9
TC7116
TC7116A
TC7117
TC7117A
TC7116/A/7117/A-7 9/17/99
2001 Microchip Technology Inc.
DS21457A
3-1/2 Digit Analog-To-Digital
Convereters with Hold
negative supply for externally-generated segment drivers,
such as decimal points or any other presentation the user
may want to include on the LCD. (Figures 5 and 6 show
such an application.) No more than a 1mA load should be
applied.
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 10 mA under these conditions.
DIGITAL SECTION
Figures 8 and 9 show the digital section for TC7116/
TC7116A and TC7117/TC7117A, respectively. For the
TC7116/TC7116A (Figure 8), 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 backplane (BP)
voltage is switched. The BP frequency is the clock fre-
quency
800. For 3 readings per second, this is a 60-Hz
square wave with a nominal amplitude of 5V. The seg-
ments are driven at the same frequency and amplitude,
and are inphase with BP when OFF, but out-of-phase
when ON. In all cases, negligible DC voltage exists across
the segments.
Figure 9 is the digital section of the TC7117/TC7117A.
It is identical to the TC7116/TC7116A, except that the
regulated supply and BP drive have been eliminated, and
the segment drive is typically 8 mA. The 1000's output (pin
19) sinks current from two LED segments, and has a 16-mA
drive capability. The TC7117/TC7117A are designed to
drive common anode LED displays.
In both devices, the polarity indication is ON for analog
inputs. If V
–
IN and V
+
IN are reversed, this indication can be
reversed also, if desired.
Figure 8. TC7116/TC7116A Digital Section
TC7116
TC7116A
LCD PHASE DRIVER
THOUSANDS
HUNDREDS
TENS
UNITS
4
BACKPLANE
21
39
37
OSC
INTERNAL DIGITAL GROUND
V
+
V
–
TEST
6.2V
500
26
35
TO SWITCH DRIVERS
FROM COMPARATOR OUTPUT
CLOCK
VTH = 1V
7-SEGMENT
DECODE
7-SEGMENT
DECODE
7-SEGMENT
DECODE
200
40
38
TYPICAL SEGMENT OUTPUT
INTERNAL DIGITAL GROUND
SEGMENT
OUTPUT
V
+
0.5mA
2mA
LATCH
2
OSC3
OSC1
÷
HLDR
70k
LOGIC CONTROL
1