON, DGND, and “Low Battery”
The COMMON and DGND (Digital GrouND) outputs of the
ICL7129 are generated from internal zener diodes
(Figure 3). COMMON is included primarily to set the com-
mon-mode voltage for battery operation or for any system
where the input signals float with respect to the power sup-
plies. It also functions as a pre-regulator for an external pre-
cision reference voltage source. The voltage between
DGND and V+ is the supply voltage for the logic section of
the ICL7129 including the display multiplexer and drivers.
Both COMMON and DGND are capable of sinking current
from external loads, but caution should be taken to ensure
that these outputs are not overloaded. Figure 4 shows the
connection of external logic circuitry to the ICL7129. This
connection will work providing that the supply current
requirements of the logic do not exceed the current sink
capability of the DGND pin. If more supply current is
required, the buffer in Figure 5 can be used to keep the load-
ing on DGND to a minimum. COMMON can source approxi-
5