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PDF TC7126 Data sheet ( Hoja de datos )
| Número de pieza | TC7126 | |
| Descripción | 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS | |
| Fabricantes | TelCom | |
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1
TC7126
TC7126A
3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS
FEATURES
s Low Temperature Drift Internal Reference
TC7126 ....................................... 80 ppm/°C Typ
TC7126A ..................................... 35 ppm/°C Typ
s Guaranteed Zero Reading With Zero Input
s Low Noise .................................................... 15 µVP-P
s High Resolution .............................................. 0.05%
s Low Input Leakage Current ...................... 1 pA Typ
10 pA Max
s Precision Null Detectors With True Polarity at
Zero
s High-Impedance Differential Input
s Convenient 9V Battery Operation With
Low Power Dissipation ........................ 500 µW Typ
900 µW Max
TYPICAL APPLICATIONS
s Thermometry
s Bridge Readouts: Strain Gauges, Load Cells, Null
Detectors
s Digital Meters and Panel Meters
— Voltage/Current/Ohms/Power, pH
s Digital Scales, Process Monitors
GENERAL DESCRIPTION
The TC7126A is a 3-1/2 digit CMOS analog-to-digital
converter (ADC) containing all the active components nec-
essary to construct a 0.05% resolution measurement sys-
tem. Seven-segment decoders, digit and polarity drivers,
voltage reference, and clock circuit are integrated on-chip.
The TC7126A directly drives a liquid crystal display (LCD),
and includes a backplane driver.
A low-cost, high-resolution indicating meter requires
only a display, four resistors, and four capacitors. The
TC7126A's extremely low power drain and 9V battery
operation make it ideal for portable applications.
The TC7126A reduces linearity error to less than 1
count. Roll-over error (the difference in readings for equal
magnitude but opposite polarity input signals) is below ±1
count. High-impedance differential inputs offer 1 pA leak-
age current and a 1012Ω input impedance. The 15 µVP-P
noise performance guarantees a "rock solid" reading, and
the auto-zero cycle guarantees a zero display reading with
a 0V input.
The TC7126A features a precision, low-drift internal
voltage reference and is functionally identical to the TC7126.
A low-drift external reference is not normally required with
the TC7126A.
2
3
4
5
TYPICAL OPERATING CIRCUIT
+
ANALOG
INPUT
–
1 MΩ
0.01 µF
180 kΩ
0.15 µF
0.1 µF
34
CR+EF
31 VI+N
33
CR–EF
2–19
22–25
SEGMENT
DRIVE
LCD
30 VI–N
32 ANALOG
COMMON
POL 20
MINUS SIGN
BP 21
V+ 1
BACKPLANE
28 VBUFF TC7126
240 kΩ
0.33
µF
29 CAZ
27 VINT
TC7126A
VR+EF 36
VR–EF 35
V – 26
OSC2 OSC3 OSC1
10 kΩ
+
9V
1 CONVERSION/SEC
39 38 COSC 40
ROSC 50 pF
TO ANALOG COMMON
(PIN 32)
560 kΩ
NOTE: Pin numbers refer to 40-pin DIP.
TELCOM SEMICONDUCTOR, INC.
ORDERING INFORMATION
PART CODE
TC7126X X XXX
A or blank*
R (reversed pins) or blank (CPL pkg only)
* "A" parts have an improved reference TC
Package Code (see below):
6
Package
Code
Package
CKW
CLW
CPL
IPL
44-Pin PQFP
44-Pin PLCC
40-Pin PDIP
40-Pin PDIP (non-A only)
AVAILABLE PACKAGES
Temperature
Range
0°C to +70°C
0°C to +70°C
0°C to +70°C
– 25°C to +85°C
7
40-Pin Plastic DIP
44-Pin Plastic Quad Flat 44-Pin Plastic Chip
Package Formed Leads Carrier PLCC
TC7126/A-8 11/6/96
3-217
8
1 page  
3-1/2 DIGIT
ANALOG-TO-DIGITAL CONVERTERS
1
TC7126
TC7126A
PIN DESCRIPTION (Cont.)
40-Pin PDIP
Pin Number
Normal (Reverse)
34 (7)
Name
CR+ EF
35 (6)
(5)
36 (4)
VR– EF
VR+ EF
TEST
37 (3)
38 (2)
40 (1)
OSC3
OSC2
OSC1
2
Description
A 0.1 µF capacitor is used in most applications. If a large common-mode voltage
exists (for example, the VIN– pin is not at analog common), and a 200 mV scale is
used, a 1 µF capacitor is recommended and will hold the roll-over error to 0.5
count.
See pin 36.
The analog input required to generate a full-scale output (1999 counts). Place 100
mV between pins 35 and 36 for 199.9 mV full scale. Place 1V between pins 35
and 36 for 2V full scale. See paragraph on reference voltage.
Lamp test. When pulled HIGH (to V+), all segments will be turned ON and the
display should read –1888. It may also be used as a negative supply for exter-
nally-generated decimal points. See paragraph under test for additional informa-
tion.
See pin 40.
See pin 40.
Pins 40, 39 and 38 make up the oscillator section. For a 48 kHz clock (3 readings
39per second), connect pin 40 to the junction of a 180 kΩ resistor and a 50 pF
capacitor. The 180 kΩ resistor is tied to pin 39 and the 50 pF capacitor is tied to
pin 38.
3
4
GENERAL THEORY OF OPERATION
(All Pin Designations Refer to the 40-Pin DIP)
Dual-Slope Conversion Principles
The TC7126A is a dual-slope, integrating analog-to-
digital converter. An understanding of the dual-slope con-
version technique will aid in following detailed TC7126A
operational theory.
The conventional dual-slope converter measurement
cycle has two distinct phases:
(1) Input signal integration
(2) Reference voltage integration (deintegration)
The input signal being converted is integrated for a
fixed time period (tSI), measured by counting clock pulses.
An opposite polarity constant reference voltage is then
integrated until the integrator output voltage returns to
zero. The reference integration time is directly proportional
to the input signal (tRI).
In a simple dual-slope converter, a complete conver-
sion requires the integrator output to "ramp-up" and "ramp-
down."
A simple mathematical equation relates the input signal,
reference voltage, and integration time:
∫1 tSI VIN(t) dt = VR tRI ,
RC 0
RC
TELCOM SEMICONDUCTOR, INC.
ANALOG
INPUT
SIGNAL
INTEGRATOR
–
+
COMPARATOR
–
+
REF
VOLTAGE
SWITCH
DRIVER
PHASE
CONTROL
CONTROL
LOGIC
POLARITY CONTROL
CLOCK
5
6
DISPLAY
COUNTER
VIN Ϸ VFULL SCALE
VIN Ϸ 1.2 VFULL SCALE
FIXED
SIGNAL
INTEGRATE
TIME
VARIABLE
REFERENCE
INTEGRATE
TIME
7
Figure 1. Basic Dual-Slope Converter
where:
VR = Reference voltage
tSI = Signal integration time (fixed)
tRI = Reference voltage integration time (variable).
3-221
8
5 Page 
3-1/2 DIGIT
ANALOG-TO-DIGITAL CONVERTERS
1
TC7126
TC7126A
200
180
NO
160 MAXIMUM
SPECIFIED
140 TYPICAL
120
100
NO
GUARANTEED MAXIMUM
80 MAXIMUM SPECIFIED
TYPICAL
60
40 TYPICAL
20
TC7126A
ICL7126
ICL7136
0
Figure 7. Analog Common Temperature Coefficient
APPLICATIONS INFORMATION
Liquid Crystal Display Sources
Several manufacturers supply standard LCDs to inter-
face with the TC7126A 3-1/2 digit analog-to-digital con-
verter.
Manufacturer Address/Phone
Representative
Part Numbers*
Crystaloid
Electronics
5282 Hudson Dr.,
Hudson, OH 44236
216-655-2429
C5335, H5535,
T5135, SX440
AND
720 Palomar Avenue
Sunnyvale, CA 94086
408-523-8200
FE 0801,
FE 0203
VGI, Inc.
1800 Vernon St., Ste. 2 I1048, I1126
Roseville, CA 95678
916-783-7878
Hamlin, Inc.
612 E. Lake St.,
Lake Mills, WI 53551
414-648-2361
3902, 3933, 3903
*NOTE: Contact LCD manufacturer for full product listing/specifications.
Decimal Point and Annunciator Drive
The TEST pin is connected to the internally-generated
digital logic supply ground through a 500Ω resistor. The
TEST pin may be used as the negative supply for external
CMOS gate segment drivers. LCD annunciators for decimal
points, low battery indication, or function indication may be
added without adding an additional supply. No more than 1
mA should be supplied by the TEST pin: its potential is
approximately 5V below V+.
TELCOM SEMICONDUCTOR, INC.
9V
+
26
V–
1
V+
240 kΩ
2
TC7126A
VR+ EF
VR– EF
ANALOG
COMMON
36
VREF
35
32
10 kΩ
3
SET VREF = 1/2 VFULL SCALE
Figure 8. TC7126A Internal Voltage Reference Connection
4
Flat Package
The TC7126A is available in an epoxy 64-pin formed-
lead flat package. A test socket for the TC7126ACBQ device
is available:
Part No.
IC 51-42
Manufacturer: Yamaichi
Distribution: Nepenthe Distribution
2471 East Bayshore
Suite 520
Palo Alto, CA 94043
(415) 856-9332
5
Ratiometric Resistance Measurements
The TC7126A's true differential input and differential
reference make ratiometric readings possible. In ratiometric
operation, an unknown resistance is measured with respect
to a known standard resistance. No accurately-defined
reference voltage is needed.
The unknown resistance is put in series with a known
standard and a current passed through the pair. The voltage
developed across the unknown is applied to the input and
the voltage across the known resistor applied to the refer-
ence input. If the unknown equals the standard, the display
will read 1000. The displayed reading can be determined
from the following expression:
Displayed reading = RUNKNOWN ϫ 1000.
RSTANDARD
The display will overrange for RUNKNOWN ≥
2 ϫ RSTANDARD.
6
7
8
3-227
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet TC7126.PDF ] | |
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