Microchip Technology TC818ACBU Datasheet

TC818A

Auto-Ranging Analog-to-Digital Converter

with 3-1/2 Digit Display

Features

• Auto-Ranging Analog-to-Digital Converter with
3-1/2 Digit Display

• AnnunciatorOutputs Permit Customizing of LCD

• Auto-Range Operation for AC and DC Voltage
and Resistance Measurements

• Two User Selected AC/DC

• Current Ranges: 20mA and 200mA

• 22 Operating Ranges: 9 DC/AC Voltage

•4AC/DCCurrent

• 9 Resistance and Low Power Ohms

• Display Hold Function

• 3-1/2 Digit Resolution in Auto-Range
Mode: 1/2000

• Extended Resolution in Manual Range
Mode: 1/3000

• Internal AC-to-DC Conversion Op Amp

• Triplex LCD Drive for Decimal Points, Digits,

• Bar Graphs, and Annunciators

• Continuity Detection and Piezoelectric
Transducer Driver

• Low Drift Internal Reference: 75ppm/°C

• 9V Battery Operation: 10mW

• Low Battery Detection and LCD Annunciator

Device Selection Table

Part Num ber Package

TC818ACBU 64-PinPQFP 0°Cto+70°C

Operating

Temperature Range

General Description

The TC818A is an integrating analog-to-digital con­verter (ADC) wi th a 3-1/2 digit numeric LCD driver,
automatic ranging, and single 9V battery operation.
The numeric display provides 0.05% resolution and a
full set of annunciators that spell out the TC818A's
many operating modes.

Automatic range selection is provided for both voltage
(DC and AC) and ohms (high and l ow power)measure­ments. Expensive and bulky mechanical range
switches are not required. Five full scale ranges are
available,with automatic selectionof external volt/ohm
attenuators over a 1 to 10,000 range. Two current
ranges, 20mA and 200mA, can be manually selected.
The auto-range feature can be bypassed, allowing
input attenuator selectionthrough a single line input.

During Manual mode operation, resolution is extended
to 3000 counts full scale. Extended resolution is also
available during 2000kΩ and 2000V full scale auto­range operation. The extendedrangeoperationis indi­catedbyaflashing1MSDandbythefullyextended bar
graph.

The TC818A includes an AC-to-DC converter for AC
voltage and current measurements. Only external
diodes/resistors/capacitors are required. Other fea­tures include a Memory mode, low battery detection,
display HOLD input, and continuity buzzer driver.

The 3-1/2 digit numeric display includes a full set of
annunciators. Decimal points are adjusted as auto­matic or manual range changes occur, and Voltage,
Current, and Ohms Operating modes are displayed.
Additionalannunciatorsare activated for manual, auto,
memory, HOLD, AC, low power ohms, and low battery
conditions.

The TC818A i s available in a surface mounted 64-pin
flat package. Combining a numeric display driver, sin­gle 9V battery operation, internal r ange switching, and
compact surface mounting, the TC818A is ideal for
advanced portable instruments.



2002 Microchip TechnologyInc. DS21475B-page 1

TC818A

Package Type

NC

OHM

20mA

BUZ

XTAL1

XTAL2

V

DISP

BP1

BP2

BP3

LOΩ/A

Ω/V

k/m/

HOLD

BCP0

AGD0

FE0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

I

NC

LCD

Backplanes

NC

BCP1

DC(Ω)/

AC(LOΩ)

-MEM

61

LCD Segment Drives

FE1

AGD1

64-Pin PQFP

DGND

RANGE

HOLD

TC818A

23 3217

22

FE2

BCP2

AGD2

SS

V

24 25

BCP3

RVIBUF

ACVH

27 28 29 3018 19 20 21

26

AC/-/AUTO

-MEM/BATT

ADO

RΩBUF

CC

V

ANNUNC

52 51 50 4964 63 62 58 57 56 55 54 5360 59

ADI

COM

R

CFI

31

DEINT

RM

X

REFL

AZ

C

REFL

C

NC

48

47

C

I

ACVL

46

45

I

I

V

44

I

43

VR4

42

VR5

41

VR2

40

VR3

39

ΩR5

ΩR4

38

ΩR3

37

ΩR2

36

35

ΩR1

34

REFHI

33

C

REFH

DS21475B-page 2



2002 Microchip TechnologyInc.

Typical Application

39pF

32.768kHz

(~ 33kHz)

6

530

9V

28

XTAL2

TC818A

CC

4

-MEM

Enable

BUZ

Audio

Transducer

REFHICOM

34

29

20mA

3

200mA

200mA

V

Ω

20mA

200mA

2

OHM

625961

63

I

RANGE

V

Ω

57

58

SS

CC

V

V

DGND

163.85mV

V

R18/24kΩ

R19/5kΩ

W

kΩ

mVA

HOLD

–+

AC

-MEM LO

AUTO

BP2

BP1

LCD Bias

0.1µF

1415161819202122

23242625131211

27

10

BP3

789

50

R7/100kΩ

R8/220Ω

Input

Resistance

AGD2

FE2 FE1BCP2 AGD1 BCP1 FE0 AGD0 BCP0 XTAL1DEINT

BCP3AC/–/

BATT

–MEM/

AUTO

HOLD

Ω/V k/m/

LOΩ/A

ANNUNC

DISP

V

X

R

31

R6/100kΩ

(PTC)

1's

Segment and Decimal Point Drive

100's 10's

1000's

Display

Annunciators

SYNC

Drivers

Backplane

Ohms Range Attenuator

REFL

ΩR5 (÷10,000)

RM

39

1.6385MΩ

µF

0.1

R4 (÷1,000)

Ω

38

373635

163.85kΩ
R3/16.385kΩ

Positive

Coefficient

Temperature

ΩR3 (÷100)

ΩR2 (÷10)

R2/1638.5Ω

Z1

Resistor

R1 (÷1)

Ω

R1/163.85Ω

6.2V

I

I

45

D3 D4

Input

Current

R15

20mA

TC818A

9Ω

1Ω

R16

200mA

DC/AC or Ω/LOΩ

Voltage Range Attenuator

(÷1)

*Not required when Resistor Network is used.

(See Applications Section for details.)

R13*

VR1

44

500kΩ

R14/9.9MΩ

Voltage

R12/1.111MΩ

Input

41

VR2 (÷10)

VR3 (÷100)

40

R11/101kΩ

VR4 (÷1,000)

43

R10/10kΩ

33

REFH

C

32

REFL

C

51

CFI

60

HOLD

47

I

C

49

AZ

C

55

RVIBUF

54

RΩBUF

46

ACVL

56

ACVH

52

ADI

R21/2.2MΩ

53

VR5 (÷10,000)

42

R9/1kΩ

COM

REF

C

R20

100kΩ

INT

C

AZ

C

150

k

ΩΩ

k

220

C1/1µF

Ω

R22/470k

ADO

0.1µF

C2/0.22µF

–

+

C4/1µF

4.7µF

C6

R23/10kΩ

D2

0.01µF

RΩBUF RVIBUF

R26/3kΩ

R24/10kΩ

HOLD

R27/2kΩ

–+

C5/1µF

D1



2002 Microchip TechnologyInc. DS21475B-page 3

TC818A

1.0 ELECTRICAL
CHARACTERISTICS

Absolute Maximum Ratings*

Supply Voltage.......................................................15V

Analog Input Voltage ..................................V

Reference Input Voltage..............................VCCto V

CC

to V

SS
SS

*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.

Voltage at Pin 43 ................................. Common ±0.7V

Power Dissipation ............................................800mW

Operating Temperature Range................ 0°C to +70°C

StorageTemperature Range..............-65°C t o +150°C

TC818A ELEC TRICAL SPECIFICATIONS

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

Symbol Parameter Min Typ Max Unit Test Conditions

Zero Input Reading -0000 0000 +0000 Digital

Reading

-0001 — +0001 Digital
Reading

-0000 0000 +0000 Digital

RE Rollover Error — — ±1 Counts 200mV Range without10MΩ

— — ±3 200mV Range with 10MΩ

— — ±1 20mA and 200mA Range
NL Linearity Error — — ±1 Count Best Case Straight Line
I
E

V
V

V

V
V

IN

N

COM
CTC

IL

OL
OH

InputLeakage Current — — 10 pA
InputNoise — 20 — µV
AC Frequency Error — ±1 — % 40 to 500Hz

— ±5 — % Error 40 to 2000Hz

OpenCircuit Voltage for Ohm
Measurements

OpenCircuit Voltage for LO
Measurements

AnalogCommon Voltage 2.8 3 3.3 V (VCC-V
CommonVoltageTemperature

Coefficient
Display MultiplexRate — 100 — Hz
Low Logic Input — — 1 µA20mA,AC,I,LOWΩ,HOLD

Logic 1 Pull-up Current — 25 — V 20mA

Low Logic Output — DGND +0.1 — V ANNUNC, DEINT: IL=100µA
HighLogicOutput — VCC- 0.1 — V ANNUNC, DEINT: IL=100µA
Buzzer DriveFrequency — 4 — kHz
Low Battery Flag Voltage 6.3 6.6 7 V V
Operating Supply Current — 0.8 1.5 mA

Ohm

— 570 660 mV Excludes 200Ω Range

— 285 350 mV Excludes 200Ω Range

— — 50 ppm/°C

Reading

200mV Rangewithout 10MΩ
Resistor

200mV Range with 10MΩ
Resistor

20mA and 200mA Range

Resistor

Resistor

BW = 0.1 to 10Hz

P-P

)

COM

Range, -MEM, OHMs
(RelativetoDGND,Pin58)

,AC,I,LOWΩ,HOLD
Range, -MEM, OHMs
(RelativetoDGND,Pin58)

to V

CC

SSA

DS21475B-page 4



2002 Microchip TechnologyInc.

2.0 PIN DESCRIPTIONS

ThedescriptionsofthepinsarelistedinTable2-1.

TABLE 2-1: PIN FUNCTION TABLE

Pin Number

(64-Pin PQFP)

1 NC No connection.
2OHM
320mA
4 BUZ Buzzer. Audio frequency, 4kHz, output for continuity indication during resistance

5 XTAL1 32.768kHz CrystalConnection.
6 XTAL2 32.768kHz CrystalConnection.
7V

8 BP1 LCD Backplane #1.

9 BP2 LCD Backplane #2.
10 BP3 LCD Backplane #3.
11 LO

12 Ω/V LCD Annunciator segment drive for resistance measurement and voltage measurement.
13 k/m/HOLD LCD Annunciator segment drive for k (“kilo-Ohms”), m (“milliamps” and “millivolts”) and

14 BCP0

15 AGD0 LCD segment drive for “a,” “g,”“d” segmentsof LSD.
16 FE0 LCD segment drive for “f” and “e” segments of LSD.
17 NC No connection.
18 BCP1 LCDsegmentdrive for “b,” “c” segments and decimal point of 2nd LSD.
19 AGD1 LCD segmentdrive for “a,” “g,”“d” segments of 2ndLSD.
20 FE1 LCD segment drive for “f” and “e” segments of 2nd LSD.
21 BCP2 LCDsegmentdrive for “b,” “c” segments and decimal point of 3rd LSD

22 AGD2 LCD segment drive for “a,” “g,”“d” segmentsof 3rd LSD.
23 FE2 LCD segment drive for “f,” “e” segmentsof 3rd LSD.
24 BCP3 LCDsegmentdrive for “b,” “c” segments and decimal point of MSD,

25 AC/-/AUTO LCD annunciatorsegment drive for AC measurements, polarity, and auto-range operation.
26 -MEM/BATT LCD annunciator segment drive for AC for low battery indicationand memory (relative

27 ANNUNC Square wave output at the backplane frequency, synchronized to BP1. ANNUNC can be

28 V
29 COM Analog circuit ground reference point. Nominally 3V below V
30 DEINT De-integrate output.
31 RM
32 C
33 C
34 REFHI Referencevoltage for voltage and currentmeasurement.Nominally 163.85mV.
35 ΩR1 Standardresistor connection for 200Ω fullscale.
36 ΩR2 Standard resistor connection for 2000Ω full scale.

Symbol Description

LogicInput. “0” (Digital Ground) for resistance measurement.
LogicInput. “0” (Digital Ground)for 20mA full scalecurrentmeasurement.

measurement. A noncontinuous 4kHz signal is output to indicate an input over range
during voltage or current measurements.

DISP

(One’s digit)

CC

REFL
REFL
REFH

Sets peak LCD drive signal: VP-VDD-V
temperaturevariation of LCD crystal threshold voltage.

Ω/A LCD Annunciator segment drive for low ohms resistance measurement and current

measurement.

HOLD mode.
LCD segment drive for “b,” “c” segmentsanddecimal point of least significant digit (LSD).

(hundred’s digit).

(thousand’s digit).

measurement).

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

Positive battery supply connection.

Ratiometric (resistance measurement) referencelowvoltage.
Reference capacitornegative terminalC
Referencecapacitor positiveterminal C

DISP.VDISP

=0.1µf.

REF

=0.1µf.

REF

TC818A

may also be used to compensate for

.

CC



2002 Microchip TechnologyInc. DS21475B-page 5

TC818A

TABLE 2-1: PIN FUNCTION TABLE (CO NTINUED)

Pin Number

(64-Pin PQFP)

37 ΩR3 Standard resistor connection for 20kΩ full scale range.
38 ΩR4 Standard resistor connection for 200kΩ full scale range.
39 ΩR5 Standard resistor connection for 2000kΩ full scale.
40 VR3 Voltage measurement ÷ 100 attenuator.
41 VR2 Voltage measurement ÷ 10 attenuator.
42 VR5 Voltage measurement ÷ 10,000 attenuator.
43 VR4 Voltage measurement ÷ 1000 attenuator.
44 V
45 I
46 ACVL Low output of AC-to-DC converter.
47 C

48 NC No connection.
49 C
50 R
51 CFI Input filter connection.
52 ADI Negative input of internalAC-to-DC operational amplifier.
53 ADO Output of internal AC-to-DC operational amplifier.
54 RΩBUF Active buffer output for resistance measurement. Integration resistor connection.

55 RVIBUF Activebuffer output for voltageand currentmeasurement.Integrationresistor connection.

56 ACVH Positive outputof AC-to-DCconverter.
57 V
58 DGND Internal logic digital ground. Ground connection for the logic "0" level.

59 RANGE
60 HOLD
61 -MEM Input to enterMemoryMeasurementmodefor relative measurements. The two LSDs are

62 DC(Ω)/

63 I
64 NC No connection.

Symbol Description

Unknown voltage input ÷ attenuator.

I

Unknown current input.

I

Integrator capacitor connection. Nominally 0.1µF. (Must have low dielectric absorption.

I

Polypropylene dielectric suggested.)

AZ

SS

AC(LO

Auto-zero capacitor connection. Nominally 0.1µF.
Unknown resistance input.

X

Nominally 220kΩ.

Nominally 15kΩ.

Negative supply connection. Connect to negative terminal of 9V battery.

Nominally 4.7V below V
Input to set manual operation and change ranges.
Input to hold display. Connect to DGND to "FREEZE" display.

storedandsubtracted from futuremeasurements.
Input that selects AC or DC option during voltage/current measurements. For resistance

Ω)

measurements, the ohms or low power (voltage)ohmsoption can be selected.
Inputto select measurement. Connect to logic "0"(digital ground) for currentmeasurement.

CC

.

3.0 DETAILED DESCRIPTION

3.1 Analog-to-Digital Converter (ADC)

The TC818A includes an integrating ADC with auto­ranging resolution of 2000 counts and manual range
resolution of 3000 counts. Figure 3-1 shows a simpli­fied schematic of the analog section. In Auto-Ranging
mode, internal logic will adjust the input voltage or
ohms attenuators so that measurementswillalways be
made i n the appropriate range.

DS21475B-page 6

Measurement ranges, logic control inputs, 3-1/2 digit
LCD formatting, and other features are identical to the
TC818A auto-ranging A/D converter. However, the
TC818A isnotpincompatiblewith, and is not a replace­ment for,the TC818A.

A display annunciator output (ANNUNC) can be used
to customize the LCD. ANNUNC is a square wave at
the backplane frequency. Connecting an annunciator
segment to the ANNUNC driver t urns the segment on;
connecting the segment to its backplane turns it off.



2002 Microchip TechnologyInc.

FIGURE 3-1: TC818A ANALOG SECTION

0.1µF

Ohms
Input

R8/220

0.1µF

Current Input

Voltage
Input

Common

D1

R24

10k

Ω

R26
3kΩ

R7/100 kΩ

Ω

R6/100kΩ

(PTC)

+

R5/1.638MΩ

R4/163.85kΩ

R3/16385Ω

R2/1638.5Ω

Z1

6.2V

R1/163.85Ω

20mA

200mA

R16/1

*Not Required when Resistor
Network is Used

C3
1µF

R27/2kΩ

R15/9

Ω

R14/9.9 M

D2

R23
10kΩ

D3

Ω

R13/500kΩ*

R12/1.11M

R11/101k

R10/10k

R9/1k

+

C4
1µF

Ω

4.7µF

RM

D4

Ω

R22
470
kΩ

C2

ACVH

R

Ω

X

REFL

R5

Ω

ΩR4

ΩR3

ΩR2

ΩR1

I 45

I

V 44

I

Ω

VR2 41

VR3 40

Ω

Ω

VR4 43

VR5 42

ADO

R21

2.2
M

ADI

0.22µF

C1/1µF

ACVH 46

50

31

39

38

37

36

35

S32S33 S31 S30

•

ΩΩ Ω Ω Ω

1/1

1/10 1/100

V

CC

V•

V•

1/10

1/100

S7

S6

AC-to-DC
Converter

53

Op Amp

Ω

52

56

S14

INT•

Ω •ACΩ

S40

INT•Ω•ACΩ

S39

INT+ Ω + DC

•• ••

V•
1/1
k

S8 S9

+

–

S15 AZ

1/1k

S10

S1

V•
1/10k

S2

S3

S4

S5

S24

S29

1/10k

W + 1

V•1/1

V•1/10

V•1/100

V•1/1k

V•1/10k

S11

S13

Buffer

+

–

S35

Ω

Ω

S34

RΩBUF

RΩBUF

S12 V • 1/1

S21 DE •

Ω 1/10k•

•

Ω

S25

1/1k

Ω

•

S26

1/100

•

Ω

1/10

S27

Ω

S28

Ω

+AC

INT•( Ω + DC)

S37

Ω

Ω

54

Ω

R
BUF
220

Ω

k

Ω

1/1•

S22 S22

DE •

S20 DE

S18 DE

S19 DE+

S16 DE+

–

+

Integrator

49 47

55

RVI

C

AZ

BUF

0.01µF

150

CAZ

Ω

k

TC818A

TC818A

V

CC

S44 HI

V

S43

CC

+

2.8V

–

ΩΩ

Ω

S38 AZ

Comparator

INT

C

10k

•

1.5Ω

•

Ω

LOΩ

REF AMP

1.5 kΩ

+

–

DE

S17 DE-

–

+

0.01µF

INT

•

ΩΩ

Ω

R18/24k

R19/5k

29

Analog
Cmmon

34

REFHI

163.85mV

≈

33 C

REFH

C

REFH

32 C

REFL

51 CFI

R20/100kΩ

V

CC

Ω

Ω

0.01µF

C6

To Digital
Section

0.1µF



2002 Microchip TechnologyInc. DS21475B-page 7

TC818A

3.2 Resistance, Voltage,Current
Measurement Selection

The TC818A is designed to measure voltage, current,
and resistance.Auto-rangingisavailableforresistance
and voltage measurements. The OHM
I

(Pin63) input controls are normally pulled internally to

V

.

CC

(Pin 2) and

By tying these pins to DGND (Pin 58), the TC818A is
configuredinternally to measure resistance,voltage,or
current.Therequiredsignal combinationsareshown in
Table 3-1.

TABLE 3-1: TC818A MEASUREMENT

SELECTION LOGIC

Function Select Pin

0 = Digital Ground

1 = Floating or Tied to V

(Pin 2) I (Pin 63)

OHM

00Voltage
0 1 Resistance
1 0 Current
11Voltage

Note 1: OHM and I are normally pulled internally high to

V

(Pin 28). This is considered a lo gic “1”.

CC

2: Logic “0” is the potential at digitalground (Pin 58).

CC

Selected

Measurement

3.3 Resistance Measurements
(Ohms and Low Power Ohms)

The TC818A can be configured to reliably m easure in­circuit resistances shunted by semiconductor junc­tions. The TC818A Low Power Ohms M easurement
mode limits the probe open circuit voltage. This pre­ventssemiconductorjunctionsi n the measured system
from turningon.

In the Resistance Measurement mode, the Ω/LO
(Pin 62) input selects the Low Power Ohms Measure­ment mode. For low power ohms measurements,

Ω/LO

Ω (Pin 62) is momentarily brought LOW to digital

ground potential. The TC818A sets up for a low power
ohms measurement, with a maximum open circuit
probe voltage of 0.35V above analog common. In the
Low Power Ohms mode, an LCD display annunciator,
LO

Ω, will be activated. On power-up, the Low Power

Ohms mode is not active.
If the Manual Operating mode has been selected, tog-

gling Ω/LO
Range mode. In Manual mode, the decision to make a
normal or low power ohms measurement should be
made before selecting the desired range.

The low power ohms measurement is not available on
the 200Ω full scale range. Open circuit voltage on this
range is below 2.8V. The standard resistance values
are listed in Table 3-2.

Ω resets the TC818A back to the Auto-

R8, a positive temperature coefficient resistor, and the

6.2V zener, Z1, provide input voltage protection during
ohms measurements.

TABLE 3-2: O HMS RANGE LADDER

NETWORK

Full-Scale

Range

200Ω 163.85Ω (R1) NO

2000Ω 1638.5kΩ (R2) YES

20kΩ 16,385Ω(R3) YES

200kΩ 163,85Ω (R4) YES

2,000kΩ 1,638,500Ω (R5) YES

Standard

Resistance

Low Power

Ohms Mode

3.4 Ratiometric Resistance
Measurements

The TC818A measures resistance ratiometrically.
Accuracy is set by the external standard resistors con­nected to Pin 35through 39. A Low Power Ohms mode
may be selected on all but the 200Ω f ull scale range.
The Low Power Ohms mode limits the voltage applied
to the measured system. This allows accurate “in­circuit” measurements when a resistor is shunted by
semiconductor junctions.

Full auto-ranging is provided. External precision stan­dard resistorsareautomaticallyswitched to providethe
proper range.

Figure 3-2 shows a detailed block diagram of the
TC818A,configuredforratiometricresistancemeasure­ments.Duringthe signal integratephase, the reference
capacitor charges to a voltage inversely proportional to
themeasured resistance, R
conversion accuracy relies on the accuracy of the
external standard resistors.

Normally, the required accuracy of the standard resis-

Ω

tanceswillbedictatedby the accuracy specificationsof
the users end product. Table 3-3 gives the equivalent
ohms per count for various f ull scale ranges to allow
users to judge the required resistor for accuracy.

TABLE 3-3: REFERENCE RESISTORS

Full Scale

Range

200k 163.85 0.1

2k 1638.5 1

20k 16385 10

200k 163,850 100

2M 1,638,500 1000

Reference Resistor Ω/Count

.Figure 3-3 shows that the

X

DS21475B-page 8



2002 Microchip TechnologyInc.