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 2000kand 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
LO/A
/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(LO)
-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
RBUF
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
R5
R4
38
R3
37
R2
36
35
R1
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
20mA
200mA
2
OHM
625961
63
I
RANGE
V
57
58
SS
CC
V
V
DGND
163.85mV
V
R18/24k
R19/5k
W
k
mVA
HOLD
–+
AC
-MEM LO
AUTO
BP2
BP1
LCD Bias
0.1µF
1415161819202122
23242625131211
27
10
BP3
789
50
R7/100k
R8/220
Input
Resistance
AGD2
FE2 FE1BCP2 AGD1 BCP1 FE0 AGD0 BCP0 XTAL1DEINT
BCP3AC/–/
BATT
–MEM/
AUTO
HOLD
/V k/m/
LO/A
ANNUNC
DISP
V
X
R
31
R6/100k
(PTC)
1's
Segment and Decimal Point Drive
100's 10's
1000's
Display
Annunciators
SYNC
Drivers
Backplane
Ohms Range Attenuator
REFL
R5 (÷10,000)
RM
39
1.6385M
µF
0.1
R4 (÷1,000)
38
373635
163.85k R3/16.385k
Positive
Coefficient
Temperature
R3 (÷100)
R2 (÷10)
R2/1638.5
Z1
Resistor
R1 (÷1)
R1/163.85
6.2V
I
I
45
D3 D4
Input
Current
R15
20mA
TC818A
9
1
R16
200mA
DC/AC or /LO
Voltage Range Attenuator
(÷1)
*Not required when Resistor Network is used.
(See Applications Section for details.)
R13*
VR1
44
500k
R14/9.9M
Voltage
R12/1.111M
Input
41
VR2 (÷10)
VR3 (÷100)
40
R11/101k
VR4 (÷1,000)
43
R10/10k
33
REFH
C
32
REFL
C
51
CFI
60
HOLD
47
I
C
49
AZ
C
55
RVIBUF
54
RBUF
46
ACVL
56
ACVH
52
ADI
R21/2.2M
53
VR5 (÷10,000)
42
R9/1k
COM
REF
C
R20
100k
INT
C
AZ
C
150
k
ΩΩ
k
220
C1/1µF
R22/470k
ADO
0.1µF
C2/0.22µF
+
C4/1µF
4.7µF
C6
R23/10k
D2
0.01µF
RBUF RVIBUF
R26/3k
R24/10k
HOLD
R27/2k
–+
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 without10M
±3 200mV Range with 10M
±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,LOW,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 200Range
285 350 mV Excludes 200Range
50 ppm/°C
Reading
200mV Rangewithout 10M Resistor
200mV Range with 10M Resistor
20mA and 200mA Range
Resistor
Resistor
BW = 0.1 to 10Hz
P-P
)
COM
Range, -MEM, OHMs (RelativetoDGND,Pin58)
,AC,I,LOW,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 /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 R1 Standardresistor connection for 200fullscale. 36 R2 Standard resistor connection for 2000full 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.
/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 R3 Standard resistor connection for 20kfull scale range. 38 R4 Standard resistor connection for 200kfull scale range. 39 R5 Standard resistor connection for 2000kfull 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 RBUF 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()/
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
)
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
R26 3k
R7/100 k
R6/100k
(PTC)
+
R5/1.638M
R4/163.85k
R3/16385
R2/1638.5
Z1
6.2V
R1/163.85
20mA
200mA
R16/1
*Not Required when Resistor Network is Used
C3 1µF
R27/2k
R15/9
R14/9.9 M
D2
R23 10k
D3
R13/500k*
R12/1.11M
R11/101k
R10/10k
R9/1k
+
C4 1µF
4.7µF
RM
D4
R22 470 k
C2
ACVH
R
X
REFL
R5
R4
R3
R2
R1
I 45
I
V 44
I
VR2 41
VR3 40
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
52
56
S14
INT•
•AC
S40
INT••AC
S39
INT+ + 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
S34
RBUF
RBUF
S12 V • 1/1
S21 DE •
1/10k
S25
1/1k
S26
1/100
1/10
S27
S28
+AC
INT•( + DC)
S37
54
R BUF 220
k
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
k
TC818A
TC818A
V
CC
S44 HI
V
S43
CC
+
2.8V
ΩΩ
S38 AZ
Comparator
INT
C
10k
1.5
LO
REF AMP
1.5 k
+
DE
S17 DE-
+
0.01µF
INT
R18/24k
R19/5k
29
Analog Cmmon
34
REFHI
163.85mV
33 C
REFH
C
REFH
32 C
REFL
51 CFI
R20/100k
V
CC
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 /LO (Pin 62) input selects the Low Power Ohms Measure­ment mode. For low power ohms measurements,
/LO
(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
, will be activated. On power-up, the Low Power
Ohms mode is not active. If the Manual Operating mode has been selected, tog-
gling /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 200full scale range. Open circuit voltage on this range is below 2.8V. The standard resistance values are listed in Table 3-2.
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
200 163.85(R1) NO
2000 1638.5k(R2) YES
20k 16,385(R3) YES
200k 163,85(R4) YES
2,000k 1,638,500(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 200f 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-
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 /Count
.Figure 3-3 shows that the
X
DS21475B-page 8
2002 Microchip TechnologyInc.
TC818A
FIGURE 3-2: RATIOMETRIC RESISTANCE MEASUREMENT FUNCTIONAL DIAGRAM
9V
V
SS
57
R8
220
(PTC)
R
R5/1638500
÷10k
X
Unknown
R4/163850
R3/16385
R2/1638.5
R1/163.85
÷10
÷100
÷1k
C
0.1µF
R6/100k
R7/100k
÷1
REF
39
38
37
36
35
33
32
31
50
V
S18
S21
S12
1
INT ( + DC)
1
DE
S29
10k
TC818A
VA
Voltage
DE +
Ohms
HI
Low Ohms
LO
V
+
S37
CC
S35
1.5k~
1.5k
~
-2.6V
V
CC
Integrator Comparator
S30
S31
S32
S33
÷1÷10÷100÷1k÷10k
S28S27S26S25S24
DE S23
DE
DE
S13
Reference
VCC -2.8V
S19DES20
Buffer
S36
S34
V
CC
28
REFHI 34
29
Analog
Common
+
R18 24k
5k
RVIBUF
150k
220k
49
C
AZ
0.1µF
C
INT
0.1µF
RBUF
5554
FIGURE 3-3: RESISTANCE MEASUR EMENT ACCURACY SET BY EXTERNAL
R
163.85k
Unknown
STANDARD RESISTOR
Example: 200kFull Scale Measurement
0.64V for Ohms
VA =
0.32V for LO Ohms
S
C
REF
+
V
R
(a )
(b)
V
R
V
X
100k
(c) “Ramp Up Voltage” = “Ramp Down Voltage”
220
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
163.85k

-------------------------------------------------

163.85 220 R
++

--------------------------------------------------------------

163.85k 220 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 10minput 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 10r esistor is used. The 200mA range requires a 1resistor; 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, /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
) 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 2M < R
Yes
< 2.999M.
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 2000kand 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) = 18.21k(20kRange)= Display 18.21k MEM
R
R
EXAMPLE 3-2: IN FIXED RANGE
RI(N) = 18.21kΩ = ≥ Display 18.2k 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 /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 0.21k
(N+1)= 19.87k(20kRange)
I
= Display 19.87 - 0.21 = 19.66k
(N+2)= 22.65kΩ (200kR ange)
I
= Display 22.7kand MEM
disappears
(200 FULL SCALE)
= Store 8.2
(N+1) = 36.7
I
= Display 36.7- 8.2 = 28.5
(N+2) = 5.8
I
= Display 5.8-8.2 = -2.4*
*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,
) 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 10M 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 200range 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 2000kand 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, /LO).
(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
N = 1 If LO
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; 200Full Scale Range N = 1; 2kFull 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
N = 1 If LO
?
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 approximately150k. 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: (852)3-410286 Fax: (852)34-39555
P
Part No.: VIM-328-DP
USA Office:
VL Electronics, Inc. 3171 LOs Feliz Blvd, #303 Los Angeles, CA 90039 Tel: (213) 738-8700
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 (714) 639-7810 TWX: 910-593-1355 TELEX: 67-8394
• Fox Electronics
5570 Enterprise Parkway Fort Myers, FL 33905 (941) 693-0099
Contact manufacturer for full specifications.
FIGURE 3-13: TYPICAL LCD
CONFIGURATION, TC818A TRIPLEX
+
-MEM
HOLD
AC
AUTO
WLO
k
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, /LO), 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 (201) 548-2800 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, 2000k OFF OFF OFF 200V, 200k OFF OFF ON 20V, 20k OFF ON OFF 2V, 2k ON OFF OF F 200V, 200 OFF OFF ON 200mV, 200 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. RBUF (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 = 10k) ± 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
)
= 150k
)
3.20.3 RBUF 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 200range
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: RCALCULATION (200
MANUAL OPERATION)
V
= 9V
CC
SW33
R
R
R
R
600
S
163.85
1
2
3
220
V
X
300
Analog Common = VCC – 3V
Where:
V
ANCOM
R
S
R
I
R
X
R
S
= Potential at Analog Common 2.7V = 220 = 163.85 = 300 = Internal switch 33 resistance600
EQUATION 3-2:
RBUF =
CC–VANCOM)RX
(RX+RS+R1+R8)
=0.63V
(V
For a 3.1V integrator swing, the value of RBUF i s easily calculated:
Where:
V T C R V
INT I
XMAX
= Integratorswing = 3.1V = Integrationtime = 100msec = Integration capacitor = 0.1µF
I
=300
XMAX
= 700mV
EQUATION 3-3:
XMAX(TI
I(VINT
)
= 200k
)
RBUF =
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 (415) 856-9332 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: (714) 788-1700 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:(480)792-7277
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
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03/01/02
DS21475B-page 24
*DS21475B*
2002 Microchip Technology Inc.
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