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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 | Microchip | |
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TC7126/A
3-1/2 Digit Analog-to-Digital Converters
Features
• Internal Reference with Low Temperature Drift
- TC7126: 80ppm/°C Typical
- TC7126A: 35ppm/°C Typical
• Zero Reading with Zero Input
• Low Noise: 15µVP-P
• High Resolution: 0.05%
• Low Input Leakage Current: 1pA Typ., 10pA Max.
• Precision Null Detectors with True Polarity at Zero
• High-Impedance Differential Input
• Convenient 9V Battery Operation with Low Power
Dissipation: 500µW Typ., 900µW Max.
Applications
• Thermometry
• Bridge Readouts: Strain Gauges, Load Cells,
Null Detectors
• Digital Meters and Panel Meters:
- Voltage/Current/Ohms/Power, pH
• Digital Scales, Process Monitors
Device Selection Table
Package
Code
Package
Temperature
Range
CPL
IPL
CKW
40-Pin PDIP
40-Pin PDIP (TC7126 Only)
44-Pin PQFP
0°C to +70°C
-25°C to +85°C
0°C to +70°C
CLW
44-Pin PLCC
0°C to +70°C
General Description
The TC7126A is a 3-1/2 digit CMOS analog-to-digital
converter (ADC) containing all the active components
necessary to construct a 0.05% resolution measure-
ment system. Seven-segment decoders, digit and
polarity drivers, voltage reference, and clock circuit are
integrated on-chip. The TC7126A directly drives a liq-
uid 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. Rollover error (the difference in readings for
equal magnitude, but opposite polarity input signals) is
below ±1 count. High-impedance differential inputs
offer 1pA leakage current and a 1012Ω input imped-
ance. The 15µVP-P noise performance ensures a "rock
solid" reading, and the auto-zero cycle ensures 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.
© 2002 Microchip Technology Inc.
DS21458B-page 1
1 page  
TC7126/A
1.0 ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings*
Supply Voltage (V+ to V-)....................................... 15V
Analog Input Voltage (either Input) (Note 1) ... V+ to V-
Reference Input Voltage (either Input) ............ V+ to V-
Clock Input ................................................... Test to V+
Package Power Dissipation (TA ≤ 70°C) (Note 2):
44-Pin PQFP............................................... 1.00W
40-Pin PLCC ............................................... 1.23W
44-Pin PDIP ................................................ 1.23W
Operating Temperature Range:
C (Commercial) Devices .................. 0°C to +70°C
I (Industrial) Devices .................... -25°C to +85°C
Storage Temperature Range .............. -65°C to +150°C
*Stresses above those listed under "Absolute Maximum
Ratings" may cause permanent damage to the device. These
are stress ratings only and functional operation of the device
at these or any other conditions above those indicated in the
operation sections of the specifications is not implied.
Exposure to Absolute Maximum Rating conditions for
extended periods may affect device reliability.
TC7126/A ELECTRICAL SPECIFICATIONS
Electrical Characteristics: VS = +9V, fCLK – 16kHz, and TA = +25°C, unless otherwise noted.
Symbol
Parameter
Min Typ Max Unit
Test Conditions
Input
ZIR Zero Input Reading
ZRD Zero Reading Drift
Ratiometric Reading
NL Linearity Error
eN
IL
CMRR
Rollover Error
Noise
Input Leakage Current
Common Mode Rejection Ratio
Scale Factor Temperature
Coefficient
-000.0 ±000.0 +000.0
— 0.2
1
999 999/1000 1000
-1 ±0.2 1
-1 ±0.2
1
— 15
—
— 1 10
— 50
—
—1
5
Digital
Reading
µV/°C
Digital
Reading
Count
Count
µVP-P
pA
µV/V
ppm/°C
VIN = 0V
Full Scale = 200mV
VIN = 0V, 0°C ≤ TA ≤ +70°C
VIN = VREF, VREF = 100mV
Full Scale = 200mV or 2V
Max Deviation From Best Fit
Straight Line
VIN- = VIN+ ≈ 200mV
VIN = 0V, Full Scale = 200mV
VIN = 0V
VCM = ±1V, VIN = 0V
Full Scale = 200mV
VIN = 199mV, 0°C ≤ TA ≤ +70°C
Ext. Ref. Temp Coeff. = 0ppm/°C
Analog Common
VCTC
Analog Common Temperature
Coefficient
——
—
— 250kΩ Between Common and V+
——
—
— 0°C ≤ TA ≤ +70°C ("C" Devices)
— 80
— ppm/°C TC7126
— 35 75 ppm/°C TC7126A
— 35 100 ppm/°C -25°C ≤ TA ≤ +85°C ("I" Device)
(TC7126A)
VC
Note
Analog Common Voltage
2.7
3.05
3.35
V 250kΩ Between Common and V+
1: Input voltages may exceed the supply voltages, provided the input current is limited to ±100µA.
2: Dissipation rating assumes device is mounted with all leads soldered to printed circuit board.
3: Refer to “Differential Input” discussion.
4: Backplane drive is in phase with segment drive for “OFF” segment, 180° out of phase for “ON” segment. Frequency is
20 times conversion rate. Average DC component is less than 50mV.
5: See “Typical Application”.
6: During Auto-Zero phase, current is 10-20µA higher. A 48kHz ocillator increases current by 8µA (Typical). Common
current is not included.
© 2002 Microchip Technology Inc.
DS21458B-page 5
5 Page 
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 inde-
pendent 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 compo-
nent value changes are required to upgrade existing
designs.
6.0 COMPONENT VALUE
SELECTION
6.1 Auto-Zero Capacitor (CAZ)
The CAZ capacitor size has some influence on system
noise. A 0.47µF capacitor is recommended for 200mV
full scale applications where 1LSB is 100µV. A 0.033µF
capacitor is adequate for 2.0V full scale applications. A
mylar type dielectric capacitor is adequate.
6.2 Reference Voltage Capacitor (CREF)
The reference voltage, used to ramp the integrator out-
put voltage back to zero during the reference integrate
phase, is stored on CREF. A 0.1µF capacitor is accept-
able when VREF- is tied to analog common. If a large
Common mode voltage exists (VREF- – analog com-
mon) and the application requires a 200mV full scale,
increase CREF to 1µF. Rollover error will be held to less
than 0.5 count. A Mylar type dielectric capacitor is
adequate.
TC7126/A
6.3 Integrating Capacitor (CINT)
CINT should be selected to maximize integrator output
voltage swing without causing output saturation. Due to
the TC7126A's superior analog common temperature
coefficient specification, analog common will normally
supply the differential voltage reference. For this case,
a ±2V full scale integrator output swing is satisfactory.
For 3 readings per second (FOSC = 48kHz), a 0.047µF
value is suggested. For 1 reading per second, 0.15µF
is recommended. If a different oscillator frequency is
used, CINT must be changed in inverse proportion to
maintain the nominal ±2V integrator swing.
An exact expression for CINT is:
EQUATION 6-1:
CINT =
(4000)
1
FOSC
VFS
RINT
VINT
Where:
FOSC = Clock frequency at Pin 38
VFS = Full scale input voltage
RINT = Integrating resistor
VINT = Desired full scale integrator output swing
At 3 readings per second, a 750Ω resistor should be
placed in series with CINT. This increases accuracy by
compensating for comparator delay. CINT must have
low dielectric absorption to minimize rollover error. A
polypropylene capacitor is recommended.
6.4 Integrating Resistor (RINT)
The input buffer amplifier and integrator are designed
with Class A output stages. The output stage idling cur-
rent is 6µA. The integrator and buffer can supply 1µA
drive current with negligible linearity errors. RINT is cho-
sen to remain in the output stage linear drive region, but
not so large that PC board leakage currents induce
errors. For a 200mV full scale, RINT is 180kΩ. A 2V full
scale requires 1.8MΩ.
Component
Value
Nominal Full Scale Voltage
200mV
2V
CAZ
RINT
CINT
Note:
0.33µF
180kΩ
0.047µF
0.033µF
1.8MΩ
0.047µF
FOSC = 48kHz (3 readings per sec).
© 2002 Microchip Technology Inc.
DS21458B-page 11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet TC7126.PDF ] | |
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