ICL7135 Datasheet, PDF (9/15 Pages) Intersil Corporation – 4 1/2 Digit, BCD Output, A/D Converter

ICL7135
Power Supplies
The ICL7135 is designed to work from ±5V supplies.
However, in selected applications no negative supply is
required. The conditions to use a single +5V supply are:
1. The input signal can be referenced to the center of the
common mode range of the converter.
2. The signal is less than ±1.5V.
See “differential input” for a discussion of the effects this will
have on the integrator swing without loss of linearity.
Typical Applications
The circuits which follow show some of the wide variety of
possibilities and serve to illustrate the exceptional versatility
of this A/D converter.
Figure 7 shows the complete circuit for a 4¹/₂ digit (±2.000V)
full scale) A/D with LED readout using the ICL8069 as a
1.2V temperature compensated voltage reference. It uses
the band-gap principal to achieve excellent stability and low
noise at reverse currents down to 50µA. The circuit also
shows a typical R-C input filter. Depending on the
application, the time-constant of this filter can be made
faster, slower, or the filter deleted completely. The ¹/₂ digit
LED is driven from the 7 segment decoder, with a zero
reading blanked by connecting a D5 signal to RBl input of the
decoder. The 2-gate clock circuit should use CMOS gates to
maintain good power supply rejection.
A suitable circuit for driving a plasma-type display is shown
in Figure 8. The high voltage anode driver buffer is made by
Dionics. The 3 AND gates and caps driving “BI” are needed
for interdigit blanking of multiple-digit display elements, and
can be omitted if not needed. The 2.5kΩ and 3kΩ resistors
set the current levels in the display. A similar arrangement
can be used with Nixie^® tubes.
The popular LCD displays can be interfaced to the outputs of
the ICL7135 with suitable display drivers, such as the
ICM7211A as shown in Figure 9. A standard CMOS 4030
QUAD XOR gate is used for displaying the ¹/₂ digit, the
polarity, and an “overrange” flag. A similar circuit can be
used with the ICL7212A LED driver and the ICM7235A
vacuum fluorescent driver with appropriate arrangements
made for the “extra” outputs. Of course, another full driver
circuit could be ganged to the one shown if required. This
would be useful if additional annunciators were needed. The
Figure shows the complete circuit for a 4¹/₂ digit (±2.000V)
A/D.
Figure 10 shows a more complicated circuit for driving LCD
displays. Here the data is latched into the ICM7211 by the
STROBE signal and “Overrange” is indicated by blanking the
4 full digits.
+5V
6.8kΩ
-5V
V_REF =
54321
ICL8069 1
1.000V
1 V-
ICL7135 ^{UR 28}
150Ω
(NOTE 1)
2 REF
2
ANALOG
10kΩ
27Ω
3
ANALOG
COMMON
GND
0.47µF
4 INT OUT
100kΩ
1µF
5 AZ_IN
OR 27
STROBE 26
R/H 25
DIG. GND 24
150Ω
4.7K
SIGNAL
INPUT
100K
0.1µF
100kΩ
1µF
6 BUF OUT
7 RC1
8 RC2
9 INPUT LO
10 INPUT HI
POL 23
CLOCK 22
BUSY 21
D1 20
D2 19
+5V 11 _V+
D3 18
12 D5
D4 17
13 B1
B8 16
14 B2
B4 15
+5V
150Ω
7447
A
B
B1
C
B2
D
B4
E
B8
F
G
RBI
47K
C RC NETWORK
R
ƒ_OSC = 0.45/RC
NOTE:
1. For finer resolution on scale factor adjust, use a 10 turn pot or a small pot in series with
a fixed resistor.
FIGURE 7. 4¹/₂ DIGIT A/D CONVERTER WITH A MULTIPLEXED COMMON ANODE LED DISPLAY
9
FN3093.3