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.

TC818A

Ω

FIGURE 3-2: RATIOMETRIC RESISTANCE MEASUREMENT FUNCTIONAL DIAGRAM

9V

V

SS

57

R8

220Ω

(PTC)

R

R5/1638500

÷10k

X

Unknown

R4/163850

R3/16385

R2/1638.5

R1/163.85

÷10

÷100

÷1k

C

0.1µF

R6/100kΩ

R7/100kΩ

Ω

Ω

÷1

REF

39

38

Ω

37

Ω

36

Ω

35

33

32

31

50

V •

S18

S21

S12

1

•

INT • ( + DC)

1

DE

S29

10k

Ω

TC818A

VA

Voltage

DE + Ω

Ohms

HI

•

Low Ohms

• LO

Ω

•

V

+

–

S37

Ω

Ω

ΩΩ

CC

S35

ΩΩ

1.5kΩ~

1.5kΩ

~

-2.6V

V

CC

Integrator Comparator

S30

S31

S32

S33

÷1÷10÷100÷1k÷10k

S28S27S26S25S24

Ω

DE S23

•

DE

DE

Ω

•

S13

•

Ω

Reference

≈ VCC -2.8V

S19DES20

Buffer

S36

S34

V

CC

28

REFHI
34

29

Analog

Common

+

R18
24k

5kΩ

RVIBUF

150kΩ

220k

49

C

AZ

0.1µF

C

INT

Ω

0.1µF

RΩBUF

5554

FIGURE 3-3: RESISTANCE MEASUR EMENT ACCURACY SET BY EXTERNAL

R

163.85kΩ

Unknown

STANDARD RESISTOR

Example: 200kΩ Full Scale Measurement

0.64V for Ohms

VA =

0.32V for LO Ohms

S

C

REF

+

V

R

(a )

(b)

V

R

V

X

100kΩ

(c) “Ramp Up Voltage” = “Ramp Down Voltage”

220

Ω

V

To Analog Buffer

R

X

X

Where:
R

= Integrating Resistor, TI= I ntegrate Time

I

C

= Integrating Capacitor, T

I

(d) R

= 163.85

X

Independentof RI,CIor Internal Voltage Reference

163.85kΩ



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



163.85 220 R

++



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



163.85kΩ 220Ω R

.

V

X

---------------- x T

..

RIC

()

(TDE)

T

I

x0.64=

X

R

X

++

V

X

=

---------------- T

I

RIC

I

()

DE =

X

I

47

x0.64=

DE

De-integrate Time



2002 Microchip TechnologyInc. DS21475B-page 9

TC818A

3.5 Voltage Measurement

Resistivedividersare automaticallychangedto provide
in range readings for 200mV to 2000V full scale read­ings (Figure 3-1). The input resistance is set by exter­nal resistorsR14/R13.The dividerleg resistorsare R9­R12. The divider leg resistors give a 200mV signal V
(Pin 44) for full scale voltages from 200mV to 2000V.

For applications which do not require a 10mΩ input
impedance, the divider network impedances may be
lowered. This wi ll reduce voltage offset errors induced
by switch leakage currents.

3.6 Current Measurement

The TC818A measures current only under manual
range operation. The two user selectable, full scale
ranges are: 20mA
surement mode by holding the I
digital ground potential. The OHM
floating or tied to the positive supply.

Tworanges ar e possible. The 20mA
selectedby connectingthe 20mA
ground. If left floating, the 200mA full scale range is
selected.

External current-to-voltage conversion resistors are
used at the current input (I
measurements, a 10Ω r esistor is used. The 200mA
range requires a 1Ω resistor; full scale is 200mV.

Printed circuit board trace resistance between analog
common and R16 must be minimized. In the 200mA
range,for example,a 0.05 trace resistance will cause a
5% current-to-voltage conversion error at I

The extended resolutionmeasurementoption operates
during current measurements.

To minimize rollover error, the potential difference
between analog common (COM, Pin 29) and system
commonmustbeminimized.

and 200mA. Select the current Mea-

input (Pin 63) LOW at

input (Pin 2) is left

full scale range is

input(Pin 3) to digital

input, Pin 45). For 20mA

I

(Pin 45).

I

The minimumAC full scale voltagerangeis 2V. The DC
full scale minimum voltageis 200mV.

AC current measurements are available on the 20mA
and 200mA full scale current ranges.

I

3.8 Conversion Timing

The TC818A analog-to-digital converter uses the con­ventional dual slope integrating conversion technique,
with an addedphase that automatically eliminates zero
offset errors. The TC818A gives a zero reading with a
0 volt input.

The TC818A is designed to operate with a low cost,
readilyavailable32.768kHzcrystal. It serves as a time­base oscillator crystal in many digital clocks. (See
External Crystal Sources.)

The external clock is divided by two. The internal clock
frequency is 16.348kHz, giving a clock period of

61.04µsec. The total conversion — auto-zero phase,

signal integrate and reference de-integrate — requires
8000 clock periods or 488.3msec. There are approxi­mately two complete conversionsper second.

The integration time is f ixed at 1638.5 clock periods or
100msec. This gives rejection of 50/60Hz AC line
noise.

The maximum reference de-integrate time, represent­ing a full scale analog input, is 3000 clock periods
(183.1msec) during manual extended resolution oper­ation. The 3000 counts are available in Manual mode,
extended resolution operation only. In Auto-Ranging
mode, the maximum de-integrate time is 2000 clock
periods. The 1000 clock periods are added to the auto­zero phase. An auto-ranging or manual conversion
takes 8000 clock periods. After a zero crossing is
detectedintheReferenceDe-integratemode,theauto­zero phase is entered. Figure 3-4 shows the basic
TC818A timing relationships.

3.7 AC-to-DC Measurements

In voltageand current measurements, the TC818A can
be configured for AC measurements.An on-chip oper­ational amplifier and external rectifier components per­form the AC-to-DC conversion.

When power is first applied, the TC818A enters the DC
Measurementmode.ForACmeasurements(current or
voltage), AC/DC (Pin 62) is momentarily brought LOW
to digital ground potential; t he TC818A sets up for AC
measurements, and the AC liquid crystal display
annunciator activates. Toggling AC/DC LOW again
returns the TC818A to DC operation.

If the Manual Operating mode has been selected, tog­gling AC/DC resets the TC818A back to the Auto­Range mode. In Manual mode operation, AC or DC
should be selected first, then t he desired range.

DS21475B-page 10



2002 Microchip TechnologyInc.

FIGURE 3-4: BASIC TC818A CONVERS I ON TIMING

TC818A

REF
DEINT
Phase

*Max.

P

3000t

P

t

DE

µ

To
Input
Signal

P

Next Conversion
Auto-Zero Cycle

Extended Resolution
Zero Crossing

P

t

CONV

Signal

INT

Phase

Fixed

1638.5t

t

I

= 8000t

TC818A

Auto-Zero

Phase

Min. Auto-Zero

Time

3361.5t

P

*In Auto-Range Operation, Maximum
is 2000t

and minimum Auto-Zero Time is 4361.5t

P

3.9 Manual Range S election

The TC818A voltage and resistance auto-ranging fea­ture can be disabled by momentarily bringing RANGE
(Pin 59) to digital ground potential (Pin 58). When the
change from auto-to-manual ranging occurs, the first
manual range selected is the last range in the Auto­Ranging mode.

The TC818A power-up circuit initially selects auto­range operation. Once the manual r ange option is
entered, range changes are made by momentarily
grounding the RANG E
remains in the ManualRange mode until the measure­ment f unction (voltage or resistance), or measurement
option (AC/DC, Ω/LO
TC818A to return to auto-rangingoperation.

The “ Auto” LCD annunciator driver is active only in the
Auto-Range mode.

Figure 3-5 shows typical operation where the manual
range selection option is used. Also shown is the
extended resolutiondisplay format.Also, see Figure 3-6
and Figure 3-7.

control input. The TC818A

Ω) changes. This causes the

External Crystal = 32.768kHz
Internal Clock Period = t

Total Conversion Time = t
= 488.3msec ≈ 2 conv/sec

Integration Time = T

Maximum Reference De-integrate Time
= t
(manual extended resolution)

= 2000(t

Maximum Auto-Zero Time
= (8000 - 3000 - 1638.5)
(t

= (8000 - 3000 - 1638.5)
(t

3000(tP) = 183.1msec

DE

) = 205.1msec (manual extended resolution)

P

) = 205.1msec (manual extended resolution)

P

= 2/32.768 = 61.04µsec

P

= 8000(tP)

CONV

= 1638.5(tP) = 100msec

I

) = 122.1msec (auto-range)

P

FIGURE 3-5: MANUAL RANGE

SELECTION RES I STANCE
MEASUREMENTS

Manual

Range

Continuity

Indicator

Output 4kHz

Audio

Frequency

Continuous

4kHz Buzzer

*Mode also operates when Auto-Ranging Operator is selected
and 2MΩ < R

Yes

< 2.999MΩ.

X

Select

Is
< 19

R

X

?

No

Is

RX > 3000

?

No

Is

RX > 2000

?

No

Display

True

Reading

Over Range

Indicator

Yes

Yes*

Display
"1" 000

"1" = > Flashing

Display Last
3 Digits and

Flash MSD

Extended Resolution

Feature

MSD



2002 Microchip TechnologyInc. DS21475B-page 11

TC818A

FIGURE 3-6: MANUAL RANGE

SELECTION CURRENT
MEASUREMENTS

Range

Select

Noncontinuous

Is

> 3000

I

X

?

No

Is

IX > 2000

?

No

Display

True

Reading

Yes

Yes

Yes

Output 4kHz

Audio

Frequency

Over Range

Indicator

Display
"1" 000

"1" = > Flashing

MSD

Display Last

3 Digits and

Flash MSD

FIGURE 3-7: M ANUAL RANGE

SELECTION VOLTAGE
MEASUREMENTS

Range

Select

Noncontinuous

Output 4kHz

Audio

Frequency

Over Range

Indicator

Is

VX > 3000

?

No

Is

VX > 2000

?

No

Display

True

Reading

Yes

Yes

Display
"1" 000

"1" = > Flashing

MSD

Display Last

3 Digits and

Flash MSD

Extended

Resolution

Feature

3.10 Extended Re solution Manual
Operation

When operated in the Manual Range mode, the
TC818A extends r esolution by 50% for current, volt­age, and resistance measurements. Resolution
increases to 3000 counts from 2000 counts. The
extended resolution feature operates only in t he
2000kΩ and 2000V ranges during auto-range
operation.

In the Extended Resolution Operating mode, readings
above 1999 are displayed with a blinking “1” most sig­nificant digit. The blinking “1” should be interpreted as
the digit 2. The three least significantdigitsdisplaydata
normally. The bar graph LCD will be fully extended.

An input over range condition causes the most signifi­cant digit ( MSD) to blink and sets the three least signif­icant digits (LSDs) to display “000.” The buzzer output
is enabled for input voltage and current signals with
readings greater than 2000 counts in both manual and
auto-range operations.

For resistance measurements, the buzzer signal does
not indicate an over range condition. The buzzer is
used to indicate continuity. Continuity is defined as a
resistance reading less than 19 counts.

DS21475B-page 12



2002 Microchip TechnologyInc.

TC818A

3.11 -MEM Operating Mode

Bringing -MEM (Pin 61) momentarily LOW configures
the TC818A “-MEM” Operating mode. The -MEM LCD
annunciator becomes active. I n this Operating mode,
subsequent measurements are made relative to the
lasttwodigits(≤99) displayedatthe time MEM is LOW.
Thisrepresents5%offullscale.Thelasttwosignificant
digits are stored and subtracted from all t he following
input conversions.

The f ollowing examples clarify operation:

EXAMPLE 3-1: IN AUTO-RANGING

RI(N) = 18.21kΩ (20kΩ Range)= ≥ Display 18.21kΩ
MEM

R

R

EXAMPLE 3-2: IN FIXED RANGE

RI(N) = 18.21kΩ = ≥ Display 18.2kΩ
MEM

R

R

EXAMPLE 3-3: IN FIXED RANGE 20V

VI(N) = 0.51V = ≥ Display 0.51V
MEM

V

V

V

On power-up, the “-MEM” mode is not active.Once the
“-MEM” is entered, bringing MEM
the TC818A to normal operation.

The “-MEM”modeisalso cancelledwheneverthe mea­surement type (resistance, voltage, current AC
Ω/LO
ator will be off in normal operation.

In the auto-rangeoperation,if the following input signal
cannot be converted on the same range as the stored
value, the “-MEM” mode is cancelled. The LCD annun­ciator is turned OFF.

= ≥ Store 0.21kΩ

(N+1)= 19.87kΩ (20kΩ Range)

I

= ≥ Display 19.87 - 0.21 = 19.66kΩ

(N+2)= 22.65kΩ (200kΩ R ange)

I

= ≥ Display 22.7kΩ and MEM

disappears

(200 FULL SCALE)

= ≥ Store 8.2Ω

(N+1) = 36.7Ω

I

= ≥ Display 36.7- 8.2 = 28.5Ω

(N+2) = 5.8Ω

I

= ≥ Display 5.8-8.2 = -2.4Ω*

*Will display minus resistance if following input is less than

offset stored at fixed range.

FULL SCALE

= ≥ Store 0.51V

(N+1) = 3.68V

I

= ≥ Display 3.68 - 0.51 = 3.17V

(N+2) = 0.23V

I

= ≥ Display 0.23 -0.51= -0.28V

(N+3) = -5.21V

I

= ≥ Display - 5.21 - 0.51 = -5.72V

LOW again returns

/DC,

Ω) or range is changed. The LCD -MEM annunci-

The “-MEM” Operating mode can be very useful in
resistance measurementswhen lead length resistance
would cause measurement errors.

3.12 Automatic Range Selection
Operation

When power is f irst applied, the TC818A enters the
auto-range operating state. The Auto-Range mode
may be entered from Manual mode by changing the
measurement function (resistance or voltage), or by
changing the measurement option (AC

The automatic voltage range selection begins on t he
most sensitive scale first: 200mV for DC or 2V for AC
measurements. The voltage range selection flow chart
is shown in Figure 3-8.

Internalinputpr otection diodestoV
(Pin 57) clamp the input voltage. The external 10MΩ
input resistance (see R14 and R13 of Functional dia­gram) limits current safely in an over range condition.

The voltage range selection is designed to maximize
resolution. For input signals less t han 9% of full scale
(count reading <180), the next most sensitive range is
selected.

An over range voltage input condition is flagged when­ever the internalcount exceeds 2000, by activating t he
buzzer output (Pin 4). This 4kHz signal can directly
drive a piezo electric acoustic transducer. An out of
range input signal causes the 4kHz signal to be on for
122msec, off f or 122msec, on for 122msec and off for
610msec (see Figure 3-14).

Duringvoltageauto-rangeoperation, the extended res­olution feature operates on the 2000V range only (see
Extended Resolution Operating mode discussion).

The r esistance automatic range selection procedure is
shown in Figure 3-9. The 200Ω range is the first range
selected, unless the LOW ohms resistance measure­ment option is selected. In LOW ohms operation, the
first full scale range tried is 2kΩ.

The r esistance range selected maximizessensitivity. If
the conversion results in a reading less than 180, the
next most sensitive full scale range is tried.

If the conversion is less than 19 in auto-range opera­tion, a continuous 4kHz signal is output at BUZ (Pin 4).
An over range input does not activate the buzzer.

Out-of-range input conditions are displayed by a blink­ing MSD with the three LSDs set to “000.”

The extended resolution feature operates only on the
2000kΩ and 2000V full scale range during auto-range
operation. A blinking “1” most significant digit is inter­preted as the digit 2. The three least significant digits
display data normally.

/DC, Ω/LOΩ).

(Pin28)andV

CC

SS



2002 Microchip TechnologyInc. DS21475B-page 13

TC818A

g

FIGURE 3-8: AUTO-RANGE

OPERATION: VOLTAGE
MEASUREMENT

N = N +1

N = 0 If DC
N = 1 If AC

Conversion

VX = (1/10N) V

VX > 2000

No

V

Flash MSD

Kth

< 180

V

X

?

N = 4

?

> 3000

X

?

Display
"1" 000

?

N = 0; 200mV Full Scale Range
N = 1; 2V Full Scale Range

N = N

K

(Remain in Range
Selected during the Kth
Conversion)

IN

Yes

N = N –1

N = 0 If DC

N = 1 If AC

No

No

Display

Voltage (V)

Yes

K = K +1

Yes

No

Yes

?

Flash MSD

Over Range

Yes

X

Extended

Resolution

Display

"1" XXX

Activate

Buzzer

FIGURE 3-9: AUTO-RANGE

OPERATION:RESISTANCE
MEASUREMENT

N = 0 If Ω

N = 1 If LOΩ

Conversion

RX = R

Continuity

Indicator

Activate

Continuous

4kHz Signal

Start: Power-on, Function or Measurement Option Chan

Buzzer

N = N +1

Yes

No

R

RX < 180

R

X

R

X

N = 0; 200Ω Full Scale Range
N = 1; 2kΩ Full Scale Range

Kth

1

IN

N

10

< 19

X

?

No

Yes

?

No

> 2000

?

Yes

N = 4

?

Yes

> 3000

No

?

Extended Resolution

Yes

(Remain in Range
Selected during the
Kth Conversion)

N = N –1

No

N = 0 If Ω

N = 1 If LOΩ

?

Yes

Display

Resistance

Display

"1" XXX

Flash MSD

K = K +1

Flash MSD

e

Display
"1" 000

Over

Range

Start: Power-on, Function or Measurement Option Change

DS21475B-page 14



2002 Microchip TechnologyInc.

TC818A

3.13 Low Battery Detection Circuit

The TC818A containsa low battery detector. When t he
9V battery supply has been depleted to a 7V nominal
value, the LCD low battery annunciatoris activated.

The low battery det ector is shown in Figure 3-10. The
low battery annunciator remains OFF with the battery
supplygreaterthan0.7V.TheannunciatorisONbefore
the supply battery has reached 6.3V.

FIGURE 3-10: LOW BATTERY

DETECTOR

V

CC

R

R

Low Battery Annunciator Displayed for V

1

V

T

R

2

V

SS

Low Battery Detector

Comparator

+

3

–

VZ ≈ 6.2V

= 73 = 6.2V

V

T

R1 + R

TC818A

To LCD
Annunciator
Selection Logic

R

2

2

S

< 7V.

3.14 Triplex Liquid Crystal Display
(LCD) Drive

The TC818A directly drives a triplexed liquid crystal
display (LCD) using 1/3 bias drive. All numeric data,
decimal point, polarity and function annunciator drive
signals are developed by the TC818A.

The LCDs must be driven with an AC signal having
zero DC component, for long display life. The liquid
crystal polarization is a function of the RMS voltage
appearing across the backplane and segment driver.
The peak drive signal applied to the LCD is:

V

CC-VDISP

For example, if V
V

, the peak drive signal is:

CC

An “OFF” LCD segment has an RM S voltage of V
across it, or 1 volt. An “ON” segment has a 0.63V
signal across it or 1.92V for VCC-V

Since the V

DISP

the “ON” and “ OFF” LCD levels for various manufactur­ers’ displays, by changing V
for V

DISP

=3V.

“OFF”segmentsmaybecomevisibleathighLCDoper­ating temperatures. A voltage with a -5 to -20mV/°C
temperature coefficient can be applied to V
accommodate the liquid crystal temperature operating
characteristics, if necessary.

is set at a potential 3V below

DISP

V

P=VCC-VDISP

=3V

DISP

=3V.

pin is available, the user may adjust

signal across it, or 1.92V

P

DISP

/3

P

to

The TC818A internally generates two intermediate
LCD drive potentials (V
divider(Figure3-11) betweenV

and VL) from a resistive

H

CC

and V

.The latter

DISP

impedance is approximately150kΩ. This drive method
is commonly known as 1/3 bias. With V
to digital ground, V

≈ 5.0V.

P

DISP

connected

The intermediate levels are needed so that drive sig­nals giving RMS “ON” and “OFF” levels can be gener­ated. Figure 3-12 shows a typical drive signal and the
resulting waveforms for “ON” and “OFF” RMS voltage
levels across a selected LCD element.

FIGURE 3-11: 1/3 BIAS LCD DRIVE

V

CC

50k

V

H

To

Triplex

Segment

Drive Logic

VP = VCC - V

"OFF" = V

"ON" = VP RMS

V

L

TC818A

11

3

3

DISP

/3 RMS

P

50k

See V

DSIP

For Proper V

50k

with Resistive
Divider

V

P

DISP

3.15 Liquid Crystal Displays (LCDs)

Most users will design their own custom LCD. How­ever, for prototyping purposes, a standard display is
available from Varitronix, Ltd. This prototype display
configurationis shown in Figure 3-13 and Table 3-4.

Varitronix Ltd.
9/F Liven House, 61-63, King Yip Street
Kwun Tong, Hong Kong
Tel: [phone]
Fax: [phone]

P

Part No.: VIM-328-DP

USA Office:

VL Electronics, Inc.
3171 LOs Feliz Blvd, #303
Los Angeles, CA 90039
Tel: [phone]



2002 Microchip TechnologyInc. DS21475B-page 15

TC818A

FIGURE 3-12: TRIPLEX LCD DRIVE WAVEFORMS

TC818A

Backplanes

123456

VP (3V)

BP1

V

P

V

H

V

L

BP2

BP3

0

V

P

V

H

V

L

0

Waveforms to Generate

f

e

FE AGD BCP

a

b

BP1

g

BP2

c

d

BACKPLANES

BP3

Segments

a (FE – BP1)

"ON"

b (BCP – BP1)

"ON"

c (BCP – BP2)

"ON"

d (AGD – BP3)

"ON"

e (FE – BP2)

"OFF"

f (FE – BP1)

"OFF"

g (AGD – BP2)

"ON"

Segments

V

P

V

H

0

1 23456

-V

L

-V

H

-V

P

V

P

V

H

V

L

0

-V

L

-V

H

-V

P

V

P

V

H

V

L

0

-V

L

-V

H

-V

P

V

P

V

H

V

L

0

-V

L

-V

P

V

P

V

H

V

L

0

-V

L

-V

P

V

P

V

H

V

L

-V

L

-V

P

V

P

V

H

V

L

0

-V

L

-V

H

-V

P

Applied
RMS Voltage

=

V

RMS

3

V

=

RMS

3

V

=

RMS

3

V

=

RMS

3

V

=

RMS

V

=

RMS

V

=

RMS

3

11

V

P

3

11

V

P

3

11

V

P

3

11

V

P

3

V

P

3

V

P

3

11

V

P

3

DS21475B-page 16



2002 Microchip TechnologyInc.

TC818A

3.16 External Crystal

The TC818A i s designed to operate wi th a 32,768Hz
crystal. This frequency is internally divided by two to
give a 61.04µsec clock period. One conversion takes
8000 clock periods or 488.3msec ( ≈ 2 conversions/
second). Integration time is 1638.5 clock periods or
100msec.

The 32kHz quartz crystal is readily available and
inexpensive. The 32kHz crystal is commonly used in
digital clocks and counters.

Several crystal sources exist. A partial l isting is:

• Statek Corporation

512 N. Main
Orange, CA 92668
[phone]
TWX: 910-593-1355
TELEX: 67-8394

• Fox Electronics

5570 Enterprise Parkway
Fort Myers, FL 33905
[phone]

Contact manufacturer for full specifications.

FIGURE 3-13: TYPICAL LCD

CONFIGURATION,
TC818A TRIPLEX

+

-MEM

–

HOLD

AC

AUTO

WLO

Ωk

mVA

TABLE 3-4: TYPICAL LCD CONFIGURATION

PAD BP1 BP2 BP3 PAD BP1 BP2 BP3

1 — — SCALE 19 — — BP3
2X0X1X220—BP2—
3 X5 X4 X3 21 BP1 — —
4X6X7X822—LOWA
5 X11 X10X923 —WV
6 X12 X13 X14 24 HOLD k m
7 X17 X16 X15 25 4B 4C —
8 X18 X19 X20 26 4A 4G 4D
9 X23 X22 X21 27 4F 4E —

10 X24 X25 X26 28 3B 3C 3P

11 X29 X28 X27 29 3A 3G 3D
12 X30 X31 X32 30 3F 3E —
13 X35 X34 X33 31 2B 2C 2P
14 X36 X37 X38 32 2A 2G 2D
15 — X40 X39 33 2A 2G 2D
16 BPI — — 34 1B 1G 1P
17 — BP2 — 35 Z -MEM —
18 — — BP3 36 AC y AUTO



2002 Microchip TechnologyInc. DS21475B-page 17

TC818A

3.17 “Buzzer” Drive Signal

The BUZ output (Pin 4) will drive a piezo electricaudio
transducer. The signal is activated to i ndicate an input
over range condition for current and voltage measure­ments, or continuity during resistancemeasurements.

During a resistance m easurement, a reading less than
19 on any full scale range causes a continuous 4kHz
signal to be output. This is used as a continuity
indication.

A voltage or current input measurement over range is
indicated by a noncontinuous 4kHz signal at the BUZ
output. The LCD most significant digit also flashes and

Figure 3-14. The BUZ output is active f or any reading
over 2000 counts in both manual and auto-range oper­ation. The buzzer is activated during an extended res­olution measurement.

The BUZ signal swings from V
(Pin 58). The signal is at V

The BUZ output is also activated for 15ms whenever a
range change is made in auto-range or manual opera­tion. Changing the type of measurement (voltage, cur­rent, or r esistance), or measurement option (AC/DC,
Ω/LOΩ), also activates the buzzer output for 15msec.
A range change during a current measurement will not
activate the buzzer output.

the three least significant digits are set to display zero.
The buzzer drive signal for over range is shown in

FIGURE 3-14: TC818A TIMING WAVEFORM FOR BUZZER OUTPUT

Power-up

V

= 250mV

IN

4000

122ms

V

CC

Noncontinuous Buzzer Signal Indicates Input Over Range

8000 12000

122ms

1 Conversion

122ms

122ms 122ms

Change

Range

610ms

Change

Range

Digital Ground

4kHz Signal

Change

Range

(Pin 28) to DGND

CC

when not active.

CC

Change Input
V

= 3.2V

IN

Integrate

TSC818A

Signals

INT

DEINT

AZ

BUZ

(Pin 4)

1000 Clock

Pulses

100ms

1638.5
CP

122ms
2000
CP

Auto-Ranging

200mV

Range

Over Range

4kHz4kHz

One Cycle of

Over Range Buzzer

Buzzer Activated due

to Power-up

2V

Range

In Range

15ms

2V

Range

In Range

15ms

Due to Manual

Range Change

2500CP

Manual Range

200mV

Range

Extended

Range

15ms

Due to

Range Change

to Previous Conversion

2V

Range

In Range

4kHz 4kHz

122ms

Buzzer Activated due

Over Range

3000CP250CP250CP250CP

2V Range

Out of Range

610ms

Buzzer Activated

due to Previous

Conversion

Over Range

DS21475B-page 18



2002 Microchip TechnologyInc.

TC818A

Vendors for piezo electric audio transducers are:

Gulton Industries

•
Piezo Products D ivision
212 Durham Avenue
Metuchen, New Jersey 08840
[phone]
Typical P/Ns: 102-95NS, 101-FB-00

•

Taiyo Yuden (USA) Inc.

Arlington Center
714 West Algonquin Road
Arlington Heights, Illinois 60005
Typical P/Ns: CB27BB, CB20BB, CB355BB

3.18 Display Decimal Point Selection

The TC818A provides a decimal point LCD drive sig­nal. The decimal point position is a function of the
selected full scale range, as shown in Table 3-5.

TABLE 3-5: DECIMAL POINT SELECTION

Full Scale Range

2000V, 2000kΩ OFF OFF OFF
200V, 200kΩ OFF OFF ON
20V, 20kΩ OFF ON OFF
2V, 2kΩ ON OFF OF F
200V, 200Ω OFF OFF ON
200mV, 200Ω OFF OFF ON
20mA OFF ON OFF
200mA OFF OFF ON

1*9 *9 *9

DP3 DP2 DP1

3.20 Component S election

3.20.1 INTEGRATION RESISTOR
SELECTION

The TC818A automatically selects one of two external
integration resistors. RVIBUF (Pin 55) is selected for
voltage and current measurement. RΩBUF (Pin 54) is
selected for resistance measurements.

3.20.2 RVIBUF SELECTION (PIN 55)

In auto-range operation, the TC818A operates with a
200mV maximum full scale potential at V
Resistive dividers at VR2 (Pin 41), VR3 (Pin 40), VR4
(Pin 43), and VR5 (Pin 42) are automatically switched
to maintain the 200V full scale potential.

In Manual mode, the Extended Operatingmode is acti­vated,giving a 300mV full scalepotentialatV

The integrator output swing should be maximized, but
saturations must be avoided. The integrator will swing
within 0.45V of V

(Pin 28) and 0.5V of VSS(Pin 57)

CC

without saturating. A ±2V swing is suggested. The
value of RVIBUF is easilycalculated,assumingaworst
case extended resolution input signal:

Where:

V

= Integrator swing = ±2V

INT

= Integration time = 100msec

t

I

C

= Integration capacitor = 0.1µF

I

= Maximum input at VI= 300mV

V

MAX

EQUATION 3-1:

(Pin 44).

I

(Pin44).

I

3.19 AC-to-DC Converter Operational
Amplifier

The TC818A contains an on-chip operational amplifier
that may be connected as a rectifier for AC-to-DC volt­age and current measurements. Typical operational
amplifier characteristics are:

• Slew Rate: 1V/µsec

• Unity Gain Bandwidth: 0.4MHz

• Open Loop Gain: 44dB

• Output VoltageSwing (Load = 10kΩ) ± 1.5V

(Referencedto Analog Common)

When the AC measurement option is selected, t he
input buffer receives an input signal through switch
S14, rather than switch S11 (see Figure 3-1). With
external circuits, the AC Operating mode can be used
to perform other types of functions within the con­straints of the internal operational amplifier. External
circuits that perform true RMS conversion, or a peak
hold function, are typical examples.

RVIBUF =

V
V

MAX(TI
INT(CI

)

= 150kΩ

)

3.20.3 RΩBUF SELECTION (PIN 54)

In ratiometric resistance measurements, the signal at
R

(Pin 50) is always positive, with respect to analog

X

common. The integrator swings negative.
The worst case integrator swing is for the 200Ω range

with the manual, extended resolution option.
The i nput voltage, V

Figure 3-15).

(Pin 50) is easily calculated (see

X



2002 Microchip TechnologyInc. DS21475B-page 19

TC818A

FIGURE 3-15: RΩ CALCULATION (200 Ω

MANUAL OPERATION)

V

= 9V

CC

SW33

R

R

R

R

≈ 600Ω

S

163.85Ω

1

2

3

220Ω

V

X

300Ω

Analog Common = VCC – 3V

Where:

V

ANCOM

R

S

R

I

R

X

R

S

= Potential at Analog Common ≈ 2.7V
= 220Ω
= 163.85Ω
= 300Ω
= Internal switch 33 resistance≈ 600Ω

EQUATION 3-2:

RΩBUF =

CC–VANCOM)RX

(RX+RS+R1+R8)

=0.63V

(V

For a 3.1V integrator swing, the value of RΩBUF i s
easily calculated:

Where:

V
T
C
R
V

INT
I

XMAX

= Integratorswing = 3.1V
= Integrationtime = 100msec
= Integration capacitor = 0.1µF

I

=300Ω

XMAX

= 700mV

EQUATION 3-3:

XMAX(TI

I(VINT

)

= 200kΩ

)

RΩBUF =

V

C

With a low battery voltage of 6.6V , analog common will
be approximately3.6Vabove the negativesupply termi­nal. With the integrator swinging down from analog com­mon toward the negative supply, a 3.1V swing will set
the integrator output to 0.5V above the negative supply.

3.21 Capacitors - C

The integration capacitor, C

INT,CAZ

INT

and C

REF

, must have low dielec­tricabsorption. A 0.1µF polypropylene capacitoris sug­gested. The aut o-zero capacitor, C
capacitor, C

, should be selected for l ow leakage

REF

, and reference

AZ

and dielectric absorption. Polystyrene capacitors are
good choices.

3.22 Reference Voltage Adjustment

The TC818A contains a low temperature drift internal
voltage reference. The analog common potential
(Pin 29) is establishedby this reference. Maximum drift
is a low 75ppm/°C. Analog common is designed to be
approximately 2.6V below V

(Pin 28). A resistive

CC

divider (R18/R19, Functional Diagram) sets the
TC818A reference input voltage (REFHI, Pin 34) to
approximately 163.85mV.

With an input voltage near full scale on the 200mV
range, R19 is adjusted for the proper reading.

3.23 Display Hold Feature

The LCD wi ll not be updated when HOLD (Pin 60) is
connectedtoGND(Pin58).Conversionsare made, but
the displayis not updated. A HOLD
ciator is activated when HOLD

The LCD HOLD

annunciator is activated through the

mode LCD annun-

is low.

triplex LCD driver signal at Pin 13.

3.24 Flat Package Socket

Sockets suitable for prototype work are available. A
USA source is:

• Nepenthe Distribution

2471 East Bayshore, Suite 520
Palo Alto, CA 94303
[phone]
TWX: 910-373-2060
“CBQ” Socket, Part No. IC51-064-042

3.25 Resistive Ladder Networks

Resistorattenuatornetworks for voltageandresistance
measurements are available from:

• Caddock Electronics

1717 Chicago Avenue
Riverside, CA 92507
Tel: [phone]
TWX: 910-332-6108

TABLE 3-6: RES I STIVE L ADDE R

NETWORKS

Attenuator

Accuracy

Attenuator Type

0.1% Voltage 1776-C441

0.25% Voltage 1776-C44

0.25% Resistance T1794-204-1

Caddock

Part Number

DS21475B-page 20



2002 Microchip TechnologyInc.

4.0 PACKAGING INFORMATION

)

4.1 Package Marking Information

Package marking data not available at this time.

4.2 Taping Form

Component Taping Orientation for 64-Pin PQFP Devices

User Direction of Feed

TC818A

PIN 1

W

Carrier Tape, Number of Components Per Reel and Reel Size

Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size

64-Pin PQFP 32 mm 24 mm 250 13 in

Note: Drawing does not represent total number of pins.

4.3 Package Dimensions

64-Pin PQFP

PIN 1

.018 (0.45)
.012 (0.30)

.031 (0.80) TYP.

Standard Reel Component Orientation
for TR Suffix Device

.555 (14.10)
.547 (13.90)

.687 (17.45)
.667 (16.95)

P

.555 (14.10)
.547 (13.90)

.687 (17.45)
.667 (16.95)

.009 (0.23)
.005 (0.13)

.130 (3.30) MAX.

7° MAX.

.041 (1.03)
.031 (0.78)

.010 (0.25) TYP.

.120 (3.05)
.100 (2.55)

Dimensions: mm (inches



2002 Microchip TechnologyInc. DS21475B-page 21

TC818A

SALES AND SUPPORT

Data Sheets

Products supportedby a preliminaryData Sheet may have an errata sheet describingminor operational differences and recom­mendedworkarounds.To determine if an errata sheetexists for a particular device, please contactone of the following:

1. Your local Microchip sales office

2. TheMicrochip Corporate Literature Center U.S. FAX:[phone]

3. The Microchip Worldwide Site (www.microchip.com)
Pleasespecify which device, revision of silicon and Data Sheet (includeLiterature#) you are using.

New Customer Notification System

Register on our web site (www.microchip.com/cn) to r eceive the most current information on our products.

DS21475B-page 22



2002 Microchip TechnologyInc.

TC818A

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,
K

EELOQ,microID,MPLAB,PIC,PICmicro,PICMASTER,

PICSTART, PRO MA TE, SEEVAL and The Embedded Control
SolutionsCompany areregiste red trademarksof MicrochipTech­nologyIncorp or ated 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 TotalEndurancearetrademarksofMicrochipTechnology
Incorporated in the U.S.A.

Serialized Quick Turn Programming (SQTP) is a service mark
of Microchip TechnologyIncorporated in t he 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
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
devices, Serial EEPROMs, microperipherals,
non-volatile memory and analog products. In
addition, Microchip’s quality system for the
design and manufacture of development
systemsisISO 9001certified.



2002 Microchip TechnologyInc. DS21475B-page 23

8-bit MCUs, KEELOQ®code hopping

WORLDWIDE SALES AND SERVICE

AMERICAS

Corporate Office

2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: [phone] Fax: [phone]
Technical Support: 480-792-7627
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03/01/02

DS21475B-page 24

*DS21475B*



2002 Microchip Technology Inc.