3-171
TELCOM SEMICONDUCTOR, INC.
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TC826
A/D CONVERTER WITH BAR GRAPH DISPLAY OUTPUT
FEATURES
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Bipolar A/D Conversion
2.5% Resolution
Direct LCD Display Drive
‘Thermometer’ Bar or Dot Display
40 Data Segments Plus Zero
Overrange Plus Polarity Indication
Precision On–Chip Reference ................ 35ppm/
°
C
Differential Analog Input
Low Input Leakage .......................................... 10pA
Display Flashes on Overrange
Display Hold Mode
Auto–Zero Cycle Eliminates Zero Adjust
Potentiometer
9V Battery Operation
Low Power Consumption ............................ 1.1mW
20mV to 2.0 V Full–Scale Operation
Non–Multiplexed LCD Drive for Maximum
Viewing Angle
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GENERAL DESCRIPTION
In many applications a graphical display is preferred
over a digital display. Knowing a process or system oper-
ates, for example, within design limits is more valuable than
a direct system variable readout. A bar or moving dot display
supplies information precisely without requiring further inter-
pretation by the viewer.
The TC826 is a complete analog–to–digital converter
with direct liquid crystal (LCD) display drive. The 40 LCD
data segments plus zero driver give a 2.5% resolution bar
display. Full–scale differential input voltage range extends
from 20mV to 2V. The TC826 sensitivity is 500
μ
v. A low drift
35 ppm/
°
C internal reference, LCD backplane oscillator and
driver, input polarity LCD driver, and overrange LCD driver
make designs simple and low cost. The CMOS design
required only 125
μ
A from a 9V battery. In +5V systems a
TC7660 DC to DC converter can supply the –5V supply. The
differential analog input leakage is a low 10pA.
Two display formats are possible. The BAR mode
display is like a ‘thermometer’ scale. The LCD segment
driver that equals the input plus all below it are on. The DOT
mode activates only the segment equal to the input. In either
mode the polarity signal is active for negative input signals.
An overrange input signal causes the display to flash and
activates the overrange annunciator. A hold mode can be
selected that freezes the display and prevents updating.
The dual slope integrating conversion method with
auto–zero phase maximizes noise immunity and eliminates
zero–scale adjustment potentiometers. Zero–scale drift is a
low 5
μ
V/
°
C. Conversion rate is typically 5 per second and
is adjustable by a single external resistor.
A compact, 0.5" square, flat package minimizes PC
board area. The high pin count LSI package makes multi-
plexed LCD displays unnecessary. Low cost, direct drive
LCD displays offer the widest viewing angle and are readily
available. A standard display is available now for TC826
prototyping work.
PIN CONFIGURATION
ORDERING INFORMATION
Part No.
Package
Temperature
0
°
C to +70
°
C
TC826CBU
64–Pin PFP
TC826-6 11/6/96
30
29
28
50
51
25
52
24
53
23
54
22
55
21
56
20
57
19
58
18
59
17
60
31
B
B
B
B
B
B
O
P
B
H
T
5
6
7
8
9
10
11
12
13
14
15
41
40
39
38
37
36
35
34
33
47
46
62
63
64
49
26
B
N
B
1
2
3
4
45
44
43
42
BAR 30
B
B
B
B
B
B
B
B
B
B
B
B
B
B
BAR 29
BAR 28
BAR 27
BAR 26
BAR 25
BAR 24
BAR 23
BAR 22
BAR 21
BAR 20
BAR 19
BAR 18
NC
16
48
32
61
OSC1
BP
ANALOG
COMMON
+IN
– IN
REF IN
C+
REF
C–
REF
VDD
VSS
OSC2
BAR 0
VBUF
CAZ
VINT
NC
N
BAR 17
BAR 16
B
B
B
TC826CBU
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