TC7126 View Datasheet(PDF) - Microchip Technology
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TC7126 Datasheet PDF : 26 Pages
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5.0 DIGITAL SECTION
The TC7126A contains all the segment drivers neces-
sary to directly drive a 3-1/2 digit LCD, including an
LCD backplane driver. The backplane frequency is the
external clock frequency divided by 800. For 3 conver-
sions 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 (visible). This AC drive configuration
results in negligible DC voltage across each LCD seg-
ment, ensuring long LCD life. The polarity segment
driver is ON for negative analog inputs. If VIN+ and VIN-
are reversed, this indicator reverses.
On the TC7126A, when the TEST pin is pulled to V+,
all segments are turned ON and the display reads -
1888. During this mode, LCD segments have a
constant DC voltage impressed.
Note:
Do not leave the display in this mode for
more than several minutes. LCDs may be
destroyed if operated with DC levels for
extended periods.
The display font and segment drive assignment are
shown in Figure 5-1.
Display Font
1000's 100's 10's
1's
TC7126/A
5.1 System Timing
The oscillator frequency is divided by four prior to
clocking the internal decade counters. The four-phase
measurement cycle takes a total of 4000 counts
(16,000 clock pulses). The 4000-count cycle is
independent of input signal magnitude.
Each phase of the measurement cycle has the following
length:
1. Auto-Zero Phase: 1000 to 3000 counts
(4000 to 12,000 clock pulses).
For signals less than full scale, the auto-zero
phase is assigned the unused reference
integrate time period.
2. Signal Integrate: 1000 counts
(4000 clock pulses).
This time period is fixed. The integration period
is:
EQUATION 5-1:
TSI = 4000
1
FOSC
Where: FOSC is the externally set clock frequency.
3. Reference Integrate: 0 to 2000 counts
(0 to 8000 clock pulses).
The TC7126A is a drop-in replacement for the TC7126
and ICL7126, which offer a greatly improved internal
reference temperature coefficient. No external
component value changes are required to upgrade
existing designs.
FIGURE 5-1:
Assignment
Display Font and Segment
© 2006 Microchip Technology Inc.
DS21458C-page 11
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