ICL-7107 Intersil, ICL-7107 Datasheet - Page 8

• Manufacturer Part Number: ICL-7107
• Description: 31/2 Digit/ LCD/LED Display/ A/D Converters
• Manufacturer: Intersil

The second function is a “lamp test”. When TEST is pulled
high (to V+) all segments will be turned on and the display
should read “1888”. The TEST pin will sink about 15mA
under these conditions.
CAUTION: In the lamp test mode, the segments have a constant DC
voltage (no square-wave). This may burn the LCD display if main-
tained for extended periods.
FIGURE 6. EXCLUSIVE ‘OR’ GATE FOR DECIMAL POINT DRIVE
†
ONE INVERTER SHOWN FOR CLARITY
THREE INVERTERS
ICL7106
TEST
TYPICAL SEGMENT OUTPUT
V+
INTERNAL DIGITAL GROUND
BP
0.5mA
2mA
DECIMAL
SELECT
POINT
V+
SEGMENT
OUTPUT
OSC 1
ICL7106, ICL7107, ICL7106S, ICL7107S
CD4030
FROM COMPARATOR OUTPUT
GND
V+
40
FIGURE 7. ICL7106 DIGITAL SECTION
†
TO SWITCH DRIVERS
OSC 2
TO LCD
DECIMAL
POINTS
CLOCK
39
COUNTER
1000’s
8
OSC 3
b
a
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 relative 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.
COUNTER
SEGMENT
DECODE
38
e
LCD PHASE DRIVER
f
100’s
INTERNAL
d
7
GROUND
g
DIGITAL
a
4
c
LATCH
b
c
SEGMENT
COUNTER
DECODE
e
f
10’s
7
d
g
LOGIC CONTROL
a
c
b
SEGMENT
COUNTER
DECODE
e
f
V
1’s
TH
7
d
g
a
= 1V
c
b
21
200
500
BACKPLANE
6.2V
37
26
1
V+
TEST
V-