Data Sheet

ICL7106, ICL7107, ICL7107S
FN3082 Rev 9.00 Page 8 of 17
October 24, 2014
Digital Section
Figures 7 and 8 show the digital section for the ICL7106 and
ICL7107, respectively. In the ICL7106, an internal digital ground
is generated from a 6V Zener diode and a large P-Channel source
follower. This supply is made stiff to absorb the relatively large
capacitive currents when the back plane (BP) voltage is switched.
The BP frequency is the clock frequency divided by 800. For three
readings/sec., this is a 60Hz square wave with a nominal
amplitude of 5V. The segments are driven at the same frequency
and amplitude and are in phase with BP when OFF, but out of
phase when ON. In all cases negligible DC voltage exists across
the segments.
Figure 8
is the Digital Section of the ICL7107. It is identical to the
ICL7106 except that the regulated supply and back plane drive
have been eliminated and the segment drive has been increased
from 2mA to 8mA, typical for instrument size common anode
LED displays. Since the 1000 output (pin 19) must sink current
from two LED segments, it has twice the drive capability or
16mA.
In both devices, the polarity indication is “on” for negative analog
inputs. If IN LO and IN HI are reversed, this indication can be
reversed also, if desired.
ICL7106
V+
BP
TEST
DECIMAL
POINT
SELECT
CD4030
GND
V+
TO LCD
DECIMAL
POINTS
FIGURE 6. EXCLUSIVE ‘OR’ GATE FOR DECIMAL POINT DRIVE
7
SEGMENT
DECODE
SEGMENT
OUTPUT
0.5mA
2mA
INTERNAL DIGITAL GROUND
TYPICAL SEGMENT OUTPUT
V+
LCD PHASE DRIVER
LATCH
7
SEGMENT
DECODE
200
LOGIC CONTROL
INTERNAL
V
TH
= 1V
7
SEGMENT
DECODE
1000’s 100’s 10’s 1’s
TO SWITCH DRIVERS
FROM COMPARATOR OUTPUT
DIGITAL
GROUND
4
CLOCK
40 39 38
OSC 1
OSC 2
OSC 3
BACKPLANE
21
V+
TEST
V-
500Ω
37
26
6.2V
COUNTER
COUNTER COUNTER COUNTER
1
c
a
b
c
d
f
g
e
a
b
a
b
c
d
f
g
e
a
b
c
d
f
g
e
THREE INVERTERS
ONE INVERTER SHOWN FOR CLARITY
FIGURE 7. ICL7106 DIGITAL SECTION