TC818A

Obsolete Device
TC818A
Auto-Ranging Analog-to-Digital Converter
with 3-1/2 Digit Display
Features
General Description
• Auto-Ranging Analog-to-Digital Converter with
3-1/2 Digit Display
• Annunciator Outputs 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
• 4 AC/DC Current
• 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
The TC818A is an integrating analog-to-digital converter (ADC) with 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.
Device Selection Table
Part Number
Package
Operating
Temperature Range
TC818ACBU
64-Pin PQFP
0°C to +70°C
Automatic range selection is provided for both voltage
(DC and AC) and ohms (high and low power) measurements. Expensive and bulky mechanical range
switches are not required. Five full scale ranges are
available, with automatic selection of 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 selection through a single line input.
During Manual mode operation, resolution is extended
to 3000 counts full scale. Extended resolution is also
available during 2000kΩ and 2000V full scale autorange operation. The extended range operation is indicated by a flashing 1 MSD and by the fully extended 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.
Additional annunciators are activated for manual, auto,
memory, HOLD, AC, low power ohms, and low battery
conditions.
The TC818A is available in a surface mounted 64-pin
flat package. Combining a numeric display driver, single 9V battery operation, internal range switching, and
compact surface mounting, the TC818A is ideal for
advanced portable instruments.
© 2005 Microchip Technology Inc.
DS21475C-page 1
TC818A
Package Type
ACVH
RVIBUF
RΩBUF
57
56
55
54
RX
VSS
58
CAZ
DGND
59
CFI
RANGE
61 60
62
ADO
HOLD
63
ADI
-MEM
64
I
DC(Ω)/
AC(LOΩ)
NC
64-Pin PQFP
53
52
51 50
49
NC
1
48 NC
47 CI
OHM
2
20mA
3
46 ACVL
BUZ
4
45 II
XTAL1
5
44 VI
XTAL2
6
VDISP
7
BP1
8
BP2
9
43 VR4
LCD
Backplanes
42 VR5
TC818A
41 VR2
40 VR3
BP3 10
39 ΩR5
LCD Segment Drives
LOΩ/A 11
38 ΩR4
Ω/V 12
k/m/
HOLD 13
37 ΩR3
BCP0 14
35 ΩR1
AGD0 15
34 REFHI
36 ΩR2
FE0 16
DS21475C-page 2
-MEM/BATT
ANNUNC
28 29
30
31
32
CREFL
27
DEINT
26
RMREFL
25
COM
24
VCC
23
AC/-/AUTO
FE1
22
FE2
BCP1
AGD1
21
BCP3
20
BCP2
19
AGD2
18
NC
33 CREFH
17
© 2005 Microchip Technology Inc.
© 2005 Microchip Technology Inc.
0.1
µF
R8/220Ω
(PTC)
R15
9Ω
200mA R16
1Ω
20mA
D3 D4
45
R1/163.85Ω 35
6.2V
II
COM
R9/1kΩ
R10/10kΩ
ADO
42
D1
D2
C5/1µF
–
+
R24/10kΩ
R23/10kΩ
C4/1µF
+
–
R22/470kΩ
53 R21/2.2MΩ
R26/3kΩ
R27/2kΩ
56
ACVH
C2/0.22µF
52
ADI
Voltage Range Attenuator
VR5 (÷10,000)
VR4 (÷1,000)
4.7µF
43
Ohms Range Attenuator
SYNC
Backplane
Drivers
*Not required when Resistor Network is used.
(See Applications Section for details.)
ΩR1 (÷1)
ΩR2 (÷10)
ΩR3 (÷100)
ΩR4 (÷1,000)
ΩR5 (÷10,000)
RMREFL
–
+
C1/1µF
TC818A
RΩBUF
220
kΩ
54
CAZ
0.1µF
49
CAZ
RVIBUF
150
kΩ
55
ACVL RΩBUF RVIBUF
46
1's
HOLD
CINT
47
CI
60
HOLD
32
C6
0.01µF
R20
100kΩ
51
CFI
BUZ
-MEM
RANGE
DC/AC or Ω/LOΩ
I
OHM
200mA
DGND
VSS
VCC
XTAL2
30
5
DEINT XTAL1
33
CREF
29
4
61
59
62
63
2
3
58
57
28
6
V
V
Audio
Transducer
200mA
20mA
Ω
200mA
20mA
Ω
R18/24kΩ
VCC
Enable
9V
32.768kHz
(~ 33kHz)
39pF
163.85mV
R19/5kΩ
34
CREFL CREFH COM REFHI
16
15
14
FE0 AGD0 BCP0
kΩ
mVA
LO W
Segment and Decimal Point Drive
10's
20
19
18
FE1 AGD1 BCP1
HOLD
22
21
13
25
26
24
23
k/m/ AC/–/ –MEM/ BCP3 FE2 AGD2 BCP2
HOLD AUTO BATT
100's
Display
1000's
Annunciators
AUTO
11
12
7 8 9 10 27
50
RX VDISP
Ω/V
ANNUNC LOΩ/A
BP1
BP2
BP3
R13*
500kΩ
Voltage R14/9.9MΩ
44 VR1 (÷1)
Input
R12/1.111MΩ 41
VR2 (÷10)
R11/101kΩ 40
VR3 (÷100)
Current
Input
R2/1638.5Ω 36
R3/16.385kΩ 37
163.85kΩ 38
1.6385MΩ 39
R6/100kΩ 31
R7/100kΩ
Z1
Positive
Temperature
Coefficient
Resistor
Resistance
Input
0.1µF
LCD Bias
AC
-MEM
TC818A
Typical Application
DS21475C-page 3
TC818A
1.0
ELECTRICAL
CHARACTERISTICS
*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 affect device reliability.
Absolute Maximum Ratings*
Supply Voltage .......................................................15V
Analog Input Voltage ..................................VCC to VSS
Reference Input Voltage..............................VCC to VSS
Voltage at Pin 43 ................................. Common ±0.7V
Power Dissipation ............................................800mW
Operating Temperature Range................ 0°C to +70°C
Storage Temperature Range ..............-65°C to +150°C
TC818A ELECTRICAL SPECIFICATIONS
Electrical Characteristics: VA = 9V, TA = +25°C, unless otherwise specified.
Symbol
Parameter
Zero Input Reading
RE
Rollover Error
Min
Typ
Max
Unit
-0000
0000
+0000
Digital
Reading
200mV Range without 10MΩ
Resistor
-0001
—
+0001
Digital
Reading
200mV Range with 10MΩ
Resistor
-0000
0000
+0000
Digital
Reading
20mA and 200mA Range
—
—
±1
Counts
200mV Range without 10MΩ
Resistor
—
—
±3
200mV Range with 10MΩ
Resistor
—
—
±1
20mA and 200mA Range
NL
Linearity Error
—
—
±1
Count
IIN
Input Leakage Current
—
—
10
pA
EN
Input Noise
—
20
—
μVP-P
AC Frequency Error
—
±1
—
%
Test Conditions
Best Case Straight Line
BW = 0.1 to 10Hz
40 to 500Hz
—
±5
—
%
Open Circuit Voltage for Ohm
Measurements
—
570
660
mV
Excludes 200Ω Range
Open Circuit Voltage for LO Ohm
Measurements
—
285
350
mV
Excludes 200Ω Range
VCOM
Analog Common Voltage
2.8
3
3.3
V
VCTC
Common Voltage Temperature
Coefficient
—
—
50
ppm/°C
Display Multiplex Rate
—
100
—
Hz
Low Logic Input
—
—
1
μA
20mA, AC, I, LOW Ω, HOLD
Range, -MEM, OHMs
(Relative to DGND, Pin 58)
Logic 1 Pull-up Current
—
25
—
V
20mA, AC, I, LOW Ω, HOLD
Range, -MEM, OHMs
(Relative to DGND, Pin 58)
VOL
Low Logic Output
—
DGND +0.1
—
V
ANNUNC, DEINT: IL = 100μA
VOH
High Logic Output
—
VCC - 0.1
—
V
ANNUNC, DEINT: IL = 100μA
kHz
VIL
Buzzer Drive Frequency
—
4
—
Low Battery Flag Voltage
6.3
6.6
7
V
Operating Supply Current
—
0.8
1.5
mA
DS21475C-page 4
Error 40 to 2000Hz
(VCC - VCOM)
VCC to VSSA
© 2005 Microchip Technology Inc.
TC818A
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
PIN FUNCTION TABLE
Pin Number
(64-Pin PQFP)
Symbol
1
NC
Description
No connection.
2
OHM
Logic Input. “0” (Digital Ground) for resistance measurement.
3
20mA
Logic Input. “0” (Digital Ground) for 20mA full scale current measurement.
4
BUZ
5
XTAL1
32.768kHz Crystal Connection.
6
XTAL2
32.768kHz Crystal Connection.
7
VDISP
Sets peak LCD drive signal: VP - VDD-VDISP. VDISP may also be used to compensate for
temperature variation of LCD crystal threshold voltage.
8
BP1
LCD Backplane #1.
9
BP2
LCD Backplane #2.
10
BP3
LCD Backplane #3.
11
LOΩ/A
Buzzer. Audio frequency, 4kHz, output for continuity indication during resistance
measurement. A noncontinuous 4kHz signal is output to indicate an input over range
during voltage or current measurements.
LCD Annunciator segment drive for low ohms resistance measurement and current
measurement.
12
Ω/V
LCD Annunciator segment drive for resistance measurement and voltage measurement.
13
k/m/HOLD
LCD Annunciator segment drive for k (“kilo-Ohms”), m (“milliamps” and “millivolts”) and
HOLD mode.
14
BCP0
LCD segment drive for “b,” “c” segments and decimal point of least significant digit (LSD).
(One’s digit)
15
AGD0
LCD segment drive for “a,” “g,” “d” segments of LSD.
16
FE0
LCD segment drive for “f” and “e” segments of LSD.
17
NC
No connection.
18
BCP1
LCD segment drive for “b,” “c” segments and decimal point of 2nd LSD.
19
AGD1
LCD segment drive for “a,” “g,” “d” segments of 2nd LSD.
20
FE1
LCD segment drive for “f” and “e” segments of 2nd LSD.
21
BCP2
LCD segment drive for “b,” “c” segments and decimal point of 3rd LSD
(hundred’s digit).
22
AGD2
LCD segment drive for “a,” “g,” “d” segments of 3rd LSD.
23
FE2
24
BCP3
25
AC/-/AUTO
26
-MEM/BATT LCD annunciator segment drive for AC for low battery indication and memory (relative
measurement).
27
ANNUNC
LCD segment drive for “f,” “e” segments of 3rd LSD.
LCD segment drive for “b,” “c” segments and decimal point of MSD,
(thousand’s digit).
LCD annunciator segment drive for AC measurements, polarity, and auto-range operation.
Square wave output at the backplane frequency, synchronized to BP1. ANNUNC can be
used to control display annunciators. Connecting an LCD segment to ANNUNC turns it on;
connecting it to its backplane turns it off.
28
VCC
Positive battery supply connection.
29
COM
Analog circuit ground reference point. Nominally 3V below VCC.
30
DEINT
31
RMREFL
De-integrate output.
Ratiometric (resistance measurement) reference low voltage.
32
CREFL
Reference capacitor negative terminal CREF = 0.1μf.
33
CREFH
Reference capacitor positive terminal CREF = 0.1μf.
34
REFHI
Reference voltage for voltage and current measurement. Nominally 163.85mV.
35
ΩR1
Standard resistor connection for 200Ω full scale.
36
ΩR2
Standard resistor connection for 2000Ω full scale.
© 2005 Microchip Technology Inc.
DS21475C-page 5
TC818A
TABLE 2-1:
PIN FUNCTION TABLE (CONTINUED)
Pin Number
(64-Pin PQFP)
Symbol
37
ΩR3
Standard resistor connection for 20kΩ full scale range.
38
ΩR4
Standard resistor connection for 200kΩ full scale range.
39
ΩR5
Standard resistor connection for 2000kΩ full scale.
40
VR3
Voltage measurement ÷ 100 attenuator.
41
VR2
Voltage measurement ÷ 10 attenuator.
42
VR5
Voltage measurement ÷ 10,000 attenuator.
43
VR4
Voltage measurement ÷ 1000 attenuator.
44
VI
Unknown voltage input ÷ attenuator.
45
II
Unknown current input.
46
ACVL
47
CI
Integrator capacitor connection. Nominally 0.1μF. (Must have low dielectric absorption.
Polypropylene dielectric suggested.)
48
NC
No connection.
49
CAZ
Auto-zero capacitor connection. Nominally 0.1μF.
50
RX
Unknown resistance input.
51
CFI
Input filter connection.
52
ADI
Negative input of internal AC-to-DC operational amplifier.
53
ADO
Output of internal AC-to-DC operational amplifier.
54
RΩBUF
Active buffer output for resistance measurement. Integration resistor connection.
Nominally 220kΩ.
55
RVIBUF
Active buffer output for voltage and current measurement. Integration resistor connection.
Nominally 15kΩ.
56
ACVH
57
VSS
58
DGND
59
RANGE
60
HOLD
Input to hold display. Connect to DGND to "FREEZE" display.
61
-MEM
Input to enter Memory Measurement mode for relative measurements. The two LSDs are
stored and subtracted from future measurements.
62
DC(Ω)/
AC(LOΩ)
Input that selects AC or DC option during voltage/current measurements. For resistance
measurements, the ohms or low power (voltage) ohms option can be selected.
63
I
64
NC
Description
Low output of AC-to-DC converter.
Positive output of AC-to-DC converter.
Negative supply connection. Connect to negative terminal of 9V battery.
Internal logic digital ground. Ground connection for the logic "0" level.
Nominally 4.7V below VCC.
Input to set manual operation and change ranges.
Input to select measurement. Connect to logic "0" (digital ground) for current measurement.
No connection.
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 measurements will always be
made in the appropriate range.
DS21475C-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 is not pin compatible with, 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 turns the segment on;
connecting the segment to its backplane turns it off.
© 2005 Microchip Technology Inc.
TC818A
FIGURE 3-1:
TC818A ANALOG SECTION
0.1µF
Ω RX 50
S12 V • 1/1
R6/100kΩ RMREFL 31
S21 DE • Ω
R7/100 kΩ
Ohms
Input R8/220 Ω
(PTC)
R5/1.638MΩ
0.1µF
Ω R5 39
TC818A
10k Ω
Ω•
S25 1/1k
R4/163.85kΩ ΩR4 38
R3/16385Ω
ΩR3 37
Z1
R2/1638.5Ω
ΩR2 36
Ω•
S26 1/100
Ω•
S27 1/10
6.2V
R1/163.85Ω
ΩR1 35
S28 Ω • 1/1
S44 Ω • HI Ω
1.5Ω
S43
VCC
+ Ω • LOΩ
–2.8V REF AMP
1.5 kΩ
+
Current Input
S33 S32 S31 S30 S29
Ω • Ω • Ω • Ω • Ω•
1/1 1/10 1/1001/1k 1/10k
VCC
W+1
S10
R15/9Ω
II 45
200mA
R16/1Ω
34 REFHI
≈163.85mV
S22
DE • Ω
VI 44
S1
*Not Required when Resistor
Network is Used
R12/1.11M Ω VR2 41
Common
S2
V•1/100
R10/10kΩ VR4 43
S4
V•1/1k
R9/1kΩ
S5
V•1/10k
VR5 42
53
R22
470
kΩ
+
AC-to-DC
Converter
Op Amp
ADO
33 CREFH
V•1/10
S3
D2
R23
10kΩ
V•1/1
R11/101kΩ VR3 40
4.7µF
S22
DE • Ω
V• V•
V• V•
1/10 1/100 1/1 1/10k
k
S6 S7 S8 S9
R13/500kΩ*
S20 DE
CREFH
0.1µF
32 CREFL
S18 DE
S19 DE+ Ω
+
Ω+AC
S11
–
S16 DE+
S17 DE51 CFI
R21
2.2
MΩ
C4
1µF
C2
ADI
R20/100kΩ
0.01µF
C6
52
0.22µF
ACVH 56
R26
3kΩ
R19/5k Ω
29
D3 D4
Voltage
Input
R14/9.9 MΩ
R24
C3
10kΩ +1µF
R18/24k Ω
Analog
Cmmon
–
20mA
D1
VCC
VCC
S24Ω • 1/10k
C1/1µF
R27/2kΩ
ACVH 46
INT•( Ω + DC)
S13
S14
INT• Ω •ACΩ
S40
+
Buffer
S38 AZ
–
S15 AZ
–
INT•Ω•ACΩ
S39
INT+ Ω + DC
S35
Ω
S37
Ω
Ω
S34Ω
54
RΩBUF
–
+
+
Comparator
To Digital
Section
Integrator
49
55
RΩ RVI C
BUF BUF AZ
220
0.01µF
k Ω 150
k Ω CAZ
47
INT
0.01µF
CINT
RΩBUF
© 2005 Microchip Technology Inc.
DS21475C-page 7
TC818A
3.2
Resistance, Voltage, Current
Measurement Selection
The TC818A is designed to measure voltage, current,
and resistance. Auto-ranging is available for resistance
and voltage measurements. The OHM (Pin 2) and
I (Pin 63) input controls are normally pulled internally to
VCC.
By tying these pins to DGND (Pin 58), the TC818A is
configured internally to measure resistance, voltage, or
current. The required signal combinations are shown in
Table 3-1.
TABLE 3-1:
TC818A MEASUREMENT
SELECTION LOGIC
Function Select Pin
0 = Digital Ground
1 = Floating or Tied to VCC
TABLE 3-2:
Full-Scale
Range
Selected
Measurement
OHM (Pin 2)
I (Pin 63)
0
0
Voltage
0
1
Resistance
1
0
Current
1
1
Voltage
Resistance Measurements
(Ohms and Low Power Ohms)
The TC818A can be configured to reliably measure incircuit resistances shunted by semiconductor junctions. The TC818A Low Power Ohms Measurement
mode limits the probe open circuit voltage. This prevents semiconductor junctions in the measured system
from turning on.
In the Resistance Measurement mode, the Ω/LOΩ
(Pin 62) input selects the Low Power Ohms Measurement mode. For low power ohms measurements,
Ω/LOΩ (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,
LOΩ, will be activated. On power-up, the Low Power
Ohms mode is not active.
If the Manual Operating mode has been selected, toggling Ω/LOΩ resets the TC818A back to the AutoRange mode. In Manual mode, the decision to make a
normal or low power ohms measurement should be
made before selecting the desired range.
OHMS RANGE LADDER
NETWORK
Standard
Resistance
Low Power
Ohms Mode
200Ω
163.85Ω (R1)
NO
2000Ω
1638.5kΩ (R2)
YES
20kΩ
16,385Ω(R3)
YES
200kΩ
163,85Ω (R4)
YES
1,638,500Ω (R5)
YES
2,000kΩ
3.4
Note 1: OHM and I are normally pulled internally high to
VCC (Pin 28). This is considered a logic “1”.
2: Logic “0” is the potential at digital ground (Pin 58).
3.3
R8, a positive temperature coefficient resistor, and the
6.2V zener, Z1, provide input voltage protection during
ohms measurements.
Ratiometric Resistance
Measurements
The TC818A measures resistance ratiometrically.
Accuracy is set by the external standard 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 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 resistors are automatically switched to provide the
proper range.
Figure 3-2 shows a detailed block diagram of the
TC818A, configured for ratiometric resistance measurements. During the signal integrate phase, the reference
capacitor charges to a voltage inversely proportional to
the measured resistance, RX. Figure 3-3 shows that the
conversion accuracy relies on the accuracy of the
external standard resistors.
Normally, the required accuracy of the standard resistances will be dictated by the accuracy specifications of
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 for accuracy.
TABLE 3-3:
REFERENCE RESISTORS
Full Scale
Range
Reference Resistor
Ω/Count
200k
163.85
0.1
2k
1638.5
1
20k
16385
10
200k
163,850
100
2M
1,638,500
1000
The low power ohms measurement is not available on
the 200Ω full scale range. Open circuit voltage on this
range is below 2.8V. The standard resistance values
are listed in Table 3-2.
DS21475C-page 8
© 2005 Microchip Technology Inc.
TC818A
FIGURE 3-2:
RATIOMETRIC RESISTANCE MEASUREMENT FUNCTIONAL DIAGRAM
9V
VSS
R5/1638500 Ω
39
S29
38
S30
37
S31
R2/1638.5Ω 36
S32
Low Ohms
S33
Ω • LO
VCC
R4/163850Ω
R3/16385 Ω
÷10k
÷1k
÷100
÷10
÷1
R1/163.85Ω
35
÷10k ÷1k
R8
220Ω
(PTC)
DE • Ω
S23
33
S20
VCC
28
Ω • HIΩ
VA
~1.5kΩ
÷100 ÷10 ÷1
S24 S25 S26 S27 S28
57
10kΩ
Ohms
R18
24kΩ
REFHI
34
~1.5kΩ
Voltage
Reference
+
DE + Ω
–
Analog
Common
VCC -2.6V
CREF
0.1µF
32
S18
DE
31
S21
DE • Ω
R6/100kΩ
R7/100kΩ
RX
TC818A
Buffer
DE
50
S12
V•
Unknown
S13
INT • ( Ω + DC)
1
1
S37
S36
Ω
S34
Ω
Ω
S35
Ω
Integrator
49
RΩBUF 54 55
RVIBUF
150kΩ
Comparator
47
CAZ
0.1µF
CINT
0.1µF
220kΩ
FIGURE 3-3:
5kΩ
29
≈ VCC -2.8V
DE S19
+
RESISTANCE MEASUREMENT ACCURACY SET BY EXTERNAL
STANDARD RESISTOR
Example: 200kΩ Full Scale Measurement
VA =
RS
163.85kΩ
0.64V for Ohms
0.32V for LO Ohms
CREF
100kΩ
+
VR
163.85kΩ
(a ) VR = ⎛ ------------------------------------------------⎞
⎝ 163.85 + 220 + R X⎠ x0.64
(b)
RX
⎞ x0.64
V X = ⎛⎝ -------------------------------------------------------------163.85kΩ + 220Ω + R X⎠
(c) “Ramp Up Voltage” = “Ramp Down Voltage”
.
VX
VX
= ----------------T
. . ----------------xT
( RI CI ) I
( R I C I ) DE
220Ω
VX
Unknown
RX
To Analog Buffer
Where:
RI = Integrating Resistor, TI = Integrate Time
CI = Integrating Capacitor, TDE = De-integrate Time
(d) RX = 163.85
(TDE)
TI
Independent of RI, CI or Internal Voltage Reference
© 2005 Microchip Technology Inc.
DS21475C-page 9
TC818A
3.5
Voltage Measurement
Resistive dividers are automatically changed to provide
in range readings for 200mV to 2000V full scale readings (Figure 3-1). The input resistance is set by external resistors R14/R13. The divider leg resistors are R9R12. The divider leg resistors give a 200mV signal VI
(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.
3.6
Current Measurement
The TC818A measures current only under manual
range operation. The two user selectable, full scale
ranges are: 20mA and 200mA. Select the current Measurement mode by holding the I input (Pin 63) LOW at
digital ground potential. The OHM input (Pin 2) is left
floating or tied to the positive supply.
Two ranges are possible. The 20mA full scale range is
selected by connecting the 20mA input (Pin 3) to digital
ground. If left floating, the 200mA full scale range is
selected.
External current-to-voltage conversion resistors are
used at the current input (II input, Pin 45). For 20mA
measurements, a 10Ω resistor is used. The 200mA
range requires a 1Ω resistor; full scale is 200mV.
Printed circuit board trace resistance between analog
common and R16 must be minimized. In the 200mA
range, for example, a 0.05 trace resistance will cause a
5% current-to-voltage conversion error at II (Pin 45).
The extended resolution measurement option operates
during current measurements.
To minimize rollover error, the potential difference
between analog common (COM, Pin 29) and system
common must be minimized.
3.7
The minimum AC full scale voltage range is 2V. The DC
full scale minimum voltage is 200mV.
AC current measurements are available on the 20mA
and 200mA full scale current ranges.
3.8
Conversion Timing
The TC818A analog-to-digital converter uses the conventional dual slope integrating conversion technique,
with an added phase 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,
readily available 32.768kHz crystal. 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 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
(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
detected in the Reference De-integrate mode, the autozero phase is entered. Figure 3-4 shows the basic
TC818A timing relationships.
AC-to-DC Measurements
In voltage and 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
Measurement mode. For AC measurements (current or
voltage), AC/DC (Pin 62) is momentarily brought LOW
to digital ground potential; the 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 the desired range.
DS21475C-page 10
© 2005 Microchip Technology Inc.
TC818A
FIGURE 3-4:
BASIC TC818A CONVERSION TIMING
TC818A
Signal
INT
Phase
Auto-Zero
Phase
REF
DEINT
Phase
Next Conversion
Auto-Zero Cycle
Extended Resolution
Zero Crossing
External Crystal = 32.768kHz
Internal Clock Period = tP = 2/32.768 = 61.04µsec
Total Conversion Time = tCONV = 8000(tP)
= 488.3msec ≈ 2 conv/sec
Integration Time = TI = 1638.5(tP) = 100msec
Min. Auto-Zero
Time
Fixed
1638.5tP
*Max.
3000tP
3361.5tP
tI
tDE
µ To
Input
Signal
tCONV = 8000tP
*In Auto-Range Operation, Maximum
is 2000tP and minimum Auto-Zero Time is 4361.5tP
3.9
Manual Range Selection
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 range option is
entered, range changes are made by momentarily
grounding the RANGE control input. The TC818A
remains in the Manual Range mode until the measurement function (voltage or resistance), or measurement
option (AC/DC, Ω/LOΩ) changes. This causes the
TC818A to return to auto-ranging operation.
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 resolution display format. Also, see Figure 3-6
and Figure 3-7.
Maximum Reference De-integrate Time
= tDE 3000(tP) = 183.1msec
(manual extended resolution)
= 2000(tP) = 122.1msec (auto-range)
Maximum Auto-Zero Time
= (8000 - 3000 - 1638.5)
(tP) = 205.1msec (manual extended resolution)
= (8000 - 3000 - 1638.5)
(tP) = 205.1msec (manual extended resolution)
FIGURE 3-5:
MANUAL RANGE
SELECTION RESISTANCE
MEASUREMENTS
Manual
Range
Select
Continuity
Indicator
Output 4kHz
Audio
Frequency
Continuous
4kHz Buzzer
Yes
Is
RX < 19
?
No
Is
RX > 3000
?
Over Range
Indicator
Yes
"1" = > Flashing
MSD
No
Is
RX > 2000
?
No
Display
"1" 000
Yes*
Display Last
3 Digits and
Flash MSD
Extended Resolution
Feature
Display
True
Reading
*Mode also operates when Auto-Ranging Operator is selected
and 2MΩ < RX < 2.999MΩ.
© 2005 Microchip Technology Inc.
DS21475C-page 11
TC818A
FIGURE 3-6:
MANUAL RANGE
SELECTION CURRENT
MEASUREMENTS
FIGURE 3-7:
MANUAL RANGE
SELECTION VOLTAGE
MEASUREMENTS
Range
Select
Range
Select
Noncontinuous
Noncontinuous
Yes
Output 4kHz
Audio
Frequency
Output 4kHz
Audio
Frequency
Over Range
Indicator
Over Range
Indicator
Is
IX > 3000
?
Yes
"1" = > Flashing
MSD
No
Is
IX > 2000
?
3.10
Display
"1" 000
Yes
Display Last
3 Digits and
Flash MSD
Is
VX > 3000
?
Yes
"1" = > Flashing
MSD
No
Is
VX > 2000
?
No
No
Display
True
Reading
Display
True
Reading
Display
"1" 000
Yes
Display Last
3 Digits and
Flash MSD
Extended
Resolution
Feature
Extended Resolution Manual
Operation
When operated in the Manual Range mode, the
TC818A extends resolution by 50% for current, voltage, and resistance measurements. Resolution
increases to 3000 counts from 2000 counts. The
extended resolution feature operates only in 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 significant digits display data
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.
DS21475C-page 12
© 2005 Microchip Technology Inc.
TC818A
3.11
-MEM Operating Mode
Bringing -MEM (Pin 61) momentarily LOW configures
the TC818A “-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 represents 5% of full scale. The last two significant
digits are stored and subtracted from all the following
input conversions.
The following examples clarify operation:
EXAMPLE 3-1:
RI (N)
MEM
IN AUTO-RANGING
= 18.21kΩ (20kΩ Range) = ≥ Display 18.21kΩ
= ≥ Store 0.21kΩ
RI (N+1)= 19.87kΩ (20kΩ Range)
= ≥ Display 19.87 - 0.21 = 19.66kΩ
RI (N+2)= 22.65kΩ (200kΩ Range)
= ≥ Display 22.7kΩ and MEM disappears
EXAMPLE 3-2:
RI (N)
MEM
IN FIXED RANGE
(200 FULL SCALE)
= 18.21kΩ = ≥ Display 18.2kΩ
= ≥ Store 8.2Ω
RI (N+1) = 36.7Ω
= ≥ Display 36.7 - 8.2 = 28.5Ω
RI (N+2) = 5.8Ω
= ≥ Display 5.8-8.2 = -2.4Ω*
*Will display minus resistance if following input is less than
offset stored at fixed range.
EXAMPLE 3-3:
VI (N)
MEM
IN FIXED RANGE 20V
FULL SCALE
= 0.51V = ≥ Display 0.51V
= ≥ Store 0.51V
VI (N+1) = 3.68V
= ≥ Display 3.68 - 0.51 = 3.17V
VI (N+2) = 0.23V
= ≥ Display 0.23 -0.51 = -0.28V
VI (N+3) = -5.21V
= ≥ Display - 5.21 - 0.51 = -5.72V
On power-up, the “-MEM” mode is not active. Once the
“-MEM” is entered, bringing MEM LOW again returns
the TC818A to normal operation.
The “-MEM” mode is also cancelled whenever the measurement type (resistance, voltage, current AC/DC,
Ω/LOΩ) or range is changed. The LCD -MEM annunciator will be off in normal operation.
In the auto-range operation, 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.
© 2005 Microchip Technology Inc.
The “-MEM” Operating mode can be very useful in
resistance measurements when lead length resistance
would cause measurement errors.
3.12
Automatic Range Selection
Operation
When power is first 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/DC, Ω/LOΩ).
The automatic voltage range selection begins on the
most sensitive scale first: 200mV for DC or 2V for AC
measurements. The voltage range selection flow chart
is shown in Figure 3-8.
Internal input protection diodes to VCC (Pin 28) and VSS
(Pin 57) clamp the input voltage. The external 10MΩ
input resistance (see R14 and R13 of Functional diagram) limits current safely in an over range condition.
The voltage range selection is designed to maximize
resolution. For input signals less 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 the 4kHz signal to be on for
122msec, off for 122msec, on for 122msec and off for
610msec (see Figure 3-14).
During voltage auto-range operation, the extended resolution feature operates on the 2000V range only (see
Extended Resolution Operating mode discussion).
The resistance automatic range selection procedure is
shown in Figure 3-9. The 200Ω range is the first range
selected, unless the LOW ohms resistance measurement option is selected. In LOW ohms operation, the
first full scale range tried is 2kΩ.
The resistance range selected maximizes sensitivity. If
the conversion results in a reading less than 180, the
next most sensitive full scale range is tried.
If the conversion is less than 19 in auto-range operation, a continuous 4kHz signal is output at BUZ (Pin 4).
An over range input does not activate the buzzer.
Out-of-range input conditions are displayed by a blinking MSD with the three LSDs set to “000.”
The extended resolution feature operates only on the
2000kΩ and 2000V full scale range during auto-range
operation. A blinking “1” most significant digit is interpreted as the digit 2. The three least significant digits
display data normally.
DS21475C-page 13
TC818A
FIGURE 3-8:
AUTO-RANGE
OPERATION: VOLTAGE
MEASUREMENT
N = 0 If DC
N = 1 If AC
FIGURE 3-9:
N = 0; 200mV Full Scale Range
N = 1; 2V Full Scale Range
AUTO-RANGE
OPERATION: RESISTANCE
MEASUREMENT
N = 0 If Ω
N = 1 If LOΩ
N = 0; 200Ω Full Scale Range
N = 1; 2kΩ Full Scale Range
N = NK
(Remain in Range
Selected during the Kth
Conversion)
Kth
Conversion
VX = (1/10N) VIN
(Remain in Range
Selected during the
Kth Conversion)
Kth
Conversion
RX = 1 RIN
10N
N = N –1
Continuity
Indicator
VX < 180
?
Activate
Buzzer
Yes
N = 0 If DC
N = 1 If AC
?
No
Yes
RX < 19
?
Continuous
4kHz Signal
N = N –1
No
Yes
RX < 180
No
Yes
?
VX > 2000
?
No
Display
Voltage (V)X
No
Yes
N = N +1
No
Extended
Resolution
No
Display
"1" XXX
Flash MSD
Activate
Buzzer
No
N = N +1
N=4
?
Yes
RX > 3000
?
Yes
Display
"1" 000
Flash MSD
K = K +1
Yes
Yes
Yes
Display
Resistance
?
N=4
?
VX > 3000
?
Yes
RX > 2000
K = K +1
N = 0 If Ω
N = 1 If LOΩ
?
Over
Range
No
Display
"1" XXX
Flash MSD
Display
"1" 000
Flash MSD
Extended Resolution
Over Range
Start: Power-on, Function or Measurement Option Change
Start: Power-on, Function or Measurement Option Change
DS21475C-page 14
© 2005 Microchip Technology Inc.
TC818A
3.13
Low Battery Detection Circuit
The TC818A contains a low battery detector. When the
9V battery supply has been depleted to a 7V nominal
value, the LCD low battery annunciator is activated.
The low battery detector is shown in Figure 3-10. The
low battery annunciator remains OFF with the battery
supply greater than 0.7V. The annunciator is ON before
the supply battery has reached 6.3V.
FIGURE 3-10:
LOW BATTERY
DETECTOR
The TC818A internally generates two intermediate
LCD drive potentials (VH and VL) from a resistive
divider (Figure 3-11) between VCC and VDISP. The latter
impedance is approximately 150kΩ. This drive method
is commonly known as 1/3 bias. With VDISP connected
to digital ground, VP ≈ 5.0V.
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:
VCC
Low Battery Detector
1/3 BIAS LCD DRIVE
VCC
TC818A
R1
VT
Comparator
+
To LCD
Annunciator
Selection Logic
R3
–
50k
R2
VZ ≈ 6.2V
VSS
R2
= 6.2V
VT = 73
R1 + R2
To
Triplex
Segment
Drive Logic
VH
50k
VL
50k
Low Battery Annunciator Displayed for VS < 7V.
3.14
TC818A
Triplex Liquid Crystal Display
(LCD) Drive
VCC - VDISP
For example, if VDISP is set at a potential 3V below
VCC, the peak drive signal is:
VP = 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 VCC -VDISP = 3V.
Since the VDISP pin is available, the user may adjust
the “ON” and “OFF” LCD levels for various manufacturers’ displays, by changing VP signal across it, or 1.92V
for VDISP = 3V.
VDISP
VP = VCC - VDISP
"OFF" = VP/3 RMS
"ON" = 11 VP RMS
3 3
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:
See VDSIP
For Proper VP
with Resistive
Divider
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
configuration is 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
Part No.: VIM-328-DP
USA Office:
VL Electronics, Inc.
3171 LOs Feliz Blvd, #303
Los Angeles, CA 90039
Tel: (213) 738-8700
“OFF” segments may become visible at high LCD operating temperatures. A voltage with a -5 to -20mV/°C
temperature coefficient can be applied to VDISP to
accommodate the liquid crystal temperature operating
characteristics, if necessary.
© 2005 Microchip Technology Inc.
DS21475C-page 15
TC818A
FIGURE 3-12:
TRIPLEX LCD DRIVE WAVEFORMS
TC818A
Segments
Backplanes
Segments
1
2
3
4
5
6
VP
VH
a (FE – BP1)
"ON"
VP (3V)
BP1
VP
VH
b (BCP – BP1)
"ON"
VL
BP2
0
VP
VH
VL
BP3
c (BCP – BP2)
"ON"
0
Waveforms to Generate
d (AGD – BP3)
"ON"
e (FE – BP2)
"OFF"
a
BP1
BP2
e
c
d
BP3
FE
AGD
DS21475C-page 16
BCP
f (FE – BP1)
"OFF"
BACKP
g
LANES
b
f
1
g (AGD – BP2)
"ON"
0
-VL
-VH
-VP
VP
VH
VL
0
-VL
-VH
-VP
VP
VH
VL
0
-VL
-VH
-VP
VP
VH
VL
0
-VL
-VP
VP
VH
VL
0
-VL
-VP
VP
VH
VL
-VL
-VP
VP
VH
VL
0
-VL
-VH
-VP
2
3
4
5
6
Applied
RMS Voltage
VRMS =
11 V
P
3 3
VRMS =
11 V
P
3 3
VRMS =
11 V
P
3 3
VRMS =
11 V
P
3 3
VRMS =
VP
3
VRMS = VP
3
VRMS =
11 V
P
3 3
© 2005 Microchip Technology Inc.
TC818A
3.16
FIGURE 3-13:
External Crystal
The TC818A 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 488.3msec ( ≈ 2 conversions/
second). Integration time is 1638.5 clock periods or
100msec.
TYPICAL LCD
CONFIGURATION,
TC818A TRIPLEX
–+
-MEM
The 32kHz quartz crystal is readily available and
inexpensive. The 32kHz crystal is commonly used in
digital clocks and counters.
LO W
HOLD
AC
kΩ
mVA
AUTO
Several crystal sources exist. A partial listing 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.
TABLE 3-4:
TYPICAL LCD CONFIGURATION
PAD
BP1
BP2
BP3
PAD
BP1
BP2
BP3
1
—
—
SCALE
19
—
—
BP3
2
X0
X1
X2
20
—
BP2
—
3
X5
X4
X3
21
BP1
—
—
4
X6
X7
X8
22
—
LOW
A
5
X11
X10
X9
23
—
W
V
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
© 2005 Microchip Technology Inc.
DS21475C-page 17
TC818A
3.17
“Buzzer” Drive Signal
Figure 3-14. The BUZ output is active for any reading
over 2000 counts in both manual and auto-range operation. The buzzer is activated during an extended resolution measurement.
The BUZ output (Pin 4) will drive a piezo electric audio
transducer. The signal is activated to indicate an input
over range condition for current and voltage measurements, or continuity during resistance measurements.
The BUZ signal swings from VCC (Pin 28) to DGND
(Pin 58). The signal is at VCC when not active.
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.
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 resistance), or measurement option (AC/DC,
Ω/LOΩ), also activates the buzzer output for 15msec.
A range change during a current measurement will not
activate the buzzer output.
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
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
122ms
122ms
122ms
610ms
122ms
122ms
VCC
Digital Ground
1 Conversion
4kHz Signal
Noncontinuous Buzzer Signal Indicates Input Over Range
Power-up
VIN = 250mV
4000
Change
Range
8000 12000
Change
Range
Change
Range
Change Input
VIN = 3.2V
1000 Clock
Pulses
INT
Integrate
TSC818A
Signals
DEINT
AZ
100ms
1638.5
CP
122ms
2000
CP
250CP
250CP
Auto-Ranging
BUZ
(Pin 4)
200mV
Range
Over Range
2V
Range
In Range
4kHz 15ms
One Cycle of
Over Range Buzzer
4kHz
Buzzer Activated due
to Power-up
DS21475C-page 18
2500CP
250CP
3000CP
Manual Range
2V
Range
In Range
200mV
Range
Extended
Range
15ms
15ms
Due to Manual
Due to
Range Change Range Change
2V
Range
In Range
4kHz
2V Range
Out of Range
4kHz
610ms
122ms
Buzzer Activated due
to Previous Conversion
Over Range
Buzzer Activated
due to Previous
Conversion
Over Range
© 2005 Microchip Technology Inc.
TC818A
Vendors for piezo electric audio transducers are:
• Gulton Industries
Piezo Products Division
212 Durham Avenue
Metuchen, New Jersey 08840
(201) 548-2800
Typical P/Ns: 102-95NS, 101-FB-00
INTEGRATION RESISTOR
SELECTION
The TC818A automatically selects one of two external
integration resistors. RVIBUF (Pin 55) is selected for
voltage and current measurement. RΩBUF (Pin 54) is
selected for resistance measurements.
3.20.2
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:
Component Selection
3.20.1
• Taiyo Yuden (USA) Inc.
Arlington Center
714 West Algonquin Road
Arlington Heights, Illinois 60005
Typical P/Ns: CB27BB, CB20BB, CB355BB
3.18
3.20
DECIMAL POINT SELECTION
RVIBUF SELECTION (PIN 55)
In auto-range operation, the TC818A operates with a
200mV maximum full scale potential at VI (Pin 44).
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 potential at VI (Pin 44).
The integrator output swing should be maximized, but
saturations must be avoided. The integrator will swing
within 0.45V of VCC (Pin 28) and 0.5V of VSS (Pin 57)
without saturating. A ±2V swing is suggested. The
value of RVIBUF is easily calculated, assuming a worst
case extended resolution input signal:
1*9
*9
*9
DP3
DP2
DP1
2000V, 2000kΩ
OFF
OFF
OFF
200V, 200kΩ
OFF
OFF
ON
20V, 20kΩ
OFF
ON
OFF
VINT = Integrator swing = ±2V
2V, 2kΩ
ON
OFF
OFF
tI
= Integration time = 100msec
200V, 200Ω
OFF
OFF
ON
OFF
OFF
ON
CI
= Integration capacitor = 0.1μF
200mV, 200Ω
20mA
OFF
ON
OFF
200mA
OFF
OFF
ON
Full Scale Range
3.19
VMAX = Maximum input at VI = 300mV
EQUATION 3-1:
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:
•
•
•
•
Where:
Slew Rate: 1V/μsec
Unity Gain Bandwidth: 0.4MHz
Open Loop Gain: 44dB
Output Voltage Swing (Load = 10kΩ) ± 1.5V
(Referenced to Analog Common)
RVIBUF =
3.20.3
VMAX(TI)
= 150kΩ
VINT(CI)
RΩBUF SELECTION (PIN 54)
In ratiometric resistance measurements, the signal at
RX (Pin 50) is always positive, with respect to analog
common. The integrator swings negative.
The worst case integrator swing is for the 200Ω range
with the manual, extended resolution option.
The input voltage, VX (Pin 50) is easily calculated (see
Figure 3-15).
When the AC measurement option is selected, the
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.
© 2005 Microchip Technology Inc.
DS21475C-page 19
TC818A
FIGURE 3-15:
RΩ CALCULATION (200Ω
MANUAL OPERATION)
VCC = 9V
SW33
RS ≈ 600Ω
3.21
The integration capacitor, CINT, must have low dielectric absorption. A 0.1μF polypropylene capacitor is suggested. The auto-zero capacitor, CAZ, and reference
capacitor, CREF, should be selected for low leakage
and dielectric absorption. Polystyrene capacitors are
good choices.
3.22
R1
163.85Ω
R2
220Ω
With an input voltage near full scale on the 200mV
range, R19 is adjusted for the proper reading.
300Ω
3.23
Analog Common = VCC – 3V
Where:
VANCOM
RS
RI
RX
RS
=
=
=
=
=
Potential at Analog Common ≈ 2.7V
220Ω
163.85Ω
300Ω
Internal switch 33 resistance ≈ 600Ω
(VCC – VANCOM)RX
(RX + RS + R1 + R8)
= 0.63V
For a 3.1V integrator swing, the value of RΩBUF is
easily calculated:
Where:
VINT
TI
CI
RXMAX
VXMAX
= Integrator swing = 3.1V
= Integration time = 100msec
= Integration capacitor = 0.1µF
= 300Ω
= 700mV
EQUATION 3-3:
RΩBUF =
VXMAX(TI)
= 200kΩ
CI(VINT)
With a low battery voltage of 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.
DS21475C-page 20
Display Hold Feature
The LCD will not be updated when HOLD (Pin 60) is
connected to GND (Pin 58). Conversions are made, but
the display is not updated. A HOLD mode LCD annunciator is activated when HOLD is low.
The LCD HOLD annunciator is activated through the
triplex LCD driver signal at Pin 13.
3.24
Flat Package Socket
Sockets suitable for prototype work are available. A
USA source is:
EQUATION 3-2:
RΩBUF =
Reference Voltage Adjustment
The TC818A contains a low temperature drift internal
voltage reference. The analog common potential
(Pin 29) is established by this reference. Maximum drift
is a low 75ppm/°C. Analog common is designed to be
approximately 2.6V below VCC (Pin 28). A resistive
divider (R18/R19, Functional Diagram) sets the
TC818A reference input voltage (REFHI, Pin 34) to
approximately 163.85mV.
VX
R3
Capacitors - CINT, CAZ and CREF
• 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
Resistor attenuator networks for voltage and resistance
measurements are available from:
• Caddock Electronics
1717 Chicago Avenue
Riverside, CA 92507
Tel: (714) 788-1700
TWX: 910-332-6108
TABLE 3-6:
RESISTIVE LADDER
NETWORKS
Attenuator
Accuracy
Attenuator Type
Caddock
Part Number
0.1%
0.25%
0.25%
Voltage
Voltage
Resistance
1776-C441
1776-C44
T1794-204-1
© 2005 Microchip Technology Inc.
TC818A
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
PIN 1
W
P
Standard Reel Component Orientation
for TR Suffix Device
Carrier Tape, Number of Components Per Reel and Reel Size
Package
64-Pin PQFP
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
32 mm
24 mm
250
13 in
Note: Drawing does not represent total number of pins.
4.3
Package Dimensions
64-Pin PQFP
7° MAX.
.009 (0.23)
.005 (0.13)
PIN 1
.018 (0.45)
.012 (0.30)
.041 (1.03)
.031 (0.78)
.555 (14.10)
.547 (13.90)
.687 (17.45)
.667 (16.95)
.031 (0.80) TYP.
.555 (14.10)
.547 (13.90)
.687 (17.45)
.667 (16.95)
.010 (0.25) TYP.
.120 (3.05)
.100 (2.55)
.130 (3.30) MAX.
Dimensions: mm (inches)
© 2005 Microchip Technology Inc.
DS21475C-page 21
TC818A
SALES AND SUPPORT
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1.
2.
3.
Your local Microchip sales office
The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
New Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
DS21475C-page 22
© 2005 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED,
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RELATED TO THE INFORMATION, INCLUDING BUT NOT
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Microchip disclaims all liability arising from this information and
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Trademarks
The Microchip name and logo, the Microchip logo, Accuron,
dsPIC, KEELOQ, microID, MPLAB, PIC, PICmicro, PICSTART,
PRO MATE, PowerSmart, rfPIC, and SmartShunt are
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AmpLab, FilterLab, Migratable Memory, MXDEV, MXLAB,
PICMASTER, SEEVAL, SmartSensor and The Embedded
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Analog-for-the-Digital Age, Application Maestro, dsPICDEM,
dsPICDEM.net, dsPICworks, ECAN, ECONOMONITOR,
FanSense, FlexROM, fuzzyLAB, In-Circuit Serial
Programming, ICSP, ICEPIC, Linear Active Thermistor,
MPASM, MPLIB, MPLINK, MPSIM, PICkit, PICDEM,
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trademarks of Microchip Technology Incorporated in the
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SQTP is a service mark of Microchip Technology Incorporated
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All other trademarks mentioned herein are property of their
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© 2005, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received ISO/TS-16949:2002 quality system certification for
its worldwide headquarters, design and wafer fabrication facilities in
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devices, Serial EEPROMs, microperipherals, nonvolatile memory and
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and manufacture of development systems is ISO 9001:2000 certified.
© 2005 Microchip Technology Inc.
DS21475C-page 23
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DS21475C-page 24
© 2005 Microchip Technology Inc.