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.

TC815

F

3.4 Voltage Measurement

Resistive dividers are automatically changed to provide
in range readings for 200mV to 2000V full scale readings
(Figure3-3). The input resistance is set by external
resistors R14/R13. The divider leg resistors are R9-R12.

FIGURE 3-3: TC815 ANALOG SECTION

Ohms
Input

Current Input

Common

D1

R24

10k

0.1µF
R7/100kΩ

Ω

R8/220

(PTC)

0.01µF

Voltage

Input

*Not required when
Resistor Network is used.

+

Ω

Z1

6.2V

20mA

200mA

R16/1

R14/9.9MΩ

C3
1µF

R26
33kΩ

R27/2kΩ

R6/100kΩ

R5/1.638MΩ

R4/163.85kΩ

R3/16385Ω

R2/1638.5Ω

R1/163.85Ω

R15/9

Ω

D2

R23
10kΩ

R12/1.11M

R11/101k

R10/10k

RM

Ω

D3

D4

R13/500kΩ*

R9/1k

Ω

4.7µF

+

C4
1µF

ΩR

REFL

ΩR

ΩR

ΩR

ΩR

ΩR

I 45

I

V 44

I

Ω

Ω

Ω

R22
470

W

k

C2

0.22 µF

ACVH

C1/1µF

ACVL 46

V

V

V

V

ADI

X

R2

R3

R4

R2

R21

2.2
M

50

31

39

5

38

4

37

3

36

2

35

1

•

ΩΩ Ω Ω Ω

1/1

V

CC

V•
1/10V•1/100

S6

41

40

43

42

AC-to-DC
Converter

53

Op Amp

ADO

Ω

52

S14

56

Ω

INT• •AC

S40

Ω

INT• •AC

S32S33 S31 S30

•• ••

1/10 1/100

S7

S39

Ω

INT+ +DC

V•
1/1
k

S8 S9

+

–

S15 AZ

1/1k

S10

S1

V•
1/10k

S2

S3

S4

S5

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 will reduce voltage offset errors induced
by switch leakage currents.

S29

1/10k

Ω

V•1/1

V•1/10

V•1/100

V•1/1k

V•1/10k

Buffer

+

–

S35 S37

Ω

S34

RBUF

RBUF

S12 V • 1/1

S21 DE •

S24 1/10k•

W

S25

S26

S27

S28

+ 1

S11

S13

Ω

Ω

54

Ω

Ω

Ω

•

Ω

1/1k

Ω

•

1/100

•

Ω

1/10

1/1•

Ω

Ω

+AC

INT•( +DC)

Ω

55

Ω

R

RVI

BUF

BUF

220

Ω

k

150
k

Ω

Ω

TC815

V

CC

10kΩ

ΩΩ

S44 HI

•

+

2.8V

–

Ω

S38 AZ

S43

INT

C

1.5k

WΩ

LO

•

REF AMP

1.5k

+

–

•

DE

S17 DE-

–

+

Comparator

0.01µF0.01µF

INT

V

CC

S22 S22

ΩΩ

DE •

S20 DE

S18 DE

S19 DE+

S16 DE+

–

+

Integrator

49 47
C

AZ

CAZ

30

RM

REFH

R18/24k

R19/5k

29

ANALOG
COM

34

REFHI

163.85mV

≈

33 C

REFH

REFH

32 C

REFL

51 CIF

R20/100kΩ

V

CC

Ω

Ω

C6

To Digital
Section

0.1µFC

0.01µ

I



2002 Microchip TechnologyInc. DS21474B-page 9

TC815

3.5 Current Measurement

The TC815 measures current only under manual range
operation. The two user selectable full scale ranges
are: 20mA
ment mode by holding the I
ground potential. The OHM
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 I
a10Ω resistor is used. The 200mA range needs a 1Ω
resistor; full scale is 200mV.

PC board trace resistance between analog common
and R16 (see Figure 2-1) 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
(Pin 45).

The extended resolutionmeasurementoption operates
during current measurements. To minimize rollover
error the potential difference between ANALOG COM
(Pin 29) and system common must be minimized.

and 200mA. Select the current Measure-

input (Pin 63) low at digital

input (Pin 2) is left floating

full scale range i s

input(Pin 3) to digital

input (Pin 45). For 20mA measurements

I

3.6 Measurement Options
(AC to DC Measurements)

In voltage and current measurements, the TC815 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 TC815 enters t he DC
Measurementmode.ForACmeasurements(current or
voltage),AC
digitalgroundpotential; the TC815 sets-up for AC mea­surements and the AC liquid crystal display annuncia­tor activates. Toggling AC
TC815 t o DC operation.

If the Manual Operating mode has been selected, tog­gling AC
Range mode. In Manual mode operation, AC or DC
operation should be selected first and then the desired
range selected.

I

The minimum AC voltage fullscale voltage range is 2V.
The DC f ull scale minimum voltage is 200mV. AC cur­rent measurements are available on the 20mA and
100mA full scale current ranges.

/DC (Pin 62) is momentarilybrought low to

/DC low again will return the

/DC will reset the TC815 back to the Auto-

DS21474B-page 10



2002 Microchip TechnologyInc.

TC815

4.0 CONVERSION TIMING

The TC815 analog-to-digital converter uses the con­ventional dual slope integrating conversion technique
with an added phase that automatically eliminateszero
offset errors. The TC815 gives a zero reading with a
zero volt input.

The TC815 is designed to operate with a 32.768kHz
crystal.The 32kHz crystal is low cost and readily avail­able; it serves as a time-base 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 deintegrate — requires
8000 clock periods or 488.3msec. There are approxi­mately two complete conversions per second.

The integration time is fixed 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 or

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 4-1 shows the basic
TC815 timing relationships.

FIGURE 4-1: BASIC T C815

CONVERSION TIMING

TC815

Auto-Zero

Phase

Min. Auto-Zero

Time

3361.5T

Signal
Integrate
Phase

P

8000 T

T

CONV

External Crystal = 32.768kHz
Internal ClockPeriod = T

Total Conversion Time= T
=488.3mec≈ 2Conv/Sec.

Integration Time= T
Maximum Reference De-integration Time =

T

=3000(TP) = 183.1msec

DE

(ManualExtended Resolution)
MinimumAuto-Zero Time

= (8000-3000-1638.5) (T

(Manual,Extended Resolution)

= (8000-2000-1638.5) (T

(Auto-Range)

Reference
De-integrate
Phase

Extended
Resolution

Zero Crossing

Fixed

1638.5 TP

*Max

3000.0 T

P

T

DE

Signal

=8000(TP)

*In Auto-Range Operation
Maximum is 2000TP and
Minimum Auto-Zero time
i s 4361.5T

T

I

To Input

P

= 2/32.768 = 61.04µsec

P

CONV

= 1638.5 (TP) = 100.0msec.

I

)=205.1msec

P

)=266.2msec

P

Next Conversion
Auto-Zero Cycle

P



2002 Microchip TechnologyInc. DS21474B-page 11

TC815

5.0 MANUAL RANGE SELECTION

The TC815 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 TC815 power-up circuit selects auto-range opera­tion initially. Once the manual range option is entered,
range changes are made by momentarily grounding
the RANGE
Manual Range mode until the measurement function

TABLE 5-1: MANUAL RANGE OPERATION

Power-on

Auto-Range

Operation

Manual Operation

control input. The TC815 remains in the

DC Volts AC Volts Ohm LO Ohm

Input

Input

23.5V 18.2V

Range Display Range Range Display Range Range Display

200mV “1”00.0V 2V “1”000V 200Ω “1”00.0Ω 2kΩ “1”.000kΩ

2V 1.000V 20V 18.20V 2kΩ “1”.000kΩ 10kΩ “1”.0.00kΩ

20V “1”0.00V — — 20kΩ 18.20Ω 200kΩ “1”.00.0kΩ

200V 23.5V — — — — 2000kΩ “1”350kΩ

DC Volts AC Volts Ohm LO Ohm

23.5V 18.2V

(voltage or resistance), or measurement option (AC
DC, Ω/LO

Ω) changes. This causesthe TC815 to return

to auto-ranging operation.
The “ Auto” LCD annunciator driver is active only in t he

Auto-Range mode. Table 5-1 shows typical operation,
where the manual range selection option is used. Also
shown is the extended resolution display format.

Also see Figure 5-1 through Figure 5-3.

18.2kΩ 2.35MΩ

18.2kΩ 2.35MΩ

/

# of Range

Changes

(See Note 4

1 200V 23.5V 20V 18.20V 20kΩ 18.20V 2000kΩ “1”350kΩ
2 200mV “1”00.0V 2V “1”.000V 200Ω “1”00.0ΩkΩ 2kΩ “1”.000kΩ
3 2V 1.000V 20V 18.20V 2kΩ “1”000kΩ 20kΩ “1”0.00kΩ
4 20V “1”3.50V 20V 18.2V 20kΩ 18.20kΩ 200kΩ “1”00.0kΩ
5 200V 23.5V 600V 19V 200kΩ 18.2kΩ 2000kΩ “1”350kΩ
6 1000V 24V 2V “1”.000V 2000kΩ 19kΩ 2kΩ “1”.000kΩ
7 200mV “1”00.0mV 20V 18.20V 200kΩ “1”00.0Ω 20kΩ “1”0.00kΩ
8 2V “1”.000V 200V 18.2V 2kΩ “1”.000kΩ 200kΩ “1”00.0kΩ

Note 1: A flashing MSD is shown as a “1”. A flashing MSD indicates the TC815 is over-ranging if all other digits are zero.

2: The first manual range selected is the last range in the Auto-Rangingmode.
3: A flashing MSD with a non-zerodisplay indicatestheTC815 has enteredtheExtended Resolution Operating mode.An

additional 1000 counts of resolution is available. This extended operation is available only in manual operation for voltage,
resistance and current measurements.

4: = Momentary ground connection.

Range Display Range Range Display Range Range Display

)

DS21474B-page 12



2002 Microchip TechnologyInc.

TC815

r

r

FIGURE 5-1: MANUAL RANGE

SELECTION:RESISTANCE
MEASUREMENTS

Manual Range

Select

Continuity
Indicator

Output 4kHz

Audio

Frequency

Continuous 4kHz
Buzzer

Yes

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

Is

< 19

R

X

?

No

Is

> 3000

R

X

?

No

Is

> 2000

R

X

?

No

Display True

Reading

Yes

"1" = > Flashing MSD

Yes*

< 2.999MΩ

X

TC815

Over Range Indicato

Display "1" 000

Display Last

3 Digits and Flash

MSD

Extended
Resolution
Feature

For resistance measurements, the buzzer signal does
notindicateanoverrangecondition.The buzzerisused
to indicate continuity. Continuity is defined as a resis­tance reading less than 19 counts.

FIGURE 5-2: MANUAL RANGE

SELECTION: CURRENT
MEASUREMENTS

Range

Select

I

> 3000

X

I

> 2000

X

Yes

Is

Yes

?

No

Is

Yes

?

No

TC815

Output 4kHz

Audio

Frequency

Over Range Indicato

Display

"1" 000

"1" = > Flashing MSD

Display Last

3 Digits and Flash

MSD

Extended
Resolution
Feature

FIGURE 5-3: MANUAL RANGE

SELECTION: VOLTAGE
MEASUREMENTS

Range Select

Is

V

> 3000

X

?

No

Is

> 2000

V

X

?

No

Display True

Reading

Yes

Yes

TC815

Output Noncontinuous

4kHz Audio

Frequency

Over Range Indicator

Display
"1" 000

"1" = > Flashing MSD

Display Last 3 Digits

and Flash

MSD

Extended Resolution
Feature

5.1 E xtended Resolution
Manual Operation

The TC815 extends resolution by 50% when operated
in the Manual Range Select mode for current, voltage,
and resistancemeasurements.Resolutionincreases to
3000 counts from 2000 counts. The extended resolu­tion feature operates only on the 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.

An input overrange condition causes the most signifi­cant digit to blink and sets the three least significant
digitsto display “000.” The buzzer output is enabled for
input voltage and current signals with readings greater
than 2000 counts i n both manual and auto-range
operation.

Display True

Reading



2002 Microchip TechnologyInc. DS21474B-page 13

TC815

6.0 -MEM OPERATING MODE

Bringing -MEM (Pin 61) momentarily low configures the
TC815 “-MEM” Operating mode. The -MEM LCD
Annunciator becomes active. In this Operating mode,
subsequent measurements are made relative to the last
two digits (-99) displayed at the time MEM is low. This
represents5% of fullscale. The lasttwosignificant digits
are stored and subtracted from all the following input
conversions. The following examples clarify operation:

EXAMPLE 6-1: IN AUTO-RANGING

R

(N)= 18.21kΩ (20kΩ Range)= > Display 18.21kΩ

I

MEM

R

(N+1) = 19.87kΩ (20kΩ Range)

I

(N+2) = 22.65kΩ (200kΩ Range)

R

I

EXAMPLE 6-2: IN FIXED RANGE

RI(N) = 18.21kΩ = > Display 18.2kΩ

MEM

(N+1) = 36.7Ω

R

I

R

(N+2) = 5.8Ω

I

*Will display minus resistance if following input is

less than offset stored at fixed range.

EXAMPLE 6-3: IN FIXED RANGE

VI(N) = 0.51V = > Display 0.51V
MEM

V

(N+1) = 3.68V

I

V

(N+2) = 0.23V

I

V

(N+3) = -5.21V

I

On power-up, the TC815 “-MEM” mode is not active.
Once the “-MEM” is entered, bringing MEM
it returns the TC815 to normal operation.

The “-MEM”modeisalso cancelledwheneverthe mea­surement type (resistance, voltage, current AC

Ω/LO

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

ator will be off in normal operation.
In the auto-rangeoperation,if the following input si gnal

cannot be converted on the same range as the stored
value, the “-MEM” mode is cancelled. The LCD annun­ciator is turned off.

The “-MEM” Operating mode can be very useful in
resistancemeasurementswhen lead length r esistance
would cause measurement errors.

= > Store 0.21k Ω

= > Display 19.87 - 0.21 = 19.66kΩ

= > Display 22.7kΩ and MEM

disappears

(200.0Ω FULL SCALE)

=>Store8.2Ω

= > Di splay 36.7 - 8.2 = 28.5Ω

= > Di splay 5.8 = 2.4Ω*

=>Store0.51V

= > Di splay 3.68 - 0.51 = 3.17V

= > Di splay 0.23 - 0.51 = -0.28V

= > Di splay - 5.21 - 0.51 = -5.72V

low again,

/DC,

7.0 AUTOMATIC RANGE
SELECTION OPERATION

When power is first applied, the TC815 enters the auto­range 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 (AD

The automatic voltage range selection begins on the
most sensitive scale first: 200mV for DC or 2.000V for
AC measurements. The voltage range selection flow
chart is given in Figure 7- 1.

Internal input protection diodes t o V
V

(Pin 57) clamp the input voltage. The external

SSA

10MΩ input r esistance (see Figure 7-1, R14 and R13)
limits current safely in an overrange condition.

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

An over range voltage input condition is flagged when­ever the internal count exceeds 2000, by activating the
buzzer output (Pin 4). This 4kHz signal can directly
drive a piezo electric acoustic transducer. An out of
range input signal causes t he 4kHz signal to be on
122msec, off for 122 msec, on for 122msec and off for
610msec (see Figure 11-1).

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 7-2. The 200Ω range is the first range
selected unless the TC815 low ohms resistance mea­surementoptionisselected.Inlowohmsoperation,the
first full scale range tried is 2kΩ.

The r esistance range selected maximizes sensitivity. If
the conversion results in a reading less than 180, the
next most sensitive f ull 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 ar e displayed by a blink­ing most significant digit with the three l east significant
digits 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).

DD

(Pin 28) and

DS21474B-page 14



2002 Microchip TechnologyInc.

FIGURE 7-1: AUTO-RANGE OPE RAT ION: VOLTAGE MEASUREMENT

p

TC815

N = N + 1

N = 0 if DC
N = 1 if AC

Conversion

VX - (1/10N) V

V

No

Kth

VX < 180

?

No

> 2000

X

?

Yes

N = 4

?

Yes

TC815

N = 0: 200.0mV Full Scale Range
N = 1: 2,000V Full Scale Range

N = N

K

Remaining in Range Selected
during the Kth Conversion

IN

Yes

No

N = N – 1

N = 0 if DC
N = 1 if AC

Yes

Display

Voltae (V

)

X

K = K + 1

Display "1" XXX

V

> 3000

X

?

Yes

Display "1" 000

Flash MSD

Start: Power-on, Function or Measurement O

No

Flash MSD

Activate

Buzzer

Over Range

tion Change



2002 Microchip TechnologyInc. DS21474B-page 15

TC815

p

FIGURE 7-2: AUTO-RANGE OPERATION: RESISTANCE MEASUREM E NT

Continuity
Indicator

Activate

Buzzer

Continuous
4kHz Signal

N = 1 if LOΩ

Conversion

RX = (1/10N) R

Yes

N = 0 if Ω

Kth

R

< 19

X

?

RX < 180

?

>2000

R

X

?

No

No

Yes

TC815

N = 0: 200.0Ω Full Scale Range
N = 1: 2,000kΩ Full Scale Range

Remaining in Range Selected
during the Kth Conversion

IN

N = N – 1

No

Yes

N = 0 if

Ω

N =1 if LOW

Yes

Display

Resistance

Ω

K = K + 1

N = N + 1

No

N = 4

?

Yes

Display "1" XXX

>3000

R

X

?

Yes

Start: Power-on, Function or Measurement O

No

Flash MSD

Extended Resolution

Over Range

Display "1" 000

Flash MSD

tion Change

DS21474B-page 16



2002 Microchip TechnologyInc.

TC815

r

8.0 LOW BATTERY DETECTION
CIRCUIT

The TC815 contains a low battery detector. When the
9V battery supply has been depleted to a 7V nominal
value, the LCD display low battery annunciator is
activated.

The low battery detector is shown in Figure 8-1. The
low battery annunciator remains OFF with the battery
supplygreaterthan0.7V. The annunciatorisONbefore
the supply battery has reached 6.3V.

FIGURE 8-1: LOW BATTERY

DETECTOR

V

CC

R

1

R

2

Low Battery Detector

V

T

R

3

6.2V

V

Z

V

V

SSA

Comparator

+

–

R

7 X = 6.2V

T

≈

R1 + R

TC815

To LCD
Annunciato
Selection
Logic

2

2

9.0 TRIPLEX LIQUID CRYSTAL
DRIVE

The TC815 directly drives a triplexed liquid crystal dis­play (LCD) using 1/3 bias drive (see Figure 9-1). All
data, decimal point, polarity and function annunciator
drive signals are developed by the TC815. A direct
connection to a triplex LCD display is possible without
external dr ive electronics. Standard and custom LCD
displaysarereadilyavailablefrom LCD manufacturers.

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
V

.

DISP

, for example,isset at a potential 3V below VCC,

IfV

DISP

the peak drive signal is:

V

P=VCC –VDISP

=3V

An “OFF” LCD segment has an RMS voltage of Vp/3
across it or 1 volt. An “ON” segment has a 0.63Vp sig­nal across it or 1.92V for V

Since the V

pin is available, the user may adjust

DISP

CC –VDISP

=3V.

the “ON” and “ OFF” LCD levels for various manufac­turer’s displays by changing Vp. The l iquid crystal
threshold voltage moves down with temperature.

CC

“OFF”segmentsmaybecomevisibleathighLCDoper­ating temperatures. A voltage with a -5 to -20mV/°C
temperature coefficient can be applied to V

DISP

to
accommodate the liquid crystal t emperature operating
characteristics, if necessary.

The TC815 internally generates two intermediate LCD
drive potentials (V
(Figure 9-1), between V

and VL) from a resistive divider

H

(Pin 28) and V

CC

DISP

(Pin 7).
The ladder impedance is approximately 150kΩ.This
drive method is commonly known as 1/3 bias. With
V

connected to digital ground VP≈ 5.0V.

DISP

The intermediate levels are needed so that drive sig­nals giving RMS “ON” and “OFF” levels can be gener­ated. Figure 9-2 shows a typical drive signal and the
resulting wave forms for “ON” and “OFF.” RMS voltage
levels across a selected LCD element. Also, see
Figure 9-3 and Table 9-1.

FIGURE 9-1: 1/3 BIAS LCD DRIVE

V

CC

28

To Triplex

Segment Drive

Logic

V

SSA

TC815

V

H

V

L

VP = VCC – V

"OFF" = VP/3 RMS

11

"ON" = VP RMS

3

3

DISP

50k

50k

50k

Set V

DISP

For Proper V
with Resistive
Divider

6

V

DISP

P

9.1 LCD Displays

Although most users will design t heir own custom LCD
display, several manufacturers offer standard displays
for the TC815. Figure 9-3 shows a typical display avail­able from Varitronix.

-

1. Varitronix Ltd.

4/F Liven House, 61-63, King Yip Street
Kwun Tong, Hong Kong
Tel: [phone]
Part No.: VIM 310-1 Pin Connector

VIM 310-2 Elastomer Connector

USA OFFICE:

VL Electronics/Varitronix
3250 Wilshire Blvd. Suite 1901
Los Angeles, CA 90010
Tel: [phone]

2. Adamant Kogyo Co., LTD

16-7, Shinden, 1-Chome, Adachi-Ku,
Tokyo, 123, Japan
Tel: Tokyo 919-1171



2002 Microchip TechnologyInc. DS21474B-page 17

TC815

P

P

P

P

P

FIGURE 9-2: TRIPLEX LCD DRIVE WAVEFO RMS

Backplanes

123456

a

f

b

g

e

c

d

BCPAGDFE

BP3

BP2

BP1

VP (3V)

BP1

VP

Backplanes

VH

BP2

VP

VH

BP3

Waveforms to Generate

VL

VL

0

0

Backplanes

123456

Segments Applied

VP
VH

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"

–VL
–VH
–VP

–VL
–VH
–VP

–VL
–VH
–VP

–VL
–VH
–VP

–VL
–VH
–VP

–VL
–VH
–VP

–VL
–VH
–VP

0

VP
VH

VL

0

VP
VH

VL

0

VP
VH

VL

0

VP
VH

VL

0

VP
VH

VL

VP
VH

VL

0

RMS Voltage

V

V

V

V

V

V

V

11

=V

RMS

33

11

=V

RMS

33

11

=V

RMS

33

11

=V

RMS

33

V

P

=

RMS

3

V

P

=

RMS

3

11

=V

RMS

33

FIGURE 9-3: TYPICAL LCD DISPLAY CONFIGURATION T C815 TRIPLEX

50.8 (+0.3–0.1)

45.0 Viewing Area Min.

Between Pads 2.54 X 17 - 43.18

C

– +

6

L

36

3

10

HOLD LOΩ

3

5.5

1.4

1

a

f

10

e

b

g

c

2.4

d

kΩ

mVA

3

1

19

- MEM

10.0 Max.

18.0 Viewing Area Min.6.24

0.5

AC

AUTO

Max.

18

Dimensions in mm (Not to Scale)

1.271.27

43 2

P4 P3 P2

2.9

3.81

22.86 (+0.3–0.1)

3.81

30.48 (+0.3–0.1)

0.2

0.2

1.1 1.1

DS21474B-page 18



2002 Microchip TechnologyInc.

TC815

TABLE 9-1:

PAD BP1 BP2 BP3 PAD COM1 COM2 COM3

1BP1 / /19/ //
2 / BP2 / 20 / / /
3 / / BP3 21 / / /
4/LOΩ A22 / / /
5/WV23///
6HOLD k m24 / / /
7b1c1/25///
8a1g1d126///

9f1e1/27///
10 b2 c2 P2 28 / / /
11 a2 g2 d2 29 / / /
12 f2 e2 / 30 / / /
13 b3 c3 P3 31 / / /
14 a3 g3 d3 32 / / /
15 f3 e3 / 33 / / /
16 b4 c4 P4 34 / / /
17 AC Auto 35 / / /
18 –MEM / 36 / / /

10.0 EXTERNAL CRYSTAL

The TC815 is designed to operate with 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 488.3 msec ( ≈ 2 conversions/
second). Integration time is 1638.5 clock periods or
100msec.

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

Several crystal sources exist. A partial listing 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.



2002 Microchip TechnologyInc. DS21474B-page 19

TC815

11.0 “BUZZER” DRIVE SIGNAL

The buzzer drive signal for over range is shown in
Figure 11-1 The buzzer output is active for any reading

The TC815 BUZ output (Pin 4) will drive a piezoelectric
audio transducer. The signal is activated to indicate an
input overrange condition for current and voltage
measurements, or continuity during resistance
measurements.

During a resistance measurement, 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 overrange is
indicated by a noncontinuous 4kHz signal at t he BUZ
output. The LCD display MSD also flashes and the

over 2000 counts in both manual and auto-range oper­ation. The buzzer is activated during an extended res­olutionmeasurement. The BUZ signal swingsfromV
(Pin 28) to Digital Ground (Pin 58).The signal is at V
when not active.

The BUZ output is also activated for 15msec whenever
a range change is made in auto-range or manual oper­ation.Changingthetypeofmeasurement(voltage, cur­rent, or resistance) or measurement option (AC

Ω/LO

Ω)willalsoactivatethebuzzeroutputfor15msec.

A range change during a current measurement will not
activate the buzzer output.

three least significant digits are set to display zero.

FIGURE 11-1: TC815 WAVEFORM FOR BUZZER OUTPUT

122ms 122ms 122ms 122ms

1 Conversion

610ms

CC
CC

/DC,

122ms

Digital Ground

4kHz Signal

Internal
TC815
Signals

Integrate

De-integrate

Auto-Zero

BUZ
(Pin 4)

Power-up

V

IN

= 250mV

4000 8000 12000

1000 Clock Pulses

100ms

1638.5CP

122ms

2000CP

200mV Range

Over Range

4kHz 4kHz 4kHz

One Cycle of Over Range

Buzzer activated due

to Power-up

Noncontinuous Buzzer Signal Indicates Input Overrange

Change Range Change Range Change Range

Buzzer

2,000V Range

In Range

2,000V Range

In Range

Due to Manual
Range Change

200mV Range

Extended Range

Range
Change

Manual RangeAuto-Ranging

2,000V Range

In Range

Due to

Due to

Range
Change

122ms 122ms122ms

Buzzer activated due to

Previous Conversion Over Range

Change Input

V

IN

4kHz15ms15ms15ms

= 3.2V

3000CP250CP2500CP250CP250CP

2,000V Range

Out of Range

610ms

Buzzer
activated due
to Previous
Over Range

DS21474B-page 20



2002 Microchip TechnologyInc.

TC815

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

11.1 Display Decimal Point Selection

The TC815 provides a decimalpoint LCD drive signal.
The decimal point position is a function of the selected
full scale range, as shown in Table 11-1.

TABLE 11-1: DECIMA L POINT SELECTION

1*9 *9 *9

Full Scale Range DP3 DP2 DP1

2000V, 2000kΩ OFF OFF OFF
200V, 200.0kΩ OFF OFF ON
20V, 20.00kΩ OFF ON OFF
2V, 2.000kΩ ON OFF OFF
200V, 200.0Ω OFF OFF OFF
200mV, 200.0Ω OFF OFF ON
20mA OFF ON OFF
200mA OFF OFF ON

11.2 AC-to-DC Converter Operational

Amplifier

The TC815 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:

•SlewRate: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, the
input buffer receives an input signal through switch
S14, rather than switch S11. With external circuits, the
AC Operatingmodecanbeusedto performothertypes
of functions within the constraintsof the internal opera­tional amplifier. External circuitsthat perform true RMS
conversion, or a peak hold function are typical
examples.

11.3 Component Selection

11.3.1 INTEGRATION RESISTOR
SELECTION

The TC815 automatically selects one of two external
integration resistors. RVBUF (pin 55) is selected for
voltage and current measurement. RΩBUF (Pin 54) is
selected for resistance measurements.

11.3.2 RVIBUF SELECTION (P IN 55)

In auto-range operation, the TC815 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 Operating mode is acti­vated,giving a 300mV full scale potentialat V

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,assuminga worst
case extended resolution input signal:

V

= Integrator swing = ±2V

INT

t

= Integration time = 100msec

I

= Integration capacitor = 0.1µF

C

I

V

= Maximum input at VI= 300mV

MAX

EQUATION 11-1:

RVIBUF =

V

MAX(TI

V

INT(CI

)

= 150kΩ

)

11.3.3 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 t he 200Ω range

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

(Pin 50) is easily calculated (see

X

Figure 11-2):

V

ANCOM

R
R
R
R

= Potential at Analog Common ≈ 2.7V
= 220Ω

8

= 163.85Ω

I

= 300Ω

X

= Internal switch 33 resistance ≈ 600Ω

S

EQUATION 11-2:

-(V

V

CC

RΩBUF =

(RX+RS+R1+R8)

ANCOM)RX

(Pin 44).

I

(Pin44).

I

=0.63V



2002 Microchip TechnologyInc. DS21474B-page 21

TC815

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

V
t

I

C
R
V

= Integrator swing = 3.1V

INT

= Integration time = 100msec
= Integration capacitor = 0.1µF

I

=300Ω

XMAX

= 700mV

X MAX

EQUAT ION 11 -3:

RΩBUF =

V

C

XMAX(TI

I(VINT

)

)

= 200kΩ

FIGURE 11-2: RΩ CALCULATION (200Ω

MANUAL OPERATION)

V

= 9V

CC

SW33

R

R

R

≈ 600Ω

S

163.85Ω

1

220Ω

2

11.5 Reference Voltage Adjustment

The TC815 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 TC815
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.

11.6 Display Hold Feature

The LCD will not be updated when HOLD (Pin 60) is
connectedtoGND(Pin58).Conversionsare made, but
the display is not updated. A HO LD
ciator is activated when HOLD

mode LCD annun-

is low.

The LCD HOLD annunciator is activated through the
triplex LCD driver signal at Pin 13.

11.7 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

V

X

R

300Ω

3

Analog Common = VCC – 3V

With a low battery voltageof 6.6V, analog common will
be approximately 3.6V above the negative supply 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.

11.4 Capacitors - C

The integration capacitor, C

INT,CAZ

, must have low dielec-

INT

and C

REF

tric absorption.A 0.1µF polypropylenecapacitorissug­gested. The auto-zero capacitor, C
capacitor, C

, should be selected for low leakage

REF

, and reference

AZ

and dielectric absorption. Polystyrene capacitors are
good choices.

11.8 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 11-2: RESISTIVE L ADDER

NETWORKS

Attenuator

Accuracy

Attenuator T ype

0.1% Voltage 1776-C441

0.25% Voltage 1776-C44

0.25% Resistance T1794-204-1

Caddock

Part Number

DS21474B-page 22



2002 Microchip TechnologyInc.

12.0 PACKAGING INFORMATION

)

12.1 Package Marking Information

Package marking data not available at this time.

12.2 Taping Form

Component Taping Orientation for 64-Pin PQFP Devices

User Direction of Feed

TC815

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.

12.3 Package Dimensions

64-Pin PQFP

PIN 1

.018 (0.45)
.012 (0.30)

.031 (0.80) TYP.

P

Standard Reel Component Orientation
for TR Suffix Device

.555 (14.10)
.547 (13.90)

.687 (17.45)
.667 (16.95)

.009 (0.23)
.005 (0.13)

7° MAX.

.041 (1.03)
.031 (0.78)

.555 (14.10)
.547 (13.90)

.687 (17.45)
.667 (16.95)



2002 Microchip TechnologyInc. DS21474B-page 23

.130 (3.30) MAX.

Dimensions: mm (inches

.010 (0.25) TYP.

.120 (3.05)
.100 (2.55)

TC815

SALES AND SUPPORT

Data Sheets

Products supportedby a preliminary DataSheetmayhave an erratasheetdescribing minor operational differences and recom­mendedworkarounds.To determine if an errata sheetexists for a particular device, please contact one of the following:

1. Your local Microchip sales office

2. The Microchip CorporateLiteratureCenter 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)toreceive the most currentinformation on our products.

DS21474B-page 24



2002 Microchip TechnologyInc.

TC815

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 MATE, SEEVAL and The Embedded Control
SolutionsCompany areregiste red trademarksof MicrochipTech­nologyIncorp or ated in the U.S.A. and other countries .

dsPIC, ECONOMONI TOR, FanSense, FlexROM, fuz zyLAB,
In-Circuit Serial Programming, ICSP, ICEPIC, microPort,
Migratable Memory, MPA SM, MPLIB, MPLINK, MPSIM,
MXDEV, PI CC, PICDEM, PICDE M.net, rfPIC, Select M ode
and Total Enduranceare trademarksof Microchip Technology
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. DS21474B-page 25

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

DS21474B-page 26

*DS21474B*



2002 Microchip Technology Inc.