• 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 berPackage
TC818ACBU64-PinPQFP0°Cto+70°C
Operating
Temperature Range
General Description
The TC818A is an integrating analog-to-digital converter (ADC) wi th a 3-1/2 digit numeric LCD driver,
automatic ranging, and single 9V battery operation.
The numeric display provides 0.05% resolution and a
full set of annunciators that spell out the TC818A's
many operating modes.
Automatic range selection is provided for both voltage
(DC and AC) and ohms (high and l ow power)measurements. Expensive and bulky mechanical range
switches are not required. Five full scale ranges are
available,with automatic selectionof external volt/ohm
attenuators over a 1 to 10,000 range. Two current
ranges, 20mA and 200mA, can be manually selected.
The auto-range feature can be bypassed, allowing
input attenuator selectionthrough a single line input.
During Manual mode operation, resolution is extended
to 3000 counts full scale. Extended resolution is also
available during 2000kΩ and 2000V full scale autorange operation. The extendedrangeoperationis indicatedbyaflashing1MSDandbythefullyextended bar
graph.
The TC818A includes an AC-to-DC converter for AC
voltage and current measurements. Only external
diodes/resistors/capacitors are required. Other features include a Memory mode, low battery detection,
display HOLD input, and continuity buzzer driver.
The 3-1/2 digit numeric display includes a full set of
annunciators. Decimal points are adjusted as automatic or manual range changes occur, and Voltage,
Current, and Ohms Operating modes are displayed.
Additionalannunciatorsare activated for manual, auto,
memory, HOLD, AC, low power ohms, and low battery
conditions.
The TC818A i s available in a surface mounted 64-pin
flat package. Combining a numeric display driver, single 9V battery operation, internal r ange switching, and
compact surface mounting, the TC818A is ideal for
advanced portable instruments.
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
12Ω/VLCD Annunciator segment drive for resistance measurement and voltage measurement.
13k/m/HOLDLCD Annunciator segment drive for k (“kilo-Ohms”), m (“milliamps” and “millivolts”) and
14BCP0
15AGD0LCD segment drive for “a,” “g,”“d” segmentsof LSD.
16FE0LCD segment drive for “f” and “e” segments of LSD.
17NCNo connection.
18BCP1LCDsegmentdrive for “b,” “c” segments and decimal point of 2nd LSD.
19AGD1LCD segmentdrive for “a,” “g,”“d” segments of 2ndLSD.
20FE1LCD segment drive for “f” and “e” segments of 2nd LSD.
21BCP2LCDsegmentdrive for “b,” “c” segments and decimal point of 3rd LSD
22AGD2LCD segment drive for “a,” “g,”“d” segmentsof 3rd LSD.
23FE2LCD segment drive for “f,” “e” segmentsof 3rd LSD.
24BCP3LCDsegmentdrive for “b,” “c” segments and decimal point of MSD,
25AC/-/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
27ANNUNCSquare wave output at the backplane frequency, synchronized to BP1. ANNUNC can be
28V
29COMAnalog circuit ground reference point. Nominally 3V below V
30DEINTDe-integrate output.
31RM
32C
33C
34REFHIReferencevoltage for voltage and currentmeasurement.Nominally 163.85mV.
35ΩR1Standardresistor connection for 200Ω fullscale.
36ΩR2Standard resistor connection for 2000Ω full scale.
SymbolDescription
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.
Negative supply connection. Connect to negative terminal of 9V battery.
Nominally 4.7V below V
Input to set manual operation and change ranges.
Input to hold display. Connect to DGND to "FREEZE" display.
storedandsubtracted from futuremeasurements.
Input that selects AC or DC option during voltage/current measurements. For resistance
Ω)
measurements, the ohms or low power (voltage)ohmsoption can be selected.
Inputto select measurement. Connect to logic "0"(digital ground) for currentmeasurement.
CC
.
3.0DETAILED DESCRIPTION
3.1Analog-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.
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
01Resistance
10Current
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
3.3Resistance Measurements
(Ohms and Low Power Ohms)
The TC818A can be configured to reliably m easure incircuit resistances shunted by semiconductor junctions. The TC818A Low Power Ohms M easurement
mode limits the probe open circuit voltage. This preventssemiconductorjunctionsi n the measured system
from turningon.
In the Resistance Measurement mode, the Ω/LO
(Pin 62) input selects the Low Power Ohms Measurement mode. For low power ohms measurements,
Ω/LO
Ω (Pin 62) is momentarily brought LOW to digital
ground potential. The TC818A sets up for a low power
ohms measurement, with a maximum open circuit
probe voltage of 0.35V above analog common. In the
Low Power Ohms mode, an LCD display annunciator,
LO
Ω, will be activated. On power-up, the Low Power
Ohms mode is not active.
If the Manual Operating mode has been selected, tog-
gling Ω/LO
Range mode. In Manual mode, the decision to make a
normal or low power ohms measurement should be
made before selecting the desired range.
The low power ohms measurement is not available on
the 200Ω full scale range. Open circuit voltage on this
range is below 2.8V. The standard resistance values
are listed in Table 3-2.
Ω resets the TC818A back to the Auto-
R8, a positive temperature coefficient resistor, and the
6.2V zener, Z1, provide input voltage protection during
ohms measurements.
TABLE 3-2:O HMS RANGE LADDER
NETWORK
Full-Scale
Range
200Ω163.85Ω (R1)NO
2000Ω1638.5kΩ (R2)YES
20kΩ16,385Ω(R3)YES
200kΩ163,85Ω (R4)YES
2,000kΩ1,638,500Ω (R5)YES
Standard
Resistance
Low Power
Ohms Mode
3.4Ratiometric Resistance
Measurements
The TC818A measures resistance ratiometrically.
Accuracy is set by the external standard resistors connected to Pin 35through 39. A Low Power Ohms mode
may be selected on all but the 200Ω f ull scale range.
The Low Power Ohms mode limits the voltage applied
to the measured system. This allows accurate “incircuit” measurements when a resistor is shunted by
semiconductor junctions.
Full auto-ranging is provided. External precision standard resistorsareautomaticallyswitched to providethe
proper range.
Figure 3-2 shows a detailed block diagram of the
TC818A,configuredforratiometricresistancemeasurements.Duringthe signal integratephase, the reference
capacitor charges to a voltage inversely proportional to
themeasured resistance, R
conversion accuracy relies on the accuracy of the
external standard resistors.
Normally, the required accuracy of the standard resis-
Ω
tanceswillbedictatedby the accuracy specificationsof
the users end product. Table 3-3 gives the equivalent
ohms per count for various f ull scale ranges to allow
users to judge the required resistor for accuracy.
Resistivedividersare automaticallychangedto provide
in range readings for 200mV to 2000V full scale readings (Figure 3-1). The input resistance is set by external resistorsR14/R13.The dividerleg resistorsare R9R12. The divider leg resistors give a 200mV signal V
(Pin 44) for full scale voltages from 200mV to 2000V.
For applications which do not require a 10mΩ input
impedance, the divider network impedances may be
lowered. This wi ll reduce voltage offset errors induced
by switch leakage currents.
3.6Current Measurement
The TC818A measures current only under manual
range operation. The two user selectable, full scale
ranges are: 20mA
surement mode by holding the I
digital ground potential. The OHM
floating or tied to the positive supply.
Tworanges ar e possible. The 20mA
selectedby connectingthe 20mA
ground. If left floating, the 200mA full scale range is
selected.
External current-to-voltage conversion resistors are
used at the current input (I
measurements, a 10Ω r esistor is used. The 200mA
range requires a 1Ω resistor; full scale is 200mV.
Printed circuit board trace resistance between analog
common and R16 must be minimized. In the 200mA
range,for example,a 0.05 trace resistance will cause a
5% current-to-voltage conversion error at I
The extended resolutionmeasurementoption operates
during current measurements.
To minimize rollover error, the potential difference
between analog common (COM, Pin 29) and system
commonmustbeminimized.
and 200mA. Select the current Mea-
input (Pin 63) LOW at
input (Pin 2) is left
full scale range is
input(Pin 3) to digital
input, Pin 45). For 20mA
I
(Pin 45).
I
The minimumAC full scale voltagerangeis 2V. The DC
full scale minimum voltageis 200mV.
AC current measurements are available on the 20mA
and 200mA full scale current ranges.
I
3.8Conversion 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.
3.7AC-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
3.9Manual Range S election
The TC818A voltage and resistance auto-ranging feature can be disabled by momentarily bringing RANGE
(Pin 59) to digital ground potential (Pin 58). When the
change from auto-to-manual ranging occurs, the first
manual range selected is the last range in the AutoRanging mode.
The TC818A power-up circuit initially selects autorange operation. Once the manual r ange option is
entered, range changes are made by momentarily
grounding the RANG E
remains in the ManualRange mode until the measurement f unction (voltage or resistance), or measurement
option (AC/DC, Ω/LO
TC818A to return to auto-rangingoperation.
The “ Auto” LCD annunciator driver is active only in the
Auto-Range mode.
Figure 3-5 shows typical operation where the manual
range selection option is used. Also shown is the
extended resolutiondisplay format.Also, see Figure 3-6
and Figure 3-7.
control input. The TC818A
Ω) changes. This causes the
External Crystal = 32.768kHz
Internal Clock Period = t
Total Conversion Time = t
= 488.3msec ≈ 2 conv/sec
Integration Time = T
Maximum Reference De-integrate Time
= t
(manual extended resolution)
= 2000(t
Maximum Auto-Zero Time
= (8000 - 3000 - 1638.5)
(t
= (8000 - 3000 - 1638.5)
(t
3000(tP) = 183.1msec
DE
) = 205.1msec (manual extended resolution)
P
) = 205.1msec (manual extended resolution)
P
= 2/32.768 = 61.04µsec
P
= 8000(tP)
CONV
= 1638.5(tP) = 100msec
I
) = 122.1msec (auto-range)
P
FIGURE 3-5:MANUAL RANGE
SELECTION RES I STANCE
MEASUREMENTS
Manual
Range
Continuity
Indicator
Output 4kHz
Audio
Frequency
Continuous
4kHz Buzzer
*Mode also operates when Auto-Ranging Operator is selected
and 2MΩ < R
Yes
< 2.999MΩ.
X
Select
Is
< 19
R
X
?
No
Is
RX > 3000
?
No
Is
RX > 2000
?
No
Display
True
Reading
Over Range
Indicator
Yes
Yes*
Display
"1" 000
"1" = > Flashing
Display Last
3 Digits and
Flash MSD
Extended Resolution
Feature
MSD
2002 Microchip TechnologyInc.DS21475B-page 11
TC818A
FIGURE 3-6:MANUAL RANGE
SELECTION CURRENT
MEASUREMENTS
Range
Select
Noncontinuous
Is
> 3000
I
X
?
No
Is
IX > 2000
?
No
Display
True
Reading
Yes
Yes
Yes
Output 4kHz
Audio
Frequency
Over Range
Indicator
Display
"1" 000
"1" = > Flashing
MSD
Display Last
3 Digits and
Flash MSD
FIGURE 3-7:M ANUAL RANGE
SELECTION VOLTAGE
MEASUREMENTS
Range
Select
Noncontinuous
Output 4kHz
Audio
Frequency
Over Range
Indicator
Is
VX > 3000
?
No
Is
VX > 2000
?
No
Display
True
Reading
Yes
Yes
Display
"1" 000
"1" = > Flashing
MSD
Display Last
3 Digits and
Flash MSD
Extended
Resolution
Feature
3.10Extended Re solution Manual
Operation
When operated in the Manual Range mode, the
TC818A extends r esolution by 50% for current, voltage, and resistance measurements. Resolution
increases to 3000 counts from 2000 counts. The
extended resolution feature operates only in t he
2000kΩ and 2000V ranges during auto-range
operation.
In the Extended Resolution Operating mode, readings
above 1999 are displayed with a blinking “1” most significant digit. The blinking “1” should be interpreted as
the digit 2. The three least significantdigitsdisplaydata
normally. The bar graph LCD will be fully extended.
An input over range condition causes the most significant digit ( MSD) to blink and sets the three least significant digits (LSDs) to display “000.” The buzzer output
is enabled for input voltage and current signals with
readings greater than 2000 counts in both manual and
auto-range operations.
For resistance measurements, the buzzer signal does
not indicate an over range condition. The buzzer is
used to indicate continuity. Continuity is defined as a
resistance reading less than 19 counts.
DS21475B-page 12
2002 Microchip TechnologyInc.
TC818A
3.11-MEM Operating Mode
Bringing -MEM (Pin 61) momentarily LOW configures
the TC818A “-MEM” Operating mode. The -MEM LCD
annunciator becomes active. I n this Operating mode,
subsequent measurements are made relative to the
lasttwodigits(≤99) displayedatthe time MEM is LOW.
Thisrepresents5%offullscale.Thelasttwosignificant
digits are stored and subtracted from all t he following
input conversions.
The f ollowing examples clarify operation:
EXAMPLE 3-1:IN AUTO-RANGING
RI(N) = 18.21kΩ (20kΩ Range)= ≥ Display 18.21kΩ
MEM
R
R
EXAMPLE 3-2:IN FIXED RANGE
RI(N)= 18.21kΩ = ≥ Display 18.2kΩ
MEM
R
R
EXAMPLE 3-3:IN FIXED RANGE 20V
VI(N)= 0.51V = ≥ Display 0.51V
MEM
V
V
V
On power-up, the “-MEM” mode is not active.Once the
“-MEM” is entered, bringing MEM
the TC818A to normal operation.
The “-MEM”modeisalso cancelledwheneverthe measurement type (resistance, voltage, current AC
Ω/LO
ator will be off in normal operation.
In the auto-rangeoperation,if the following input signal
cannot be converted on the same range as the stored
value, the “-MEM” mode is cancelled. The LCD annunciator is turned OFF.
= ≥ Store 0.21kΩ
(N+1)= 19.87kΩ (20kΩ Range)
I
= ≥ Display 19.87 - 0.21 = 19.66kΩ
(N+2)= 22.65kΩ (200kΩ R ange)
I
= ≥ Display 22.7kΩ and MEM
disappears
(200 FULL SCALE)
= ≥ Store 8.2Ω
(N+1) = 36.7Ω
I
= ≥ Display 36.7- 8.2 = 28.5Ω
(N+2) = 5.8Ω
I
= ≥ Display 5.8-8.2 = -2.4Ω*
*Will display minus resistance if following input is less than
offset stored at fixed range.
FULL SCALE
= ≥ Store 0.51V
(N+1) = 3.68V
I
= ≥ Display 3.68 - 0.51 = 3.17V
(N+2) = 0.23V
I
= ≥ Display 0.23 -0.51= -0.28V
(N+3) = -5.21V
I
= ≥ Display - 5.21 - 0.51 = -5.72V
LOW again returns
/DC,
Ω) or range is changed. The LCD -MEM annunci-
The “-MEM” Operating mode can be very useful in
resistance measurementswhen lead length resistance
would cause measurement errors.
3.12Automatic Range Selection
Operation
When power is f irst applied, the TC818A enters the
auto-range operating state. The Auto-Range mode
may be entered from Manual mode by changing the
measurement function (resistance or voltage), or by
changing the measurement option (AC
The automatic voltage range selection begins on t he
most sensitive scale first: 200mV for DC or 2V for AC
measurements. The voltage range selection flow chart
is shown in Figure 3-8.
Internalinputpr otection diodestoV
(Pin 57) clamp the input voltage. The external 10MΩ
input resistance (see R14 and R13 of Functional diagram) limits current safely in an over range condition.
The voltage range selection is designed to maximize
resolution. For input signals less t han 9% of full scale
(count reading <180), the next most sensitive range is
selected.
An over range voltage input condition is flagged whenever the internalcount exceeds 2000, by activating t he
buzzer output (Pin 4). This 4kHz signal can directly
drive a piezo electric acoustic transducer. An out of
range input signal causes the 4kHz signal to be on for
122msec, off f or 122msec, on for 122msec and off for
610msec (see Figure 3-14).
Duringvoltageauto-rangeoperation, the extended resolution feature operates on the 2000V range only (see
Extended Resolution Operating mode discussion).
The r esistance automatic range selection procedure is
shown in Figure 3-9. The 200Ω range is the first range
selected, unless the LOW ohms resistance measurement option is selected. In LOW ohms operation, the
first full scale range tried is 2kΩ.
The r esistance range selected maximizessensitivity. If
the conversion results in a reading less than 180, the
next most sensitive full scale range is tried.
If the conversion is less than 19 in auto-range operation, a continuous 4kHz signal is output at BUZ (Pin 4).
An over range input does not activate the buzzer.
Out-of-range input conditions are displayed by a blinking MSD with the three LSDs set to “000.”
The extended resolution feature operates only on the
2000kΩ and 2000V full scale range during auto-range
operation. A blinking “1” most significant digit is interpreted as the digit 2. The three least significant digits
display data normally.
/DC, Ω/LOΩ).
(Pin28)andV
CC
SS
2002 Microchip TechnologyInc.DS21475B-page 13
TC818A
g
FIGURE 3-8:AUTO-RANGE
OPERATION: VOLTAGE
MEASUREMENT
N = N +1
N = 0 If DC
N = 1 If AC
Conversion
VX = (1/10N) V
VX > 2000
No
V
Flash MSD
Kth
< 180
V
X
?
N = 4
?
> 3000
X
?
Display
"1" 000
?
N = 0; 200mV Full Scale Range
N = 1; 2V Full Scale Range
N = N
K
(Remain in Range
Selected during the Kth
Conversion)
IN
Yes
N = N –1
N = 0 If DC
N = 1 If AC
No
No
Display
Voltage (V)
Yes
K = K +1
Yes
No
Yes
?
Flash MSD
Over Range
Yes
X
Extended
Resolution
Display
"1" XXX
Activate
Buzzer
FIGURE 3-9:AUTO-RANGE
OPERATION:RESISTANCE
MEASUREMENT
N = 0 If Ω
N = 1 If LOΩ
Conversion
RX = R
Continuity
Indicator
Activate
Continuous
4kHz Signal
Start: Power-on, Function or Measurement Option Chan
Buzzer
N = N +1
Yes
No
R
RX < 180
R
X
R
X
N = 0; 200Ω Full Scale Range
N = 1; 2kΩ Full Scale Range
Kth
1
IN
N
10
< 19
X
?
No
Yes
?
No
> 2000
?
Yes
N = 4
?
Yes
> 3000
No
?
Extended Resolution
Yes
(Remain in Range
Selected during the
Kth Conversion)
N = N –1
No
N = 0 If Ω
N = 1 If LOΩ
?
Yes
Display
Resistance
Display
"1" XXX
Flash MSD
K = K +1
Flash MSD
e
Display
"1" 000
Over
Range
Start: Power-on, Function or Measurement Option Change
DS21475B-page 14
2002 Microchip TechnologyInc.
TC818A
3.13Low 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.
3.14Triplex Liquid Crystal Display
(LCD) Drive
The TC818A directly drives a triplexed liquid crystal
display (LCD) using 1/3 bias drive. All numeric data,
decimal point, polarity and function annunciator drive
signals are developed by the TC818A.
The LCDs must be driven with an AC signal having
zero DC component, for long display life. The liquid
crystal polarization is a function of the RMS voltage
appearing across the backplane and segment driver.
The peak drive signal applied to the LCD is:
V
CC-VDISP
For example, if V
V
, the peak drive signal is:
CC
An “OFF” LCD segment has an RM S voltage of V
across it, or 1 volt. An “ON” segment has a 0.63V
signal across it or 1.92V for VCC-V
Since the V
DISP
the “ON” and “ OFF” LCD levels for various manufacturers’ displays, by changing V
for V
DISP
=3V.
“OFF”segmentsmaybecomevisibleathighLCDoperating temperatures. A voltage with a -5 to -20mV/°C
temperature coefficient can be applied to V
accommodate the liquid crystal temperature operating
characteristics, if necessary.
is set at a potential 3V below
DISP
V
P=VCC-VDISP
=3V
DISP
=3V.
pin is available, the user may adjust
signal across it, or 1.92V
P
DISP
/3
P
to
The TC818A internally generates two intermediate
LCD drive potentials (V
divider(Figure3-11) betweenV
and VL) from a resistive
H
CC
and V
.The latter
DISP
impedance is approximately150kΩ. This drive method
is commonly known as 1/3 bias. With V
to digital ground, V
≈ 5.0V.
P
DISP
connected
The intermediate levels are needed so that drive signals giving RMS “ON” and “OFF” levels can be generated. Figure 3-12 shows a typical drive signal and the
resulting waveforms for “ON” and “OFF” RMS voltage
levels across a selected LCD element.
FIGURE 3-11:1/3 BIAS LCD DRIVE
V
CC
50k
V
H
To
Triplex
Segment
Drive Logic
VP = VCC - V
"OFF" = V
"ON" = VP RMS
V
L
TC818A
11
3
3
DISP
/3 RMS
P
50k
See V
DSIP
For Proper V
50k
with Resistive
Divider
V
P
DISP
3.15Liquid 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
FEAGDBCP
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
123456
-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
3.16External 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
The BUZ output (Pin 4) will drive a piezo electricaudio
transducer. The signal is activated to i ndicate an input
over range condition for current and voltage measurements, or continuity during resistancemeasurements.
During a resistance m easurement, a reading less than
19 on any full scale range causes a continuous 4kHz
signal to be output. This is used as a continuity
indication.
A voltage or current input measurement over range is
indicated by a noncontinuous 4kHz signal at the BUZ
output. The LCD most significant digit also flashes and
Figure 3-14. The BUZ output is active f or any reading
over 2000 counts in both manual and auto-range operation. The buzzer is activated during an extended resolution measurement.
The BUZ signal swings from V
(Pin 58). The signal is at V
The BUZ output is also activated for 15ms whenever a
range change is made in auto-range or manual operation. Changing the type of measurement (voltage, current, or r esistance), or measurement option (AC/DC,
Ω/LOΩ), also activates the buzzer output for 15msec.
A range change during a current measurement will not
activate the buzzer output.
the three least significant digits are set to display zero.
The buzzer drive signal for over range is shown in
FIGURE 3-14:TC818A TIMING WAVEFORM FOR BUZZER OUTPUT
Power-up
V
= 250mV
IN
4000
122ms
V
CC
Noncontinuous Buzzer Signal Indicates Input Over Range
8000 12000
122ms
1 Conversion
122ms
122ms122ms
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
3.18Display 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.
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.
3.20.2RVIBUF 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
3.19AC-to-DC Converter Operational
Amplifier
The TC818A contains an on-chip operational amplifier
that may be connected as a rectifier for AC-to-DC voltage and current measurements. Typical operational
amplifier characteristics are:
• Slew Rate: 1V/µsec
• Unity Gain Bandwidth: 0.4MHz
• Open Loop Gain: 44dB
• Output VoltageSwing (Load = 10kΩ) ± 1.5V
(Referencedto Analog Common)
When the AC measurement option is selected, t he
input buffer receives an input signal through switch
S14, rather than switch S11 (see Figure 3-1). With
external circuits, the AC Operating mode can be used
to perform other types of functions within the constraints of the internal operational amplifier. External
circuits that perform true RMS conversion, or a peak
hold function, are typical examples.
RVIBUF =
V
V
MAX(TI
INT(CI
)
= 150kΩ
)
3.20.3RΩBUF SELECTION (PIN 54)
In ratiometric resistance measurements, the signal at
R
(Pin 50) is always positive, with respect to analog
X
common. The integrator swings negative.
The worst case integrator swing is for the 200Ω range
with the manual, extended resolution option.
The i nput voltage, V
Figure 3-15).
(Pin 50) is easily calculated (see
X
2002 Microchip TechnologyInc.DS21475B-page 19
TC818A
FIGURE 3-15:RΩ CALCULATION (200 Ω
MANUAL OPERATION)
V
= 9V
CC
SW33
R
R
R
R
≈ 600Ω
S
163.85Ω
1
2
3
220Ω
V
X
300Ω
Analog Common = VCC – 3V
Where:
V
ANCOM
R
S
R
I
R
X
R
S
= Potential at Analog Common ≈ 2.7V
= 220Ω
= 163.85Ω
= 300Ω
= Internal switch 33 resistance≈ 600Ω
EQUATION 3-2:
RΩBUF =
CC–VANCOM)RX
(RX+RS+R1+R8)
=0.63V
(V
For a 3.1V integrator swing, the value of RΩBUF i s
easily calculated:
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.
3.21Capacitors - 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.
3.22Reference 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.
3.23Display 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.
3.24Flat 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
3.25Resistive 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%Voltage1776-C441
0.25%Voltage1776-C44
0.25%ResistanceT1794-204-1
Caddock
Part Number
DS21475B-page 20
2002 Microchip TechnologyInc.
4.0PACKAGING INFORMATION
)
4.1Package Marking Information
Package marking data not available at this time.
4.2Taping 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.
4.3Package 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.
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
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