TC7117 TelCom, TC7117 Datasheet - Page 9

• Manufacturer Part Number: TC7117
• Description: 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS WITH HOLD
• Manufacturer: TelCom

3-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTERS 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 1 mA load should be
applied.
pulled HIGH (to V
the display should read –1888. The TEST pin will sink
about 10 mA under these conditions.
DIGITAL SECTION
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)
The second function is a "lamp test." When TEST is
Figures 8 and 9 show the digital section for TC7116/
OSC 1
TELCOM SEMICONDUCTOR, INC.
INTERNAL DIGITAL GROUND
TYPICAL SEGMENT OUTPUT
40
TC7116A
TC7116
FROM COMPARATOR OUTPUT
+
OSC
), all segments will be turned ON and
0.5 mA
2 mA
CLOCK
39
2
TO SWITCH DRIVERS
SEGMENT
OUTPUT
V
+
OSC 3
38
INTERNAL DIGITAL GROUND
Figure 8. TC7116/TC7116A Digital Section
THOUSANDS
÷
4
7-SEGMENT
HUNDREDS
LOGIC CONTROL
DECODE
voltage is switched. The BP frequency is the clock fre-
quency
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.
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.
inputs. If V
reversed also, if desired.
LCD PHASE DRIVER
Figure 9 is the digital section of the TC7117/TC7117A.
In both devices, the polarity indication is ON for analog
HLDR
1
7-SEGMENT
LATCH
DECODE
800. For 3 readings per second, this is a 60-Hz
TENS
–
IN
and V
V TH = 1V
70 k
+
IN
7-SEGMENT
are reversed, this indication can be
DECODE
UNITS
21
÷
500
6.2V
200
BACKPLANE
35
37
26
TC7116A
TC7117A
V
V –
TEST
TC7116
TC7117
+
3-211
1
2
3
4
5
6
7
8