Datasheet

13
FN3093.3
Typical Integrator Amplifier Output Waveform (INT Pin)
Design Information Summary Sheet
• CLOCK INPUT
The ICL7135 does not have an internal oscillator. It
requires an external clock.
f
CLOCK
(Typ) = 120kHz
• CLOCK PERIOD
t
CLOCK
= 1 / f
CLOCK
• INTEGRATION PERIOD
t
INT
= 10,000 x t
CLOCK
• 60/50Hz REJECTION CRITERION
t
INT
/ t
60Hz
or t
INT
/ t
50Hz
= Integer
• OPTIMUM INTEGRATION CURRENT
I
INT
= 20µA
• FULL-SCALE ANALOG INPUT VOLTAGE
V
lNFS
(Typ) = 200mV or 2V
• INTEGRATE RESISTOR
• INTEGRATE CAPACITOR
• INTEGRATOR OUTPUT VOLTAGE SWING
•V
INT
MAXIMUM SWING:
(V- + 0.5) < V
INT
< (V+ - 0.5V)
V
INT
Typically = 2.7V
• DISPLAY COUNT
• CONVERSION CYCLE
t
CYC
= t
CL0CK
x 40002
when f
CLOCK
= 120kHz, t
CYC
= 333ms
• COMMON MODE INPUT VOLTAGE
(V- + 1V) < V
lN
< (V+ - 0.5V)
• AUTO-ZERO CAPACITOR
0.01µF < C
AZ
< 1µF
• REFERENCE CAPACITOR
0.1µF < C
REF
< 1µF
• POWER SUPPLY: DUAL ±5V
V+ = +5V to GND
V- = -5V to GND
• OUTPUT TYPE
4 BCD Nibbles with Polarity and Overrange Bits
There is no internal reference available on the ICL7135. An
external reference is required due to the ICL7135’s 4
1
/
2
digit resolution.
R
INT
V
INFS
I
INT
-----------------=
C
INT
t
INT
()I
INT
()
V
INT
--------------------------------=
V
INT
t
INT
()I
INT
()
C
INT
--------------------------------=
COUNT 10 000,
V
IN
V
REF
-----------------
×=
AUTO ZERO PHASE
(COUNTS)
30001 - 10001
INTEGRATE
PHASE FIXED
10000 COUNTS
DE-INTEGRATE PHASE
1 - 20001 COUNTS
TOTAL CONVERSION TIME = 40002 x t
CLOCK
ICL7135