ICL7136_14 Datasheet, PDF (11/15 Pages) Intersil Corporation – 31/2 Digit LCD, Low Power Display, A/D Converter with Overrange Recovery

ICL7136
Reference Voltage
The analog input required to generate full scale output (2000
counts) is: V_lN = 2V_REF. Thus, for the 200mV and 2V scale,
V_REF should equal 100mV and 1V, respectively. However, in
many applications where the A/D is connected to a
transducer, there will exist a scale factor other than unity
between the input voltage and the digital reading. For
instance, in a weighing system, the designer might like to
have a full scale reading when the voltage from the
transducer is 0.662V. Instead of dividing the input down to
200mV, the designer should use the input voltage directly
and select V_REF = 0.341V. Suitable values for integrating
resistor and capacitor would be 330kΩ and 0.047µF. This
makes the system slightly quieter and also avoids a divider
network on the input. Another advantage of this system
occurs when a digital reading of zero is desired for V_IN ≠ 0.
Temperature and weighing systems with a variable fare are
examples. This offset reading can be conveniently
generated by connecting the voltage transducer between
IN HI and COMMON and the variable (or fixed) offset
voltage between COMMON and IN LO.
Typical Applications
The ICL7136 may be used in a wide variety of
configurations. The circuits which follow show some of the
possibilities, and serve to illustrate the exceptional versatility
of these A/D converters.
The following application notes contain very useful
information on understanding and applying this part and are
available from Intersil.
Application Notes
NOTE #
DESCRIPTION
AN016 “Selecting A/D Converters”
AN017 “The Integrating A/D Converter”
AN018 “Do’s and Don’ts of Applying A/D Converters”
AN023 “Low Cost Digital Panel Meter Designs”
AN032
“Understanding the Auto-Zero and Common Mode
Performance of the ICL7136/7/9 Family”
AN046
AN052
“Building a Battery-Operated Auto Ranging DVM with
the ICL7106”
“Tips for Using Single Chip 3¹/₂ Digit A/D Converters”
OSC 1 40
OSC 2 39
OSC 3 38
TEST 37
REF HI 36
REF LO 35
C_REF 34
C_REF 33
COMMON 32
IN HI 31
IN LO 30
A-Z 29
BUFF 28
INT 27
V - 26
G2 25
C3 24
A3 23
G3 22
BP 21
TO PIN 1
180kΩ
50pF
SET V_REF
= 100mV
0.1µF
20kΩ 240kΩ
1MΩ
0.47µF
180kΩ
0.01µF
0.047µF
TO DISPLAY
TO BACKPLANE
+
IN
-
+
9V
-
Values shown are for 200mV full scale, 3 readings/sec., floating
supply voltage (9V battery).
FIGURE 8. ICL7136 USING THE INTERNAL REFERENCE
OSC 1 40
OSC 2 39
TO PIN 1
180kΩ
OSC 3 38
TEST 37
50pF
SET V_REF
= 100mV
REF HI 36
REF LO 35
C_REF 34
C_REF 33
COMMON 32
IN HI 31
IN LO 30
A-Z 29
BUFF 28
INT 27
0.1µF
0.01µF
1.8M
0.047µF
250kΩ 240kΩ
1MΩ
0.01µF
V - 26
G2 25
C3 24
A3 23
TO DISPLAY
G3 22
BP/GND 21
V+
+
IN
-
V-
FIGURE 9. RECOMMENDED COMPONENT VALUES FOR 2V
FULL SCALE
11
FN3086.6
July 21, 2005