Microchip Technology TC815CBU Datasheet

TC815

3-1/2 Digit Auto-Ranging A/D Converter with

Triplex LCD Drive and Display Hold Function

Features

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

- TwoUser Selected AC/DC Current Ranges

20mA and 200mA

• 22 Operating Ranges

- 9 D C/AC Voltage

- 4 AC/DC Current

- 9 R esistance and Low Power Ohms

• Display HOLD Function

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

- 1/2000

• Extended Resolution in Manual Mode: 1/3000

• Memory Mode for Relative Measurements:

-±5%F.S.

• Internal AC to DC Conversion Op Amp

• Triplex LCD Drive for Decimal Points, Digits
and Annunciators

• Continuity Detection and Piezoelectric
Transducer Driver

• CompactSurface Mounted 64-pin
Plastic Flat Package

• Low Drift Internal Reference: 75ppm/°C

• 9V Battery Operation: 10mW

• Low Battery Detection and LCD Annunciator

Device Selection Table

Part Num ber Package

TC815CBU 64-PinPQFP 0°Cto+70°C

Operating

Temperature Range

General Description

The TC815 is a 3-1/2 digit integrating analog-to-digital
converter with triplex LCD display drive and automatic
ranging. A display hold function is on-chip. Input volt­age/ohm attenuators ranging from 1 to 1/10,000 are
automatically selected. Five full scale ranges are pro­vided. The CMOS TC815 contains all the logic and
analog switches needed to manufacture an auto­ranging instrument for ohms and voltage measure­ments.Userselected20mA and 200mA current ranges
are available. Full scale range and decimal point LCD
annunciators are automatically set in auto-range oper­ation. Auto-range operation is available during ohms
(high and low power ohms) and voltage ( AC and DC)
measurements, eliminating expensive range switches
in hand-held DMM designs. The auto-range feature
may be bypassed allowing decimal point selection and
input attenuator selection control through a single line
input. Expensive r otary switches are not required.

During Manual mode operation, resolution is extended
to 3000 counts full scale. The extended range opera­tion is indicated by a flashing 1 MSD. The extended
resolution is also available during 200kΩ and 2000V
full scale auto-range operation.

The Memory mode subtracts a reading, up to ±5% of
full scale from subsequent measurements. Typical
applicationsinvolve probe resistancecompensationfor
resistance measurements, tolerance measurements,
and tare weight measurements.

The TC815 includes an AC to DC converter for
AC measurements. Only external diodes/resistors/
capacitors are required.

A complete LCD annunciator set describes the TC815
meter function and measurement range during ohms,
voltage and current operation. AC measurements are
indicatedaswellasauto-rangeoperation.A low battery
detection circuit also sets the l ow battery display
annunciator. The triplex LCD display dr ive levels may
be set and temperature compensation applied via the
V

pin. With HOLD low, the display is not updated.

DISP

A HOLD mode LCD annunciator is activated.
The “low ohms” measurement option allows in-circuit

resistance measurements by preventing semiconduc­tor junctions from being forward biased.



2002 Microchip TechnologyInc. DS21474B-page 1

TC815

A continuity buzzer output i s activated with inputs less
than 1% of full scale. An overrange input signal also
enablesthe buzzer,exceptduringresistance measure­ments, and flashes the MSD display.

Package Type

64-Pin PQFP

RANGE

-MEM

NC

OHM

20mA

BUZ

XTAL1

XTAL2

V

DISP

BP1

BP2

BP3

LOΩ/A

Ω/V

k/m/

HOLD

BCP0

AGD0

FE0

I

NC

DC/AC

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

NC

BCP1

Ω/LOWΩ

61

AGD1

FE1

HOLD

BCP2

TC815

AGD2

DGND

24 25 26 27 28 29 3018 19 20 21 22 23 3217

FE2

SSA

ACVH

V

BCP3

AC/–/AUTO

Featuring single 9V battery operation, 10mW power
consumption, a precision internal voltage reference
(75ppm/°C max TC) and a compact surface mounted
64-pin quad flat package, the TC815 is ideal for porta­ble instruments.

X

AZ

R

CFI

AD1

AD0

RΩBUF

RVIBUF

CC

SSD

V

V

-MEM/BATT

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

ANALOG COM

31

REFH

RM

REFL

RM

C

REFL

C

NC

48

47

C

I

46

ACVL

45

I

I

V

44

I

43

VR4

42

VR5

41

VR2

40

VR3

39

ΩR5

38

ΩR4

37

ΩR3

36

ΩR2

35

ΩR1

34

REFHI

33

C

REFH

DS21474B-page 2



2002 Microchip TechnologyInc.

Typical Application and Test Circuit

TC815

Tri-Plex

LCD Display

HOLD LO

– +

-MEM

kΩ

AC

mVA

EnableAudio

AUTO

32.768kHz

( 33kHz)

6

Transducer

54

XTAL1BUZ

BCP3 BCP2FE2 AGD2 BCP1FE1 AGD1 BCP0FE0 AGD0

26 24 23 22 21 20 19 18 16 15 14

-MEM/

V K/m

Ω

/A

1150 7 8 9 10 12 13 25

Ω

39pf

9V

+ –

57

28

CC

SSA

V

V

XTAL2

1's10's100's

Segment & Decimal Point Drive

1000's

BATT

AC/–/AUTO

HOLD

Display

Annunciators

27

V

SSD

V

58

Digital GND

SIA

Ω

SIB

20mA

3

20mA

V

Ω

200mA

2

OHMS

20mA

63

I

200mA

TC815

with HOLD Function

3-1/2 Digit Auto-Ranging DMM

30

61

59

62

REFH

-MEM
RM

ANALOG

DC/AC or Ω/LOWΩ

Manual RANGE Change

REFHI

COM

REFH

C

REFL

INT HOLD CIF C

AZ

BUF RVIBUF C

Ω

ADI ACVH ACVL R

CC

To V

153.850mV

R19/5kΩ R18/24kΩ

REF

C

0.1µF

R20

100

kΩ

INT

0.1µF0.1µF

C

AZ

C

150

kΩ

200

kΩ

C1/1µF

C2/0.22µF

C6

0.01µF

RΩBUF RVIBUF

R26/3kΩ

R27/2kΩ

C4/µf

– +

R23/10kΩ

R22/470kΩ

R21/2.2MΩ

Drivers

Backplane

Ohms Range Attenuator

LCD Bias

0.1µF

Peak Drive Signal ≈ 5V.

If LCD Bias is Connected to DIG GND,



2002 Microchip TechnologyInc. DS21474B-page 3

RX VDISP BP1 BP2 BP3 LO

RMREFL

ΩR5 (÷ 10,000)

ΩR4 (÷ 1,000)

ΩR3 (÷ 100)

38

31

39

R6/100kΩ

R7/100kΩ

0.01

R8/220Ω (PTC)

µF

R5/1.6385MΩ

Ohms

Input

Positive

36

R2/1638.5Ω

R4/163.85kΩ37R3/16.385kΩ

Z1

Resistor

Coefficient

Temperature

ΩR2 (÷ 10)

R1 (÷ 1)

35

R1/163.85

6.2V

I

I

45

20mA

Input

Current

D3 D4

R15

9Ω

1Ω

R16

200mA

(÷1)

I

V

444140

R13

500kΩ

R14/9.9MΩ

Input

Voltage

(÷10)

R2

V

R12/1.11MΩ

ADO

Voltage Range Attenuator

42 53 52 56 46 54 55 49 47 60 51 32 33 29 34

(÷100)

(÷1,000)

(÷10,000)

R3

R4

R5

V

V

V

43

R10/10kΩ

R11/101kΩ

4.7µf

R9/1kΩ

Common

D2

– +

C5/1µf

R24/10kΩ

D1

*Not Required when Resistor Network is used.

TC815

1.0 ELECTRICAL
CHARACTERISTICS

Absolute Maximum Ratings*

Supply Voltage (V+ to V–) .....................................15V

Analog Input Voltage (Either Input) ................V+ to V-

*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 f or
extended periods may affectdevice reliability.

Reference Input Voltage.................................. V+ to V-

Voltage at Pin 45 ........................................GND ±0.7V

Power Dissipation (T

≤ 70°C)

A

64-Pin Plastic Flat Package ...........................1.14W

Operating Temperature Range:

Commercial Package (C) ....................0°C to +70°C

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

TC815 ELECTRICAL SPECIFICATIONS

Electrical Characteristics: VA=9V,TA= +25°C, unless otherwise specified(see TypicalApplication and Test CircuitFigure).

Symbol Parameter Min Typ Max Unit Test Conditions

Zero Input Reading Input Resistor -0000 0000 +0000 Digital Reading 200mV Range w/o 10MΩ Input

-0001 — +0001 Digital Reading 200mV Range w/10MΩ Input

-0000 0000 +0000 Digital Reading 20mA and 200mA Range

RE RolloverError — — ±1 Count 200mV Rangew/o 10MΩ

— — ±3 200mV Rangew/10MΩ Input

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

V
V

V

IN

N

COM
CTC

IL

Input Leakage Current — — 10 pA
Input Noise — 20 — µV
AC Frequency Error — ±1 — % 40Hz to 500Hz

— ±5 — % 40Hz to 200Hz

Open Circuit Voltage — 570 660 mV Excludes 200Ω Range

Open Circuit Voltage — 285 350 mV Excludes 200Ω Range

Analog Common Voltage 2.5 2.6 3.3 V (V+-V
CommonVoltage Temperature

Coefficient
Display Multiplex Rate — 100 — Hz
Low Logic Input — — 1 V 20mA,AC,I,LOWΩ,HOLD

Logic 1 Pull-up Current — 25 — µA20mA

Buzzer Drive Frequency — 4 — kHz
Low Battery Flag Voltage 6.3 6.6 7.0 V V
Operating Supply Current — 0.8 1.5 mA

— — 50 ppm/°C

p-p

Input Resistor

BW = 0.1 to 10Hz

for OHM Measurements

for LO OHM Measurement

)

COM

Range, -MEM, OHMs
(Relative to DGND Pin 58)

,AC,I,LOWΩ,HOLD
Range, -MEM, OHMs
(Relative to DGND Pin 58)

to V

CC

SSA

DS21474B-page 4



2002 Microchip TechnologyInc.

2.0 PIN DESCRIPTIONS

ThedescriptionsofthepinsarelistedinTable2-1.

TABLE 2-1: PIN FUNCTION TABLE

Pin Number

(64-Pin Plastic)

Quad Flat Package

1 NC Logic Input. “0” (Digital Ground) for resistance measurement.
2OHM
320mA
4 BUZ Audio frequency, 4kHz, output for continuity indication during resistance measurement. A

5 XTAL1 32.768kHz Crystal Connection.
6 XTAL2 32.768kHz Crystal Connection.
7V

8 BP1 LCD Backplane#1.

9 BP2 LCD Backplane#2.
10 BP3 LCD Backplane #3.
11 LOΩ/A LCD Annunciator segment drive for low ohms resistancemeasurement and current

12 Ω/V LCD Annunciator segmentdriveforresistancemeasurement and voltagemeasurement.
13 k/m/HOLD LCD Annunciator segmentdrivefork (“kilo-ohms”), m (“milliamps” and

14 BCP0

15 ADG0 LCD segment drive for “a,” “g,” “d” segmentsof LSD.
16 FE0 LCD segment drive for “f” and “e” segments of LSD.
17 NC Noconnection.
18 BCP1 LCD segmentdrivefor“b,” “c” segments and decimal point of 2nd LSD.
19 AGD1 LCD segment drive for “a,” “g,” “d” segmentsof 2nd LSD (Ten’s digit).
20 FE1 LCD segment drive for “f” and “e” segments of 2nd LSD.
21 BCP2 LCD segmentdrivefor“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 “b,” “c” segments and decimalpointof3rd LSD.
24 BCP3 LCD segmentdrivefor“b,” “c” segments and decimal point of MSD

25 AC/-/AUTO LCD annunciator drive signal for AC measurements, polarity, and auto-range operation.
26 -MEM/BATT LCD annunciator drive signal for low battery indication and Memory

27 V

28 V
29 ANALOG

30 RM
31 RM
32 C
33 C
34 REFHI Reference voltage for voltageandcurrentmeasurement;nominally 163.85mV.

Symbol Description

Logic Input. “0” (Digital Ground) for 20mA full scale current measurement.
Audio frequency, 4kHz, output for continuity indication during resistance measurement.

non-continuous 4kHz signal is output to indicate an input overrange during voltageor
current measurements.

DISP

(One’s digit)

SSD

CC

COM

REFH

REFL

REFL

REFH

Setspeak LCD drive signal: VP-VDD-V
temperature variation of LCD crystal threshold voltage.

measurement.

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

(Hundred’sdigit).

(Thousand’sdigit).

(Relative Measurement) mode.
Negative battery supplyconnection for internaldigital circuits. Connect to negativeterminal

of battery.
Positive battery supply connection.
Analogcircuit ground reference point. Nominally 2.6V below V

Ratiometric (Resistance measurement) referencehigh voltage.
Ratiometric (Resistance measurement) reference low voltage.
Reference capacitor negative terminal C
Reference capacitor positive terminal C

DISP.VDISP

0.1µf.

REF

0.1µf.

REF

TC815

mayalsobeusedtocompensatefor

.

CC



2002 Microchip TechnologyInc. DS21474B-page 5

TC815

TABLE 2-1: PIN FUNCTION TABLE (CONT INUED)

Pin Number

(64-Pin Plastic)

Quad Flat Package

35 ΩR1 Standard resistorconnection for 200Ω full scale.
36 ΩR2 Standard resistorconnection for 2000Ω full scale.
37 ΩR3 Standard resistorconnection for 20kΩ full scale range.
38 ΩR4 Standard resistorconnection for 200kΩ full scale range.
39 ΩR5 Standard resistor connection for 2000kΩ full scale range.
40 VR3 Voltage measurement ÷ 100 attenuator.
41 VR2 Voltage measurement ÷ 10 attenuator.
42 VR5 Voltage measurement ÷ 10,000attenuator.
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 AD1 Negative input of internal AC to DC operational amplifier.
53 AD0 Output of internal AC to DC operational amplifier.
54 RΩBUF Activebuffer output for resistance measurement.Integration resistor connection. Integrator

55 RVIBUF Active buffer output for voltage and current measurement. Integration resistorconnection.

56 ACVH Positive output of AC to DC converter.
57 V
58 DGND
59 RANGE
60 HOLD
61 -MEM Input to enter Memory Measurement mode for relative measurements. The two LSD’s are

62 DS/AC

63 I

64 NC No connection.

Symbol Description

Unknown voltage input ÷ 1 attenuator.

I

I

AZ

X

SSA

Ω/LOWΩ

Unknown current input.

Integratorcapacitor connection. Nominally 0.1µf. (Lowdielectric absorption.Polypropylene

I

dielectrics suggested.)

Auto-zero capacitor connection; nominally 0.1µf.
Unknown resistanceinput.

resistor nominally220kΩ.

Integration resistor nominally 150kΩ.

Negative supply connection for analog circuits. Connect to negative terminal of 9V battery.
Internal logic digital ground. The logic “0” level.Nominally 4.7V belowVCC.
Input to set manual operation and change ranges.
Inputto hold display. Connect to DIG GND.

stored and subtracted from future measurements.
Input that selects AC or DC option during voltage/current measurements. For resistance

measurements, Ω/LOWΩ, the ohms or low power (voltage) ohms option can be selected.
Inputto selectcurrent measurement. Set to logic “0” (Digitalground) for

current measurement

DS21474B-page 6



2002 Microchip TechnologyInc.

TC815

3.0 DETAILED DESCRIPTION

3.1 Resistance, Voltage, Current
Measurement Selection

The TC815 is designed to measure voltage, current,
and resistance.Auto-rangingisavailableforresistance
and voltage measurements. The OHMS
I

(Pin63) input controls are normally pulled internally to

V

By tying these pins to Digital Ground (Pin 58), the

CC.

TC815 is configured internally to measure resistance,
voltage, or current. The required signal combinations
are shown in Table 3-1.

TABLE 3-1: MEASUREMENT SELECTION

LOGIC

Function Select Pin

OHM (Pin 2) I

0 0 Voltage
0 1 Resistance
1 0 Current
1 1 Voltage

Note 1: 0=DigitalGround

2: 1 = Floating or Tied to V
3: OHM and I are normally pulled internally high to

V

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

CC

4: Logic “0” is the potentialat digital ground (Pin 58).

(Pin 63)

CC

3.2 Resistance Measurements
(Ohms and Low Power O hm s)

The TC815 can be configured to reliably measure in­circuit resistances shunted by semiconductor junc­tions. The TC815 Low Power Ohms Measurement
mode limits the probe open circuit voltage. This pre­ventssemiconductorjunctionsi n the measured system
from turning on.

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

Ω/LOW

Ω (Pin 62) is momentarily brought low to digital

ground potential. The TC815 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,
LOW

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

Ohms mode is not active.
If the Manual mode has been selected, toggling

Ω/LOW

Ω will reset the TC815 back to the Auto-Range

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

(Pin 2) and

Selected

Measurement

The low power ohms measurement is not available on
the 100Ω f ull scale range. Open circuit voltage on this
range is below 2.8V. The standard resistance values
are listed in Table 3-2.

R8, a positive temperature coefficient resistor, and the

6.2V zener Z1 in Figure 3-1, provide input voltage pro­tection during ohms measurements.

TABLE 3-2: OHMS RANGE LADDER

NETWORK

Full Scale

Range

200Ω 163.85Ω (R1) NO

2000Ω 1638.5 kΩ (R2) YES

20kΩ 16,385Ω (R3) YES

200kΩ 16385Ω (R 4) YES

2,000kΩ 1,638,500Ω (R5) YES

Standard

Resistance

Low Power

Ohms Mode

3.3 Ratiometric Resistance
Measurements

The TC815 measures r esistance ratiometrically. Accu­racy is set by theexternalstandard resistors connected
to Pin 35 through 39. A Low Power Ohms mode may
be selected on all but the 200Ω full scale range. The
Low Power Ohms modelimitsthevoltageapplied to the
measured system. This allows accurate “in-circuit”
measurementswhen a resistor is shunted by semicon­ductorjunctions.Full auto-ranging is provided.External
precisionstandardresistorsareautomaticallyswitched
to provide the proper range.

Figure 3-1 shows a detailed block diagram of the
TC815 configured for ratiometric resistance measure­ments.Duringthesignalintegratephase,thereference
capacitorchargesto a voltage inversely proportionalto
the measured resistance, R
conversion accuracy relies on the accuracy of the

Ω

external standard resistors only.
Normally the required accuracy of the standard resis-

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

TABLE 3-3: REFERENCE RESISTORS

Full Scale

Range

200k 163.85 0.1

2k 1638.5 1

20k 16385 10

200k 163850 100

2M 1638500 1000

Reference

Resistor

. Figure 3-2 shows the

X

Ω/Count



2002 Microchip TechnologyInc. DS21474B-page 7

TC815

FIGURE 3-1: RATIOMETRIC RESISTANCE MEASUREMENT FUNCTIONAL DIAGRAM

9V

V

SSA

5730

V

CC

28

30

REFHI
34

29

Common

R8

220Ω

R

X

R5/1638500Ω

R4/163850Ω

R3/16385Ω

R2/1638.5Ω

R1/163.85Ω

÷10

÷100

÷1k

÷10k

C

0.1µF

R6/100kΩ

R7/100k

Unknown

÷1

REF

V

SSD

DE

DE S23

•

S29

S30

S31

S32

S33

Ω

•

DE

DE • Ω

~

CC

10kΩ

1.5kV

- 2.6V

Ohms

ΩΩ

•

HI

VA

÷1÷10÷100÷1k÷10k

Voltage

S19DES20

Reference

VCC - 2.8V

≈

DE + Ω

S28S27S26S25S24

~

Low Ohms

• LO

Ω

•

V

+

–

1.5kΩ

CC

V

TC815

Buffer

S35

ΩΩ

Integrator Comparator

S36

S34

S37

Ω

Ω

39

38

37

36

35

33

32

50

31

Ω

50

V •

S18

S21

S12 S13

1

•

INT • (Ω + DC)

1

Analog

R18
24kΩ

5kΩ

RVIBUF

150kΩ

220kΩ

49

C

AZ

0.1µF

C

INT

0.1µF

RΩBUF

5554

FIGURE 3-2: RESISTANCE MEASUREMENT ACCURACY SET BY EXTERNAL

STANDARD RESISTOR

Example: 200kΩ Full Scale Measurement

163.85kΩ

(a )

(b)



V

V

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

R



163.85 220 R

++



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

X



163.85kΩ 220Ω R

R

X

++

x0.64=

X

X

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

.

..

V

X

---------------- x T
RIC

()

I

=

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

I

()

V

RIC

X

I

Where:
R

= Integrating Resistor, TI= I ntegrate Time

I

= Integrating Capacitor, T

C

(d) R

I

= 163.85

X

(TDE)

T

I

DE =

Independentof RI,CIor Internal Voltage Ref erence

R

16.385k

Unknown

0.64V for Ohms

VA

0.32V for LO Ohms

+

S

C

REF

100 kΩ

V

R

V

R

220Ω

V

X

R

X

To Analog Buffer

47

x0.64=

DE

Deintegrate Time

DS21474B-page 8



2002 Microchip TechnologyInc.