ICL7136_14 Datasheet, PDF (9/15 Pages) Intersil Corporation – 31/2 Digit LCD, Low Power Display, A/D Converter with Overrange Recovery

ICL7136
V+
V+
BP
ICL7136
DECIMAL
POINT
SELECT
TO LCD
DECIMAL
POINTS
TEST
CD4030
GND
FIGURE 5. EXCLUSIVE “OR” GATE FOR DECIMAL POINT DRIVE
Digital Section
Figures 6 shows the digital section for the ICL7136. In the
ICL7136, 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/second 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.
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.
a
a
a
a
f bf bf b
gc
g
g
b
ec ecec
d
d
d
BACKPLANE
21
LCD PHASE DRIVER
TYPICAL SEGMENT OUTPUT
V+
0.5mA
2mA
SEGMENT
OUTPUT
INTERNAL DIGITAL GROUND
† THREE INVERTERS
ONLY ONE INVERTER SHOWN
FOR CLARITY
7
SEGMENT
DECODE
7
SEGMENT
DECODE
7
SEGMENT
DECODE
LATCH
1000’s
100’s
10’s
1’s
COUNTER COUNTER COUNTER COUNTER
TO SWITCH DRIVERS
FROM COMPARATOR OUTPUT
CLOCK
†
÷4
LOGIC CONTROL
INTERNAL
DIGITAL
GROUND
V_TH = 1V
40
39
38
÷200
1
V+
6.2V
500Ω
TEST
37
26
V-
OSC 1
OSC 2
OSC 3
FIGURE 6. ICL7136 DIGITAL SECTION
9
FN3086.6
July 21, 2005