3-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTERS WITH HOLD
TC7116
TC7116A
TC7117
1
2
3
4
5
6
7
8
TC7117A
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 1 mA 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.
voltage is switched. The BP frequency is the clock fre-
quency Ϭ800. 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 in-phase 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.
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)
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.
TC7116
TC7116A
BACKPLANE
21
LCD PHASE DRIVER
TYPICAL SEGMENT OUTPUT
+
V
7-SEGMENT
DECODE
7-SEGMENT
DECODE
7-SEGMENT
DECODE
÷
200
0.5 mA
SEGMENT
OUTPUT
LATCH
TENS
2 mA
INTERNAL DIGITAL GROUND
THOUSANDS
UNITS
HUNDREDS
TO SWITCH DRIVERS
FROM COMPARATOR OUTPUT
35
37
+
V
ϳ70 kΩ
CLOCK
6.2V
÷
4
LOGIC CONTROL
TEST
V
500Ω
TH = 1V
26
–
INTERNAL DIGITAL GROUND
V
40
OSC
39
OSC
38
OSC
1
HLDR
1
2
3
Figure 8. TC7116/TC7116A Digital Section
TELCOM SEMICONDUCTOR, INC.
3-211
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
