TC7106CPL datasheet(10/34 Pages) MICROCHIP

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TC7106/A/TC7107/A

DS21455D-page 10

5.0

DIGITAL SECTION (TC7106A)

The TC7106A (Figure 5-2) contains all the segment

drivers necessary to directly drive a 3-1/2 digit liquid

crystal display (LCD). An LCD backplane driver is

included. The backplane frequency is the external

clock

frequency

divided

800.

For

three

conversions per second, the backplane frequency is

60Hz with a 5V nominal amplitude. When a segment

driver is in phase with the backplane signal, the

segment is “OFF.” An out of phase segment drive

signal causes the segment to be “ON” or visible. This

AC drive configuration results in negligible DC voltage

across each LCD segment. This insures long LCD

display life. The polarity segment driver is “ON” for

negative analog inputs. If VIN+ and VIN- are reversed,

this indicator will reverse.

When the TEST pin on the TC7106A is pulled to V+, all

segments are turned “ON.” The display reads -1888.

During this mode, the LCD segments have a constant

voltage

impressed.

NOT

LEAVE

THE

DISPLAY

THIS

MODE

FOR

THAN

SEVERAL MINUTES! LCD displays may be destroyed

if operated with DC levels for extended periods.

The display font and the segment drive assignment are

shown in Figure 5-1.

FIGURE 5-1:

Display Font and Segment

Assignment

In the TC7106A, an internal digital ground is generated

from a 6-volt zener diode and a large P channel source

follower. This supply is designed to absorb the large

capacitive currents when the backplane voltage is

switched.

Display Font

1000s'

100s'

10s'

1s'

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