3-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTERS WITH HOLD
TC7116
TC7116A
TC7117
TC7117A
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 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.
In both devices, the polarity indication is ON for analog
inputs. If V
–
and V
+
are reversed, this indication can be
IN
IN
reversed also, if desired.
1
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.
2
3
4
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)
TC7116
TC7116A
BACKPLANE
21
LCD PHASE DRIVER
TYPICAL SEGMENT OUTPUT
+
V
0.5 mA
SEGMENT
OUTPUT
2 mA
LATCH
7-SEGMENT
DECODE
7-SEGMENT
DECODE
5
7-SEGMENT
DECODE
÷ 200
INTERNAL DIGITAL GROUND
THOUSANDS
HUNDREDS
TENS
UNITS
6
35
70 kΩ
6.2V
500Ω
26
V–
V
+
TO SWITCH DRIVERS
FROM COMPARATOR OUTPUT
CLOCK
÷4
LOGIC CONTROL
VTH = 1V
40
OSC 1
39
OSC 2
38
OSC 3
INTERNAL DIGITAL GROUND
1
HLDR
37
TEST
7
Figure 8. TC7116/TC7116A Digital Section
8
3-211
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
