ICL7104-14CPL Intersil, ICL7104-14CPL Datasheet - Page 11

• Manufacturer Part Number: ICL7104-14CPL
• Description: 14 BIT A/D CONVERTER
• Manufacturer: Intersil

Specifications of ICL7104-14CPL

• Rohs Status: RoHS non-compliant
• Other names: NT5018

Integrating Resistor
The integrating resistor is determined by the full scale input
voltage and the output current of the buffer used to charge
the integrator capacitor. This current should be small
compared to the output short circuit current such that
thermal effects are kept to a minimum and linearity is not
affected. Values of 5 to 40µA give good results with a
nominal of 20µA. The exact value may be chosen by:
NOTE: If gain is used in the buffer amplifier then
Integrating Capacitor
The product of integrating resistor and capacitor is selected
INTERNAL CLOCK
R
INTERNAL LATCH
STATUS OUTPUT
I NT
INTEGRATOR
=
R
full scale voltage (see note)
------------------------------------------------------------------------ -
IN T
OUTPUT
=
(
--------------------------------------------------------------------------------------- -
Bu fferGa in
20µA
NUMBER OF COUNTS TO ZERO CROSSING
AZ PHASE I
) (full scale voltage)
5kΩ
20µA
300pF
10kΩ
-16
-14
OUT
PROPORTIONAL TO V
REF
FIGURE 7. ADDING BUFFER GAIN TO ICL8068
6
3
+15V
5
REF.
INT.
8
+BUF IN
DETECTED
FIGURE 8. CONVERSION TIMING
POLARITY
INT PHASE II
7
-15V
PHASE I
32768
8192
1
13
10
-
BUFFER
BUF IN
10-50K
+
IN
100kΩ
-
A1
ICL7104
COUNTS
TO ICL7104
11
8068
BUF OUT
9
to give 9 volt swing for full scale inputs. This is a compromise
between possibly saturating the integrator (at +14 volts) due
to tolerance build-up between the resistor, capacitor and
clock and the errors a lower voltage swing could induce due
to offsets referred to the output of the comparator. In
general, the value of C
A very important characteristic of the integrating capacitor is
that it have low dielectric absorption to prevent roll-over or
ratiometric errors. A good test for dielectric absorption is to
use the capacitor with the input tied to the reference.
This ratiometric condition should read half scale (100...000)
and any deviation is probably due to dielectric absorption.
Polypropylene capacitors give undetectable errors at rea-
sonable cost. Polystyrene and polycarbonate capacitors
may also be used in less critical applications.
+INT IN
C
R
I NT
INT
PHASE II
32768
8192
=
11
12

--------------------------------------------------------------------------------------------------------- -
INTEG.
(32768 for - 16)
-INT IN
+
-
(8192 for -14)
C
A2
Integrator Output Voltage Swing
INT
-1.2V
INT OUT
14
ZERO CROSSING
OCCURS
COMP.
+
-
A3
DEINT PHASE III
ZERO CROSSING
DETECTED
AFTER ZERO CROSSING,
ANALOG SECTION WILL
BE IN AUTOZERO
CONFIGURATION
PHASE III
INT
65536
16384


×
2
20µA
is given by:
COMP
OUT
-15V
+5V
×
clock period
AZ