TC7126ARCPL [MICROCHIP]
3-1/2 Digit Analog-to-Digital Converters; 3-1 / 2位模拟 - 数字转换器型号: | TC7126ARCPL |
厂家: | MICROCHIP |
描述: | 3-1/2 Digit Analog-to-Digital Converters |
文件: | 总22页 (文件大小:553K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
TC7126/A
3-1/2 Digit Analog-to-Digital Converters
Features
General Description
• Internal Reference with Low Temperature Drift
- TC7126: 80ppm/°C Typical
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.
- TC7126A: 35ppm/°C Typical
• Zero Reading with Zero Input
• Low Noise: 15µV
P-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
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.
• Convenient 9V Battery Operation with Low Power
Dissipation: 500µW Typ., 900µW Max.
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
Applications
• Thermometry
• Bridge Readouts: Strain Gauges, Load Cells,
Null Detectors
12
offer 1pA leakage current and a 10 Ω input imped-
ance. The 15µV
noise performance ensures a "rock
P-P
• Digital Meters and Panel Meters:
- Voltage/Current/Ohms/Power, pH
• Digital Scales, Process Monitors
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.
Device Selection Table
Package
Code
Temperature
Range
Package
CPL
IPL
40-Pin PDIP
0°C to +70°C
40-Pin PDIP (TC7126 Only) -25°C to +85°C
CKW
CLW
44-Pin PQFP
44-Pin PLCC
0°C to +70°C
0°C to +70°C
2002 Microchip Technology Inc.
DS21458B-page 1
TC7126/A
Package Type
44-Pin PLCC
44-Pin PQFP
6
5
4
3
2
1
44 43 42 41 40
44 43 42 41 40 39 38 37 36 35 34
NC
NC
33 NC
1
2
3
4
V
-
F
G
E
7
8
39
38
37
36
35
34
33
32
31
30
29
REF
1
32 G
2
C
+
1
REF
C
31
30
29
TEST
OSC3
3
C
-
9
1
REF
A
ANALOG
COMMON
3
D
10
2
G
NC
OSC2
OSC1
5
6
3
V
+
TC7126CKW
TC7126ACKW
C
11
12
13
14
15
16
17
IN
TC7126CLW
TC7126ACLW
2
28 BP
NC
NC
27 POL
7
B
2
V
-
IN
AB
26
V+
8
4
A
2
C
AZ
D
1
25 E
24 F
9
3
F
2
V
BUFF
INT
C
1
10
11
3
E
2
V
B
1
B
3
23
D
3
V-
25 26 27 28
18 19 20 21 22 23 24
19 20 21 22
12 13 14 15 16 17 18
40-Pin PDIP (Normal)
44-Pin PDIP (Reverse)
OSC1
OSC2
OSC3
TEST
1
2
40 OSC1
1
2
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
V+
V+
Normal Pin
Reverse Pin
Configuration
D
1
D
1
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
OSC2
Configuration
C
1
C
1
3
3
OSC3
TEST
B
1
4
4
B
1
V
+
A
1
A
1
5
5
1's
V
V
+
REF
1's
REF
REF
V
-
REF
F
1
F
1
6
6
-
C
+
-
G
1
G
1
7
C
C
+
7
REF
REF
TC7126CPL
TC7126ACPL
TC7126IPL
TC7126RCPL
TC7126ARCPL
TC7126RIPL
C
E
1
E
1
-
8
8
REF
REF
ANALOG
COMMON
ANALOG
COMMON
9
9
D
C
B
D
C
B
2
2
2
TC7126AIPL
TC7126ARIPL
V
+
10
11
12
13
14
15
16
17
18
19
20
10
11
12
13
14
15
16
17
18
19
20
V
+
IN
2
IN
V
-
V
-
IN
2
2
2
2
IN
10's
10's
C
A
C
V
A
AZ
AZ
V
F
F
BUFF
2
2
BUFF
INT
V
E
E
V
INT
2
2
D
V-
G
V-
D
3
3
B
B
G
2
3
3
2
100's
100's
C
3
F
E
F
E
C
A
3
3
3
100's
100's
A
3
3
3
4
3
G
3
AB
AB
1000's
G
1000's
4
3
BP
(Backplane)
POL
(Minus Sign)
POL
(Minus Sign)
BP
(Backplane)
NC = No Internal Connection
DS21458B-page 2
2002 Microchip Technology Inc.
TC7126/A
Typical Application
0.1µF
33
TC7126
TC7126A
34
LCD
C
REF
+
C
REF
-
1MΩ
31
Segment
Drive
2–19
+
V
+
IN
22–25
Analog
Input
–
0.01µF
20
30
32
POL
BP
V
-
IN
Minus Sign
21
Backplane
ANALOG
COMMON
1
V+
28
V
BUFF
240kΩ
+
9V
0.33
180kΩ
0.15µF
36
µF
V
+
REF
29
10kΩ
C
AZ
35
26
V
-
REF
27
V
INT
V-
1 Conversion/Sec
OSC2 OSC3 OSC1
C
OSC
39
38
40
To Analog Common (Pin 32)
50pF
R
OSC
560kΩ
Note: Pin numbers refer to 40-pin DIP.
2002 Microchip Technology Inc.
DS21458B-page 3
TC7126/A
Functional Block Diagram
DS21458B-page 4
2002 Microchip Technology Inc.
TC7126/A
*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.
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 (T ≤ 70°C) (Note 2):
A
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
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
-000.0
±000.0
+000.0
Digital
VIN = 0V
Reading
Full Scale = 200mV
ZRD
NL
Zero Reading Drift
—
0.2
1
µV/°C
VIN = 0V, 0°C ≤ TA ≤ +70°C
VIN = VREF, VREF = 100mV
Ratiometric Reading
999
999/1000
1000
Digital
Reading
Linearity Error
-1
±0.2
1
Count
Full Scale = 200mV or 2V
Max Deviation From Best Fit
Straight Line
Rollover Error
-1
—
—
—
±0.2
15
1
1
Count
µVP-P
pA
VIN- = VIN+ ≈ 200mV
VIN = 0V, Full Scale = 200mV
VIN = 0V
eN
Noise
—
10
—
IL
Input Leakage Current
Common Mode Rejection Ratio
CMRR
50
µV/V
VCM = ±1V, VIN = 0V
Full Scale = 200mV
Scale Factor Temperature
Coefficient
—
1
5
ppm/°C
VIN = 199mV, 0°C ≤ TA ≤ +70°C
Ext. Ref. Temp Coeff. = 0ppm/°C
Analog Common
VCTC Analog Common Temperature
—
—
—
—
—
—
—
80
35
35
—
—
—
250kΩ Between Common and V+
0°C ≤ TA ≤ +70°C ("C" Devices)
TC7126
Coefficient
—
—
ppm/°C
ppm/°C
ppm/°C
75
100
TC7126A
-25°C ≤ TA ≤ +85°C ("I" Device)
(TC7126A)
VC
Analog Common Voltage
2.7
3.05
3.35
V
250kΩ Between Common and V+
Note 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
TC7126/A
TC7126/A ELECTRICAL SPECIFICATIONS (CONTINUED)
Electrical Characteristics: VS = +9V, fCLK – 16kHz, and TA = +25°C, unless otherwise noted.
Symbol
Parameter
Min
Typ
Max
Unit
Test Conditions
LCD Drive
VSD
VBD
LCD Segment Drive Voltage
LCD Backplane Drive Voltage
4
4
5
5
6
6
VP-P
VP-P
V+ to V- = 9V
V+ to V- = 9V
Power Supply
IS Power Supply Current
—
55
100
µA
VIN = 0V, V+ to V- = 9V (Note 6)
Note 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.
DS21458B-page 6
2002 Microchip Technology Inc.
TC7126/A
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
PIN FUNCTION TABLE
Pin Number
(40-Pin PDIP)
Normal
(Reversed)
Symbol
Description
1
(40)
(39)
(38)
(37)
(36)
(35)
(34)
(33)
(32)
(31)
(30)
(29)
(28)
(27)
(26)
(25)
(24)
(23)
(22)
(21)
(20)
(19)
(18)
(17)
(16)
(15)
(14)
V+
D1
C1
B1
Positive supply voltage.
2
Activates the D section of the units display.
Activates the C section of the units display.
Activates the B section of the units display.
Activates the A section of the units display.
Activates the F section of the units display.
Activates the G section of the units display.
Activates the E section of the units display.
Activates the D section of the tens display.
Activates the C section of the tens display.
Activates the B section of the tens display.
Activates the A section of the tens display.
Activates the F section of the tens display.
Activates the E section of the tens display.
Activates the D section of the hundreds display.
Activates the B section of the hundreds display.
Activates the F section of the hundreds display.
Activates the E section of the hundreds display.
Activates both halves of the 1 in the thousands display.
Activates the negative polarity display.
3
4
5
A1
6
F1
7
G1
E1
8
9
D2
C2
B2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
A2
F2
E2
D3
B3
F3
E3
AB4
POL
BP
G3
A3
LCD Backplane drive output (TC7106A). Digital Ground (TC7107A).
Activates the G section of the hundreds display.
Activates the A section of the hundreds display.
Activates the C section of the hundreds display.
Activates the G section of the tens display.
C3
G2
V-
Negative power supply voltage.
VINT
The integrating capacitor should be selected to give the maximum voltage swing that
ensures component tolerance buildup will not allow the integrator output to saturate.
When analog common is used as a reference and the conversion rate is 3 readings
per second, a 0.047µF capacitor may be used. The capacitor must have a low
dielectric constant to prevent rollover errors. See Section 6.3, Integrating Capacitor
for additional details.
28
29
(13)
(12)
VBUFF
CAZ
Integration resistor connection. Use a 180kΩ resistor for a 200mV full-scale range
and a 1.8MΩ resistor for a 2V full scale range.
The size of the auto-zero capacitor influences system noise. Use a 0.33µF capacitor
for 200mV full scale, and a 0.033µF capacitor for 2V full scale. See Section 6.1,
Auto-Zero Capacitor for additional details.
30
31
32
(11)
(10)
(9)
VIN
VIN
-
The analog LOW input is connected to this pin.
+
The analog HIGH input signal is connected to this pin.
ANALOG This pin is primarily used to set the Analog Common mode voltage for battery opera-
COMMON tion, or in systems where the input signal is referenced to the power supply. It also
acts as a reference voltage source. See Section 7.3, Analog Common for additional
details.
33
(8)
CREF
-
See Pin 34.
2002 Microchip Technology Inc.
DS21458B-page 7
TC7126/A
TABLE 2-1:
PIN FUNCTION TABLE (CONTINUED)
Pin Number
(40-Pin PDIP)
Normal
(Reversed)
Symbol
Description
34
(7)
CREF
+
A 0.1µF 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 200mV scale is
used, a 1µF capacitor is recommended and will hold the rollover error to 0.5 count.
35
36
(6)
(5)
VREF
VREF
-
See Pin 36.
+
The analog input required to generate a full scale output (1999 counts). Place 100mV
between Pins 35 and 36 for 199.9mV full scale. Place 1V between Pins 35 and 36 for
2V full scale. See Section 6.6, Reference Voltage for additional information.
37
(4)
TEST
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 externally
generated decimal points. See Section 7.4, TEST for additional information.
38
39
40
(3)
(2)
(1)
OSC3
OSC2
OSC1
See Pin 40.
See Pin 40.
Pins 40, 39 and 38 make up the oscillator section. For a 48kHz clock (3 readings,
39 per second), connect Pin 40 to the junction of a 180kΩ resistor and a 50pF
capacitor. The 180kΩ resistor is tied to Pin 39 and the 50pF capacitor is tied to
Pin 38.
DS21458B-page 8
2002 Microchip Technology Inc.
TC7126/A
A simple mathematical equation relates the input sig-
nal, reference voltage and integration time:
3.0
DETAILED DESCRIPTION
(All Pin Designations Refer to 40-Pin PDIP.)
EQUATION 3-1:
3.1
Dual Slope Conversion Principles
T
0
V T
SI
1
RC
R
RI
V
(t)d =
t
IN
RC
The TC7126A is a dual slope, integrating analog-to-
digital converter. An understanding of the dual slope
conversion technique will aid in following the detailed
TC7126/A operation theory.
Where:
V
= Reference voltage
R
T
T
= Signal integration time (fixed)
SI
RI
The conventional dual slope converter measurement
cycle has two distinct phases:
= Reference voltage integration time (variable)
For a constant V
:
• Input Signal Integration
IN
• Reference Voltage Integration (De-integration)
EQUATION 3-2:
The input signal being converted is integrated for a fixed
T
RI
R-------
time period (T ). Time is measured by counting clock
V
= V
SI
IN
T
SI
pulses. An opposite polarity constant reference voltage
is then integrated until the integrator output voltage
returns to zero. The reference integration time is directly
The dual slope converter accuracy is unrelated to the
integrating resistor and capacitor values, as long as
they are stable during a measurement cycle. Noise
immunity is an inherent benefit. Noise spikes are inte-
grated or averaged to zero during integration periods.
Integrating ADCs are immune to the large conversion
errors that plague successive approximation converters
in high noise environments. Interfering signals with fre-
quency components at multiples of the averaging period
will be attenuated. Integrating ADCs commonly operate
with the signal integration period set to a multiple of the
50Hz/60Hz power line period (see Figure 3-2).
proportional to the input signal (T ) (see Figure 3-1).
RI
FIGURE 3-1:
BASIC DUAL SLOPE
CONVERTER
Analog
Input
Signal
Integrator
Comparator
–
–
+
+
Switch
Driver
Clock
FIGURE 3-2:
NORMAL MODE
REJECTION OF DUAL
SLOPE CONVERTER
Phase
REF
Control
Logic
Control
Voltage
Polarity Control
30
20
10
Counter
Display
V
V
≈ V
IN
IN
REF
≈ 1.2 V
REF
Fixed Variable
Signal Reference
Integrate Integrate
Time Time
In a simple dual slope converter, a complete conver-
sion requires the integrator output to “ramp-up” and
“ramp-down.”
t = Measurement Period
0
0.1/t
1/t
10/t
Input Frequency
2002 Microchip Technology Inc.
DS21458B-page 9
TC7126/A
4.3
Reference Integrate Phase
4.0
ANALOG SECTION
The third phase is reference integrate or de-integrate.
- is internally connected to analog common and V
In addition to the basic integrate and de-integrate dual
slope cycles discussed above, the TC7126A design
incorporates an auto-zero cycle. This cycle removes
buffer amplifier, integrator and comparator offset volt-
age error terms from the conversion. A true digital zero
reading results without external adjusting potentiome-
ters. A complete conversion consists of three phases:
V
+
IN
IN
is connected across the previously charged reference
capacitor. Circuitry within the chip ensures that the
capacitor will be connected with the correct polarity to
cause the integrator output to return to zero. The time
required for the output to return to zero is proportional to
the input signal and is between 0 and 2000 counts. The
digital reading displayed is:
1. Auto-Zero phase
2. Signal Integrate phase
3. Reference Integrate phase
EQUATION 4-2:
V
IN
1000
4.1
Auto-Zero Phase
V
REF
During the auto-zero phase, the differential input signal
is disconnected from the circuit by opening internal
analog gates. The internal nodes are shorted to analog
common (ground) to establish a zero input condition.
Additional analog gates close a feedback loop around
the integrator and comparator. This loop permits com-
parator offset voltage error compensation. The voltage
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
level established on C compensates for device offset
AZ
voltages. The auto-zero phase residual is typically
10µV to 15µV. The auto-zero cycle length is 1000 to
3000 clock periods.
4.2
Signal Integrate Phase
The auto-zero loop is entered and the internal differen-
tial inputs connect to V + and V -. The differential
driver is ON for negative analog inputs. If V + and V
are reversed, this indicator reverses.
-
IN
IN
IN
IN
input signal is integrated for a fixed time period. The
TC7126/A signal integration period is 1000 clock
periods or counts. The externally set clock frequency is
divided by four before clocking the internal counters.
The integration time period is:
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.
EQUATION 4-1:
4
T
=
x 1000
SI
F
OSC
Where: F
= external clock frequency.
OSC
The display font and segment drive assignment are
shown in Figure 5-1.
The differential input voltage must be within the device
Common mode range when the converter and mea-
sured system share the same power supply common
(ground). If the converter and measured system do not
FIGURE 5-1:
DISPLAY FONT AND
SEGMENT ASSIGNMENT
share the same power supply common, V - should be
tied to analog common.
IN
Display Font
Polarity is determined at the end of signal integrate
phase. The sign bit is a true polarity indication, in that
signals less than 1LSB are correctly determined. This
allows precision null detection limited only by device
noise and auto-zero residual offsets.
1000's 100's
10's
1's
DS21458B-page 10
2002 Microchip Technology Inc.
TC7126/A
5.1
System Timing
6.3
Integrating Capacitor (CINT
)
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.
C
should be selected to maximize integrator output
INT
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.
Each phase of the measurement cycle has the following
length:
For 3 readings per second (F = 48kHz), a 0.047µF
value is suggested. For 1 reading per second, 0.15µF
is recommended. If a different oscillator frequency is
OSC
1. Auto-Zero Phase: 1000 to 3000 counts
(4000 to 12,000 clock pulses).
used, C
must be changed in inverse proportion to
INT
maintain the nominal 2V integrator swing.
For signals less than full scale, the auto-zero
phase is assigned the unused reference integrate
time period.
An exact expression for C
is:
INT
EQUATION 6-1:
2. Signal Integrate: 1000 counts
(4000 clock pulses).
1
V
R
FS
(4000)
F
This time period is fixed. The integration period is:
OSC
INT
C
=
INT
V
INT
EQUATION 5-1:
Where:
F
1
T
= 4000
SI
F
= Clock frequency at Pin 38
= Full scale input voltage
OSC
OSC
V
FS
Where: F
is the externally set clock frequency.
OSC
R
= Integrating resistor
INT
V
= Desired full scale integrator output swing
INT
3. Reference Integrate: 0 to 2000 counts
(0 to 8000 clock pulses).
At 3 readings per second, a 750Ω resistor should be
placed in series with C . This increases accuracy by
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.
INT
compensating for comparator delay. C
must have
INT
low dielectric absorption to minimize rollover error. A
polypropylene capacitor is recommended.
6.4
Integrating Resistor (RINT)
6.0
6.1
COMPONENT VALUE
SELECTION
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
Auto-Zero Capacitor (CAZ)
drive current with negligible linearity errors. R is cho-
INT
sen to remain in the output stage linear drive region, but
not so large that PC board leakage currents induce
The C capacitor size has some influence on system
AZ
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.
errors. For a 200mV full scale, R
is 180kΩ. A 2V full
INT
scale requires 1.8MΩ.
Nominal Full Scale Voltage
Component
Value
6.2
Reference Voltage Capacitor (CREF)
200mV
2V
The reference voltage, used to ramp the integrator out-
put voltage back to zero during the reference integrate
C
0.33µF
180kΩ
0.033µF
1.8MΩ
AZ
R
INT
phase, is stored on C
. A 0.1µF capacitor is accept-
REF
C
0.047µF
0.047µF
INT
able when V
- is tied to analog common. If a large
REF
Common mode voltage exists (V
- – analog com-
Note:
FOSC = 48kHz (3 readings per sec).
REF
mon) and the application requires a 200mV full scale,
increase C to 1µF. Rollover error will be held to less
REF
than 0.5 count. A Mylar type dielectric capacitor is
adequate.
2002 Microchip Technology Inc.
DS21458B-page 11
TC7126/A
6.5
Oscillator Components
7.0
DEVICE PIN FUNCTIONAL
DESCRIPTION
C
should be 50pF; R
is selected from the
OSC
OSC
equation:
(Pin Numbers Refer to the 40-Pin PDIP.)
EQUATION 6-2:
7.1
Differential Signal Inputs
VIN+ (Pin 31), VIN- (Pin 30)
0.45
RC
F
=
OSC
The TC7126A is designed with true differential inputs
and accepts input signals within the input stage
Common mode voltage range (V ). Typical range is
V+ – 1V to V- + 1V. Common mode voltages are
removed from the system when the TC7126A operates
from a battery or floating power source (isolated from
For a 48kHz clock (3 conversions per second),
R = 180kΩ.
CM
Note that F
is 44 to generate the TC7126A's inter-
OSC
nal clock. The backplane drive signal is derived by
dividing F by 800.
OSC
measured system), and V - is connected to analog
IN
To achieve maximum rejection of 60Hz noise pickup,
the signal integrate period should be a multiple of
60Hz. Oscillator frequencies of 24kHz, 12kHz, 80kHz,
60kHz, 40kHz, etc. should be selected. For 50Hz rejec-
tion, oscillator frequencies of 20kHz, 100kHz,
66-2/3kHz, 50kHz, 40kHz, etc. would be suitable. Note
that 40kHz (2.5 readings per second) will reject both
50Hz and 60Hz.
common (V
) (see Figure 7-2).
COM
In systems where Common mode voltages exist, the
TC7126A's 86 dB Common mode rejection ratio mini-
mizes error. Common mode voltages do, however,
affect the integrator output level. A worst case condition
exists if a large positive V
a full scale negative differential signal. The negative
signal drives the integrator output positive along with
exists in conjunction with
CM
V
(see Figure 7-1). For such applications, the inte-
CM
6.6
Reference Voltage Selection
grator output swing can be reduced below the recom-
mended 2V full scale swing. The integrator output
will swing within 0.3V of V+ or V- without increased
linearity error.
A full scale reading (2000 counts) requires the input
signal be twice the reference voltage.
Required Full Scale Voltage*
V
REF
FIGURE 7-1:
COMMON MODE
VOLTAGE REDUCES
AVAILABLEINTEGRATOR
20mV
2V
100mV
1V
Note:
VFS = 2VREF.
SWING (V
≠ V )
COM
IN
In some applications, a scale factor other than unity
may exist between a transducer output voltage and the
required digital reading. Assume, for example, a pres-
C
I
Input
Buffer
R
I
+
+
–
2
–
+
sure transducer output for 2000lb/in is 400mV. Rather
V
I
than dividing the input voltage by two, the reference
voltage should be set to 200mV. This permits the trans-
ducer input to be used directly.
V
IN
Integrator
– V
–
t
I
The differential reference can also be used where a
V
=
V
I
[
CM
IN
[
R
C
V
I
I
digital zero reading is required when V is not equal to
CM
IN
Where:
4000
zero. This is common in temperature measuring instru-
mentation. A compensating offset voltage can be
t = Integration time =
I
F
OSC
C = Integration capacitor
I
applied between analog common and V -. The trans-
IN
R = Integration resistor
I
ducer output is connected between V + and analog
IN
common.
DS21458B-page 12
2002 Microchip Technology Inc.
TC7126/A
The TC7126A offers a significantly improved analog
common temperature coefficient. This potential pro-
vides a very stable voltage, suitable for use as a refer-
ence. The temperature coefficient of analog common is
typically 35ppm/°C for the TC7126A and 80 ppm/°C for
the TC7126.
7.2
Differential Reference
VREF+ (Pin 36), VREF- (Pin 35)
The reference voltage can be generated anywhere
within the V+ to V- power supply range.
To prevent rollover type errors being induced by large
Common mode voltages, C
should be large com-
REF
pared to stray node capacitance.
FIGURE 7-2:
COMMON MODE VOLTAGE REMOVED IN BATTERY OPERATION WITH
= ANALOG COMMON
V
IN
Segment
Drive
LCD
Measured
System
V
C
V
INT
POL BP
OSC1
BUFF
AZ
V
+
IN
TC7126A
V+
OSC3
V
-
IN
V-
OSC2
V-
GND
ANALOG
COMMON
V
- V +
REF REF
V+
V+
V-
GND
Power
Source
+
9V
With sufficiently high total supply voltage (V+ – V- > 7V),
analog common is a very stable potential with excellent
temperature stability (typically 35ppm/°C). This poten-
tial can be used to generate the TC7126A's reference
voltage. An external voltage reference will be unneces-
sary in most cases because of the 35ppm/°C tempera-
ture coefficient. See Section 7.5, TC7126A Internal
Voltage Reference discussion.
7.3
Analog Common (Pin 32)
The analog common pin is set at a voltage potential
approximately 3V below V+. The potential is between
2.7V and 3.35V below V+. Analog common is tied inter-
nally to an N-channel FET capable of sinking 100µA.
This FET will hold the common line at 3V should an
external load attempt to pull the common line toward
V+. Analog common source current is limited to 1µA.
Therefore, analog common is easily pulled to a more
negative voltage (i.e., below V+ – 3V).
7.4
TEST (Pin 37)
The TEST pin potential is 5V less than V+. TEST may
be used as the negative power supply connection for
external CMOS logic. The TEST pin is tied to the inter-
nally generated negative logic supply through a 500Ω
resistor. The TEST pin load should be no more than
1mA. See Section 5.0, Digital Section for additional
information on using TEST as a negative digital logic
supply.
The TC7126A connects the internal V + and V -
IN
IN
inputs to analog common during the auto-zero phase.
During the reference integrate phase, V - is con-
IN
nected to analog common. If V - is not externally con-
IN
nected to analog common, a Common mode voltage
exists, but is rejected by the converter's 86dB Com-
mon mode rejection ratio. In battery operation, analog
common and V - are usually connected, removing
IN
If TEST is pulled HIGH (to V+), all segments plus the
minus sign will be activated. DO NOT OPERATE IN
THIS MODE FOR MORE THAN SEVERAL MINUTES.
With TEST = V+, the LCD segments are impressed
with a DC voltage which will destroy the LCD.
Common mode voltage concerns. In systems where
V - is connected to power supply ground or to a given
IN
voltage, analog common should be connected to V -.
IN
The analog common pin serves to set the analog sec-
tion reference, or common point. The TC7126A is spe-
cifically designed to operate from a battery, or in any
measurement system where input signals are not refer-
enced (float) with respect to the TC7126A's power
source. The analog common potential of V+ – 3V gives
a 7V end of battery life voltage. The common potential
has a 0.001%/% voltage coefficient and a 15Ω output
impedance.
2002 Microchip Technology Inc.
DS21458B-page 13
TC7126/A
7.5
TC7126A Internal Voltage
Reference
8.0
8.1
TYPICAL APPLICATIONS
Liquid Crystal Display Sources
The TC7126A's analog common voltage temperature
stability has been significantly improved (Figure 7-3).
The "A" version of the industry standard TC7126
device allows users to upgrade old systems and design
new systems, without external voltage references.
External R and C values do not need to be changed.
Figure 7-4 shows analog common supplying the
necessary voltage reference for the TC7126A.
Several manufacturers supply standard LCDs to inter-
face with the TC7126A, 3-1/2 digit analog-to-digital
converter.
Representative
Part Numbers*
Manufacturer
Address/Phone
Crystaloid
Electronics
5282 Hudson Dr.
Hudson, OH 44236
216-655-2429
C5335, H5535,
T5135, SX440
FIGURE 7-3:
ANALOG COMMON TEMP.
COEFFICIENT
AND
720 Palomar Ave.
Sunnyvale, CA 94086
408-523-8200
FE 0801
FE 0203
200
180
VGI, Inc.
Hamlin, Inc.
1800 Vernon St., Ste. 2 LD-B709BZ
Roseville, CA 95678
916-783-7878
LD-H7992AZ
No
Maximum
Specified
160
140
120
100
612 E. Lake St.
Lake Mills,
3902, 3933,
3903
Typical
WI 53551
414-648-2361
No
Maximum
Note:
Contact LCD manufacturer for full product listing/
specifications.
Maximum
Specified
80
60
40
20
Typical
8.2
Decimal Point and Annunciator
Drive
Typical
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 exter-
nal CMOS gate segment drivers. LCD annunciators for
decimal points, low battery indication, or function indi-
cation may be added, without adding an additional sup-
ply. No more than 1mA should be supplied by the TEST
pin; its potential is approximately 5V below V+ (see
Figure 8-1).
TC7126A
ICL7126
ICL7136
0
FIGURE 7-4:
TC7126A INTERNAL
VOLTAGE REFERENCE
CONNECTION
9V
+
FIGURE 8-1:
DECIMAL POINT AND
ANNUNCIATOR DRIVES
26
V-
1
240kΩ
Simple Inverter for Fixed Decimal Point
or Display Annunciator
V+
V+
V+
TC7126A
4049
36
V
+
-
TC7126A
BP
10kΩ
REF
To LCD
Decimal
Point
21
37
V
REF
GND
35
TEST
V
To
REF
Backplane
32
Multiple Decimal Point or
Annunciator Driver
ANALOG
COMMON
V+
SET V
= 1/2 V
V+
REF
REF
BP
To LCD
Decimal
Point
To LCD
Decimal
Point
TC7126A
4030
GND
TEST
DS21458B-page 14
2002 Microchip Technology Inc.
TC7126/A
EQUATION 8-1:
Displayed (Reading) =
8.3
Flat Package
R
The TC7126 is available in an epoxy 64-pin formed
lead package. A test socket for the TC7126ACBQ
device is available:
UNKNOWN
x 1000
R
STANDARD
Part Number:
Manufacturer:
Distribution:
IC 51-42
Yamaichi
Nepenthe Distribution
2471 East Bayshore, Ste. 520
Palo Alto, CA 94043
(650) 856-9332
The display will over range for R
≥ 2 x
UNKNOWN
R
(see Figure 8-2).
STANDARD
FIGURE 8-2:
LOW PARTS COUNT
RATIOMETRIC
RESISTANCE
MEASUREMENT
8.4
Ratiometric Resistance
Measurements
V+
V
V
+
-
REF
The TC7126A’s true differential input and differential
reference make ratiometric reading possible. In a ratio-
metric operation, an unknown resistance is measured
with respect to a known standard resistance. No
accurately defined reference voltage is needed.
R
REF
STANDARD
LCD
V
+
IN
TC7126A
R
UNKNOWN
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 is
applied to the reference input. If the unknown equals
the standard, the display will read 1000. The displayed
reading can be determined from the following
expression:
V
-
IN
ANALOG
COMMON
FIGURE 8-3:
3-1/2 DIGIT TRUE RMS AC DMM
9V
+
26
V-
1N4148
1µF
200mV
27
1
1MΩ
10MΩ
1
2
3
4
5
6
7
14
13
12
V+
V
IN
29
240kΩ
10kΩ
TC7126A
9MΩ
C1
2V
0.02µF
36
35
AD636
11
10
9
V
V
+
-
REF
REF
28
40
47kΩ
1Ω
6.8µF
C2
900kΩ
90kΩ
10kΩ
+
32
31
ANALOG
COMMON
20V
10%
1MΩ 10%
8
V
+
IN
0.01
µF
2.2
µF
30
26
20kΩ
38
39
V
+
200V
OUT
10%
V-
BP
Segment
Drive
C1 = 3pF to 10pF, Variable
C2 = 132pF, Variable
COM
LCD
2002 Microchip Technology Inc.
DS21458B-page 15
TC7126/A
FIGURE 8-4:
INTEGRATED CIRCUIT TEMPERATURE SENSOR
9V
2
Constant 5V
V+
V+
V
V
+
REF
51kΩ
51kΩ
6
5
3
TC7126A
V
OUT
50kΩ
50kΩ
R
4
R
5
R
R
-
2
REF
8
2
3
–
ADJ
NC
1
1/2
LM358
V
V
+
-
REF02
IN
TEMP
+
4
Temperature
Dependent Output
IN
V
=
OUT
1.86V @
+25°C
COMMON
V-
1
GND
4
FIGURE 8-5:
TEMPERATURE SENSOR
FIGURE 8-6:
POSITIVE TEMPERATURE
COEFFICIENT RESISTOR
TEMPERATURE SENSOR
+
9V
9V
+
160kΩ
300kΩ
300kΩ
V+
V-
5.6kΩ
160kΩ
V
V
-
IN
V+
V-
R
20kΩ
V
IN
-
1
1N4148
R
50kΩ
1N4148
Sensor
1
+
IN
TC7126A
TC7126A
V
V
V
+
IN
R
2
V
V
+
REF
0.7%/°C
R
2
R
3
50kΩ
+
-
REF
REF
PTC
20kΩ
-
REF
COMMON
COMMON
DS21458B-page 16
2002 Microchip Technology Inc.
TC7126/A
9.0
9.1
PACKAGING INFORMATION
Package Marking Information
Package marking data not available at this time.
9.2
Taping Form
Component Taping Orientation for 44-Pin PLCC Devices
User Direction of Feed
PIN 1
W
P
Standard Reel Component Orientation
for TR Suffix Device
Carrier Tape, Number of Components Per Reel and Reel Size
Package
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
44-Pin PLCC
32 mm
24 mm
500
13 in
Note: Drawing does not represent total number of pins.
Component Taping Orientation for 44-Pin PQFP Devices
User Direction of Feed
PIN 1
W
P
Standard Reel Component Orientation
for TR Suffix Device
Carrier Tape, Number of Components Per Reel and Reel Size
Package
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
44-Pin PQFP
24 mm
16 mm
500
13 in
Note: Drawing does not represent total number of pins.
2002 Microchip Technology Inc.
DS21458B-page 17
TC7126/A
9.3
Package Dimensions
40-Pin PDIP (Wide)
PIN 1
.555 (14.10)
.530 (13.46)
2.065 (52.45)
2.027 (51.49)
.610 (15.49)
.590 (14.99)
.200 (5.08)
.140 (3.56)
.040 (1.02)
.020 (0.51)
.015 (0.38)
.008 (0.20)
.150 (3.81)
.115 (2.92)
3° MIN.
.700 (17.78)
.610 (15.50)
.110 (2.79)
.090 (2.29)
.070 (1.78)
.045 (1.14)
.022 (0.56)
.015 (0.38)
Dimensions: inches (mm)
44-Pin PLCC
PIN 1
.021 (0.53)
.013 (0.33)
.050 (1.27) TYP.
.695 (17.65)
.685 (17.40)
.630 (16.00)
.591 (15.00)
.656 (16.66)
.650 (16.51)
.032 (0.81)
.026 (0.66)
.020 (0.51) MIN.
.656 (16.66)
.650 (16.51)
.120 (3.05)
.090 (2.29)
.695 (17.65)
.685 (17.40)
.180 (4.57)
.165 (4.19)
Dimensions: inches (mm)
DS21458B-page 18
2002 Microchip Technology Inc.
TC7126/A
9.3
Package Dimensions (Continued)
44-Pin PQFP
7° MAX.
.009 (0.23)
.005 (0.13)
PIN 1
.041 (1.03)
.026 (0.65)
.018 (0.45)
.012 (0.30)
.398 (10.10)
.390 (9.90)
.557 (14.15)
.537 (13.65)
.031 (0.80) TYP.
.010 (0.25) TYP.
.398 (10.10)
.390 (9.90)
.083 (2.10)
.075 (1.90)
.557 (14.15)
.537 (13.65)
.096 (2.45) MAX.
Dimensions: inches (mm)
2002 Microchip Technology Inc.
DS21458B-page 19
TC7126/A
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
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 Device Selection Table)
SALES AND SUPPORT
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recom-
mended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1. Your local Microchip sales office
2. The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
3. The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
New Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
DS21458B-page 20
2002 Microchip Technology Inc.
TC7126/A
Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
No representation or warranty is given and no liability is
assumed by Microchip Technology Incorporated with respect
to the accuracy or use of such information, or infringement of
patents or other intellectual property rights arising from such
use or otherwise. Use of Microchip’s products as critical com-
ponents in life support systems is not authorized except with
express written approval by Microchip. No licenses are con-
veyed, implicitly or otherwise, under any intellectual property
rights.
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© 2002, Microchip Technology Incorporated, Printed in the
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2002 Microchip Technology Inc.
DS21458B-page 21
WORLDWIDE SALES AND SERVICE
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Singapore, 188980
Tel: 65-6334-8870 Fax: 65-6334-8850
Taiwan
Microchip Technology Taiwan
11F-3, No. 207
Tung Hua North Road
Taipei, 105, Taiwan
Tel: 886-2-2717-7175 Fax: 886-2-2545-0139
EUROPE
Denmark
Microchip Technology Nordic ApS
Regus Business Centre
Lautrup hoj 1-3
Ballerup DK-2750 Denmark
Tel: 45 4420 9895 Fax: 45 4420 9910
Kokomo
France
2767 S. Albright Road
Kokomo, Indiana 46902
Tel: 765-864-8360 Fax: 765-864-8387
Los Angeles
Microchip Technology SARL
Parc d’Activite du Moulin de Massy
43 Rue du Saule Trapu
Batiment A - ler Etage
91300 Massy, France
Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79
Germany
Microchip Technology GmbH
Gustav-Heinemann Ring 125
D-81739 Munich, Germany
Tel: 49-89-627-144 0 Fax: 49-89-627-144-44
18201 Von Karman, Suite 1090
Irvine, CA 92612
Tel: 949-263-1888 Fax: 949-263-1338
New York
150 Motor Parkway, Suite 202
Hauppauge, NY 11788
Tel: 631-273-5305 Fax: 631-273-5335
San Jose
Microchip Technology Inc.
2107 North First Street, Suite 590
San Jose, CA 95131
Tel: 408-436-7950 Fax: 408-436-7955
Toronto
Hong Kong
Italy
Microchip Technology Hongkong Ltd.
Unit 901-6, Tower 2, Metroplaza
223 Hing Fong Road
Kwai Fong, N.T., Hong Kong
Tel: 852-2401-1200 Fax: 852-2401-3431
Microchip Technology SRL
Centro Direzionale Colleoni
Palazzo Taurus 1 V. Le Colleoni 1
20041 Agrate Brianza
Milan, Italy
6285 Northam Drive, Suite 108
Mississauga, Ontario L4V 1X5, Canada
Tel: 905-673-0699 Fax: 905-673-6509
India
Tel: 39-039-65791-1 Fax: 39-039-6899883
United Kingdom
Arizona Microchip Technology Ltd.
505 Eskdale Road
Winnersh Triangle
Wokingham
Berkshire, England RG41 5TU
Tel: 44 118 921 5869 Fax: 44-118 921-5820
Microchip Technology Inc.
India Liaison Office
Divyasree Chambers
1 Floor, Wing A (A3/A4)
No. 11, O’Shaugnessey Road
Bangalore, 560 025, India
Tel: 91-80-2290061 Fax: 91-80-2290062
03/01/02
DS21458B-page 22
2002 Microchip Technology Inc.
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