Microchip Technology TC820CPL, TC820CLW, TC820CKW Datasheet

TC820

3-3/4 Digit A/D Converter with Frequency Counter

and Logic Probe

Features

• Multiple Analog Measurement System

- Digit A/D Converter

- Frequency Counter

- Logic Probe

• Low Noise A/D Converter:

- Differential Inputs: (1pA Bias Current)

- On-Chip 50ppm/°C Voltage Reference

• Frequency Counter:

- 4MHz Maximum Input Frequency

- Auto-RangingOver Four Decade Range

• Logic Probe:

- Two LCD Annunciators

- Buzzer Driver

• 3-3/4 Digit Display with Over Range Indicator

• LCD Display Driver with Bui lt-in Contrast Control

• Data Hold Input for Comparison Measurements

• Low Battery Detect with LCD Annunciator

• Under Range and Over Range Outputs

• On-Chip Buzzer Driver with Control Input

• 40-Pin Plastic DIP, 44-Pin Plastic Flat Pack, or
44-Pin PLCC Packages

General Description

The TC820 is a 3-3/4 digit, multi-measurement system
especiallysuitedforuse in portable instruments.It inte­grates a dual slope A/D converter, auto-ranging fre­quency counter and logic pr obe into a single 44-pin
surface mount, or 40-pin through hole package. The
TC820 operates from a single 9V input voltage (bat­tery) and features a built-in battery low flag. Function
and decimal pointselectionareaccomplishedwithsim­ple logic inputs designed for direct connection to an
external microcontroller or rotary switch.

Device Selection Table

Part

Number

TC820CPL 3-3/4 Digits 40-Pin PDIP 0°Cto+70°C

TC820CKW 3-3/4Digits 44-PinPQFP 0°Cto+70°C

TC820CLW 3-3/4 Digits 44-Pin PLCC 0°Cto+70°C



2002 Microchip TechnologyInc. DS21476B-page 1

Resolution Package

Operating

Temp. Range

TC820

S

Package Type

44-Pin PLCC

BC3P2

OFE2

AGD2

BC2P1

PKFE1

AGD1

BP1BT

BP3

BP2

BP1

V

DISP

BC3P2

OFE2

AGD2

BC2P1

PKFE1

AGD1

BC1BT

BP3

BP2

BP1

V

DISP

AGD3

HFE3

BC4P3

6543 1442

7

8

9

10

11

12

13

14

15

16

17

18 19 20 21 23 24

DGND

AGD4

TC820CLW

LOGIC

ANNUNC

RANGE/FREQ

44-Pin PQFP

AGD3

BC4P3

HFE3

44 43 42 41 39 3840

1

2

3

4

5

6

7

8

9

10

11

12 13 14 15 17 18

DGND

AGD4

TC820CKW

LOGIC

ANNUNC

RANGE/FREQ

22

L–E4

16

DP0/LO

DD

L-E4

V

DP1/HI

DP0/LO

DD

V

DP1/HI

OSC3

OSC242OSC141EOC/HOLD

43

25

26

BUZIN

BUZOUT

FREQ/VOLTS

OSC1

OSC3

OSC2

37 36 35 34

19

20

21 22

BUZIN

BUZOUT

FREQ/VOLTS

INT

V

40

27 28

UR

PKHOLD

INT

V

EOC/HOLD

33

32

31

30

29

28

27

26

25

24

23

UR

PKHOLD

39

38

37

36

35

34

33

32

31

30

29

C

V

VIN+

V

V

V

C

C

COM

V

OR

C

AZ

V

BUFF

VIN+

V

IN

V

REF

V

REF

C

REF

C

REF

COM

V

SS

OR

AZ

BUFF

-

IN

REF

REF

REF

REF

SS

-

-

+

-

+

-

+

-

+

Segments L-E4

Segments AGD4

Segments BC4P3

Segments HFE3

Segments AGD3

Segments BC3P2

Segments OFE2

Segments AGD2

Segments BC2P1

Segments PKFE1

Segments AGD1

Segments BC1BT

BP3

BP2

BP1

DGND

ANNUNC

LOGIC

RANGE/FREQ

DP0/LO

40-Pin PDIP

1

2

3

4

5

6

7

8

9

TC820CPL

10

11

12

13

14

15

16

17

18

19

20

V

40

DD

OSC3

39

38

OSC2

OSC1

37

V

36

INT

C

35

AZ

V

34

BUFF

+

V

33

IN

-

V

32

IN

-

V

31

REF

+

V

30

REF

C

29

28

27

26

25

24

23

22

21

-

REF

+

C

REF

COM

V

SS

PKHOLD

FREQ/VOLT

BUZIN

BUZOUT

DP1/HI

DS21476B-page 2



2002 Microchip TechnologyInc.

Typical Applications

/

TC820

Triplex LCD

EOC

Under Range

Over Range

Analog Input

Full Scale Select

Frequency Input

Logic Probe

Input

Low Drift Voltage

Differential
Reference

3-3/4 Digit A/D

Converter

Analog GND

Auto-Ranging

Frequency

Counter

Logic Probe

Digital Ground

Logic High

Logic Low

To LCD
and Buzzer

Over Range PKHold Low Batt

Clock

Oscillator

TC820

Peak Hold

Comparator

Peak
Hold

Triple LCD

Drivers

Low

Battery

Detect

+

9V

Annunciator Drive

Decimal

Point

Drivers

Buzzer

Driver

Function

Select

Volts

Frequency

Logic

Buzzer
Control

Decimal
Point
Select

Function
Select

C

REF

VIN+

VIN-

V

REF

V

REF

Common

V

DD

V

SS

+C

+

-

REF-VBUFF

DGND

C

Detect

UR OR

AZ

Low
Batt

V

INT

To LCD

A/D Control

DEINT

Under Range

Over Range

Range Frequency

Range

Input

EOC/

HOLD

EOC

÷2

TC820

PEAK
HOLD

OSC3OSC2OSC1

Logic
Low

Frequency Counter Input

A/D Counter Select

SEL

B

A

Low Batt

ANNUNC

V

÷8

DISP

BUZIN

Range

A/D Counter

(3999 Counts)

Comparator

A > B

Display

Latch

Logic

Triples
Drivers

SEG0 • • • BP3

Low

Buzzer
Driver

Range/
Frequency

Frequency
Volts

Logic

DP0/LO

15

DP1/HI



2002 Microchip TechnologyInc. DS21476B-page 3

TC820

1.0 ELECTRICAL
CHARACTERISTICS

Absolute Maximum Ratings*

Supply Voltage (VDDto GND) ................................15V

*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 affectdevice reliability.

Analog Input Voltage:

(Either Input) (Note 1) ............................ V

Reference Input Voltage(Either Input)....... VDDto V

DD

to V

SS
SS

Digital Inputs...........................................VDDto DGND

....................................... VDDto (DGND – 0.3V)

V

DISP

Package Power Dissipation (T

–70°C)(Note 2):

A

40-Pin Plastic DIP ......................................... 1.23W

44-Pin PLCC ..................................................1.23W

44-Pin Plastic Flat Package (PQFP) ..............1.00W

Operating Temperature Range:

"C" Devices ......................................... 0°C to +70°C

"E" Devices.......................................-40°C to +85°C

StorageTemperature Range..............-65°C to +150°C

TC820 ELECTRICAL SPECIFICATIONS

Electrical Characteristics: VS=9V,TA= 25°C, unless otherwise specified.

Symbol Parameter Min Typ Max Units Test Conditions

Zero Input Reading -000 ±000 +000 Digital

Reading

RE Rollover Error -1 ±0.2 +1 Counts V

NL Nonlinearity

(Maximum Deviation From Best
Straight Line Fit)

Ratiometric Reading 1999 1999/2000 2000 — V

CMRR Common Mode Rejection Ratio — 50 — µV/V V

VCMR Common Mode Voltage Range V
e

N

I

IN

V

COM

V

CTC

Note 1: Inputvoltages may exceedthesupply voltages providedthat input currentis limited to ±100µA.Currentabove this value

Noise (P-P Value Not
Exceeded95% of Time)

Input LeakageCurrent — — — — VIN=0V

AnalogCommonVoltage 3.15 3.3 3.45 V 25kΩ between Common and

Common Voltage Temperature
Coefficient

may result in invaliddisplay readings,butwillnotdestroy the deviceif limitedt o ±1mA.

2: Dissipation ratings assumedevice is mounted with all leads solderedto printed circuit board.

-1 ±0.2 +1 Count Full Scale = 400mV

+1.5 — VDD– 1 Input High, Input Low

SS

—15 —µVVIN=0V

—1 10pAT
—20 —pA0°C≤ T
—100 —pA-40°C≤ T

—— ——25kΩ BetweenCommon and

—35 50ppm/°C0°C≤ TA≤ +70°C
—50 ——-40°C≤ T

=0V

V

IN

Full Scale= 400mV

= ±390mV

IN

Full Scale= 400mV

IN=VREF
CM

Full Scale= 400mV
(V

FS

Full Scale= 400mV

A

V

DD(VSS-VCOM

V

DD

,TC820

=±1V,VIN=0V

=200mV)

=25°C

≤ +70°C

A

≤ +85°C

A

≤ +85°C

A

)

DS21476B-page 4



2002 Microchip TechnologyInc.

TC820

TC820 ELECTRICAL SPECIFICATIONS (CONTINUED)

Electrical Characteristics: VS=9V,TA= 25°C, unless otherwise specified.

Symbol Parameter Min Typ Max Units Test Conditions

TC

ZS

TC

FS

I

S

V

IL

V

IH

V

OL

Note 1: Inputvoltages may exceedthesupply voltages providedthat input current is limitedto±100µA. Current above thisvalue

Zero Reading Drift — — — — VIN=0V

—0.2 ——0°C≤ T
—1 ——-40°C≤ T

Scale Factor Temperature
Coefficient

—— ——V
—1 5ppm/°C0°C≤ T
— 5 — ppm/°C -40°C ≤ T

Supply Current — 1 1.5 mA VIN=0V
Peak-to-Peak Backplane

4.25 4.7 5.3 V V

Drive Voltage
Buzzer Frequency — 5 — kHz F
Counter TIme-Base Period — 1 — Second F
Low Battery Flag Voltage 6.7 7 7.3 V V
Input Low Voltage — — DGND + 1.5 V
Input High Voltage VDD–1.5 — — V
Output Low Voltage,

VDD–1.5 — DGND+0.4 V IL=50µA

UR, OR Outputs
Control Pin Pull-down Current — 5 — µAV

may result in invaliddisplay readings,butwillnotdestroy the deviceif limitedt o ±1mA.

2: Dissipation ratings assumedevice is mounted with all leads solderedto printed circuit board.

≤ +70°C

A

≤ +85°C

A

=399mV

IN

≤ +70°C

A

≤ +85°C

=9V

S

=DGND

DISP

=40kHz

OSC

=40kHz

OSC

to V

DD

IN=VDD

A

SS

Ext Ref = 0ppm/°C

V



2002 Microchip TechnologyInc. DS21476B-page 5

TC820

2.0 PIN DESCRIPTIONS

ThedescriptionsofthepinsarelistedinTable2-1.

TABLE 2-1: PIN F UNCTION TABLE

Pin Number

(40-PDIP)

1 40 L-E4 LCD segment driver for L ("logic LOW"), polarity, and "e" segment of most significant

2 41 AGD4 LCD segment drive for "a," "g," and "d" segments of MSD.
3 42 BC4P3 LCD segmentdrivefor "b" and "c" segmentsof MSD and decimal point 3.
4 43 HFE3 LCD segment drive for H ("logic HIGH"), and "f" and "e" segmentsof third LSD.
5 44 AGD3 LCD segment drive for "a," "g," and "d" segments of third LSD.
6 1 BC3P2 LCD segmentdrive for "b" and "c" segmentsof third LSD and decimal point 2.
7 2 OFE2 LCD segmentdrive for "over range," and "f" and "e" segments of second LSD.
8 3 AGD2 LCD segment drive for "a," "g," and "d" segmentsof second LSD.

9 4 BC2P1 LCD segmentdrivefor "b " and "c" segmentsof second LSD and decimal point 1.
10 5 PKFE1 LCD segment drive for "hold peak reading," and "f" and "e" segmentsof LSD.
11 6 AGD1 LCD segment drive for "a," "g," and "d" segments of LSD.
12 7 BC1BT LCD segmentdrivefor"b"and "c" segments of LSD and "low battery."
13 8 BP3 LCD backplane#3.
14 9 BP2 LCD backplane#2.
15 10 BP1 LCD backplane#1.
—11V

16 12 DGND Internal logicdigital ground,thelogic "0" level. Nominally4.7VbelowV
17 13 ANNUNC Square-wave output at the backplane frequency, synchronized t o BP1. ANNUNC can be

18 14 LOGIC Logic mode control input. When connected to V

19 15 RANGE/

20 16 DP0/LO D ual purpose input. Decimalpoint select input for voltagemeasurements. In logic mode,

Pin Number

(44-PQFP)

Symbol Description

digit (MSD).

DISP

FREQ

Sets peak LCD drive signal: V
compensate for temperature variation of LCD crystal threshold voltage.

used to control display annunciators. Connecting an LCD segment to ANNUNC turns it
on; connecting it to its backplane turns it off.

LCD displays "OL"andthedecimal pointinputs controlthe HIGH and LOWannunciators.
When the "low" annunciator is on, the buzzer will also be on. When unconnectedor con­nected to DGND, the TC820 is in the Voltage/FrequencyMeasurementmode.Thispin
has a 5µA internal pull-down to DGND

Dual purposeinput. In Rangemode,whenconnected to VDD, the integration time
will be 200 counts instead of 2000 counts

connecting this pin to V
pull-down to DGND in Volts mode only. Decimalpoint logic:

willturn on the "low" LCD segment. Thereis an internal5µA

DD

PEAK

=(VDD)–V

.

DISP.VDISP

DD

mayalsobeusedto

DD

, the converteris in Logic mode. The

.

DP1

00 None
01 DP1
10 DP2
11 DP3

21 17 DP1/HI Dual purpose input. Decimalpoint selectinput for voltagemeasurements. In Logic mode,

22 18 BUZOUT Buzzer output. Audio frequency, 5kHz, output which drives a piezoelectric buzzer.
23 19 BUZIN Buzzercontrol input.Connecting BUZIN to V

24 20 FREQ/

VOLTS

DS21476B-page 6

connecting this pin to V
pull-down to DGND in Volts mode only.

OR’ed (internally)withthe "logiclevel low" input. There is an internal 5µApull-downto
DGND.

Voltage or frequencymeasurement selectinput. When unconnected,or connected
VOLTS to DGND, the A/D converter function is active. When connected to V
frequency counter function is active. This pin has an internal 5µA pull-down to DGND.

DPQ Decimal Point Selected

will turn on the "high" LCD segment. There is an internal 5µA

DD

turns the buzzer on. BUZIN is logically

DD



2002 Microchip TechnologyInc.

DD

,the

TC820

TABLE 2-1: PIN FUNCTION TABLE (CONTINUED)

Pin Number

(40-PDIP)

25 21 PKHOLD Peak hold input. When connectedto VDD, the converter will only update the display if a

— 22 UR Under range output.Thisoutputwill be HIGH when the digitalreading is 380

— 23 OR Over range output. This output will be HIGH when the analog signal inputis greater

26 24 V
27 25 COM Analog circuit ground reference point. Nominally 3.3V below V
28 26 C
29 27 C
30 28 V
31 29 V
32 30 V
33 31 V
34 32 V
35 33 C
36 34 V
—35EOC

37 36 OSC1 Crystal oscillator (input)connection.
38 37 OSC2 Crystal oscillator (output) connection.
39 38 OSC3 RC oscillator connection.
40 39 V

Pin Number

(44-PQFP)

Symbol Description

new conversion value is greaterthanthepreceding value.Thus,thepeakreading will be
storedand held indefinitely. When unconnected, or connected to DGND, the converter
will operate normally. This pin has an internal 5µA pull-down to DGND.

countsor less.

than full scale. The LCD will display"OL"whenthe inputis over ranged.
Negative supply connection. Connect to negativeterminal of 9V battery.

SS

+ P ositive connection for referencecapacitor.

REF

- Negative connection for reference capacitor.

REF

+ High differential reference input connection.

REF

- Low differential reference input connection.

REF

- Low analog input signal connection.

IN

+ High analoginput signalconnection.

IN

Buffer output. Connect to integration resistor.

BUFF

Auto-zero capacitor connection.

AZ

Integrator output. Connect to integration capacitor.

INT

/

Bi-directionalpin. Pulses low (i.e., from VDDto DGND) at the end of each conversion. If

HOLD

connected to V

LCD segmentdrive for "a," "g,"and "d" segmentsof MSD.

DD

, conversions will continue,butthe displayisnot updated.

DD

DD

.



2002 Microchip TechnologyInc. DS21476B-page 7

TC820

3.0 DETAILED DESCRIPTION

The TC820 is a 3-3/4 digit measurement system com­bining an integrating analog-to-digital converter, fre­quency counter, and logic level tester in a single
package. The TC820 supersedes the TC7106 in new
designs by improving performance and reducing sys­tem cost. The TC820 adds features that are difficult,
expensive,orimpossibleto provide with olderA/D con­verters (see Table 3-1). The high level of integration
permitsTC820basedinstruments to deliver higher per­formance and more f eatures, while actually reducing
partscount.Fabricated in low power CMOS, the TC820
directly drives a 3-3/4 digit (3999 maximum) LCD.

With a maximum range of 3999 counts,the TC820 pro­vides 10 times greater resolution in the 200mV to
400mV range than traditional 3-1/2 digit meters. An
auto-zerocycleensuresazero reading with a 0V input.
CMOS processing reduces analog input biascurrent to
only 1pA. Rollover error (the difference in readings for
equal magnitude but opposite polarity input signals) is
less than ±1 count. Differential reference inputs permit
ratiometric measurements for ohms or bridge trans­ducer applications.

The TC820's frequency counter option simplifies
design of an instrument well-suited to both analog and
digitaltroubleshooting: voltage,current,and resistance
measurements, plus precise frequency measurements
to 4MHz ( higher frequencies can be measured with an
external pr escaler), and a simple logic probe. The fre­quency counter will automatically adjust its range to
match the input frequency, over a four-decade range.

Two logic level measurement inputs permit a TC820
based meter to function as a logic probe. When com­binedwithexternallevel shifters,theTC820willdisplay
logiclevelson the LCD and also turn on a piezoelectric
buzzer when the measured l ogic level is low.

Other TC820 features simplify instrument design and
reduce parts count. On-chip decimal point dr ivers are
included, as is a low battery detection annunciator. A
piezoelectricbuzzer can be controlled with an external
switch or by the logic probe inputs. Two oscillator
optionsareprovided: a crystalcanbeusedifhighaccu­racy frequency measurements are desired, or a simple
RC option can be used for low-end instruments.

A "peak reading hold" input allows the TC820 to retain
the highest A/D or frequency reading. This feature is
useful in measuring motor starting current, maximum
temperature, and similar applications.

A family of instruments can be created with the TC820.
No additional design effort is required to create instru­ments with 3-3/4 digit resolution.

The TC820 operates from a single 9V battery, with typ­ical power of 10mW.Packages include a 40-pin plastic
DIP, 44- pin plastic flat package (PQFP), and 44-pin
PLCC.

TABLE 3-1: COMPETITIVE EVALUATION

Features Comparison TC820 7106

3-3/4 Digit Resolution Yes No
Auto-Ranging Frequency

Counter
Logic Probe Yes No
Decimal Point Drive Yes No
Peak Reading Hold

(Frequency or Voltage)

Display Hold Yes No
Simple10:1RangeChange Yes No
Buzzer Drive Yes No
Low Battery Detection

withAnnunciator
Over Range Detection

withAnnunciator
Low Drift Reference Y e s No
Under Range/Over Range

Logic Output
Input Overload Display "OL" "1"
LCD Annunciator Driver Yes No
LCD Drive Type Triplexed Direct
LCD Pin Connections 15 24
LCD Elements 36 23

Yes No

Yes No

Yes No

Yes No

Yes No

3.1 General Theory of Operation

3.1.1 DUAL SLOPE CONVER SION
PRINCIPLES

The TC820 analog-to-digital converter operates on t he
principle of dual slope integration. An understanding of
the dual slope conversion technique will aid the user in
followingthedetailedTC820theoryof operationfollow­ing this section. A conventional dual slope converter
measurement cycle has t wo distinct phases:

1. Input Signal Integration

2. Reference Voltage Integration (De-integration)

Referring to Figure 3-1, the unknown input signal to be
convertedisintegratedfromzerofora fixedtimeperiod
(t

), measured by counting clock pulses. A constant

INT

reference voltage of the opposite polarity is then inte­grated until the integrator output voltage returns to
zero. The reference integration (de-integration) time
(t

) is then directly proportional to the unknown

DEINT

input voltage (V

).

IN

DS21476B-page 8



2002 Microchip TechnologyInc.

TC820

g

T

In a simple dual slope converter, a complete conver­sion requires the integrator output to "ramp-up" from
zero and "ramp-down" back to zero. A simple mathe­maticalequationrelates the inputsignal,referencevolt­age, and integration time.

EQUATION 3-1:

1

R

INTCINT

Where: V

REF

t

INT

t

DEINT

For a constant V

t

INT

V

IN

∫

0

= Ref erence Voltage
= I ntegration Time
= De- integration Time

:

INT

(t)dt =

V

REFtDEINT

R

INTCINT

EQUATION 3-2:

t

REF

DEINT

t

INT

VIN=V

FIGURE 3-1: BASIC DUAL SLOPE

CONVERTER

Analog

Input Signal

REF

Voltage

Output

Integrator

Fixed Signal

Integrate Time

R

Polarity Control

Accuracy in a dual slope converter is unrelated to the
integrating resistor and capacitor values as long as
they are stable during a measurement cycle. An inher­ent benefit of the dual slope technique is noise immu­nity. Noise spikes are integrated or averaged to zero
during the integration periods, making integrating
ADCs 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 (integrating)
period, will be attenuated (Figure 3-2). Integrating
ADCs commonly operate with the signal integration
period set to a multiple of the 50/60Hz power line
period.

C

Integrator

–

+

Switch

Driver

Phase
Control

Display

V

= V

IN

VIN = 1.2V

Variable Reference
Inte

rate Time

Comparator

–

+

Control

Logioc

REF

REF

Clock

Counter

FIGURE 3-2: NORMAL MODE

REJECTION O F DUAL
SLOPE CONVERTER

30

T = Measurement

Period

20

10

Normal Mode Rejection (dB)

0

0.1/T 1/T 10/
Input Frequency

3.2 Analog Section

In addition to the basic integrate and de-integrate dual
slope phases discussed above, the TC820 design
incorporates a "zero integrator output" phase and an
"auto-zero" phase. These additional phases ensure
thatthe integratorstartsat0V(evenaftera severe over
range conversion), and that all offset voltage errors
(buffer amplifier, integrator and comparator) are
removed f rom t he conversion. A true digital zero read­ing is assured without any external adjustments.

A complete conversion consists of four distinctphases:

1. Zero IntegratorOutput

2. Auto-Zero

3. Signal Integrate

4. Reference De-integrate

3.2.1 ZE RO INTEGRATOR OUTPUT
PHASE

This phase guarantees that the integrator output is at
0V before the system zero phase is entered, ensuring
that the true system offset voltages will be compen­sated for even after an over range conversion. The
duration of this phase is 500 counts plus the unused
de-integrate counts.

3.2.2 AUTO-ZERO PHASE

During the auto-zero phase, the differentialinputsignal
is disconnectedfrom the measurement circuit by open­ing internalanalogswitches,andthe internalnodesare
shortedtoAnalogCommon(0V
input condition. Additional analog switches close a
feedback loop around the integrator and comparator to
permitcomparatoroffset voltageerrorcompensation.A
voltageestablishedon C

then compensatesforinter-

AZ

nal device offset voltages during the m easurement
cycle.The auto-zerophaseresidualis typically10µVto
15µV. The auto-zero duration is 1500 counts.

)toestablishazero

REF



2002 Microchip TechnologyInc. DS21476B-page 9