MICROCHIP TC7136CLW

TC7136/TC7136A
Low Power 3-1/2 Digit Analog-to-Digital Converter
Features
General Description
• Fast Over Range Recovery, Ensured First Reading
Accuracy
• Low Temperature Drift Internal Reference
- TC7136: 70ppm/°C (Typ.)
- TC7136A: 35ppm/°C (Typ.)
• 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.)
The TC7136 and TC7136A are low power, 3-1/2 digit
with liquid crystal display (LCD) drivers and analog-todigital converters. These devices incorporate an "integrator output zero" phase, which enables over range
recovery. The performance of existing TC7126,
TC7126A and ICL7126 based systems may be
upgraded with minor changes to external, passive
components.
Applications
The TC7136 and TC7136A limit linearity error to less
than 1 count on 200mV or 2V full scale ranges. The 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 currents and a 1012Ω input impedance. The
differential reference input allows ratiometric measurements for ohms or bridge transducer measurements.
The 15µVP-P noise performance ensures a "rock solid"
reading. The auto-zero cycle enables a zero display
readout for a 0V input.
• Thermometry
• Bridge Readouts: Strain Gauges, Load Cells,
Null Detectors
• Digital Meters: Voltage/Current/Ohms/Power, pH
• Digital Scales, Process Monitors
• Portable Instrumentation
Device Selection Table
Part Number
Package
Temperature
Range
0°C to +70°C
TC7136 CPI
40-Pin PDIP
TC7136 CKW
44-Pin PQFP
0°C to +70°C
TC7136 CLW
44-Pin PLCC
0°C to +70°C
TC7136A CPI
40-Pin PDIP
0°C to +70°C
TC7136A CKW
44-Pin PQFP
0°C to +70°C
TC7136A CLW
44-Pin PLCC
0°C to +70°C
 2002 Microchip Technology Inc.
The TC7136A has an improved internal zener reference voltage circuit which maintains the analog common temperature drift to 35ppm/°C (typical) and
75ppm/°C (maximum). This represents an improvement of two to four times over similar 3-1/2 digit converters. The costly, space consuming external
reference source may be removed.
DS21461B-page 1
TC7136/TC7136A
Package Type
OSC3
TEST
REF HI
REF HI
REF LO
CREF+
CREF-
ANALOG
COMMON
IN HI
IN LO
AZ
BUFF
INT
V-
3
OSC2
D1
4
OSC1
C1
5
V+
B1
6
44-Pin PQFP
NC
A1
44-Pin PLCC
2
1
44
43
42
41
40
44 43
42
41 40 39
38
37
36
35
34
F1
7
39 REF LO
NC 1
33 NC
G1
8
38 CREF+
NC 2
32 G2
E1
9
37 CREF-
TEST 3
31 C3
ANALOG
36
COMMON
OSC3 4
30 A3
D2 10
TC7136CLW
TC7136ACLW
C2 11
35 IN HI
NC 5
29 G3
TC7136CKW
TC7136ACKW
28 BP
34 NC
OSC2 6
B2 13
33 IN LO
OSC1 7
27 POL
A2 14
32 AZ
V+
26 AB4
31 BUFF
D1 9
25 E3
E2 16
30 INT
C1 10
24 F3
D3 17
29 V-
B1 11
23 B3
25
26
27
28
12 13
14
15 16
17
18
19
AB4
POL
NC
BP
G3
A3
C3
G2
A1
G1
E1
C2
B2
A2
1's
10's
V+
1
2
C1
3
OSC1
1
OSC2
OSC2
2
38 OSC3
OSC3
3
38 C1
4
37 B1
Reverse Pin
Configuration
40 V+
39 D1
B1
4
37 TEST
A1
5
36 VREF+
VREF+
5
36 A1
F1
6
35 VREF-
VREF-
6
35
G1
7
34 CREF+
CREF+
7
E1
8
33 CREF-
CREF-
8
D2
9
TC7136CPL
TC7136ACPL
ANALOG 9
COMMON
VIN+ 10
34 G1
TC7136RCPL
TC7136ARCPL
33 E1
C2 10
B2 11
30 VIN-
VIN- 11
30 B2
12
29 CAZ
CAZ
12
29 A2
VBUFF
13
28
VINT
A2
28 VBUFF
32 D2
31 C2
14
27 E2
26 V-
V-
15
26 D3
B3
16
25 G2
G2
16
25 B3
F3 17
24 C3
C3
17
24
E3
18
23 A3
A3
18
23 E3
AB4
19
22 G3
POL 20
(MINUS SIGN)
27 VINT
100's
100's
G3 19
21 BP
(Backplane)
BP 20
(Backplane)
10's
F2
D3 15
14
1's
F1
32 ANALOG
COMMON
31 VIN+
E2
1000's
40 OSC1
39
TEST
F2 13
100's
Normal Pin
Configuration
21 22
40-Pin PDIP
40-Pin PDIP
D1
20
D3
24
E2
23
D2
21 22
F1
20
F3
18 19
E3
8
B3
F2 15
F2
NC 12
F3
22 AB4
100's
1000's
21 POL
(Minus Sign)
NC = No Internal Connection
DS21461B-page 2
 2002 Microchip Technology Inc.
TC7136/TC7136A
Typical Application
0.1µF
1MΩ
+
Analog
Input
–
33
34
CREF+
31
9-19 Segment
22-25 Drive
VIN+
0.01µF
30 V IN
LCD
CREF-
TC7136
TC7136A POL 20
BP
32 ANALOG
COMMON
V+
28
180kΩ
0.15µF
0.47
µF
29
21
Minus Sign
Backplane
1
VBUFF
240kΩ
+
9V
VREF+
36
10kΩ
CAZ
VREFV-
27 V
INT
OSC2
OSC3 OSC1
39
38 COSC 40
ROSC 50pF
35
26
1 Conversion/Sec
To Analog Common (Pin 32)
560kΩ
 2002 Microchip Technology Inc.
DS21461B-page 3
DS21461B-page 4
VIN-
ANALOG
COMMON
VIN+
32
31
INT
INT
10
µA
CREF+
34
DE (–)
DE
(+)
–
+
+
–
ZI
V+ – 2.8V
33
CREF- VBUFF
26
V-
ZI &
AZ
35
VREF-
AZ & DE (±)
DE (+)
DE
(–)
ZI & AZ
36
VREF+
CREF
1
LOW
TEMPCO
VREF
V
RINT
28
TC7136/A
VINT
CINT
ROSC
39
OSC2
Clock
–
+
27
Comparator
40
OSC1
AZ
+
–
Integrator
29
CAZ
V+
COSC
÷4
LCD
Hundreds
7-Segment
Decode
VTH = 1V
Control Logic
Tens
Data Latch
7-Segment
Decode
LCD Segment Drivers
Internal Digital Ground
FOSC
To Switch
38
OSC3
To Digital
Section
Thousands
Segment
Output
Internal Digital Ground
2mA
0.5mA
Typical Segment Input
Units
7-Segment
Decode
BP
500Ω
6.2V
÷ 200
21
26
37
1
V-
TEST
V+
TC7136/TC7136A
Functional Block Diagram
 2002 Microchip Technology Inc.
TC7136/TC7136A
1.0
ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings*
Supply Voltage (V+ to V-)....................................... 15V
Analog Input Voltage (Either Input) (Note 1)... V+ to VReference Input Voltage (Either Input)............ V+ to VClock Input .................................................TEST to V+
Package Power Dissipation (TA ≤ 70°C) (Note 2):
Plastic DIP ................................................... 1.23W
Plastic Quad Flat Package .......................... 1.00W
PLCC ........................................................... 1.23W
Operating Temperature Range:
C Devices.......................................... 0°C to +70°C
I 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.
TC7136 AND TC7136A ELECTRICAL SPECIFICATIONS
Electrical Characteristics: VS = 9V, fCLK = 16kHz, and TA = +25°C, unless otherwise noted.
Symbol
Parameter
Min
Typ
Max
-000.0
±000.0
+000.0
Unit
Test Conditions
Input
Zero Input Reading
Zero Reading Drift
Ratiometric Reading
—
0.2
1
999
999/1000
1000
Digital VIN = 0V, Full Scale = 200mV
Reading
µV/°C
VIN = 0V, 0°C ≤ TA ≤ +70°C
Digital VIN = VREF, VREF = 100mV
Reading
NL
Non-Linearity Error
—
1
±0.2
Count
ER
Rollover Error
-1
-1
±0.2
1 Count
eN
Noise
—
15
—
µVP-P
IL
Input Leakage Current
—
1
10
pA
CMRR
Common Mode Rejection Ratio
—
50
—
µV/V
TCSF
Scale Factor Temperature
Coefficient
—
1
5
ppm/°C
Full Scale = 20mV or 2V Max.
Deviation from best 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
Note 1:
2:
3:
4:
Input voltages may exceed supply voltages when input current is limited to 100µA.
Dissipation rating assumes device is mounted with all leads soldered to PC board.
Refer to "Differential Input" discussion.
Backplane drive is in phase with segment drive for "OFF" segment and 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: A 48kHz oscillator increases current by 20µA (typical). Common current not included.
 2002 Microchip Technology Inc.
DS21461B-page 5
TC7136/TC7136A
TC7136 AND TC7136A ELECTRICAL SPECIFICATIONS (CONTINUED)
Electrical Characteristics: VS = 9V, fCLK = 16kHz, and TA = +25°C, unless otherwise noted.
Symbol
Parameter
Min
Typ
Max
Unit
Test Conditions
Analog Common
VCTC
Analog Common Temperature
Coefficient
TC7136A
—
35
75
ppm/°C
0°C ≤ TA ≤ +70°C
TC7136
—
70
150
ppm/°C
"C" Commercial Temp. Range Devices
TC7136A
—
35
100
ppm/°C
-25°C ≤ TA ≤ +85°C
TC7136
—
70
150
ppm/°C
"I" Industrial Temp. Range Devices
2.7
3.05
3.35
V
250kΩ Between Common and V+
Analog Common Voltage
VC
250kΩ between Common and V+
LCD Drive
VSD
LCD Segment Drive Voltage
4
5
6
VP-P
V+ to V- = 9V
VBD
LCD Backplane Drive Voltage
4
5
6
VP-P
V+ to V- = 9V
—
70
100
µA
Power Supply
Power Supply Current
IS
VIN = 0V, V+ to V- = 9V (Note 6)
Note 1:
2:
3:
4:
Input voltages may exceed supply voltages when input current is limited to 100µA.
Dissipation rating assumes device is mounted with all leads soldered to PC board.
Refer to "Differential Input" discussion.
Backplane drive is in phase with segment drive for "OFF" segment and 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: A 48kHz oscillator increases current by 20µA (typical). Common current not included.
DS21461B-page 6
 2002 Microchip Technology Inc.
TC7136/TC7136A
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
PIN DESCRIPTION
Pin Number
(40-Pin PDIP)
Normal
(Reverse)
Symbol
1
(40)
V+
Positive supply voltage.
2
(39)
D1
Activates the D section of the units display.
3
(38)
C1
Activates the C section of the units display.
4
(37)
B1
Activates the B section of the units display.
5
(36)
A1
Activates the A section of the units display.
6
(35)
F1
Activates the F section of the units display.
7
(34)
G1
Activates the G section of the units display.
8
(33)
E1
Activates the E section of the units display.
9
(32)
D2
Activates the D section of the tens display.
10
(31)
C2
Activates the C section of the tens display.
11
(30)
B2
Activates the B section of the tens display.
12
(29)
A2
Activates the A section of the tens display.
13
(28)
F2
Activates the F section of the tens display.
14
(27)
E2
Activates the E section of the tens display.
15
(26)
D3
Activates the D section of the hundreds display.
16
(25)
B3
Activates the B section of the hundreds display.
17
(24)
F3
Activates the F section of the hundreds display.
18
(23)
E3
Activates the E section of the hundreds display.
19
(22)
AB4
20
(21)
POL
21
(20)
BP
Backplane drive output.
22
(19)
G3
Activates the G section of the hundreds display.
23
(18)
A3
Activates the A section of the hundreds display.
24
(17)
C3
Activates the C section of the hundreds display.
25
(16)
G2
Activates the G section of the tens display.
26
(15)
V-
27
(14)
VINT
28
(13)
VBUFF
Integration resistor connection. Use a 180kΩ for a 20mV full scale range and a
1.8MΩ for 2V full scale range.
29
(12)
CAZ
The size of the auto-zero capacitor influences the system noise. Use a 0.47µF
capacitor for a 200mV full scale and a 0.1µF capacitor for a 2V full scale.
See Section 6.1, Auto-Zero Capacitor for more details.
Description
Activates both halves of the 1 in the thousands display.
Activates the negative polarity display.
Negative power supply voltage.
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.
30
(11)
VIN -
The low input signal is connected to this pin.
31
(10)
VIN +
The high input signal is connected to this pin.
32
(9)
ANALOG
COMMON
33
(8)
CREF-
 2002 Microchip Technology Inc.
This pin is primarily used to set the Analog Common mode voltage for battery
operation, or in systems where the input signal is referenced to the power supply.
See Section 7.3, Analog Common for more details. It also acts as a reference
voltage source.
See Pin 34.
DS21461B-page 7
TC7136/TC7136A
TABLE 2-1:
PIN DESCRIPTION (CONTINUED)
Pin Number
(40-Pin PDIP)
Normal
(Reverse)
Symbol
34
(7)
CREF+
Description
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, which will hold the rollover error to
0.5 count.
(6)
VREF-
See Pin 36.
(5)
VREF+
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.
36
(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.
37
(3)
OSC3
See Pin 40.
38
(2)
OSC2
See Pin 40.
39
(1)
OSC1
Pins 40, 39 and 38 make up the oscillator section. For a 48kHz clock
(3 readings 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.
35
DS21461B-page 8
 2002 Microchip Technology Inc.
TC7136/TC7136A
3.0
DETAILED DESCRIPTION
FIGURE 3-1:
BASIC DUAL SLOPE
CONVERTER
(All Pin Designations Refer to 40-Pin PDIP.)
CINT
3.1
Dual Slope Conversion Principles
The TC7136/A is a dual slope, integrating analog-todigital converter. An understanding of the dual slope
conversion technique will aid in following detailed
TC7136/A operational theory.
Analog Input
Signal
Clock
Control
Logic
Polarity Control
Counter
Integrator
Output
Display
VIN ≈ VREF
VIN ≈ 1/2 VREF
Fixed
Signal
Integrate
Time
Variable
Reference
Integrate
Time
FIGURE 3-2:
EQUATION 3-1:
NORMAL MODE
REJECTION OF DUAL
SLOPE CONVERTER
30
1
--------V IN ( t ) dt
RC ∫0
V R t RI
= -----------RC
Where:
VR = Reference voltage
tSI = Signal integration time (fixed)
tRI = Reference voltage integration time
(variable)
Normal Mode Rejection (dB)
t SI
20
10
t = Measured Period
For a constant VIN:
0
EQUATION 3-2:
V
Phase
Control
REF
Voltage
In a simple dual slope converter, a complete conversion requires the integrator output to "ramp up" and
"ramp down."
A simple mathematical equation relates the input
signal, reference voltage, and integration time:
+
Switch
Driver
Input signal integration
Reference voltage integration (de-integration)
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).
Comparator
–
+
The conventional dual slope converter measurement
cycle has two distinct phases (see Figure 3-1).
1.
2.
Integrator
–
0.1/t
IN
=
t RI
V -------Rt
SI
 2002 Microchip Technology Inc.
1/t
Input Frequency
10/t
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 integrated 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
frequency 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.
DS21461B-page 9
TC7136/TC7136A
4.0
ANALOG SECTION
In addition to the basic integrate and de-integrate dual
slope cycles discussed above, the TC7136 and
TC7136A designs incorporate an "integrator output
zero cycle" and an "auto-zero cycle." These additional
cycles ensure the integrator starts at 0V (even after a
severe over range conversion) and that all offset voltage errors (buffer amplifier, integrator and comparator)
are removed from the conversion. A true digital zero
reading is assured without any external adjustments.
The differential input voltage must be within the device
Common mode range when the converter and measured system share the same power supply common
(ground). If the converter and measured system do not
share the same power supply common, VIN- should be
tied to analog common.
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.
A complete conversion consists of four distinct phases:
1.
2.
3.
4.
4.1
Integrator output zero phase
Auto-zero phase
Signal integrate phase
Reference de-integrate phase
Integrator Output Zero Phase
This phase ensures the integrator output is at 0V
before the system zero phase is entered. This ensures
that true system offset voltages will be compensated
for, even after an over range conversion. The count for
this phase is a function of the number of counts
required by the de-integrate phase. The count lasts
from 11 to 140 counts for non over range conversions
and from 31 to 640 counts for over range conversions.
4.2
Auto-Zero Phase
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 comparator offset voltage error compensation. The voltage
level established on CAZ compensates for device offset
voltages. The auto-zero phase residual is typically
10µV to 15µV.
4.4
Reference Integrate Phase
The third phase is reference integrate or de-integrate.
VIN- is internally connected to analog common and
VIN+ 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
internal clock periods. The digital reading displayed is:
EQUATION 4-2:
V
IN
1000 = ---------------V REF
FIGURE 4-1:
INT
1000
1-2000
DENT
11-140
ZI
AZ
910-2900
The auto-zero duration is from 910 to 2900 counts for
non over range conversions and from 300 to 910
counts for over range conversions.
4.3
Signal Integration Phase
The auto-zero loop is entered and the internal differential inputs connect to VIN+ and VIN-. The differential
input signal is integrated for a fixed time period. The
TC7136/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:
4000
FIGURE 4-2:
INT
DEINT
CONVERSION TIMING
DURING OVER RANGE
OPERATION
1000
2001-2090
31-640
EQUATION 4-1:
tSI =
CONVERSION TIMING
DURING NORMAL
OPERATION
4
x 1000
FOSC
ZI
AZ
300-910
4000
Where FOSC = external clock frequency.
DS21461B-page 10
 2002 Microchip Technology Inc.
TC7136/TC7136A
5.0
DIGITAL SECTION
Each phase of the measurement cycle has the
following length:
The TC7136/A contains all the segment drivers necessary to directly drive a 3-1/2 digit LCD. An LCD backplane driver is included. The backplane frequency is
the external clock frequency divided by 800. For three
conversions 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, or visible. This AC drive
configuration results in negligible DC voltage across
each LCD segment, ensuring long LCD life. The polarity segment driver is ON for negative analog inputs. If
VIN+ and VIN- are reversed, this indicator would
reverse.
On the TC7136/A, when the TEST pin is pulled to V+,
all segments are turned ON. The display reads -1888.
During this mode, the 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.
1.
Auto-zero phase: 3000 to 2900 counts
(1200 to 11,600 clock pulses)
Signal integrate: 1000 counts
(4000 clock pulses)
2.
This time period is fixed. The integration period is:
EQUATION 5-1:
Where:
1 
 FOSC 
tSI = 4000 
FOSC is the externally set clock frequency.
3.
4.
The TC7136 is a drop-in replacement for the TC7126
and ICL7126. The TC7136A offers a greatly improved
internal reference temperature coefficient. Minor component value changes are required to upgrade existing
designs and improve the noise performance.
6.0
COMPONENT VALUE
SELECTION
6.1
Auto-Zero Capacitor (CAZ)
The display font and segment drive assignment are
shown in Figure 5-1.
FIGURE 5-1:
DISPLAY FONT AND
SEGMENT ASSIGNMENT
Display Font
1000's
5.1
100's
10's
1's
System Timing
The oscillator frequency is divided by 4 prior to clocking
the internal decade counters. The four-phase measurement cycle takes a total of 4000 counts, or 16,000
clock pulses. The 4000 count cycle is independent of
input signal magnitude.
Reference integrate: 0 to 2000 counts
Zero integrator: 11 to 640 counts
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 0.1µF
capacitor is adequate for 2V full scale applications. A
Mylar type dielectric capacitor is adequate.
6.2
Reference Voltage Capacitor
(CREF)
The reference voltage, used to ramp the integrator output voltage back to zero during the reference integrate
phase, is stored on CREF. A 0.1µF capacitor is acceptable when VREF- is tied to analog common. If a large
Common mode voltage exists (VREF- ≠ analog common) 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.
6.3
Integrating Capacitor (CINT)
CINT should be selected to maximize integrator output
voltage swing without causing output saturation. Analog common will normally supply the differential voltage
reference in 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
one 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.
 2002 Microchip Technology Inc.
DS21461B-page 11
TC7136/TC7136A
An exact expression for CINT is:
6.5
EQUATION 6-1:
C OSC should be 50pF. R OSC is selected from the
equation:
1 
 FOSC  
(4000) 
CINT =
VFS
RINT


Oscillator Components
EQUATION 6-2:
VINT
FOSC =
Where:
FOSC = Clock frequency at Pin 38
VFS
Note that FOSC is ÷ 4 to generate the TC7136A's internal clock. The backplane drive signal is derived by
dividing FOSC by 800.
= Full scale input voltage
RINT = Integrating resistor
VINT = Desired full scale integrator output swing
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 current is 6µA. The integrator and buffer can supply 1µA
drive currents with negligible linearity errors. RINT is
chosen 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, R INT is 180kΩ. A
2V full scale requires 1.8MΩ (see Table 6-1).
TABLE 6-1:
Component
Value
CAZ
Nominal Full Scale Voltage
200mV
2V
0.47µF
0.1µF
180kΩ
1.8MΩ
CINT
0.047µF
0.047µF
FOSC = 48kHz (3 reading per sec).
ROSC = 180kΩ, COSC = 50pF.
DS21461B-page 12
To achieve maximum rejection of 60Hz noise pickup,
the signal integrate period should be a multiple of
60Hz. Oscillator frequencies of 240kHz, 120kHz,
80kHz, 60kHz, 40kHz, etc. should be selected. For
50Hz rejection, oscillator frequencies of 200kHz,
100kHz, 66-2/3kHz, 50kHz, 40kHz, etc. would be suitable. Note that 40kHz (2.5 readings per second) will
reject both 50Hz and 60Hz.
6.6
Reference Voltage Selection
A full scale reading (2000 counts) requires the input
signal be twice the reference voltage.
Required Full Scale Voltage*
VREF
200mV
100mV
2V
1V
Note:
RINT
Note:
0.45
RC
*VREF = 2VREF.
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 pressure transducer output for 2000 lb/in2 is 400mV. Rather
than dividing the input voltage by two, the reference
voltage should be set to 200mV. This permits the transducer input to be used directly. The differential reference can also be used when a digital zero reading is
required, when VIN is not equal to zero. This is common
in temperature measuring instrumentation. A compensating offset voltage can be applied between analog
common and VIN-. The transducer output is connected
between VIN+ and analog common.
 2002 Microchip Technology Inc.
TC7136/TC7136A
7.0
DEVICE PIN FUNCTIONAL
DESCRIPTION
7.1
Differential Signal Inputs
VIN+ (Pin 31), VIN- (Pin 30)
The TC7136/A is designed with true differential inputs
and accepts input signals within the input stage Common mode voltage range (VCM). The typical range is
FIGURE 7-1:
V+ – 1V to V- + 1V. Common mode voltages are
removed from the system when the TC7136A operates
from a battery or floating power source (isolated from
measured system), Common mode voltage removed
in battery operation with VIN = analog common and VINis connected to analog common (VCOM) (see
Figure 7-1).
COMMON MODE VOLTAGE REMOVED IN BATTERY OPERATION WITH
VIN = ANALOG COMMON
Segment
Drive
Measured
System
VBUF
V+
V+
V-
VGND
CAZ
VINT
POL BP
OSC1
TC7136
TC7136A
OSC3
LCD
OSC2
V-
ANALOG
COMMON VREF- VREF+ V+
V+ V-
GND
Power
Source
+
9V
In systems where Common mode voltages exist, the
86dB Common mode rejection ratio minimizes error.
Common mode voltages do, however, affect the integrator output level. A worst case condition exists if a
large positive VCM exists in conjunction with a full scale
negative differential signal. The negative signal drives
the integrator output positive along with VCM (see
Figure 7-2.) For such applications, the integrator output swing can be reduced below the recommended 2V
full scale swing. The integrator output will swing within
0.3V of V+ or V- without increased linearity error.
FIGURE 7-2:
COMMON MODE
VOLTAGE REDUCES
AVAILABLE INTEGRATOR
SWING (VCOM ≠ VIN)
CI
Input Buffer
+
+
RI
–
VIN
–
VI
+
Integrator
–
VCM
tI
VCM = VIN
VI =
CI
Where:
4000
tI = Integration time =
FOSC
CI = Integration capacitor
[
[
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, CREF should be large compared to stray node capacitance. The TC7136/A offers
a significantly improved analog common temperature
coefficient. This potential provides a very stable voltage, suitable for use as a voltage reference. The
temperature coefficient of analog common is typically
35ppm/°C.
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 internally to an N-channel FET, capable of sinking 100µA.
This FET will hold the common line at 3V below V+ if an
external load attempts to pull the common line toward
V+. Analog common source current is limited to 1µA.
Analog common is, therefore, easily pulled to a more
negative voltage (i.e., below V+ – 3V).
RI = Integration resistor
 2002 Microchip Technology Inc.
DS21461B-page 13
TC7136/TC7136A
The analog common pin serves to set the analog section reference, or common point. The TC7136A is specifically designed to operate from a battery, or in any
measurement system where input signals are not referenced (float), with respect to the TC7136A 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.
With
sufficiently
high
total
supply
voltage
(V+ – V- > 7V), analog common is a very stable potential with excellent temperature stability (typically
35ppm/°C for TC7136A. This potential can be used to
generate the TC7136A's reference voltage. An external
voltage reference will be unnecessary in most cases,
because of the 35ppm/°C temperature coefficient. See
Section 7.5, TC7136A Internal Voltage Reference
discussion.
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 internally generated negative logic supply through a 500Ω
resistor. The TEST pin load should not be more than
1mA. See Section 8.0, Typical Applications for additional information on using TEST as a negative digital
logic supply.
FIGURE 7-3:
ANALOG COMMON
TEMPERATURE
COEFFICIENT
200
180
Analog Common Temperature
Coefficient (ppm/°C)
The TC7136/A connects the internal VIN+ and VINinputs to analog common during the auto-zero phase.
During the reference integrate phase, VIN- is connected
to analog common. If VIN- is not externally connected to
analog common, a Common mode voltage exists, but
is rejected by the converter's 86dB Common mode
rejection ratio. In battery operation, analog common
and VIN- are usually connected, removing Common
mode voltage concerns. In systems where VIN- is connected to the power supply ground or to a given
voltage, analog common should be connected to VIN-.
160
Maximum
No Maximum
Specified
140
Typical
120
100
Maximum
80
Typical
60
Typical
40
20
TC7136A
TC7136
ICL7136
0
FIGURE 7-4:
TC7136A INTERNAL
VOLTAGE REFERENCE
CONNECTION
9V
26
V-
+
1
V+
240kΩ
TC7136
TC7136A
VREF+
36
10kΩ
VREF
VREF- 35
ANALOG 32
COMMON
Set VREF = 1/2 VREF
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.
7.5
TC7136A Internal Voltage
Reference
The TC7136 analog common voltage temperature stability has been significantly improved (Figure 7-3). The
"A" version of the industry standard TC7136 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; however,
noise performance will be improved by increasing CAZ
(see Section 6.1, Auto-Zero Capacitor). Figure 7-4
shows analog common supplying the necessary
voltage reference for the TC7136/A.
DS21461B-page 14
 2002 Microchip Technology Inc.
TC7136/TC7136A
8.0
TYPICAL APPLICATIONS
8.1
Liquid Crystal Display Sources
Several manufacturers supply standard LCDs to interface with the TC7136A 3-1/2 digit analog-to-digital
converter.
Representative
Part Numbers*
Manufac.
Address/Phone
Crystaloid
Electronics
5282 Hudson Dr.
Hudson, OH 44236
216-655-2429
C5335, H5535,
T5135, SX440
AND
720 Palomar Ave.
Sunnyvale, CA 94086
408-523-8200
FE 0201, 0501
FE 0203, 0701
FE 2201
VGI, Inc.
1800 Vernon St. Ste.2,
Roseville,
CA 95678
916-783-7878
I1048, I1126
Hamlin, Inc.
612 E. Lake St.
Lake Mills,
WI 53551
414-648-236100
3902, 3933, 3903
Note:
8.2
Contact LCD manufacturer for full product listing/
specifications.
EQUATION 8-1:
Displayed(Reading) =
Ratiometric Resistance
Measurements
The TC7136A'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.
 2002 Microchip Technology Inc.
RUNKNOWN
x 1000
RSTANDARD
The display will over range for:
RUNKNOWN ≥ 2 x R STANDARD
FIGURE 8-1:
DECIMAL POINT AND
ANNUNCIATOR DRIVES
Simple Inverter for Fixed Decimal Point
or Display Annunciator
V+
V+
TC7136
TC7136A
BP
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 1mA should be supplied by the TEST
pin; its potential is approximately 5V below V+.
8.3
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 reference input. If the unknown equals the standard, the display will read 1000. The displayed reading
can be determined from the following expression:
TEST
4049
To LCD
Decimal Point
21
GND
37
To LCD Backplane
Multiple Decimal Point or
Annunciator Driver
V+
V+
BP
TC7136
TC7136A
TEST
To LCD
Decimal Point
Decimal
Point
Select
4030
GND
DS21461B-page 15
TC7136/TC7136A
FIGURE 8-2:
LOW PARTS COUNT
RATIOMETRIC
RESISTANCE
MEASUREMENT
FIGURE 8-4:
+
VREF+ V+
5.6kΩ
V+
1N4148 R1
20kΩ
LCD
VIN+
TC7136
TC7136A
RUNKNOWN
0.7%/°C
PTC
VIN-
+
R2
50kΩ
R1
50kΩ
R3
R2
20kΩ
TC7136
TC7136A
VREF+
COMMON
9V
300kΩ
V+
VIN-
1N4148
Sensor
VIN-
VREF-
TEMPERATURE SENSOR
300kΩ
V-
VIN+
ANALOG
COMMON
FIGURE 8-3:
9V
160kΩ
VREF-
RSTANDARD
160kΩ
POSITIVE TEMPERATURE
COEFFICIENT RESISTOR
TEMPERATURE SENSOR
V-
VIN+
TC7136
TC7136A
VREF+
VREFCOMMON
DS21461B-page 16
 2002 Microchip Technology Inc.
TC7136/TC7136A
9.0
PACKAGING INFORMATION
9.1
Package Marking Information
Package marking data not available at this time.
9.2
Taping Form
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
44-Pin PQFP
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
24 mm
16 mm
500
13 in
Note: Drawing does not represent total number of pins.
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
44-Pin PLCC
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
32 mm
24 mm
500
13 in
Note: Drawing does not represent total number of pins.
 2002 Microchip Technology Inc.
DS21461B-page 17
TC7136/TC7136A
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)
.150 (3.81)
.115 (2.92)
.110 (2.79)
.090 (2.29)
.070 (1.78)
.045 (1.14)
.015 (0.38)
.008 (0.20)
3° MIN.
.700 (17.78)
.610 (15.50)
.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)
DS21461B-page 18
 2002 Microchip Technology Inc.
TC7136/TC7136A
9.3
Package Dimensions (Continued)
44-Pin PQFP
7° MAX.
.009 (0.23)
.005 (0.13)
PIN 1
.018 (0.45)
.012 (0.30)
.041 (1.03)
.026 (0.65)
.398 (10.10)
.390 (9.90)
.557 (14.15)
.537 (13.65)
.031 (0.80) TYP.
.398 (10.10)
.390 (9.90)
.557 (14.15)
.537 (13.65)
.010 (0.25) TYP.
.083 (2.10)
.075 (1.90)
.096 (2.45) MAX.
Dimensions: inches (mm)
 2002 Microchip Technology Inc.
DS21461B-page 19
TC7136/TC7136A
SALES AND SUPPORT
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1.
2.
3.
Your local Microchip sales office
The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
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.
DS21461B-page 20
 2002 Microchip Technology Inc.
TC7136/TC7136A
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 components in life support systems is not authorized except with
express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property
rights.
Trademarks
The Microchip name and logo, the Microchip logo, FilterLab,
KEELOQ, microID, MPLAB, PIC, PICmicro, PICMASTER,
PICSTART, PRO MATE, SEEVAL and The Embedded Control
Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.
dsPIC, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB,
In-Circuit Serial Programming, ICSP, ICEPIC, microPort,
Migratable Memory, MPASM, MPLIB, MPLINK, MPSIM,
MXDEV, PICC, PICDEM, PICDEM.net, rfPIC, Select Mode
and Total Endurance are trademarks of Microchip Technology
Incorporated in the U.S.A.
Serialized Quick Turn Programming (SQTP) is a service mark
of Microchip Technology Incorporated in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2002, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received QS-9000 quality system
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The Company’s quality system processes and
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devices, Serial EEPROMs, microperipherals,
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systems is ISO 9001 certified.
 2002 Microchip Technology Inc.
DS21461B-page 21
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03/01/02
*DS21461B*
DS21461B-page 22
 2002 Microchip Technology Inc.