21461b.book

2002 Microchip Technology Inc.

DS21461B-page 1

TC7136/TC7136A

Features

· 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: 15

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

· Convenient 9V Battery Operation with Low Power

Dissipation: 500

W (Typ.)/900

W (Max.)

Applications

· 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

General Description

The TC7136 and TC7136A are low power, 3-1/2 digit
with liquid crystal display (LCD) drivers and analog-to-
digital converters. These devices incorporate an "inte-
grator output zero" phase, which enables over range
recovery.

The

performance

existing

TC7126,

TC7126A and ICL7126 based systems may be
upgraded with minor changes to external, passive
components.

The TC7136A has an improved internal zener refer-
ence voltage circuit which maintains the analog com-
mon temperature drift to 35ppm/°C (typical) and
75ppm/°C (maximum). This represents an improve-
ment of two to four times over similar 3-1/2 digit con-
verters.

The

costly,

space

consuming

external

reference source may be removed.

The TC7136 and TC7136A limit linearity error to less
than 1 count on 200mV or 2V full scale ranges. The roll-
over error (the difference in readings for equal magni-
tude, but opposite polarity input signals) is below ±1
count. High-impedance differential inputs offer 1pA
leakage currents and a 10

input impedance. The

differential reference input allows ratiometric measure-
ments for ohms or bridge transducer measurements.
The 15

P-P

noise performance ensures a "rock solid"

reading. The auto-zero cycle enables a zero display
readout for a 0V input.

Part Number

Package

Temperature

Range

TC7136 CPI

40-Pin PDIP

C to +70

TC7136 CKW

44-Pin PQFP

C to +70

TC7136 CLW

44-Pin PLCC

C to +70

TC7136A CPI

40-Pin PDIP

C to +70

TC7136A CKW

44-Pin PQFP

C to +70

TC7136A CLW

44-Pin PLCC

C to +70

Low Power 3-1/2 Digit Analog-to-Digital Converter

TC7136/TC7136A

DS21461B-page 2

2002 Microchip Technology Inc.

Package Type

TC7136CPL

TC7136ACPL

OSC1

TEST

REF

ANALOG
COMMON

V+

Normal Pin

Configuration

10's

100's

1000's

100's

OSC2

OSC3

REF

BUFF

INT

V-

BP
(Backplane)

POL

(MINUS SIGN)

TC7136RCPL

TC7136ARCPL

100's

1000's

100's

Reverse Pin

Configuration

1's

V+

POL
(Minus Sign)

1's

10's

OSC1

TEST

REF

ANALOG

COMMON

OSC2

OSC3

REF

BUFF

INT

V-

(Backplane)

NC = No Internal Connection

TC7136CKW

TC7136ACKW

REF HI

ANALOG COMMON

UFF

INT

V-

IN HI

OSC3

TEST

V+

OSC2

OSC1

REF LO

REF

IN LO

POL

ANALOG
COMMON

REF LO

POL

IN HI

IN LO

OSC1

OSC2

OSC3

TEST

REF HI

BUFF

INT

TC7136CLW

TC7136ACLW

44-Pin PLCC

40-Pin PDIP

44-Pin PQFP

40-Pin PDIP

V-

V+

REF

2002 Microchip Technology Inc.

DS21461B-page 5

TC7136/TC7136A

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):

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: V

= 9V, f

CLK

= 16kHz, and T

= +25°C, unless otherwise noted.

Symbol

Parameter

Min

Typ

Max

Unit

Test Conditions

Input

Zero Input Reading

-000.0

±000.0

+000.0

Digital

Reading

= 0V, Full Scale = 200mV

Zero Reading Drift

0.2

V/°C

= 0V, 0°C

+70°C

Ratiometric Reading

999

999/1000

1000

Digital

Reading

= V

REF

, V

REF

= 100mV

Non-Linearity Error

±0.2

Count

Full Scale = 20mV or 2V Max.
Deviation from best Straight Line

Rollover Error

-1

±0.2

1 Count

- = V

200mV

Noise

P-P

= 0V, Full Scale = 200mV

Input Leakage Current

= 0V

CMRR

Common Mode Rejection Ratio

V/V

= ±1V, V

= 0V, Full Scale = 200mV

Scale Factor Temperature
Coefficient

ppm/°C

= 199mV, 0°C

+70°C

Ext. Ref. Temp. Coeff. = 0ppm/°C

Note

Input voltages may exceed supply voltages when input current is limited to 100

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.

See "Typical Application".

A 48kHz oscillator increases current by 20

A (typical). Common current not included.

TC7136/TC7136A

DS21461B-page 6

2002 Microchip Technology Inc.

Analog Common

CTC

Analog Common Temperature
Coefficient

250k

between Common and V+

TC7136A

ppm/°C

0°C

+70°C

TC7136

150

ppm/°C

"C" Commercial Temp. Range Devices

TC7136A

100

ppm/°C

-25°C

+85°C

TC7136

150

ppm/°C

"I" Industrial Temp. Range Devices

Analog Common Voltage

2.7

3.05

3.35

250k

Between Common and V+

LCD Drive

LCD Segment Drive Voltage

P-P

V+ to V- = 9V

LCD Backplane Drive Voltage

P-P

V+ to V- = 9V

Power Supply

Power Supply Current

100

= 0V, V+ to V- = 9V (Note 6)

TC7136 AND TC7136A ELECTRICAL SPECIFICATIONS (CONTINUED)

Electrical Characteristics: V

= 9V, f

CLK

= 16kHz, and T

= +25°C, unless otherwise noted.

Symbol

Parameter

Min

Typ

Max

Unit

Test Conditions

Note

Input voltages may exceed supply voltages when input current is limited to 100

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.

See "Typical Application".

A 48kHz oscillator increases current by 20

A (typical). Common current not included.

2002 Microchip Technology Inc.

DS21461B-page 7

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

Description

(40)

V+

Positive supply voltage.

(39)

Activates the D section of the units display.

(38)

Activates the C section of the units display.

(37)

Activates the B section of the units display.

(36)

Activates the A section of the units display.

(35)

Activates the F section of the units display.

(34)

Activates the G section of the units display.

(33)

Activates the E section of the units display.

(32)

Activates the D section of the tens display.

(31)

Activates the C section of the tens display.

(30)

Activates the B section of the tens display.

(29)

Activates the A section of the tens display.

(28)

Activates the F section of the tens display.

(27)

Activates the E section of the tens display.

(26)

Activates the D section of the hundreds display.

(25)

Activates the B section of the hundreds display.

(24)

Activates the F section of the hundreds display.

(23)

Activates the E section of the hundreds display.

(22)

Activates both halves of the 1 in the thousands display.

(21)

POL

Activates the negative polarity display.

(20)

Backplane drive output.

(19)

Activates the G section of the hundreds display.

(18)

Activates the A section of the hundreds display.

(17)

Activates the C section of the hundreds display.

(16)

Activates the G section of the tens display.

(15)

V-

Negative power supply voltage.

(14)

INT

The integrating capacitor should be selected to give the maximum voltage swing
that ensures component tolerance buildup will not allow the integrator output to sat-
urate. When analog common is used as a reference and the conversion rate is 3
readings per second, a 0.047

F 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.

(13)

BUFF

Integration resistor connection. Use a 180k

for a 20mV full scale range and a

1.8M

for 2V full scale range.

(12)

The size of the auto-zero capacitor influences the system noise. Use a 0.47

capacitor for a 200mV full scale and a 0.1

F capacitor for a 2V full scale.

See Section 6.1, Auto-Zero Capacitor for more details.

(11)

The low input signal is connected to this pin.

(10)

The high input signal is connected to this pin.

(9)

ANALOG

COMMON

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.

(8)

REF

See Pin 34.

TC7136/TC7136A

DS21461B-page 8

2002 Microchip Technology Inc.

(7)

REF

A 0.1

F capacitor is used in most applications. If a large Common mode voltage

exists (for example, the V

- pin is not at analog common) and a 200mV scale is

used, a 1

F capacitor is recommended, which will hold the rollover error to

0.5 count.

(6)

REF

See Pin 36.

(5)

REF

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.

(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.

(3)

OSC3

See Pin 40.

(2)

OSC2

See Pin 40.

(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 180k

resistor and a

50pF capacitor. The 180k

resistor is tied to Pin 39 and the 50pF capacitor is tied

to Pin 38.

TABLE 2-1:

PIN DESCRIPTION (CONTINUED)

Pin Number

(40-Pin PDIP)

Normal

(Reverse)

Symbol

Description

2002 Microchip Technology Inc.

DS21461B-page 9

TC7136/TC7136A

3.0

DETAILED DESCRIPTION

(All Pin Designations Refer to 40-Pin PDIP.)

3.1

Dual Slope Conversion Principles

The TC7136/A is a dual slope, integrating analog-to-
digital converter. An understanding of the dual slope
conversion technique will aid in following detailed
TC7136/A operational theory.

The conventional dual slope converter measurement
cycle has two distinct phases (see Figure 3-1).

Input signal integration

Reference voltage integration (de-integration)

The input signal being converted is integrated for a
fixed time period (t

), 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 (t

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:

EQUATION 3-1:

For a constant V

EQUATION 3-2:

FIGURE 3-1:

BASIC DUAL SLOPE
CONVERTER

FIGURE 3-2:

NORMAL MODE
REJECTION OF DUAL
SLOPE CONVERTER

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 convert-
ers 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.

---------

( )

------------

Where:

= Reference voltage

= Signal integration time (fixed)

= Reference voltage integration time

(variable)

--------

REF

Voltage

Analog Input

Signal

Display

Switch

Driver

Control

Logic

Integrator

Output

Clock

Counter

Polarity Control

Phase
Control

REF

1/2 V

REF

Variable
Reference
Integrate
Time

Fixed

Signal

Integrate

Time

Integrator

Comparator

INT

Normal Mode Rejection (dB)

0.1/t

1/t

10/t

Input Frequency

t = Measured Period

TC7136/TC7136A

DS21461B-page 10

2002 Microchip Technology Inc.

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 volt-
age errors (buffer amplifier, integrator and comparator)
are removed from the conversion. A true digital zero
reading is assured without any external adjustments.

A complete conversion consists of four distinct phases:

Integrator output zero phase

Auto-zero phase

Signal integrate phase

Reference de-integrate phase

4.1

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 com-
parator offset voltage error compensation. The voltage
level established on C

compensates for device offset

voltages. The auto-zero phase residual is typically
10

V to 15

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 differen-
tial inputs connect to V

+ and V

-. The differential

input signal is integrated for a fixed time period. The
TC7136/A signal integration period is 1000 clock peri-
ods or counts. The externally set clock frequency is
divided by four before clocking the internal counters.
The integration time period is:

EQUATION 4-1:

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
share the same power supply common, V

- 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.

4.4

Reference Integrate Phase

The third phase is reference integrate or de-integrate.
V

- is internally connected to analog common and

+ is connected across the previously charged refer-

ence 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 propor-
tional to the input signal and is between 0 and 2000
internal clock periods. The digital reading displayed is:

EQUATION 4-2:

FIGURE 4-1:

CONVERSION TIMING
DURING NORMAL
OPERATION

FIGURE 4-2:

CONVERSION TIMING
DURING OVER RANGE
OPERATION

x 1000

OSC

Where F

OSC

= external clock frequency.

1000

REF

----------------

INT

DENT

4000

910-2900

1-2000

1000

11-140

4000

DEINT

INT

1000

2001-2090

31-640

300-910

2002 Microchip Technology Inc.

DS21461B-page 11

TC7136/TC7136A

5.0

DIGITAL SECTION

The TC7136/A contains all the segment drivers neces-
sary to directly drive a 3-1/2 digit LCD. An LCD back-
plane 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 seg-
ment 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 polar-
ity segment driver is ON for negative analog inputs. If
V

+ and V

- 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.

The display font and segment drive assignment are
shown in Figure 5-1.

FIGURE 5-1:

DISPLAY FONT AND
SEGMENT ASSIGNMENT

5.1

System Timing

The oscillator frequency is divided by 4 prior to clocking
the internal decade counters. The four-phase mea-
surement cycle takes a total of 4000 counts, or 16,000
clock pulses. The 4000 count cycle is independent of
input signal magnitude.

Each phase of the measurement cycle has the
following length:

Auto-zero phase: 3000 to 2900 counts
(1200 to 11,600 clock pulses)

Signal integrate: 1000 counts
(4000 clock pulses)

This time period is fixed. The integration period is:

EQUATION 5-1:

Reference integrate: 0 to 2000 counts

Zero integrator: 11 to 640 counts

The TC7136 is a drop-in replacement for the TC7126
and ICL7126. The TC7136A offers a greatly improved
internal reference temperature coefficient. Minor com-
ponent value changes are required to upgrade existing
designs and improve the noise performance.

6.0

COMPONENT VALUE
SELECTION

6.1

Auto-Zero Capacitor (C

)

The C

capacitor size has some influence on system

noise. A 0.47

F capacitor is recommended for 200mV

full scale applications, where 1LSB is 100

V. A 0.1

capacitor is adequate for 2V full scale applications. A
Mylar type dielectric capacitor is adequate.

6.2

Reference Voltage Capacitor
(C

REF

)

The reference voltage, used to ramp the integrator out-
put voltage back to zero during the reference integrate
phase, is stored on C

REF

. A 0.1

F capacitor is accept-

able when V

REF

- is tied to analog common. If a large

Common mode voltage exists (V

REF

analog com-

mon) and the application requires a 200mV full scale,
increase C

REF

to 1

F. Rollover error will be held to less

than 0.5 count. A Mylar type dielectric capacitor is
adequate.

6.3

Integrating Capacitor (C

INT

)

INT

should be selected to maximize integrator output

voltage swing without causing output saturation. Ana-
log 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
(F

OSC

= 48kHz), a 0.047

F value is suggested. For

one reading per second, 0.15

F is recommended. If a

different oscillator frequency is used, C

INT

must be

changed in inverse proportion to maintain the nominal
±2V integrator swing.

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.

Display Font

1000's

100's

10's

1's

Where:

= 4000

OSC

is the externally set clock frequency.

TC7136/TC7136A

DS21461B-page 12

2002 Microchip Technology Inc.

An exact expression for C

INT

is:

EQUATION 6-1:

INT

must have low dielectric absorption to minimize

rollover

error.

polypropylene

capacitor

recommended.

6.4

Integrating Resistor (R

INT

)

The input buffer amplifier and integrator are designed
with Class A output stages. The output stage idling cur-
rent is 6

A. The integrator and buffer can supply 1

drive currents with negligible linearity errors. R

INT

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 180k

. A

2V full scale requires 1.8M

(see Table 6-1).

TABLE 6-1:

Note:

OSC

= 48kHz (3 reading per sec).

OSC

= 180k

OSC

= 50pF.

6.5

Oscillator Components

OSC

should be 50pF. R

OSC

is selected from the

equation:

EQUATION 6-2:

Note that F

OSC

is ÷ 4 to generate the TC7136A's inter-

nal clock. The backplane drive signal is derived by
dividing F

OSC

by 800.

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 suit-
able. 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.

Note:

REF

= 2V

REF.

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-
sure transducer output for 2000 lb/in

is 400mV. Rather

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. The differential refer-
ence can also be used when a digital zero reading is
required, when V

is not equal to zero. This is common

in temperature measuring instrumentation. A compen-
sating offset voltage can be applied between analog
common and V

-. The transducer output is connected

between V

+ and analog common.

Component

Value

Nominal Full Scale Voltage

200mV

0.47

0.1

INT

180k

1.8M

INT

0.047

(4000)

OSC

INT

Where:

OSC

= Clock frequency at Pin 38

= Full scale input voltage

INT

= Integrating resistor

INT

= Desired full scale integrator output swing

Required Full Scale Voltage*

REF

200mV

100mV

OSC

0.45

2002 Microchip Technology Inc.

DS21461B-page 13

TC7136/TC7136A

7.0

DEVICE PIN FUNCTIONAL
DESCRIPTION

7.1

Differential Signal Inputs
V

+ (Pin 31), V

- (Pin 30)

The TC7136/A is designed with true differential inputs
and accepts input signals within the input stage Com-
mon mode voltage range (V

). The typical range is

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 V

= analog common and V

connected

analog

common

COM

)

(see

Figure 7-1).

FIGURE 7-1:

COMMON MODE VOLTAGE REMOVED IN BATTERY OPERATION WITH
V

= ANALOG COMMON

In systems where Common mode voltages exist, the
86dB Common mode rejection ratio minimizes error.
Common mode voltages do, however, affect the inte-
grator output level. A worst case condition exists if a
large positive V

exists in conjunction with a full scale

negative differential signal. The negative signal drives
the integrator output positive along with V

(see

Figure 7-2.) For such applications, the integrator out-
put 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

COM

)

7.2

Differential Reference
V

REF

+ (Pin 36), V

REF

- (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

REF

should be large com-

pared to stray node capacitance. The TC7136/A offers
a significantly improved analog common temperature
coefficient. This potential provides a very stable volt-
age, 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 inter-
nally to an N-channel FET, capable of sinking 100

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 1

Analog common is, therefore, easily pulled to a more
negative voltage (i.e., below V+ 3V).

BUF

INT

POL

Segment

Drive

OSC1

OSC3

OSC2

V-

V+

REF

ANALOG
COMMON

V-

V+

GND

Measured

System

Power

Source

LCD

TC7136

TC7136A

V-

V+

V-

Integrator

[

= V

Input Buffer

= Integration capacitor

= Integration resistor

4000
F

OSC

= Integration time =

Where:

TC7136/TC7136A

DS21461B-page 14

2002 Microchip Technology Inc.

The TC7136/A connects the internal V

+ and V

inputs to analog common during the auto-zero phase.
During the reference integrate phase, V

- is connected

to analog common. If V

- 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 V

- are usually connected, removing Common

mode voltage concerns. In systems where V

- is con-

nected to the power supply ground or to a given
voltage, analog common should be connected to V

The analog common pin serves to set the analog sec-
tion reference, or common point. The TC7136A 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 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 poten-
tial 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 inter-
nally generated negative logic supply through a 500

resistor. The TEST pin load should not be more than
1mA. See Section 8.0, Typical Applications for addi-
tional information on using TEST as a negative digital
logic supply.

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 sta-
bility 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 C

(see Section 6.1, Auto-Zero Capacitor). Figure 7-4
shows analog common supplying the necessary
voltage reference for the TC7136/A.

FIGURE 7-3:

ANALOG COMMON
TEMPERATURE
COEFFICIENT

FIGURE 7-4:

TC7136A INTERNAL
VOLTAGE REFERENCE
CONNECTION

Typical

Maximum

Typical

No Maximum

Specified

200

180

160

140

120

100

Analog Common Temperature

Coefficient (ppm/

°
C)

TC7136

TC7136A

ICL7136

V-

ANALOG

COMMON

TC7136

TC7136A

REF

240k

10k

REF

Set V

REF

= 1/2 V

REF

V+

2002 Microchip Technology Inc.

DS21461B-page 15

TC7136/TC7136A

8.0

TYPICAL APPLICATIONS

8.1

Liquid Crystal Display Sources

Several manufacturers supply standard LCDs to inter-
face with the TC7136A 3-1/2 digit analog-to-digital
converter.

Note:

Contact LCD manufacturer for full product listing/
specifications.

8.2

Decimal Point and Annunciator
Drive

The TEST pin is connected to the internally generated
digital logic supply ground through a 500

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+.

8.3

Ratiometric Resistance
Measurements

The TC7136A's true differential input and differential
reference make ratiometric readings possible. In ratio-
metric 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 reference input. If the unknown equals the stan-
dard, the display will read 1000. The displayed reading
can be determined from the following expression:

EQUATION 8-1:

The display will over range for:

UNKNOWN

2 x R

STANDARD

FIGURE 8-1:

DECIMAL POINT AND
ANNUNCIATOR DRIVES

Manufac.

Address/Phone

Representative

Part Numbers*

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
414-648-2361

3902, 3933, 3903

Displayed(Reading) =

UNKNOWN

STANDARD

x 1000

V+

TC7136

TC7136A

V+

TC7136

TC7136A

4049

4030

TEST

GND

To LCD
Decimal Point

To LCD Backplane

To LCD
Decimal Point

Decimal

Point

Select

Multiple Decimal Point or

Annunciator Driver

Simple Inverter for Fixed Decimal Point

or Display Annunciator

2002 Microchip Technology Inc.

DS21461B-page 17

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

Standard Reel Component Orientation
for TR Suffix Device

Package

Carrier Width (W)

Pitch (P)

Part Per Full Reel

Reel Size

44-Pin PQFP

24 mm

16 mm

500

13 in

Carrier Tape, Number of Components Per Reel and Reel Size

Note: Drawing does not represent total number of pins.

PIN 1

Component Taping Orientation for 44-Pin PLCC Devices

User Direction of Feed

Standard Reel Component Orientation
for TR Suffix Device

Note: Drawing does not represent total number of pins.

Package

Carrier Width (W)

Pitch (P)

Part Per Full Reel

Reel Size

44-Pin PLCC

32 mm

24 mm

500

13 in

Carrier Tape, Number of Components Per Reel and Reel Size

2002 Microchip Technology Inc.

DS21461B-page 21

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 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.

Trademarks

The Microchip name and logo, the Microchip logo, FilterLab,
K

, microID,

MPLAB, PIC, PICmicro, PICMASTER,

PICSTART, PRO MATE, SEEVAL and The Embedded Control
Solutions Company are registered trademarks of Microchip Tech-
nology 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.

Printed on recycled paper.

Microchip received QS-9000 quality system
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999
and Mountain View, California in March 2002.
The Company's quality system processes and
procedures are QS-9000 compliant for its
PICmicro

8-bit MCUs, K

code hopping

devices, Serial EEPROMs, microperipherals,
non-volatile memory and analog products. In
addition, Microchip's quality system for the
design and manufacture of development
systems is ISO 9001 certified.

DS21461B-page 22

2002 Microchip Technology Inc.

AMERICAS

Corporate Office

2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7200 Fax: 480-792-7277
Technical Support: 480-792-7627
Web Address: http://www.microchip.com

Rocky Mountain

2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7966 Fax: 480-792-7456

Atlanta

500 Sugar Mill Road, Suite 200B
Atlanta, GA 30350
Tel: 770-640-0034 Fax: 770-640-0307

Boston

2 Lan Drive, Suite 120
Westford, MA 01886
Tel: 978-692-3848 Fax: 978-692-3821

Chicago

333 Pierce Road, Suite 180
Itasca, IL 60143
Tel: 630-285-0071 Fax: 630-285-0075

Dallas

4570 Westgrove Drive, Suite 160
Addison, TX 75001
Tel: 972-818-7423 Fax: 972-818-2924

Detroit

Tri-Atria Office Building
32255 Northwestern Highway, Suite 190
Farmington Hills, MI 48334
Tel: 248-538-2250 Fax: 248-538-2260

Kokomo

2767 S. Albright Road
Kokomo, Indiana 46902
Tel: 765-864-8360 Fax: 765-864-8387

Los Angeles

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

6285 Northam Drive, Suite 108
Mississauga, Ontario L4V 1X5, Canada
Tel: 905-673-0699 Fax: 905-673-6509

ASIA/PACIFIC

Australia

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Suite 22, 41 Rawson Street
Epping 2121, NSW
Australia
Tel: 61-2-9868-6733 Fax: 61-2-9868-6755

China - Beijing

Microchip Technology Consulting (Shanghai)
Co., Ltd., Beijing Liaison Office
Unit 915
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Tel: 86-10-85282100 Fax: 86-10-85282104

China - Chengdu

Microchip Technology Consulting (Shanghai)
Co., Ltd., Chengdu Liaison Office
Rm. 2401, 24th Floor,
Ming Xing Financial Tower
No. 88 TIDU Street
Chengdu 610016, China
Tel: 86-28-6766200 Fax: 86-28-6766599

China - Fuzhou

Microchip Technology Consulting (Shanghai)
Co., Ltd., Fuzhou Liaison Office
Unit 28F, World Trade Plaza
No. 71 Wusi Road
Fuzhou 350001, China
Tel: 86-591-7503506 Fax: 86-591-7503521

China - Shanghai

Microchip Technology Consulting (Shanghai)
Co., Ltd.
Room 701, Bldg. B
Far East International Plaza
No. 317 Xian Xia Road
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Tel: 86-21-6275-5700 Fax: 86-21-6275-5060

China - Shenzhen

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Co., Ltd., Shenzhen Liaison Office
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Renminnan Lu
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Tel: 86-755-2350361 Fax: 86-755-2366086

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India

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Tel: 91-80-2290061 Fax: 91-80-2290062

Japan

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Tel: 81-45-471- 6166 Fax: 81-45-471-6122

Korea

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Tel: 82-2-554-7200 Fax: 82-2-558-5934

Singapore

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Tel: 65-6334-8870 Fax: 65-6334-8850

Taiwan

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Tel: 886-2-2717-7175 Fax: 886-2-2545-0139

EUROPE

Denmark

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Tel: 45 4420 9895 Fax: 45 4420 9910

France

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Germany

Microchip Technology GmbH
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Tel: 49-89-627-144 0 Fax: 49-89-627-144-44

Italy

Microchip Technology SRL
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Tel: 39-039-65791-1 Fax: 39-039-6899883

United Kingdom

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505 Eskdale Road
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Berkshire, England RG41 5TU
Tel: 44 118 921 5869 Fax: 44-118 921-5820

03/01/02

*DS21461B*

ORLDWIDE

ALES

AND

ERVICE

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