TC7135 DATA SHEET (11/28/2007) DOWNLOAD

TC7135
4-1/2 Digit A/D Converter
Features
General Description
•
•
•
•
•
•
•
•
The TC7135 4-1/2 digit A/D Converter (ADC) offers
50 ppm (1 part in 20,000) resolution with a maximum
nonlinearity error of 1 count. An auto-zero cycle
reduces zero error to below 10 µV and zero drift to
0.5 µV/°C. Source impedance errors are minimized by
a 10 pA maximum input current. Rollover error is
limited to ±1 count.
•
•
•
•
•
Low Rollover Error: ±1 Count Max
Nonlinearity Error: ±1 Count Max
Reading for 0V Input
True Polarity Indication at Zero for Null Detection
Multiplexed BCD Data Output
TTL-Compatible Outputs
Differential Input
Control Signals Permit Interface to UARTs and
Microprocessors
Blinking Display Visually Indicates Overrange
Condition
Low Input Current: 1 pA
Low Zero Reading Drift: 2 µV/°C
Auto-Ranging Supported with Overrange and
Underrange Signals
Available in PDIP and Surface-Mount Packages
Microprocessor-based measurement systems are
supported by the BUSY, STROBE and RUN/HOLD
control signals. Remote data acquisition systems with
data transfer via UARTs are also possible. The
additional control pins and multiplexed BCD outputs
make the TC7135 the ideal converter for display or
microprocessor-based measurement systems.
Applications
• Precision Analog Signal Processor
• Precision Sensor Interface
• High Accuracy DC Measurements
Functional Block Diagram
Set VREF = 1V
VREF IN
100 kΩ
5V
TC7135
1
2
V–
UNDERRANGE
REF IN
OVERRANGE
3 ANALOG
STROBE
COMMON
Analog GND
4
RUN/HOLD
INT OUT
1 µF
0.47 µF
5
DIGTAL GND
AZ IN
6
BUFF OUT POLARITY
100 kΩ
7
CLOCK IN
CREF–
Signal
1 µF 8
100 kΩ
BUSY
Input
CREF+
9
–INPUT
(LSD) D1
0.1 µF
10
D2
+INPUT
11
D3
+5V
V+
12
D5 (MSD)
D4
13
B1 (LSB)
(MSB) B8
14
B2
B4
© 2007 Microchip Technology Inc.
28
27
26
25
24
23
22
21
Clock Input
120 kHz
20
19
18
17
16
15
DS21460D-page 1
TC7135
Package Types
AZ IN 5
25 RUN/HOLD
BUFF OUT 6
22 CLOCK IN
–INPUT 9
21 BUSY
+INPUT 10
20 D1 (LSD)
V+ 11
NC
NC
D2
D1
BUSY
CLOCK IN
POLARITY
STROBE 36
20 D3
19 D4
UNDERRANGE 38
18 B8
V– 39
TC7135
REF IN 40
D3
D4
B4
(MSB) B8
B2
21 NC
OVERRANGE 37
12 13 14 15 16 17 18
(LSB) B1
22 NC
NC 35
19 D2
(MSD) D5
DIGITAL GND
NC 34
23 POLARITY
TC7135
REF CAP+ 8
RUN/HOLD
33 32 31 30 29 28 27 26 25 24 23
24 DIGTAL GND
REF CAP– 7
NC
NC
2
44-Pin MQFP
STROBE
1 28 27 26
3
OR
V–
4
UR
INT OUT
ANALOG
COM
REF IN
28-Pin PLCC
17 B4
16 B2
COMMON ANALOG 41
15 B1
NC 42
14 D5
NC 43
13 NC
NC 44
BUFF OUT
CREF–
5
6
7
CREF+
8
–INPUT
9
TC7135
NC
NC
V+
+INPUT
–INPUT
CREF+
CREF–
INT OUT
9 10 11
NC
NC
NC
D2
D1
BUSY
64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49
24 DIGiTAL GND
23 POLARITY
NC 2
47 NC
NC 3
46 NC
NC 4
45 D3
NC 5
44 D4
NC 6
43 B8
22 CLOCK IN
21 BUSY
20 D1 (LSD)
19 D2
V+ 11
18 D3
(MSD) D5 12
17 D4
B2 14
8
NC 1
+INPUT 10
(LSB) B1 13
CLOCK IN
25 RUN/HOLD
AZ IN
7
6
5
NC
4
POL
26 STROBE
DGND
27 OVERRANGE
3
RUN/HOLD
2
STROBE
REF IN
NC
28 UNDERRANGE
NC
1
NC
V–
ANALOG
COM
INT OUT
4
64-Pin MQFP
NC
28-Pin PDIP
3
BUFF OUT
2
AZ IN
1
NC
12 NC
16 B8 (MSB)
15 B4
48 NC
l
42 B4
OVERRANGE 7
TC7135
UNDERRANGE 8
41 B2
NC 9
40 NC
V– 10
39 B1
REF IN 11
38 D5
ANALOG COM 12
37 NC
NC 13
36 NC
NC 14
35 NC
NC 15
34 NC
NC 16
33 NC
DS21460D-page 2
V+
NC
+INPUT
NC
–INPUT
NC
CREF+
NC
NC
CREF–
BUFF OUT
NC
AZ IN
NC
NC
NOTE: NC = No internal connection.
INT OUT
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
© 2007 Microchip Technology Inc.
TC7135
1.0
ELECTRICAL SPECIFICATIONS
† Notice: 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†
Positive Supply Voltage.....................................................+6V
Negative Supply Voltage ...................................................- 9V
Analog Input Voltage (Pin 9 or 10) ...............V+ to V- (Note 2)
Reference Input Voltage (Pin 2) ................................. V+ to VClock Input Voltage ................................................... 0V to V+
Operating Temperature Range .......................... 0°C to +70°C
Storage Temperature Range........................ –65°C to +150°C
Package Power Dissipation; (TA ≤ 70°C)
28-Pin PDIP .......................................................... 1.14Ω
28-Pin PLCC ......................................................... 1.00Ω
44-Pin MQFP..........................................................................
64-Pin MQFP ........................................................ 1.14Ω
DC CHARACTERISTICS
Electrical Specifications: Unless otherwise indicated, TA = +25°C, FCLOCK = 120 kHz, V+ = +5V, V- = -5V.
(see Functional Block Diagram).
Parameters
Sym
Min.
Typ.
Max.
Units
-0.0000
±0.0000
+0.0000
Display Reading
Conditions
Analog
Display Reading with Zero Volt
Input
Zero Reading Temperature
Coefficient
TCZ
—
0.5
2
µV/°C
Full Scale Temperature
Coefficient
TCFS
—
—
5
ppm/°C
Nonlinearity Error
Differential Linearity Error
NL
—
0.5
1
Count
DNL
—
0.01
—
LSB
Display Reading in Ratiometric
Operation
± Full Scale Symmetry Error
(Rollover Error)
+0.9995
±FSE
—
Input Leakage Current
IIN
Noise
eN
Input Low Current
IIL
Input High Current
IIH
+0.9999 +1.0000
Note 2, Note 3
VIN = 0V, (Note 4)
VIN = 2V,
(Note 4, Note 5)
Note 6
Note 6
Display Reading
VIN = VREF, (Note 2)
Count
-VIN = +VIN, (Note 7)
0.5
1
—
1
10
pA
—
15
—
µVP-P
—
10
100
µA
VIN = 0V
—
0.08
10
µA
VIN = +5V
IOL = 1.6 mA
Note 3
Peak-to-Peak Value not
Exceeded 95% of Time
Digital
Output Low Voltage
VOL
—
0.2
0.4
V
Output High Voltage;
VOH
2.4
4.4
5
V
IOH = 1 mA
4.9
4.99
5
V
IOH = 10 µA
0
200
1200
kHz
B1, B2, B4, B8, D1 –D5
Busy, Polarity, Overrange,
Underrange, Strobe
Clock Frequency
Note 1:
2:
3:
4:
5:
6:
7:
8:
FCLK
Note 8
Limit input current to under 100 µA if input voltages exceed supply voltage.
Full-scale voltage = 2V
VIN = 0V
30°C ≤ TA ≤ +70°C
External reference temperature coefficient less than 0.01 ppm/°C.
-2V ≤ VIN ≤ +2V. Error of reading from best fit straight line.
IVIN| = 1.9959
Specification related to clock frequency range over which the TC7135 correctly performs its various functions.
Increased errors result at higher operating frequencies.
© 2007 Microchip Technology Inc.
DS21460D-page 3
TC7135
DC CHARACTERISTICS (CONTINUED)
Electrical Specifications: Unless otherwise indicated, TA = +25°C, FCLOCK = 120 kHz, V+ = +5V, V- = -5V.
(see Functional Block Diagram).
Parameters
Sym
Min.
Typ.
Max.
Units
Conditions
Positive Supply Voltage
V+
4
5
6
V
Negative Supply Voltage
V-
-3
-5
-8
V
Positive Supply Current
I+
—
1
3
mA
Negative Supply Current
I-
—
0.7
3
mA
FCLK = 0 Hz
PD
—
8.5
30
mW
FCLK = 0 Hz
Power Supply
Power Dissipation
Note 1:
2:
3:
4:
5:
6:
7:
8:
FCLK = 0 Hz
Limit input current to under 100 µA if input voltages exceed supply voltage.
Full-scale voltage = 2V
VIN = 0V
30°C ≤ TA ≤ +70°C
External reference temperature coefficient less than 0.01 ppm/°C.
-2V ≤ VIN ≤ +2V. Error of reading from best fit straight line.
IVIN| = 1.9959
Specification related to clock frequency range over which the TC7135 correctly performs its various functions.
Increased errors result at higher operating frequencies.
DS21460D-page 4
© 2007 Microchip Technology Inc.
TC7135
2.0
PIN DESCRIPTIONS
The description of the pins are listed in Table 2-1.
TABLE 2-1:
PIN FUNCTION TABLE
Pin Number
28-Pin PDIP,
28-Pin PLCC
Pin Number
44-Pin MQFP*
Pin Number
64-Pin MQFP*
1
39
10
V–
2
40
11
REF IN
3
41
12
ANALOG COMMON
4
2
18
INT OUT
5
3
20
AZ IN
6
4
22
BUFF OUT
7
5
23
CREF–
Reference capacitor input. Reference capacitor
negative connection.
8
6
26
CREF+
Reference capacitor input. Reference capacitor
positive connection.
9
7
28
–INPUT
Analog input. Analog input negative connection.
Symbol
10
8
30
+INPUT
11
9
32
V+
Description
Negative power supply input.
External reference input.
Reference point for REF IN.
Integrator output. Integrator capacitor connection.
Auto-zero inpt. Auto-zero capacitor connection.
Analog input buffer output. Integrator resistor
connection.
Analog input. Analog input positive connection.
Positive power supply input.
12
14
38
D5
Digit drive output. Most Significant Digit (MSD)
13
15
39
B1
Binary Coded Decimal (BCD) output. Least Significant
bit (LSb).
14
16
41
B2
BCD output.
15
17
42
B4
BCD output.
16
18
43
B8
BCD output. Most Significant bit (MSb).
17
19
44
D4
Digit drive output.
18
20
45
D3
Digit drive output.
19
25
52
D2
Digit drive output.
20
26
53
D1
21
27
54
BUSY
22
28
55
CLOCK IN
Clock input. Conversion clock connection.
23
29
57
POLARITY
Polarity output. A positive input is indicated by a logic
high output. The polarity output is valid at the
beginning of the reference integrate phase and
remains valid until determined during the next
conversion.
Digit drive output. Least Significant Digit (LSD).
Busy output. At the beginning of the signal-integration
phase, BUSY goes high and remains high until the
first clock pulse after the integrator zero crossing.
24
30
58
DGND
25
31
59
RUN/HOLD
Run/Hold input. When at a logic high, conversions are
performed continuously. A logic low holds the current
data as long as the low condition exists.
26
36
60
STROBE
Strobe output. The STROBE output pulses low in the
center of the digit drive outputs.
27
37
7
OVERRANGE
Overrange output. A logic high indicates that the
analog input exceeds the full-scale input range.
28
38
8
UNDERRANGE
Underrange output. A logic high indicates that the
analog input is less than 9% of the full-scale input
range.
*
Digital logic reference input.
Pins not identified or documented are NC (no connects).
© 2007 Microchip Technology Inc.
DS21460D-page 5
TC7135
3.0
DETAILED DESCRIPTION
All pin designations refer to the 28-pin PDIP package.
3.1
Dual-Slope Conversion Principles
The TC7135 is a dual-slope, integrating A/D converter.
An understanding of the dual-slope conversion
technique will aid in following the detailed TC7135
operational theory.
The conventional dual-slope converter measurement
cycle has two distinct phases:
1.
2.
Input signal integration.
Reference voltage integration (de-integration).
The dual-slope converter accuracy is unrelated to the
integrating resistor and capacitor values, as long as
they are stable during a measurement cycle. An
inherent benefit is noise immunity. Noise spikes are
integrated, or averaged, to zero during the integration
periods.
Integrated ADCs are immune to the large conversion
errors that plague successive approximation converters
in high-noise environments (see Figure 3-1).
Analog Input
Signal
+
REF
Voltage
Integrator
Output
3.2
=
Signal integration time (fixed)
TDEINT
=
Reference voltage integration time
(variable)
Clock
Control
Logic
Counter
≈ VREF
≈ 1/2 VREF
Variable
Reference
Integrate
Time
FIGURE 3-1:
Where:
TINT
Polarity Control
VIN
VIN
Fixed
Signal
Integrate
Time
EQUATION 3-1:
Reference voltage
Phase
Control
Display
A simple mathematical equation relates the input
signal, reference voltage and integration time:
V REF T DEINT
1 - T INT
----------------------V IN ( T )DT = ------------------------------R INT C INT ∫0
R INT C INT
+
Switch
Drive
In a simple dual-slope converter, a complete
conversion requires the integrator output to “ramp-up”
and “ramp-down”.
=
Comparator
-
The input signal being converted is integrated for a
fixed time period. Time is measured by counting clock
pulses. An opposite polarity constant reference voltage
is then integrated until the integrator output voltage
returns to zero. The reference integration time is
directly proportional to the input signal.
VREF
Integrator
Basic Dual-Slope Converter.
Operational Theory
The TC7135 incorporates a system zero phase and
integrator output voltage zero phase to the normal twophase dual-slope measurement cycle. Reduced
system errors, fewer calibration steps and a shorter
overrange recovery time result.
For a constant VIN:
The TC7135 measurement cycle contains four phases:
1.
2.
3.
4.
EQUATION 3-2:
V REF T DEINT
V IN = ------------------------------T INT
System zero.
Analog input signal integration.
Reference voltage integration.
Integrator output zero.
Internal analog gate status for each phase is shown in
Figure 3-1.
TABLE 3-1:
INTERNAL ANALOG GATE STATUS
Conversion Cycle Phase
System Zero
SWI
SWRI+
SWRI-
SWZ
SWR
SW1
SWIZ
Reference Figures
—
—
—
Closed
Closed
Closed
—
Figure 3-2
Closed
—
—
—
—
—
—
Figure 3-3
Reference Voltage Integration
—
Closed*
—
—
—
Closed
—
Figure 3-4
Integrator Output Zero
—
—
—
—
—
Closed
Closed
Figure 3-5
Input Signal Integration
* Assumes a positive polarity input signal. SWRI would be closed for a negative input signal.
DS21460D-page 6
© 2007 Microchip Technology Inc.
TC7135
3.2.3
Analog
Input Buffer
RINT
+
–
SWI
SWZ
Analog
Common
SWI
IN
–
SWZ
SW1
FIGURE 3-2:
3.2.2
[ Differential Input ]
Reading = 10, 000 ----------------------------------------------V REF
+IN
REF
IN
+
Integrator –
To
Digital
Section
Switch Open
Switch Closed
System Zero Phase.
ANALOG INPUT SIGNAL
INTEGRATION
The TC7135 integrates the differential voltage between
the +INPUT and -INPUT pins. The differential voltage
must be within the device Common mode range; -1V
from either supply rail, typically. The input signal
polarity is determined at the end of this phase.
Analog
Common
SWI
IN
SWZ
SW1
FIGURE 3-4:
Integration Cycle.
3.2.4
Analog
Common
SWI
IN
FIGURE 3-3:
Phase.
SWRI-
SWZ
Comparator
+
+
–
To
Integrator
Digital
Section
–
SWZ
SW1
Switch Open
Switch Closed
CREF
SWR
SWZ
SWRI+
SWRIREF
IN
Analog
Common
SWI
IN
FIGURE 3-5:
Phase.
CINT
CSZ
SWRI-
SWIZ SWZ
Reference Voltage
Analog
Input Buffer
RINT
+
–
SWI
CINT
CSZ
CREF
SWR
SWRI+
REF
IN
SWRI+
SWRI-
+IN
Switch Open
Switch Closed
This phase ensures the integrator output is at 0V when
the system zero phase is entered. It also ensures that
the true system offset voltages are compensated for.
This phase normally lasts 100 to 200 clock cycles. If an
overrange condition exists, the phase is extended to
6200 clock cycles (see Figure 3-5).
SWRI+
Analog
Input Buffer
RINT
+
–
Comparator
–
+
+
To
Integrator –
Digital
Section
INTEGRATOR OUTPUT ZERO
+IN
SWI
CINT
CSZ
SWIZ SWZ
CREF
SWR
SWZ
Comparator
+
Analog
Input Buffer
RINT
+
–
SWI
CSZ
SWRI-
SWR
CINT
SWIZ SWZ
CREF
SWRI+
REF
IN
SWRI+
SWRI-
+IN
EQUATION 3-3:
SWRI-
The external input signal is disconnected from the
internal circuitry by opening the two SWI switches. The
internal input points connect to the ANALOG
COMMON pin. The reference capacitor charges to the
reference voltage potential through SWR. A feedback
loop, closed around the integrator and comparator,
charges the CAZ capacitor with a voltage to compensate for buffer amplifier, integrator and comparator
offset voltages (see Figure 3-2).
The previously charged reference capacitor is connected with the proper polarity to ramp the integrator
output back to zero (see Figure 3-4). The digital
reading displayed is:
SWRI+
During this phase, errors due to buffer, integrator and
comparator offset voltages are compensated for by
charging CAZ (auto-zero capacitor) with a compensating error voltage. With a zero input voltage, the
integrator output will remain at zero.
REFERENCE VOLTAGE
INTEGRATION
SWRI-
SYSTEM ZERO
SWRI+
3.2.1
SWIZ SWZ
SWZ
SW1
Comparator
–
+
+
–
To
Integrator
Digital
Section
Switch Open
Switch Closed
Integrator Output Zero
Input Signal Integration
© 2007 Microchip Technology Inc.
DS21460D-page 7
TC7135
4.0
4.1
ANALOG SECTION
FUNCTIONAL DESCRIPTION
Differential Inputs
The TC7135 operates with differential voltages
(+INPUT, pin 10 and -INPUT, pin 9) within the input
amplifier Common mode range, which extends from 1V
below the positive supply to 1V above the negative
supply. Within this Common mode voltage range, an
86 dB Common mode rejection ratio is typical.
The integrator output also follows the Common mode
voltage and must not be allowed to saturate. A worstcase condition exists, for example, when a large
positive Common mode voltage with a near full scale
negative differential input voltage is applied. The
negative input signal drives the integrator positive when
most of its swing has been used up by the positive
Common mode voltage. For these critical applications,
the integrator swing can be reduced to less than the
recommended 4V full scale swing, resulting in some
loss of accuracy. The integrator output can swing within
0.3V of either supply without loss of linearity.
4.2
4.3
Reference Voltage Input
The reference voltage input (REF IN) must be a
positive voltage with respect to ANALOG COMMON. A
reference voltage circuit is shown in Figure 4-1.
V+
V+
TC7135
REF
IN
10 kΩ
MCP1525
2.5 VREF
10 kΩ
1 µF
ANALOG
COMMON
Analog Ground
FIGURE 4-1:
Reference.
Using An External
Analog Common Input
The ANALOG COMMON pin is used as the -INPUT
return during auto-zero and de-integrate. If -INPUT is
different from ANALOG COMMON, a Common mode
voltage exists in the system. However, this signal is
rejected by the excellent CMRR of the converter. In
most applications, –INPUT will be set at a fixed, known
voltage (power supply common, for instance). In this
application, ANALOG COMMON should be tied to the
same point, thus removing the Common mode voltage
from the converter. The reference voltage is referenced
to ANALOG COMMON.
DS21460D-page 8
© 2007 Microchip Technology Inc.
TC7135
5.0
DIGITAL SECTION
FUNCTIONAL DESCRIPTION
The major digital subsystems within the TC7135 are
illustrated in Figure 5-1, with timing relationships
shown in Figure 5-2. The multiplexed BCD output data
can be displayed on LCD or LED displays. The digital
section is best described through a discussion of the
control signals and data outputs.
Polarity
D5
MSB
D4
D3
Digit
Drive
D2
Signal
D1
13 B1
14 B2
15 B4
16 B8
LSB
Data
Output
Multiplexer
From
Analog
Section
Latch
Polarity
FF
Latch
Latch
Zero
Cross
Detect
Latch
Latch
Counters
Control Logic
24
DGND
FIGURE 5-1:
22
Clock
In
25
RUN/
HOLD
27
Overrange
28
Underrange
26
STROBE
21
Busy
Digital Section Functional Diagram.
© 2007 Microchip Technology Inc.
DS21460D-page 9
TC7135
5.2
Integrator
Output
During the measurement cycle, the STROBE control
line is pulsed low five times. The five low pulses occur
in the center of the digit drive signals (D1, D2, D3, D5)
(see Figure 5-3).
Signal
System Integrate Reference
Zero 10,000
Integrate
10,001 Counts
20,001
Counts (Fixed) Counts (Max)
Full Measurement Cycle
40,002 Counts
D5 (MSD) goes high for 201 counts when the
measurement cycles end. In the center of the D5 pulse,
101 clock pulses after the end of the measurement
cycle, the first STROBE occurs for one half clock pulse.
After the D5 digit strobe, D4 goes high for 200 clock
pulses. The STROBE then goes low 100 clock pulses
after D4 goes high. This continues through the D1 digit
drive pulse.
Busy
Overrange when
Applicable
Underrange when
Applicable
Expanded Scale Below
Digit Scan
D5
D4
D3
D2
D1
* First D5 of System Zero and
Reference Integrate One Count
Longer
100
Counts
STROBE
Auto-Zero
Digit Scan
for Overrange
* D5
STROBE Output
Signal
Integrate
Reference
Integrate
The digit drive signals will continue to permit display
scanning. STROBE pulses are not repeated until a new
measurement is completed. The digit drive signals will
not continue if the previous signal resulted in an
overrange condition.
The active-low STROBE pulses aid BCD data transfer
to UARTs, processors and external latches. For more
information, please refer to Application Note 784
(DS00784).
*
D4
TC7135
Outputs
Busy
D3
D2
*
D1
FIGURE 5-2:
Outputs.
5.1
Timing Diagrams For
RUN/HOLD Input
B1 B8
D5
(MSD)
Data
D4
Data
D3
Data
D2
Data
STROBE
D5
D4
When RUN/HOLD changes to a logic ‘0’, the measurement cycle in progress will be completed, with the data
held and displayed as long as the logic ‘0’ condition
exists.
D2
D3
D1
D1
(LSD)
Data
D5
Data
Note Absence
of STROBE
200
Counts
When left open, this pin assumes a logic ‘1’ level. With
a RUN/HOLD = 1, the TC7135 performs conversions
continuously, with a new measurement cycle beginning
every 40,002 clock pulses.
A positive pulse (>300 nsec) at RUN/HOLD initiates a
new measurement cycle. The measurement cycle in
progress when RUN/HOLD initially assumed the logic
‘0’ state must be completed before the positive pulse
can be recognized as a single conversion run
command.
End of Conversion
201
Counts
200
Counts
200
Counts
200
Counts
200
Counts
200
Counts
*Delay between Busy going Low and First STROBE pulse is
dependent on Analog Input.
FIGURE 5-3:
Strobe Signal Low Five
Times Per Conversion.
The new measurement cycle begins with a 10,001
count auto-zero phase. At the end of this phase, the
busy signal goes high.
DS21460D-page 10
© 2007 Microchip Technology Inc.
TC7135
5.3
BUSY Output
At the beginning of the signal integration phase, BUSY
goes high and remains high until the first clock pulse
after the integrator zero crossing. BUSY returns to the
logic ‘0’ state once the measurement cycle ends in an
overrange condition. The internal display latches are
loaded during the first clock pulse after BUSY and are
latched at the clock pulse end. The BUSY signal does
not go high at the beginning of the measurement cycle,
which starts with the auto-zero cycle.
5.4
OVERRANGE Output
If the input signal causes the reference voltage integration time to exceed 20,000 clock pulses, the OVERRANGE output is set to a logic ‘1’. The OVERRANGE
output register is set when BUSY goes low and is reset
at the beginning of the next reference integration
phase.
5.5
UNDERRANGE Output
If the output count is 9% of full scale or less (-1800
counts), the UNDERRANGE register bit is set at the
end of BUSY. The bit is set low at the next signal
integration phase.
© 2007 Microchip Technology Inc.
5.6
POLARITY Output
A positive input is registered by a logic ‘1’ polarity
signal. The polarity bit is valid at the beginning of
reference integrate and remains valid until determined
during the next conversion.
The polarity bit is valid even for a zero reading. Signals
less than the converter's LSB will have the signal
polarity determined correctly. This is useful in null
applications.
5.7
Digit Drive Outputs
Digit drive signals are positive-going signals. The scan
sequence is D5 to D1. All positive pulses are 200 clock
pulses wide, with the exception D5, which is 201 clock
pulses wide.
All five digits are scanned continuously, unless an
overrange condition occurs. In an overrange condition,
all digit drives are held low from the final STROBE
pulse until the beginning of the next reference integrate
phase. The scanning sequence is then repeated. This
provides a blinking visual display indication.
5.8
BCD Data Outputs
The binary coded decimal (BCD) bits B8, B4, B2 and B1
are positive-true logic signals. The data bits become
active at the same time as the digit drive signals. In an
overrange condition, all data bits are at a logic ‘0’ state.
DS21460D-page 11
TC7135
6.0
TYPICAL APPLICATIONS
6.1.3
6.1
Component Value Selection
The size of the auto-zero capacitor has some influence
on the noise of the system, with a larger capacitor
reducing the noise. The reference capacitor should be
large enough such that stray capacitance to ground
from its nodes is negligible.
6.1.1
INTEGRATING RESISTOR
The integrating resistor RINT is determined by the fullscale input voltage and the output current of the buffer
used to charge the integrator capacitor (CINT). Both the
buffer amplifier and the integrator have a class A output
stage, with 100 µA of quiescent current. A 20 µA drive
current gives negligible linearity errors. Values of 5 µA
to 40 µA give good results. The exact value of an
integrating resistor for a 20 µA current is easily
calculated.
EQUATION 6-1:
Scale VoltageR INT = Full
------------------------------------------20 μ A
6.1.2
INTEGRATING CAPACITOR (CINT)
The product of integrating resistor and capacitor should
be selected to give the maximum voltage swing that
ensures the tolerance build-up will not saturate the
integrator swing (approximately 0.3V from either
supply). For ±5V supplies and ANALOG COMMON tied
to supply ground, a ±3.5V to ±4V full scale integrator
swing is adequate. A 0.10 µF to 0.47 µF is
recommended. In general, the value of CINT is given
by:
AUTO-ZERO AND REFERENCE
CAPACITORS
The dielectric absorption of the reference and autozero capacitors are only important at power-on or when
the circuit is recovering from an overload. Smaller or
cheaper capacitors can be used if accurate readings
are not required for the first few seconds of recovery.
6.1.4
REFERENCE VOLTAGE
The analog input required to generate a full-scale
output is VIN = 2 VREF.
The stability of the reference voltage is a major factor in
the overall absolute accuracy of the converter. For this
reason, it is recommended that a high-quality reference
be used where high-accuracy absolute measurements
are being made.
6.2
6.2.1
Conversion Timing
LINE FREQUENCY REJECTION
A signal integration period at a multiple of the 60 Hz
line frequency will maximize 60 Hz “line noise”
rejection. A 100 kHz clock frequency will reject 50 Hz,
60 Hz and 400 Hz noise. This corresponds to five
readings per second (see Table 6-1 and Table 6-2).
EQUATION 6-2:
C INT
[ 10, 000 × clock period ] × I INT
= --------------------------------------------------------------------------integrator output voltage swing
10, 000 ) ( clock period ) × 20 μ A
= (----------------------------------------------------------------------------integrator output voltage swing
A very important characteristic of the integrating
capacitor CINT is that it has low dielectric absorption to
prevent rollover or ratiometric errors. A good test for
dielectric absorption is to use the capacitor with the
input tied to the reference. This ratiometric condition
should read half scale 0.9999, with any deviation
probably due to dielectric absorption. Polypropylene
capacitors give undetectable errors at reasonable cost.
Polystyrene and polycarbonate capacitors may also be
used in less critical applications.
DS21460D-page 12
TABLE 6-1:
CONVERSION RATE VS.
CLOCK FREQUENCY
Oscillator Frequency
(kHz)
Conversion Rate
(Conv./Sec.)
100
2.5
120
3
200
5
300
7.5
400
10
800
20
1200
30
© 2007 Microchip Technology Inc.
TC7135
TABLE 6-2:
LINE FREQUENCY
REJECTION VS. CLOCK
FREQUENCY
Oscillator Frequency
(kHz)
Line Frequency
Rejection
(Hz)
300
60
200
150
120
100
40
33-1/3
250
50
166-2/3
100
50, 60,400
The conversion rate is easily calculated:
EQUATION 6-3:
Frequency (Hz)Reading 1/sec = Clock
---------------------------------------------------4000
6.3
High-Speed Operation
The maximum conversion rate of most dual-slope A/D
converters is limited by the frequency response of the
comparator. The comparator in this circuit follows the
integrator ramp with a 3 µs delay, at a clock frequency
of 160 kHz (6 µs period). Half of the first reference integrate clock period is lost in delay. This means that the
meter reading will change from 0 to 1 with a 50 µV
input, 1 to 2 with 150 µV, 2 to 3 at 250 µV, etc. This transition at midpoint is considered desirable by most
users. However, if the clock frequency is increased
appreciably above 200 kHz, the instrument will flash
"1" on noise peaks, even when the input is shorted.
For many dedicated applications where the input signal
is always of one polarity, the delay of the comparator
need not be a limitation. Since the nonlinearity and
noise do not increase substantially with frequency, clock
rates of up to ~1 MHz may be used. For a fixed clock
frequency, the extra count (or counts) caused by
comparator delay will be a constant and can be
subtracted out digitally.
The clock frequency may be extended above 160 kHz
without this error, however, by using a low value
resistor in series with the integrating capacitor. The
effect of the resistor is to introduce a small pedestal
voltage on to the integrator output at the beginning of
the reference integrate phase. By careful selection of
the ratio between this resistor and the integrating
© 2007 Microchip Technology Inc.
The minimum clock frequency is established by
leakage on the auto-zero and reference capacitors.
With most devices, measurement cycles as long as 10
seconds give no measurable leakage error.
The clock used should be free from significant phase or
frequency jitter. Several suitable low-cost oscillators
are shown in Section 6.0 “Typical Applications”. The
multiplexed output means that if the display takes
significant current from the logic supply, the clock
should have good PSRR.
6.4
125
100
resistor (a few tens of ohms in the recommended
circuit), the comparator delay can be compensated and
the maximum clock frequency extended by
approximately a factor of 3. At higher frequencies,
ringing and second-order breaks will cause significant
nonlinearities in the first few counts of the instrument.
Zero Crossing Flip Flop
The flip flop interrogates the data once every clock
pulse after the transients of the previous clock pulse and
half clock pulse have died down. False zero crossings
caused by clock pulses are not recognized. Of course,
the flip flop delays the true zero crossing by up to one
count in every instance. If a correction were not made,
the display would always be one count too high.
Therefore, the counter is disabled for one clock pulse at
the beginning of the reference integrate (de-integrate)
phase. This one-count delay compensates for the delay
of the zero crossing flip flop and allows the correct
number to be latched into the display. Similarly, a onecount delay at the beginning of auto-zero gives an
overload display of 0000 instead of 0001. No delay
occurs during signal integrate so that true ratiometric
readings result.
6.5
Generating a Negative Supply
A negative voltage can be generated from the positive
supply by using a TC7135 (see Figure 6-1).
+5V
V+
11
TC7135
1
V–
8
(-5V)
5
TC7660
10 µF
+
4
24
FIGURE 6-1:
Generator.
+
2
3
10 µF
Negative Supply Voltage
DS21460D-page 13
TC7135
+5V
20 19 18 17 12
D1 D2 D3 D4 D5
4
INT OUT
0.33 µF
1 µF
5
AZ IN
4.7 kΩ
23
POL
6 BUFF
OUT
CREF – 7
100 kΩ
22 F
TC7135
1 µF
200 kHz
IN
CREF+ 8
100 kΩ
10
+
+INPUT
Analog
16
1 µF
B8
9
Input
15
–INPUT
–
B4
14
B2
3 ANALOG
13
B1
COMMON
REF
V– IN
V+
1 2
11
V+
5V
c
7
7
7
X7
Blank MSD On Zero
5
6
D
2
C
1
B
7
A
9 15
RBI
16
DM7447A
+5V
1 µF
4-1/2 Digit ADC With Multiplexed Common Anode Led Display.
R2
+5V
R1
C
16 kΩ
FO
56 kΩ
2
Gates are 74C04
1.
7
MCP1525
100 kΩ
FIGURE 6-2:
b
0.22 µF
3 –
RC Oscillator Circuit.
30 kΩ
16 kΩ
390 pF
R2
100 kΩ
+5V
R4
2 kΩ
C2
10 pF
2
R2
100 kΩ
C1
0.1 µF
FIGURE 6-4:
DS21460D-page 14
1
4
a. If R1 = R2 = R1, F≅ 0.55/RC
b. If R2 >> R1, F ≅ 0.45/R1C
c. If R2 << R1, F ≅ 0.72/R1C
FIGURE 6-3:
VOUT
7
LM311
R1 R2
1
- , R P = -----------------F O = ------------------------------------------------R1 + R2
2C ( 0.41R P + 0.7R 1 )
2. Examples:
a. F = 120 kHz, C = 420 pF
R1 = R2 ≈ 10.9 kΩ
b. F = 120 kHz, C = 420pF, R2 = 50 kΩ
R1 = 8.93 kΩ
c. F = 120 kHz, C = 220 pF, R2 = 5 kΩ
R1 = 27.3 kΩ
8
+
1 kΩ
6
+
LM311
3
4
–
1
7
VOUT
R3
50 kΩ
Comparator Clock Circuits.
© 2007 Microchip Technology Inc.
TC7135
+5V
+5V
SET VREF = 1V
5V
28
TC7135 UR
27
OR
REF IN
26
3 ANALOG
STROBE
GND
1
MCP1525
1 µF
100
kΩ
V–
2
Analog
GND
4 INT
RUN/HOLD
OUT
1 µF
0.33 µF
5
DGND
AZ IN
6 BUFF
POLARITY
100 kΩ 7 OUT
CREF+
CLK IN
1 µF 8
100
CREF –
BUSY
kΩ
9
–INPUT (LSD) D1
+
SIG
0.1
10 +INPUT
D2
IN
µF
11
D3
+5V
V+
12
D4
D5 (MSD)
150Ω
47
kΩ
9
25
10
150Ω 11
24
12
7
23
13 MC14513 6
22
14
5
21
15
4
20
16
3
19
17
2
18
18
1
8
+5V
17
13
16
B1 (LSB) (MSB) B8
14
B4 15
B2
FOSC = 200 kHz
FIGURE 6-5:
4-1/2 Digit ADC With Multiplexed Common Cathode LED Display.
© 2007 Microchip Technology Inc.
DS21460D-page 15
TC7135
7.0
PACKAGING INFORMATION
7.1
Package Marking Information
28-Pin PLCC
Example:
1
1
M
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TC7135
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0741256
28-Pin PDIP (Wide)
Example:
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44-Pin MQFP
Example:
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64-Pin MQFP
Example:
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Legend: XX...X
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*
Note:
DS21460D-page 16
M
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Customer-specific information
Year code (last digit of calendar year)
Year code (last 2 digits of calendar year)
Week code (week of January 1 is week ‘01’)
Alphanumeric traceability code
Pb-free JEDEC designator for Matte Tin (Sn)
This package is Pb-free. The Pb-free JEDEC designator ( e3 )
can be found on the outer packaging for this package.
In the event the full Microchip part number cannot be marked on one line, it will
be carried over to the next line, thus limiting the number of available
characters for customer-specific information.
© 2007 Microchip Technology Inc.
TC7135
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DS21460D-page 19
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© 2007 Microchip Technology Inc.
TC7135
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© 2007 Microchip Technology Inc.
DS21460D-page 21
TC7135
NOTES:
DS21460D-page 22
© 2007 Microchip Technology Inc.
TC7135
APPENDIX A:
REVISION HISTORY
Revision D (November 2007)
The following is the list of modifications:
1.
2.
Updates package marking information for pbfree markings.
Updated package outline drawings and added
landing pattern to applicable package outline
drawing.
Revision C (January 2004)
The following is the list of modifications:
1.
Undocumented Changes
Revision B (May 2002)
The following is the list of modifications:
1.
Undocumented changes
Revision A (March 2001)
• Original Release of this Document.
© 2007 Microchip Technology Inc.
DS21460D-page 23
TC7135
NOTES:
DS21460D-page 24
© 2007 Microchip Technology Inc.
TC7135
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
PART NO.
X
/XX
Device
Temperature
Range
Package
Examples:
a)
b)
Device
TC7135: 4-1/2 Digit A/D, BCD Output
c)
Temperature Range
C
d)
Package
LI
= Plastic Leaded Chip Carrier (PLCC), 28-lead
LI713 = Plastic Leaded Chip Carrier (PLCC), 28-lead,
Tape and Reel
PI
= Plastic DIP, (600 mil Body), 28-lead
KW = Plastic Metric Quad Flatpack, (MQFP), 44-lead
BU
= Plastic Metric Quad Flatpack, (MQFP), 64-lead
= 0°C to +70°C
© 2007 Microchip Technology Inc.
TC7135CLI:
4-1/2 Digit A/D, BCD Output,
PLCC package.
TC7135CPI:
4-1/2 Digit A/D, BCD Output,
PDIP package.
TC7135CLI713: 4-1/2 Digit A/D, BCD Output,
PLCC package,
Tape and Reel.
TC7135CBU:
4-1/2 Digit A/D, BCD Output,
MQFP package.
DS21460D-page 25
TC7135
NOTES:
DS21460D-page 26
© 2007 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, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, Accuron,
dsPIC, KEELOQ, KEELOQ logo, microID, MPLAB, PIC,
PICmicro, PICSTART, PRO MATE, rfPIC and SmartShunt are
registered trademarks of Microchip Technology Incorporated
in the U.S.A. and other countries.
AmpLab, FilterLab, Linear Active Thermistor, Migratable
Memory, MXDEV, MXLAB, SEEVAL, SmartSensor and The
Embedded Control Solutions Company are registered
trademarks of Microchip Technology Incorporated in the
U.S.A.
Analog-for-the-Digital Age, Application Maestro, CodeGuard,
dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN,
ECONOMONITOR, FanSense, FlexROM, fuzzyLAB,
In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi,
MPASM, MPLAB Certified logo, MPLIB, MPLINK, PICkit,
PICDEM, PICDEM.net, PICLAB, PICtail, PowerCal,
PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, Select
Mode, Smart Serial, SmartTel, Total Endurance, UNI/O,
WiperLock and ZENA are trademarks of Microchip
Technology Incorporated in the U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated
in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2007, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received ISO/TS-16949:2002 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
© 2007 Microchip Technology Inc.
DS21460D-page 27
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10/05/07
DS21460D-page 28
© 2007 Microchip Technology Inc.