Datasheet
TC7116/A/TC7117/A
DS21457D-page 10 2002-2012 Microchip Technology Inc.
FIGURE 3-4: Exclusive “OR” Gate for
Decimal Point Drive
3.2 Digital Section
Figure 3-5 and Figure show the digital section for
TC7116/TC7116A and TC7117/TC7117A, respectively.
For the TC7116/TC7116A (Figure 3-5), an internal dig-
ital 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 frequency 4800. For 3 readings
per 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.
Figure 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 8mA. The 1000’s out-
put (Pin 19) sinks current from two LED segments, and
has a 16mA 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 3-5: TC7116/TC7116A Digital Section
TC7116
TC7116A
Decimal
Point
Select
V+
V+
TEST
GND
4030
To LCD
Decimal
Point
BP
TC7116
TC7116A
LCD Phase Driver
Thousands
Hundreds
Tens Units
4
Backplane
21
39
37
OSC2
Internal Digital Ground
V+
V-
TES
T
6.2V
500Ω
26
35
To Switch Drivers
From Comparator Output
Clock
V
TH
= 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
OSC3OSC1
÷
÷
HLDR
~70kΩ
Logic Control
1