Document Outline
- Return to Contents
- List of Figures
- 2. Basic Dual-Slope Converter
- 3. Line Frequency Deviation
- 4. Integrating Converter Normal Mode Rejection
- 5. Comparator Output
- 6. Noise
- 7. Overshoot
- 8. Typical Dual Slope A/D Converter System Timing
- 8. TC510 Design Example (See "Design Example")
- 9. TC510 to IBM Compatible Printer Port
- 10. TC514 Design Example (See "Design Example")
- 11. TC514 to IBM Compatible Printer Port
- List of Tables
- 1. Internal Analog Gate Status
- 1. CREF and CAZ Selection
- 2. Recommend Capacitor for CINT
- Features
- Ordering Information
- Functional Block Diagram
- General Description
- General Description (Cont.)
- Absolute Maximum Ratings*
- Electrical Characteristics
- Electrical Characteristics: (Cont.)
- Pin Configurations
- Pin Descriptions
- Pin Description (Cont.)
- General Theory of Operation
- Dual-Slope Conversion Principles
- TC500/500A/510/514 Converter Operation
- Auto-Zero Phase (AZ)
- Analog Input Signal Integration Phase (INT)
- Reference Voltage Deintegration Phase (DINT)
- Integrator Output Zero Phase (IZ)
- Analog Section
- Differential Inputs
- Analog Common
- Differential Reference
- Phase Control Inputs
- Comparator Output
- Applications
- Component Value Selection
- Design Considerations
- Auto-Zero Phase
- Input Signal Integrate Phase
- Reference Deintegration
- Integrator Output Zero phase
- Design Example
- Using the TC510/514
- Negative Supply Voltage Converter (TC510, TC514)
- Analog Input Multiplexer (TC514)
- Evaluation Kit (TC500EV)
- Typical Performance Characteristics of Internal DC-TO-DC Converter
- WIMA Corporation Capacitor Representatives
3-19
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
PRECISION ANALOG FRONT ENDS
FEATURES
s
Precision (up to 17 Bits) A/D Converter "Front End"
s
3-Pin Control Interface to Microprocessor
s
Flexible: User Can Trade-Off Conversion Speed
for Resolution
s
Single Supply Operation (TC510/514)
s
4 Input, Differential Analog MUX (TC514)
s
Automatic Input Voltage Polarity Detection
s
Low Power Dissipation ........... TC500/500A: 10mW
TC510/514: 18mW
s
Wide Analog Input Range .......
4.2V (TC500A/510)
s
Directly Accepts Bipolar and Differential Input
Signals
GENERAL DESCRIPTION
The TC500/500A/510/514 family are precision analog
front ends that implement dual slope A/D converters having
a maximum resolution of 17 bits plus sign. As a minimum,
each device contains the integrator, zero crossing compara-
tor and processor interface logic. The TC500 is the base
(16 bit max) device and requires both positive and negative
power supplies. The TC500A is identical to the TC500,
except it has improved linearity allowing it to operate to a
maximum resolution of 17 bits. The TC510 adds an on-
board negative power supply converter for single supply
operation. The TC514 adds both a negative power supply
converter and a 4 input differential analog multiplexer.
Each device has the same processor control interface
consisting of 3 wires: control inputs A and B and zero-
crossing comparator output (CMPTR). The processor ma-
nipulates A, B to sequence the TC5xx through four phases
of conversion: Auto Zero, Integrate, Deintegrate and Inte-
grator Zero. During the Auto Zero phase, offset voltages in
the TC5xx are corrected by a closed-loop feedback mecha-
nism. The input voltage is applied to the integrator during the
Integrate phase. This causes an integrator output dv/dt
directly proportional to the magnitude of the input voltage.
The higher the input voltage, the greater the magnitude of
the voltage stored on the integrator during this phase. At the
start of the Deintegrate phase, an external voltage reference
is applied to the integrator, and at the same time, the external
host processor starts its on-board timer. The processor main-
FUNCTIONAL BLOCK DIAGRAM
LEVEL
SHIFT
CONTROL LOGIC
ANALOG
SWITCH
CONTROL
SIGNALS
ACOM
+
VREF
+
BUF
CAZ
BUFFER
INTEGRATOR
SWR
SWIZ
CMPTR 1
CMPTR 2
CMPTR
OUTPUT
DGND
CONTROL LOGIC
SW1
TC500
TC500A
TC510
TC514
CREF
CREF
SWR
CREF
CAZ
RINT
CINT
CINT
SWRI
+
SWRI
+
SWRI
SWRI
SWZ
SWI
SWZ
VS
OSC
+
+
+
PHASE
DECODING
LOGIC
POLARITY
DETECTION
DC-TO-DC
CONVERTER
(TC510 & TC514)
+
A B
0
0
ZERO INTEGRATOR OUTPUT
0
1
AUTO-ZERO
1
0
SIGNAL INTEGRATE
1
1
DEINTEGRATE
VREF
VOUT
COUT
1.0
F
1.0
F
VSS
SWI
B
A
A0
A1
DIF.
MUX
(TC514)
CH1
+
CH2
+
CH3
+
CH4
+
CH1
CH2
CH3
CH4
CAP CAP+
(TC500
TC500A)
CONVERTER STATE
TC500
TC500A
TC510
TC514
TC500/A/510/514-3 10/3/96
ORDERING INFORMATION
Part No.
Package
Temp. Range
TC500ACOE
16-Pin SOIC
0
C to +70
C
TC500ACPE
16-Pin Plastic DIP (Narrow)
0
C to +70
C
TC500COE
16-Pin SOIC
0
C to +70
C
TC500CPE
16-Pin Plastic DIP (Narrow)
0
C to +70
C
TC510COG
24-Pin SOIC
0
C to +70
C
TC510CPF
24-Pin Plastic DIP (300 Mil.)
0
C to +70
C
TC514COI
28-Pin SOIC
0
C to +70
C
TC514CPJ
28-Pin Plastic DIP (300 Mil.)
0
C to +70
C
TC500EV
Evaluation Kit for TC500/500A/510/514
EVALUATION
KIT
AVAILABLE
3-20
TELCOM SEMICONDUCTOR, INC.
* Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under "Absolute Maximum Ratings" may cause perma-
nent 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.
GENERAL DESCRIPTION (Cont.)
tains this state until a transition occurs on the CMPTR output,
at which time the processor halts its timer. The resulting
timer count is the converted analog data. Integrator Zero
(the final phase of conversion) removes any residue remain-
ing in the integrator in preparation for the next
conversion.
The TC500/500A/510/514 offer high resolution (up to 17
bits) superior 50Hz/60Hz noise rejection, low power opera-
tion, minimum I/O connections, low input bias currents and
lower cost compared to other converter technologies having
similar conversion speeds.
ABSOLUTE MAXIMUM RATINGS
*
TC510/514 Positive Supply Voltage
(V
DD
to GND) .................................................. +10.5V
TC500/500A Supply Voltage
(V
DD
to V
SS
) ....................................................... +18V
TC500/500A Positive Supply Voltage
(V
DD
to GND) ..................................................... +12V
TC500/500A Negative Supply Voltage
(V
SS
to GND) ...................................................... 8V
Analog Input Voltage (V
+
IN
or V
_
IN
) .................... V
DD
to V
SS
Logic Input Voltage .................. V
DD
+0.3V to GND 0.3V
Voltage on OSC ..... 0.3V to (V
DD
+0.3V) for V
DD
< 5.5V
Ambient Operating Temperature Range ...... 0
C to +70
C
Storage Temperature Range ................ 65
C to +150
C
Lead Temperature (Soldering, 10 sec) ................. +300
C
ELECTRICAL CHARACTERISTICS:
TC510/514: V
DD
= +5V, TC500/500A: V
S
=
5V unless otherwise
specified. C
AZ
= C
REF
= 0.47
F
T
A
= +25
C
T
A
= 0
C to +70
C
Symbol Parameter
Test Conditions
Min
Typ
Max
Min
Typ
Max
Unit
Analog
Resolution
Note 1
60
--
--
--
--
--
V
ZSE
Zero-Scale Error
TC500/510/514
--
--
0.005
--
0.005
0.012
% F.S.
with Auto Zero Phase
TC500A
--
--
0.003
--
0.003
0.009
ENL
End Point Linearity
TC500/510/514, Notes 1, 2,
--
0.005
0.015
--
0.015
0.060
% F.S.
TC500A
--
--
0.010
--
0.010
0.045
% F.S.
NL
Best Case Straight
TC500/510/514, Notes 1, 2,
--
0.003
0.008
--
--
--
% F.S.
Line Linearity
TC500A
--
--
0.005
--
--
--
% F.S.
ZS
TC
Zero-Scale
Over Operating
--
--
--
1
2
V/
C
Temperature
Temperature Range
Coefficient
SYE
Full-Scale Symmetry
Note 3
--
0.01
--
--
0.03
--
% F.S.
Error (Roll-Over Error)
FS
TC
Full-Scale Temperature
Over Operating
--
--
--
--
10
--
ppm/
C
Coefficient
Temperature Range
External Reference
TC = 0ppm/
C
I
IN
Input Current
V
IN
= 0V
--
6
--
--
--
--
pA
V
CMR
Common-Mode
V
SS
+1.5
--
V
DD
1.5 V
SS
+1.5
--
V
DD
1.5
V
Voltage Range
Integrator Output Swing
V
SS
+0.9
--
V
DD
0.9 V
SS
+0.9
--
V
SS
+0.9
V
Analog Input Signal Range ACOM = GND = 0V
V
SS
+1.5
--
V
DD
1.5 V
SS
+1.5
--
V
SS
+1.5
V
V
REF
Voltage Reference Range V
_
REF
V
+
REF
V
SS
+1
--
V
DD
1
V
SS
+1
--
V
DD
1
V
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-21
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
ELECTRICAL CHARACTERISTICS: (Cont.)
T
A
= +25
C
T
A
= 0
C to +70
C
Symbol
Parameter
Test Conditions
Min
Typ
Max
Min
Typ
Max
Unit
Digital
V
OH
Comparator Logic 1,
I
SOURCE
= 400
A
4
--
--
4
--
--
V
Output High
V
OL
Comparator Logic 0,
I
SINK
= 2.1mA
--
--
0.4
--
--
0.4
V
Output Low
V
IH
Logic 1, Input High Voltage
3.5
--
--
3.5
--
--
V
V
IL
Logic 0, Input Low Voltage
--
--
1
--
--
1
V
I
L
Logic Input Current
Logic 1 or 0
--
--
--
--
0.3
--
A
t
D
Comparator Delay
--
2
--
--
3
--
sec
Multiplexer (TC514 Only)
Maximum Input Voltage
V
DD
= 5V
2.5
--
2.5
2.5
--
2.5
V
R
DSON
Drain/Source ON Resistance
V
DD
= 5V
--
6
10
--
--
--
k
Power (TC510/514 Only)
I
S
Supply Current
V
DD
= 5V, A = 1, B = 1
--
1.8
2.4
--
--
3.5
mA
P
D
Power Dissipation
V
DD
= 5V
--
18
--
--
--
--
mW
V
DD
Positive Supply
4.5
--
5.5
4.5
--
5.5
V
Operating Voltage Range
R
OUT
Operating Source Resistance
I
OUT
= 10mA
--
60
85
--
--
100
Oscillator Frequency (Note 3)
--
100
--
--
--
--
kHz
I
OUT
Maximum Current Out
V
DD
= 5V
--
--
10
--
--
10
mA
Power (TC500/500A Only)
I
S
Supply Current
V
S
=
5V, A = B = 1
--
1
1.5
--
--
2.5
mA
P
D
Power Dissipation
V
DD
= 5V, V
SS
= 5V
--
10
--
--
--
--
mW
V
DD
Positive Supply
4.5
--
7.5
4.5
--
7.5
V
Operating Voltage Range
V
SS
Negative Supply
4.5
--
7.5
4.5
--
7.5
V
Operating Voltage Range
NOTES: 1. Integrate time
66msec, auto-zero time
66msec, V
INT
(peak)
4V.
2. End point linearity at
1/4,
1 /2,
3/4 F.S. after full-scale adjustment.
3. Roll-over error is related to C
INT
, C
REF
, C
AZ
characteristics.
3-22
TELCOM SEMICONDUCTOR, INC.
1
2
3
4
16
15
14
CAP
5
6
7
8
13
19
18
17
9
10
11
12
20
21
22
23
24
DGND
V
A
B
C
REF
C
INT
C
AZ
BUF
ACOM
N/C
N/C
N/C
TC510CPF
C
REF
REF
V
REF
+
VOUT
VOUT
VOUT
+
V
C
REF
C
INT
C
AZ
BUF
ACOM
N/C
N/C
N/C
C
REF
REF
V
REF
+
+
VDD
OSC
CMPTR OUT
VIN
VIN
+
N/C
N/C
CAP
+
CAP
DGND
A
B
VDD
OSC
CMPTR OUT
VIN
VIN
+
N/C
N/C
CAP
+
1
2
3
4
5
6
7
8
24
21
20
19
18
17
16
15
14
13
9
10
11
12
23
22
TC510COG
1
2
3
4
20
19
18
CAP
5
6
7
8
17
23
22
21
9
10
11
12
24
25
26
27
28
DGND
V
A
B
C
REF
C
INT
C
AZ
BUF
ACOM
CH4
CH3
CH2
TC514CPJ
C
REF
REF
V
REF
+
+
VDD
OSC
CMPTR OUT
CAP
+
16
15
13
14
CH1
N/C
CH1+
CH2+
CH3+
CH4+
A0
A1
V
VOUT
C
REF
C
INT
C
AZ
BUF
ACOM
C
REF
REF
V
REF
+
+
CAP
DGND
VDD
OSC
CMPTR OUT
CAP
+
1
2
3
4
5
6
7
8
28
25
24
23
22
21
20
19
18
17
9
10
11
12
27
26
TC514COI
N/C
13
14
16
15
CH4
CH3
CH2
CH1
A
B
CH1+
CH2+
CH3+
CH4+
A0
A1
1
2
3
4
16
15
14
13
BUF
CMPTR OUT
5
6
7
12
11
10
9
A
8
VSS
CINT
DIGITAL GND
B
+
VDD
+
+
ACOM
ACOM
TC500/
TC500A
CPE
VIN
VIN
VREF
VREF
CREF
CREF
CAZ
1
2
3
4
15
16
14
13
5
6
7
12
11
10
9
8
TC500/
TC500A
COE
BUF
VSS
CINT
+
VREF
CREF
CREF
CAZ
CMPTR OUT
A
DIGITAL GND
B
VDD
+
+
VIN
VIN
VREF
PIN CONFIGURATIONS
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-23
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
PIN DESCRIPTION
Pin No
Pin No
Pin No
(TC500, 500A) (TC510)
(TC514)
Symbol
Description
1
2
2
C
INT
Integrator output. Integrator capacitor connection.
2
Not Used
Not Used
V
SS
Negative power supply input (TC500/500A only).
3
3
3
C
AZ
Auto-zero input. The Auto-zero capacitor connection.
4
4
4
BUF
Buffer output. The Integrator capacitor connection.
5
5
5
ACOM
This pin is grounded in most applications. It is recommended that
ACOM and the input common pin (V
IN
or
C
HN
) be within the
analog common mode range (CMR).
6
6
6
C
REF
Input. Negative reference capacitor connection.
7
7
7
C
+
REF
Input. Positive reference capacitor connection.
8
8
8
V
REF
Input. External voltage reference () connection.
9
9
9
V
+
REF
Input. External voltage reference (+) connection.
10
15
Not Used
V
IN
Negative analog input.
11
16
Not Used
V
+
IN
Positive analog input.
12
18
22
A
Input. Converter phase control MSB. (See input B.)
13
17
21
B
Input. Converter phase control LSB. The states of A, B place the
TC5xx in one of four required phases. A conversion is complete
when all four phases have been executed:
00: Integrator Zero
Phase control input pins: AB =
01: Auto Zero
10: Integrate
11: Deintegrate
14
19
23
CMPTR OUT
Zero crossing comparator output. CMPTR is HIGH during the
Integration phase when a positive input voltage is being integrated
and is LOW when a negative input voltage is being integrated. A
HIGH-to-LOW transition on CMPTR signals the processor that the
Deintegrate phase is completed. CMPTR is undefined during the
Auto-Zero phase. It should be monitored to time the Integrator Zero
phase (see text).
15
23
27
DGND
Input. Digital ground.
16
21
25
V
DD
Input. Power supply positive connection.
22
26
CAP
+
Input. Negative power supply converter capacitor (+) connection.
24
28
CAP
Input. Negative power supply converter capacitor () connection.
1
1
V
OUT
Output. Negative power supply converter output and reservoir
capacitor connection. This output can be used to power other
devices in the circuit requiring a negative bias voltage.
20
24
OSC
Oscillator control input. The negative power supply converter normally
runs at a frequency of 100kHz. The converter oscillator frequency can
be slowed down (to reduce quiescent current) by connecting an
external capacitor between this pin and V
DD
. (See Typical Character-
istics Curves).
18
CH1
+
Positive analog input pin. MUX channel 1.
13
CH1
Negative analog input pin. MUX channel 1.
17
CH2
+
Positive analog input pin. MUX channel 2.
12
CH2
Negative analog input pin. MUX channel 2.
16
CH3
+
Positive analog input pin. MUX channel 3.
11
CH3
Negative analog input pin. MUX channel 3.
15
CH4
+
Positive analog input pin. MUX channel 4.
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-24
TELCOM SEMICONDUCTOR, INC.
Figure 2. Basic Dual-Slope Converter
PHASE
CONTROL
COMPARATOR
INTEGRATOR
OUTPUT
INTEGRATOR
CINT
ANALOG
INPUT
(VIN)
SWITCH DRIVER
REF
VOLTAGE
CONTROL
LOGIC
POLARITY
CONTROL
S1
I/O
TIMER
COUNTER
ROM
RAM
MICROCOMPUTER
A
B
CMPTR OUT
VSUPPLY
TINT
TC510
VINT
VIN
VFULL SCALE
VIN
1/2 VFULL SCALE
TDEINT
+
RINT
VINT
+
PIN DESCRIPTION (Cont.)
Pin No
Pin No
Pin No
(TC500/A)
(TC510)
(TC514)
Symbol
Description
10
CH4
Negative analog input pin. MUX channel 4
20
A0
Multiplexer input channel select input LSB. (See A1).
19
A1
Multiplexer input channel select input MSB.
00 = Channel 1
Phase control input pins: A1, A0 =
01 = Channel 2
10 = Channel 3
11 = Channel 4
GENERAL THEORY OF OPERATION
Dual-Slope Conversion Principles (Figure 2)
Actual data conversion is accomplished in two phases:
input signal Integration and reference voltage Deintegration.
The integrator output is initialized to 0V prior to the start
of Integration. During Integration, analog switch S1 con-
nects V
IN
to the integrator input where it is maintained for a
fixed time period (t
INT
). The application of V
IN
causes the
integrator output to depart 0V at a rate determined by the
magnitude of V
IN
, and a direction determined by the
polarity
of V
IN
. The Deintegration phase is initiated immediately at
the expiration of t
INT
.
During Deintegration, S1 connects a reference voltage
(having a polarity opposite that of V
IN
) to the integrator input.
At the same time, an external precision timer is started. The
Deintegration phase is maintained until the comparator
output changes state, indicating the integrator has returned
to its starting point of 0V. When this occurs, the precision
timer is stopped. The Deintegration time period (t
DEINT
), as
measured by the precision timer, is directly proportional to
the magnitude of the applied input voltage.
A simple mathematical equation relates the Input
Signal, Reference Voltage and Integration time:
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-25
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
0.01
0.1
1.0
NORMAL MODE REJECTION (dB)
80
70
60
50
40
30
20
t = 0.1 sec
LINE FREQUENCY DEVIATION FROM 60 Hz (%)
NORMAL
MODE
REJECTION
= 20 LOG
DEV = DEVIATION FROM 60 Hz
t = INTEGRATION PERIOD
SIN 60 t (1
)
DEV
100
DEV
100
60
t (1
)
Figure 3. Line Frequency Deviation
Figure 4.. Integrating Converter Normal Mode Rejection
30
20
10
0
0.1/T
1/T
10/T
INPUT FREQUENCY
NORMAL MODE REJECTION (dB)
T = MEASUREMENT
PERIOD
1 t
INT
V
IN
(t) dt =
V
REF
t
DEINT
R
INT
C
INT
0
R
INT
C
INT
where:
V
REF
= Reference Voltage
t
INT
= Signal Integration time (fixed)
t
DEINT
= Reference Voltage Integration time (variable)
For a constant V
IN
:
V
IN
= V
REF
t
DEINT
t
INT
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. Input noise spikes
are integrated (averaged to zero) during the integration
periods. Integrating ADCs are immune to the large conver-
sion errors that plague successive approximation convert-
ers in high-noise environments.
Integrating converters provide inherent noise rejection
with at least a 20dB/decade attenuation rate. Interference
signals with frequencies at integral multiples of the integra-
tion period are, theoretically, completely removed since the
average value of a sine wave of frequency (1/t) averaged
over a period (t) is zero.
Integrating converters often establish the integration
period to reject 50/60Hz line frequency interference signals.
The ability to reject such signals is shown by a normal mode
rejection plot (Figure 4). Normal mode rejection is limited in
practice to 50 to 65dB, since the line frequency can deviate
by a few tenths of a percent (Figure 3).
TC500/500A/510/514 CONVERTER OPERATION
The TC500/500A/510/514 incorporates an Auto zero
and Integrator phase in addition to the input signal Integrate
and reference Deintegrate phases. The addition of these
phases reduce system errors and calibration steps, and
shorten overrange recovery time. A typical measurement
cycle uses all four phases in the following order:
(1) Auto zero
(2) Input signal integration
(3) Reference deintegration
(4) Integrator output zero
The internal analog switch status for each of these
phases is summarized in Table 1. This table is referenced
to the
Functional Block Diagram on the first page of this data
sheet.
Auto-Zero Phase (AZ)
During this phase, errors due to buffer, integrator and
comparator offset voltages are nulled out by charging C
AZ
(auto-zero capacitor) with a compensating error voltage.
The external input signal is disconnected from the
internal circuitry by opening the two SW
I
switches. The
internal input points connect to analog common. The refer-
ence capacitor is charged to the reference voltage potential
through SW
R
. A feedback loop, closed around the integrator
and comparator, charges the C
AZ
capacitor with a voltage to
compensate for buffer amplifier, integrator and comparator
offset voltages.
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-26
TELCOM SEMICONDUCTOR, INC.
Analog Input Signal Integration Phase (INT)
The TC5xx integrates the differential voltage between
the (V
+
IN
) and (V
IN
) inputs. The differential voltage must be
within the device's common-mode range V
CMR
.
The input signal polarity is normally checked via soft-
ware at the end of this phase: CMPTR = 1 for positive
polarity; CMPTR = 0 for negative polarity.
Reference Voltage Deintegration Phase (DINT)
The previously charged reference capacitor is con-
nected with the proper polarity to ramp the integrator output
back to zero. An externally-provided, precision timer is used
to measure the duration of this phase. The resulting time
measurement is proportional to the magnitude of the applied
input voltage.
Integrator Output Zero Phase (IZ)
This phase guarantees the integrator output is at 0V
when the Auto Zero phase is entered and that only system
offset voltages are compensated. This phase is used at the
end of the reference voltage deintegration phase and MUST
be used for ALL TC5xx applications having resolutions of 12
bits or more. If this phase is not used, the value of the Auto-
Zero capacitor (C
AZ
) must be about 2 to 3 times the value of
the integration capacitor (C
INT
) to reduce the effects of
charge-sharing. The Integrator Output Zero phase should
be programmed to operate until the Output of the Compara-
tor returns "HIGH". The overall Timing System is shown in
Figure 8.
ANALOG SECTION
Differential Inputs (V
+
IN
, V
IN
)
The TC5xx operates with differential voltages within the
input amplifier common-mode range. The amplifier com-
mon-mode range extends from 1.5V below positive supply
to 1.5V above negative supply. Within this common-mode
voltage range, common-mode rejection is typically 80dB.
Full accuracy is maintained, however, when the inputs are
no less than 1.5V from either supply.
The integrator output also follows the common-mode
voltage. The integrator output must not be allowed to satu-
rate. A worst-case 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. The integrator output can swing within 0.9V
of either supply without loss of linearity.
Analog Common
Analog common is used as V
IN
return during system-
zero and reference deintegrate. If V
IN
is different from analog
common, a common-mode voltage exists in the system.
This signal is rejected by the excellent CMR of the converter.
In most applications, V
IN
will be set at a fixed known voltage
(i.e., power supply common). A common-mode voltage will
exist when V
IN
is not connected to analog common.
Differential Reference (V
+
REF
, V
REF
)
The reference voltage can be anywhere within 1V of the
power supply voltage of the converter. Roll-over error is
caused by the reference capacitor losing or gaining charge
due to stray capacitance on its nodes. The difference in
reference for (+) or () input voltages will cause a roll-over
error. This error can be minimized by using a large reference
capacitor in comparison to the stray capacitance.
Phase Control Inputs (A, B)
The A, B unlatched logic inputs select the TC5xx oper-
ating phase. The A, B inputs are normally driven by a
microprocessor I/O port or external logic.
Table 1. Internal Analog Gate Status
Internal Analog Gate Status
Conversion Phase
SW
I
SW
+
RI
SW
RI
SW
Z
SW
R
SW
1
SW
IZ
Auto-Zero (A = 0, B = 1)
Closed
Closed
Closed
Input Signal Integration
Closed
(A = 1, B = 0)
Reference Voltage
Closed*
Closed
Deintegration (A =1, B= 1)
Integrator Output Zero
Closed
Closed
Closed
(A = 0, B = 0)
*Assumes a positive polarity input signal. SW
RI
would be closed for a negative input signal.
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-27
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
Figure 5. Comparator Output
INTEGRATOR
OUTPUT
ZERO
CROSSING
COMPARATOR
OUTPUT
REFERENCE
DEINTEGRATE
SIGNAL
INTEGRATE
INTEGRATOR
OUTPUT
ZERO
CROSSING
COMPARATOR
OUTPUT
REFERENCE
DEINTEGRATE
SIGNAL
INTEGRATE
B. Negative Input Signal
A. Positive Input Signal
Comparator Output
By monitoring the comparator output during the fixed
signal integrate time, the input signal polarity can be deter-
mined by the microprocessor controlling the conversion.
The comparator output is HIGH for positive signals and LOW
for negative signals during the signal-integrate phase (see
timing diagram).
During the reference deintegrate phase, the comparator
output will make a HIGH-to-LOW transition as the integrator
output ramp crosses zero. The transition is used to signal the
processor that the conversion is complete.
The internal comparator delay is 2
sec, typically. Figure
5 shows the comparator output for large positive and nega-
tive signal inputs. For signal inputs at or near zero volts,
however, the integrator swing is very small. If common-
mode noise is present, the comparator can switch several
times during the beginning of the signal-integrate period. To
ensure that the polarity reading is correct, the comparator
output should be read and stored at the end of the signal
integrate phase.
The comparator output is undefined during the Auto-
Zero Phase and is used to time the Integrator Output Zero
phase. (See
Integrator Output Zero Phase of System Timing
section).
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-28
TELCOM SEMICONDUCTOR, INC.
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
APPLICATIONS
Component Value Selection
The procedure outlined below allows the user to arrive
at values for the following TC5xx design variables:
(1) Integration Phase Timing
(2) Integrator Timing Components (R
INT
, C
INT
)
(3) Auto Zero and Reference Capacitors
(4) Voltage Reference
Select Integration Time
Integration time must be picked as a multiple of the
period of the line frequency. For example, t
INT
times of
33msec, 66msec and 132msec maximize 60Hz line rejec-
tion.
D
INT
and I
Z
Phase Timing
The duration of the DINT phase is a function of the
amount of voltage stored on the integrator during TINT, and
the value of V
REF
. The DINT phase must be initiated imme-
diately following I
NT
and terminated when an integrator
output zero-crossing is detected. In general, the maximum
number of counts chosen for DINT is twice that of INT (with
V
REF
chosen at V
IN
(max)/2).
Calculate Integrating Resistor (R
INT
)
The desired full-scale input voltage and amplifier output
current capability determine the value of R
INT
. The buffer
and integrator amplifiers each have a full-scale current of
20
A.
The value of R
INT
is therefore directly calculated as
follows:
R
INT
(in M
) =
V
IN MAX
20
where: V
IN MAX
= Maximum input voltage (full count voltage)
R
INT
=Integrating Resistor (in M
)
For loop stability, R
INT
should be
50k
.
Select Reference (C
REF
) and Auto Zero (C
AZ
) Capacitors
C
REF
and C
AZ
must be low leakage capacitors (such as
polypropylene). The slower the conversion rate, the larger
the value C
REF
must be. Recommended capacitors for C
REF
and C
AZ
are shown in Table 1. Larger values for C
AZ
and
C
REF
may also be used to limit roll-over errors.
Table 1. C
REF
and C
AZ
Selection
Conversions Typical Value of Suggested *
Per Second
C
REF
, C
AZ
(
F)
Part Number
>7
0.1
WIMA MK12 .1/63/20
2 to 7
0.22
WIMA MK12 .22/63/20
2 or less
0.47
WIMA MK12 .47/63/20
*WIMA Corp. listing on the last page of this data sheet.
Calculate Integrating Capacitor (C
INT
)
The integrating capacitor must be selected to maximize
integrator output voltage swing. The integrator output volt-
age swing is defined as the absolute value of V
DD
(or V
SS
)
less 0.9V (i.e.,
V
DD
0.9V
or
V
SS
+0.9V
). Using the 20
A
buffer maximum output current, the value of the integrating
capacitor is calculated using the following equation.
C
INT
= (in
F) =
where: t
INT
= Integration Period
V
S
= Applied Supply Voltage
It is critical that the integrating capacitor has a very low
dielectric absorption. Polypropylene capacitors are an ex-
ample of one such chemistry. Polyester and Polybicarbonate
capacitors may also be used in less critical applications.
Table 2 summarizes recommended capacitors for C
INT
.
Table 2. Recommend Capacitor for C
INT
Value
Suggested Part Number*
0.1
WIMA MK12 .1/63/20
0.22
WIMA MK12 .22/63/20
0.33
WIMA MK12 .33/63/20
0.47
WIMA MK12 .47/63/20
*WIMA Corp. listing on the last page of this data sheet.
Calculate V
REF
The reference deintegration voltage is calculated
using:
V
REF
(in Volts) =
(V
S
0.9) (C
INT
) (R
INT
)
2(t
INT
)
(t
INT
) (20 x 10
6
)
(V
S
0.9)
3-29
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
Figure 6. Noise
S
N
TH
Low
REF
S
N
TH
Normal
V
REF
S
N
TH
High
30
V
V
REF
SLOPE (S) =
N
TH
= Noise Threshold
V
REF
R
INT
C
INT
Figure 7. Overshoot
INTEGRATOR
OUTPUT
COMPARATOR
OUTPUT COMP
INTEGRATE
PHASE
DEINTEGRATE PHASE
INTEGRATOR
ZERO PHASE
ZERO
CROSSING
OVERSHOOT
Figure 8 shows the overall timing for a typical system in
which a TC5xx is interfaced to a microcontroller. The
microcontroller drives the A, B inputs with I/O lines and
monitors the comparator output, CMPTR, using an I/O line
or dedicated timer-capture control pin. It may be necessary
to monitor the state of the CMPTR output in addition to
having it control a timer directly for the Reference Deintegra-
tion phase. (This is further explained below.)
The timing diagram in Figure 8 is not to scale as the
timing in a real system depends on many system parameters
and component value selections. There are four critical
timing events (as shown in Figure 8): sampling the input
polarity; capturing the deintegration time; minimizing over-
shoot and properly executing the Integrator Output Zero
phase.
Auto-Zero Phase
The length of this phase is usually set to be equal to the
Input Signal Integration time. This decision is virtually arbi-
trary since the magnitudes of the various system errors are
not known. Setting the Auto-Zero time equal to the Input
Integrate time should be more than adequate to null out
system errors. The system may remain in this phase indefi-
nitely, i.e., Auto-Zero is the appropriate idle state for a TC5xx
device.
Input Signal Integrate Phase
The length of this phase is constant from one conversion
to the next and depends on system parameters and compo-
nent value selections. The calculation of t
INT
is shown
elsewhere in this data sheet. At some point near the end of
this phase, the microcontroller should sample CMPTR to
determine the input signal polarity. This value is, in effect,
the Sign Bit for the overall conversion result. Optimally,
CMPTR should be sampled just before this phase is termi-
nated by changing AB from 10 to 11. The consideration here
)
DESIGN CONSIDERATIONS
Noise
The threshold noise (NTH) is the algebraic sum of the
integrator noise and the comparator noise. This value is
typically 30
V. Figure 6 shows how the value of the refer-
ence voltage can affect the final count. Such errors can be
reduced by increased integration times, in the same way
that 50/60Hz noise is rejected. The signal-to-noise ratio is
related to the integration time (t
INT
) and the integration time
constant (R
INT)
(C
INT
) as follows:
S/N (dB) = 20 Log
V
IN
t
INT
30 x 10
6
(R
INT
) (C
INT
)
System Timing
To obtain maximum performance from the TC5xx, the
overshoot at the end of the Deintegration phase must be
minimized. Also, the Auto Zero phase must be terminated as
soon as the comparator output returns high. (See timing
diagram, Figure 8).
(
3-30
TELCOM SEMICONDUCTOR, INC.
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
Figure 8. Typical Dual Slope A/D Converter System Timing
,,
,,
AUTO -ZERO
INTEGRATE
FULL SCALE INPUT
REFERENCE
DEINTEGRATE
OVERSHOOT
INTEGRATOR
OUTPUT
ZERO
CONVERTER
STATUS
TIME
INTEGRATOR
VOLTAGE
COMPARATOR
OUTPUT
AB INPUTS
CONTROLLER
OPERATION
NOTES
COMPARATOR DELAY
BEGIN CONVERSION
WITH AUTO-ZERO PHASE
(POSITIVE INPUT SHOWN)
SAMPLE INPUT POLARITY
The length of this phase
is chosen almost arbitrarily
but needs to be long enough
to null out worst case errors
(see text)
MINIMIZING OVERSHOOT
WILL MINIMIZE I.O.Z. TIME
READY FOR NEXT
CONVERSION
(AUTO-ZERO IS IDLE
STATE)
TIME INPUT
INTEGRATION
PHASE
CAPTURE
DEINTEGRATION
TIME
INTEGRATOR
OUTPUT
ZERO PHASE
COMPLETE
UNDEFINED
A = 0
B = 1
A = 1
0 FOR NEGATIVE INPUT
1 FOR POSITIVE INPUT
B = 0
B = 1
B = 0
A = 1
A = 0
VINT
TYPICALLY = tINT
tINT
0
A
B
COMPARATOR DELAY +
PROCESSOR LATENCY
is that, during the initial stage of input integration when the
integrator voltage is low, the comparator may be affected by
noise and its output unreliable. Once integration is well
underway, the comparator will be in a defined state.
Reference Deintegration
The length of this phase must be precisely measured
from the transition of AB from 10 to 11 to the falling edge of
CMPTR. The comparator delay contributes some error in
timing this phase. The typical delay is specified to be 2
sec.
This should be considered in the context of the length of a
single count when determining overall system performance
and possible single-count errors. Additionally, Overshoot
will result in charge accumulating on the integrator after its
output crosses zero. This charge must be nulled during the
Integrator Output Zero phase.
Integrator Output Zero phase
The comparator delay and the controller's response
latency may result in Overshoot causing charge buildup on
the integrator at the end of a conversion. This charge must
be removed or performance will degrade. The Integrator
Output Zero phase should be activated (AB = 00) until
CMPTR goes high. It is absolutely critical that this phase be
terminated immediately so that Overshoot is not allowed to
occur in the opposite direction. At this point, it can be
assured that the integrator is near zero. Auto Zero should be
entered (AB = 01) and the TC5xx held in this state until the
next cycle is begun.
3-31
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
USING THE TC510/514
Negative Supply Voltage Converter (TC510, TC514)
A capacitive charge pump is employed to invert the
voltage on V
DD
for negative bias within the TC510/514. This
voltage is also available on the V
OUT
pin to provide negative
bias elsewhere in the system. Two external capacitors are
required to perform the conversion.
Timing is generated by an internal state machine driven
from an on-board oscillator. During the first phase, capacitor
C
F
is switched across the power supply and charged to V
+
S
.
This charge is transferred to capacitor C
OUT
during the
second phase. The oscillator normally runs at 100kHz to
ensure minimum output ripple. This frequency can be re-
duced by placing a capacitor from OSC to V
DD
. The relation-
ship between the capacitor value is shown in the typical
characteristics curves at the end of this data sheet.
Analog Input Multiplexer (TC514)
The TC514 is equipped with a four input differential
analog multiplexer. Input channels are selected using select
inputs (A1, A0). These are high-true control signals
(i.e., channel 0 is selected when (A1, A0 = 00).
EVALUATION KIT (TC500EV)
The TC500EV consists of a pre-assembled, 4 inch by 6
inch printed circuit board that connects to the serial port of
any PC or dumb terminal. Design software is also included.
TC500EV helps reduce design time and optimize converter
performance. Please contact your local TelCom representa-
tive for more information.
Design Example
Given:
Required Resolution:
16 Bits (65,536 counts).
Maximum V
IN
:
2V
Power Supply Voltage: +5V
60Hz System
Step 1: Pick integration time (t
INT
) as a multiple of the
line frequency:
1/60Hz = 16.6msec. Use 4x line frequency = 66msec
Step 2: Calculate R
INT
R
INT
(in M
) = V
INMAX
/20 = 2/20 = 100k
Step 3: Calculate C
INT
for maximum (4V) integrator
output swing:
C
INT
(in
F) = (t
INT
) (20 x 10
6
) / (V
S
0.9)
= (.066) (20 x 10
6
) / (4.1)
= .32
F (use closest value: 0.33
F)
NOTE: TelCom recommended capacitor:
WIMA p/n: MK12 .33/63/10
Step 4: Choose C
REF
and C
AZ
based on conversion rate:
Conversions/sec
= 1/(t
AZ
+ t
INT
+ 2 t
INT
+ 2msec)
= 1/(66msec + 66msec +132msec+2msec)
= 3.7 conversions/sec
From which C
AZ
= C
REF
= 0.22
F (see Table 1)
NOTE: TelCom recommended capacitor:
WIMA p/n: MK12 .22/63/10
Step 5: Calculate V
REF
V
REF
(in Volts) = (V
S
0.9) (C
INT
) (R
INT
)
2(t
INT
)
= (4.1) (0.33 x 10
6
) (10
5
) / 2(.066)
= 1.025V
3-32
TELCOM SEMICONDUCTOR, INC.
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
Figure 8. TC510 Design Example (See "Design Example")
Figure 9. TC510 to IBM Compatible Printer Port
MICRO
CONTROLLER
INPUT+
INPUT
+5V
+5V
PIN 2
PIN 19
PIN 2
PIN 19
CINT
0.33
F
VIN
TYPICAL WAVEFORMS
1
F
1
F
CAZ
0.22
F
CREF
VIN
RINT
100k
1
2
3
4
16
15
CAP
5
6
7
9
19
18
17
8
21
22
23
24
DGND
V
V
OUT
A
B
C
REF
C
INT
C
AZ
BUF
ACOM
TC510
C
REF
REF
V
REF
+
+
V
IN
V
IN
+
CAP
+
V
DD
CMPTR
0.22
F
C1
0.01
F
R2
10k
R1
10k
+5V
TC05
+
R3, 10k
PC
PRINTER
PORT
PORT
0378
HEX
INPUT
+
+5V
10k
10k
10k
100k
100k
1
F
1
F
1
21
2
2
3
3
4
16
15
CAP
5
6
7
8
19
10
18
17
9
22
23
24
DGND
V
V
OUT
V
DD
A
B
C
REF
C
INT
C
AZ
BUF
ACOM
TC510
TC04
C
REF
REF
V
REF
+
+
V
IN
V
IN
+
CAP
+
CMPTR
0.22
F
0.22
F
0.01
F
0.01
F
0.33
F
3-33
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
MICRO
CONTROLLER
+5V
5V
+
PIN 2
PIN 23
PIN 2
PIN 23
CINT
0.33
F
VIN
TYPICAL WAVEFORMS
1
F
1
F
CAZ
0.22
F
CREF
0.22
F
VIN
RINT
100k
1
2
3
4
CAP
5
6
7
23
22
21
25
26
27
28
DGND
V
V
OUT
A
B
C
REF
C
INT
C
AZ
BUF
ACOM
TC514
C
REF
REF
V
REF
+
+
CAP
+
V
DD
CMPTR
ANALOG
MUX LOGIC
INPUT 1+
INPUT 1
INPUT 2+
INPUT 2
INPUT 3+
INPUT 3
INPUT4+
INPUT4
18
13
A1
CH1+
17
12
CH2+
CH2
16
11
CH3+
CH3
15
10
CH4+
CH4
22
19
A0
CH1
9
8
C1, .01
F
10k
10k
10k
+5V
TC05
+
Figure 11. TC514 to IBM Compatible Printer Port
Figure 10. TC514 Design Example (See "Design Example")
IBM
PRINTER PORT
PORT
0378
HEX
+5V
10k
100k
1
F
1
F
1
25
2
2
3
3
4
CAP
5
6
7
8
23
10
22
21
9
26
27
28
DGND
V
OUT
V
DD
A
B
C
REF
TC514
TC04
+
+
BUF
0.22
F
10k
10k
0.22
F
0.01
F
0.33
F
CH1+
INPUT 1
+
18
13
INPUT 2
+
17
12
INPUT 3
+
16
11
INPUT 4
+
15
10
CAP+
C
REF
V
REF
V
REF
C
AZ
C
INT
ACOM
CH1
CH2+
CH2
CH3+
CH3
CH4+
CH4
CMPTR
ANALOG MUX
CONTROL LOGIC
A0
A1
20
19
3-34
TELCOM SEMICONDUCTOR, INC.
TYPICAL PERFORMANCE CHARACTERISTICS OF INTERNAL DC-TO-DC CONVERTER
LOAD CURRENT (mA)
OUTPUT CURRENT (mA)
5
4
3
2
1
0
1
2
3
4
5
0
10
20
30
40
50
60
70
0
6
8
10
4
2
14
16
18
12
20
80
OUTPUT VOLTAGE (V)
Output Voltage vs Load Current
0
1
3
2
4
5
7
6
8
OUTPUT VOLTAGE (V)
Output Voltage vs. Output Current
OSCILLATOR CAPACITANCE (pF)
100
10
1
1
10
100
1000
OSCILLATOR FREQUENCY (kHz)
Oscillator Frequency vs. Capacitance
LOAD CURRENT (mA)
0
3
4
5
6
1
2
7
8
9
10
0
25
50
75
100
125
150
175
200
OUTPUT RIPPLE (mV PK-PK)
Output Ripple vs. Load Current
TEMPERATURE (
C)
70
80
90
100
60
50
40
50
0
25
25
50
75
100
OUTPUT SOURCE RESISTANCE (
)
Output Source Resistance vs. Temperature
T
A
= 25
C
V+ = 5V
T
A
= +25
C
V+ = 5V
T
A
= 25
C
Slope 60
V+ = 5V, T
A
= 25
C
Osc. Freq. = 100kHz
CAP = 1
F
CAP = 10
F
V+ = 5V
I
OUT
= 10mA
TEMPERATURE (
C)
125
150
100
75
50
50
0
25
25
50
75
125
100
OSCILLATOR FREQUENCY (kHz)
Oscillator Frequency vs. Temperature
V+ = 5V
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
3-35
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
Australia:
ADILAM ELECTRONICS (PTY.) LTD.
P.O. Box 664
3 Nicole Close
Bayswater 3153
Tel.: 3-761-4466
Fax: 3-761-4161
Canada:
R-THETA INC.
130 Matheson Blvd. East, Unit 2
Mississauga, Ont. L4Z1Y6
Tel.: 905-890-0221
Fax: 905-890-1628
Hong Kong:
REALTRONICS CO. LTD.
E-3, Hung-On Building
2, King's Road
Tel.: 25-70-1151
Fax: 28-06-8474
India:
SUSAN AGENCIES
P.O. Box 2138
Srirampuram P.O.
Bangalore-560 021
Tel.: 080-332-0662
Fax: 080-332-4338
Israel:
M.G.R. TECHNOLOGY
P.O. Box 2229
Rehavot 76121
Tel.: 972-841-1719
Fax: 972-841-4178
Japan:
UNIDUX INC.
5-1-21, Kyonan-Cho
Musashino-Shi
Tokyo 180
Tel.: 04-2232-4111
Fax: 04-2232-0331
Malaysia:
MA ELECTRONICS (M) SDN BHD
346-B Jalan Jelutong
11600 Penang
Tel.: 604-281-4518
Fax: 604-281-4515
Singapore:
MICROTRONICS ASSOC. (PTE.) LTD.
8, Lorong Bakar Batu
03-01, Kolam Ayer Ind. Park
Singapore 1334
Tel.: 65-748-1835
Tlx: 34 929
Fax: 65-743-3065
South Africa:
KOPP ELECTRONICS LIMITED
P.O. Box 3853
2128 Rivonia
Tel.: 011-444-2333
Fax: 011-444-1706
South Korea:
YONG JUN ELECTRONIC CO.
#201, Sungwook Bldg.
1460-16, Seocho-Dong
Seocho-Ku
Seoul, Korea
Tel.: 25-231-8002
Fax: 25-231-803
Taiwan, R.O.C.:
SOLOMON TECHNOLOGY CORP.
7th Floor No. 2
Lane 47, Sec. 3
Nan Kang Road
Taipei
Tel.: 886-2788-8989
Fax: 886-288-8275
Thailand:
MICROTRONICS THAI LTD.
50/68 T.T. Court
Cheng Wattana Road
Amphur Pak-Kreed
Nonthaburi 11120
Tel.: 66-2584-5807, Ext. 102
Fax: 66-2583-3775
USA:
THE INTER-TECHNICAL GROUP, INC.
WIMA DIVISION
175 Clearbrook Road
P.O. Box 535
Elmsford, NY 10523-0535
Tel.: 914-347-2474
Fax: 914-347-7230
TAW ELECTRONICS, INC.
4215, W. Burbank, Blvd.
Burbank, CA, 91505
Tel.: 818-846-3911
Fax: 818-846-1194
Venezuela:
MAGNETICA, S.A.
Apartado 78117
Caracas 1074 A
Tel.: 58-2241-7509
Fax: 58-2241-5542
WIMA Corporation Capacitor Representatives (Tables 1 and 2 in Applications Section)
PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
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