TI1 ADC0838 Adc0831/adc0832/adc0834/adc0838 8-bit serial i/o a/d converters with multiplexer option Datasheet

ADC0831,ADC0832,ADC0834,ADC0838
ADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with
Multiplexer Options
Literature Number: SNAS531A
ADC0831/ADC0832/ADC0834/ADC0838
8-Bit Serial I/O A/D Converters with Multiplexer Options
General Description
The ADC0831 series are 8-bit successive approximation A/D
converters with a serial I/O and configurable input multiplexers with up to 8 channels. The serial I/O is configured to
comply with the NSC MICROWIRE™ serial data exchange
standard for easy interface to the COPS™ family of processors, and can interface with standard shift registers or µPs.
The 2-, 4- or 8-channel multiplexers are software configured
for single-ended or differential inputs as well as channel
assignment.
The differential analog voltage input allows increasing the
common-mode rejection and offsetting the analog zero input
voltage value. In addition, the voltage reference input can be
adjusted to allow encoding any smaller analog voltage span
to the full 8 bits of resolution.
Features
n NSC MICROWIRE compatible — direct interface to
COPS family processors
n Easy interface to all microprocessors, or operates
“stand-alone”
n
n
n
n
n
n
n
n
n
n
Operates ratiometrically or with 5 VDC voltage reference
No zero or full-scale adjust required
2-, 4- or 8-channel multiplexer options with address logic
Shunt regulator allows operation with high voltage
supplies
0V to 5V input range with single 5V power supply
Remote operation with serial digital data link
TTL/MOS input/output compatible
0.3" standard width, 8-, 14- or 20-pin DIP package
20 Pin Molded Chip Carrier Package (ADC0838 only)
Surface-Mount Package
Key Specifications
n
n
n
n
n
Resolution
Total Unadjusted Error
Single Supply
Low Power
Conversion Time
8 Bits
± 1⁄2 LSB and ± 1 LSB
5 VDC
15 mW
32 µs
Typical Application
00558301
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
COPS™ and MICROWIRE™ are trademarks of National Semiconductor Corporation.
© 2002 National Semiconductor Corporation
DS005583
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ADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer Options
July 2002
ADC0831/ADC0832/ADC0834/ADC0838
Connection Diagrams
ADC0832 2-Channel MUX
Small Outline Package (WM)
ADC0838 8-Channel Mux
Small Outline/Dual-In-Line Package (WM and N)
00558341
Top View
ADC0831 Single
Differential Input
Dual-In-Line Package (N)
00558308
Top View
ADC0834 4-Channel MUX
Small Outline/Dual-In-Line Package (WM and N)
00558332
Top View
ADC0831 Single Differential Input
Small Outline Package (WM)
00558330
COM internally connected to A GND
Top View
Top View
ADC0832 2-Channel MUX
Dual-In-Line Package (N)
00558342
Top View
ADC0838 8-Channel MUX
Molded Chip Carrier (PCC) Package (V)
00558331
COM internally connected to GND.
VREF internally connected to VCC.
Top View
Top View
00558333
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Part Number
ADC0831CCN
Analog Input
Total
Channels
Unadjusted Error
1
±1
2
±1
ADC0831CCWM
ADC0832CIWM
ADC0832CCN
ADC0832CCWM
ADC0834BCN
4
ADC0834CCN
± 1⁄2
±1
ADC0834CCWM
ADC0838BCV
8
ADC0838CCV
± 1⁄2
±1
ADC0838CCN
Package
Temperature
Molded (N)
0˚C to +70˚C
Range
SO(M)
0˚C to +70˚C
SO(M)
−40˚C to +85˚C
Molded (N)
0˚C to +70˚C
SO(M)
0˚C to +70˚C
Molded (N)
0˚C to +70˚C
Molded (N)
0˚C to +70˚C
SO(M)
0˚C to +70˚C
PCC (V)
0˚C to +70˚C
PCC (V)
0˚C to +70˚C
Molded (N)
0˚C to +70˚C
ADC0838CIWM
SO(M)
−40˚C to +85˚C
ADC0838CCWM
SO(M)
0˚C to +70˚C
See NS Package Number M14B, M20B, N08E, N14A,
N20A or V20A
3
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ADC0831/ADC0832/ADC0834/ADC0838
Ordering Information
ADC0831/ADC0832/ADC0834/ADC0838
Absolute Maximum Ratings
Dual-In-Line Package (Plastic)
(Notes 1,
Molded Chip Carrier Package
Vapor Phase (60 sec.)
2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
+
Current into V (Note 3)
260˚C
215˚C
Infrared (15 sec.)
220˚C
ESD Susceptibility (Note 5)
2000V
15 mA
Supply Voltage, VCC (Note 3)
Operating Ratings (Notes 1, 2)
6.5V
Voltage
Logic Inputs
Analog Inputs
4.5 VDC to 6.3 VDC
Temperature Range
TMIN≤TA≤TMAX
−0.3V to VCC +
0.3V
ADC0832/8CIWM
−40˚C to +85˚C
ADC0834BCN,
ADC0838BCV,
± 5 mA
± 20 mA
Input Current per Pin (Note 4)
Package
Storage Temperature
Supply Voltage, VCC
−0.3V to VCC +
0.3V
ADC0831/2/4/8CCN,
ADC0838CCV,
−65˚C to +150˚C
ADC0831/2/4/8CCWM
Package Dissipation
at TA =25˚C (Board Mount)
0˚C to +70˚C
0.8W
Lead Temperature (Soldering 10
sec.)
Converter and Multiplexer Electrical Characteristics The following specifications apply for
VCC = V+ = VREF = 5V, VREF ≤ VCC +0.1V, TA = Tj = 25˚C, and fCLK = 250 kHz unless otherwise specified. Boldface limits
apply from TMIN to TMAX.
Conditions
CIWM Devices
BCV, CCV, CCWM, BCN
and CCN Devices
Parameter
Typ
Tested
Design
Typ
Tested
Design
(Note 12)
Limit
Limit
(Note 12)
Limit
Limit
(Note 13)
(Note 14)
± 1⁄2
± 1⁄2
±1
±1
±1
± 1⁄2
± 1⁄2
±1
±1
±1
(Note 13) (Note 14)
Units
CONVERTER AND MULTIPLEXER CHARACTERISTICS
Total Unadjusted Error
VREF =5.00 V
ADC0838BCV
(Note 6)
ADC0834BCN
ADC0838CCV
ADC0831/2/4/8CCN
ADC0831/2/4/8CCWM
LSB
(Max)
±1
ADC0832/8CIWM
Minimum Reference
3.5
1.3
3.5
1.3
1.3
kΩ
3.5
5.9
3.5
5.4
5.9
kΩ
Input Resistance (Note 7)
Maximum Reference
Input Resistance (Note 7)
Maximum Common-Mode
Input Range (Note 8)
VCC +0.05
VCC +0.05 VCC+0.05
V
Minimum Common-Mode
Input Range (Note 8)
GND −0.05
GND −0.05 GND−0.05
V
± 1/16
DC Common-Mode Error
Change in zero
15 mA into V+
error from VCC =5V
VCC =N.C.
to internal zener
VREF =5V
± 1⁄4
operation (Note 3)
VZ, internal
diode breakdown
MIN 15 mA into V+
MAX
(at V+) (Note 3)
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± 1/16
± 1⁄4
± 1⁄4
LSB
LSB
1
1
1
6.3
6.3
6.3
8.5
8.5
8.5
V
Conditions
CIWM Devices
BCV, CCV, CCWM, BCN
and CCN Devices
Parameter
Typ
Tested
Design
Typ
Tested
Design
(Note 12)
Limit
Limit
(Note 12)
Limit
Limit
(Note 13)
(Note 14)
± 1⁄4
± 1⁄4
LSB
−0.2
−1
µA
+0.2
+1
µA
−0.2
−1
µA
+0.2
+1
µA
(Note 13) (Note 14)
Units
CONVERTER AND MULTIPLEXER CHARACTERISTICS
Power Supply Sensitivity
VCC =5V ± 5%
± 1/16
± 1⁄4
IOFF, Off Channel Leakage
On
Channel=5V,
−0.2
Current (Note 9)
Off
Channel=0V
−1
On
Channel=0V,
+0.2
Off
Channel=5V
+1
ION, On Channel Leakage
On
Channel=0V,
−0.2
Current (Note 9)
Off
Channel=5V
−1
On
Channel=5V,
+0.2
Off
Channel=0V
+1
± 1⁄4
± 1/16
DIGITAL AND DC CHARACTERISTICS
VIN(1), Logical “1” Input
VCC =5.25V
2.0
2.0
2.0
V
VCC =4.75V
0.8
0.8
0.8
V
Voltage (Min)
VIN(0), Logical “0” Input
Voltage (Max)
IIN(1), Logical “1” Input
VIN =5.0V
0.005
1
0.005
1
1
µA
VIN =0V
−0.005
−1
−0.005
−1
−1
µA
2.4
2.4
V
Current (Max)
IIN(0), Logical “0” Input
Current (Max)
VOUT(1), Logical “1” Output
VCC =4.75V
Voltage (Min)
IOUT =−360 µA
IOUT =−10 µA
4.5
4.5
4.5
V
VOUT(0), Logical “0” Output
VCC =4.75V
0.4
0.4
0.4
V
−3
−3
µA
Voltage (Max)
IOUT =1.6 mA
IOUT, TRI-STATE Output
VOUT =0V
2.4
−0.1
−3
−0.1
Current (Max)
VOUT =5V
0.1
3
0.1
+3
+3
µA
ISOURCE, Output Source
VOUT =0V
−14
−6.5
−14
−7.5
−6.5
mA
VOUT =VCC
16
8.0
16
9.0
8.0
mA
0.9
2.5
0.9
2.5
2.5
mA
2.3
6.5
2.3
6.5
6.5
mA
Current (Min)
ISINK, Output Sink Current (Min)
ICC, Supply Current (Max)
ADC0831, ADC0834,
ADC0838
ADC0832
Includes
Ladder
Current
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ADC0831/ADC0832/ADC0834/ADC0838
Converter and Multiplexer Electrical Characteristics The following specifications apply for
VCC = V+ = VREF = 5V, VREF ≤ VCC +0.1V, TA = Tj = 25˚C, and fCLK = 250 kHz unless otherwise specified. Boldface limits
apply from TMIN to TMAX. (Continued)
ADC0831/ADC0832/ADC0834/ADC0838
AC Characteristics
The following specifications apply for VCC = 5V, tr = tf = 20 ns and 25˚C unless otherwise specified.
Parameter
fCLK, Clock Frequency
Conditions
Typ
Tested
Design
Limit
(Note 12)
Limit
Limit
Units
(Note 13)
(Note 14)
Min
10
Max
tC, Conversion Time
kHz
400
Not including MUX Addressing Time
8
kHz
1/fCLK
Clock Duty Cycle
Min
40
(Note 10)
Max
60
%
250
ns
90
ns
tSET-UP, CS Falling Edge or
%
Data Input Valid to CLK
Rising Edge
tHOLD, Data Input Valid
after CLK Rising Edge
tpd1, tpd0 — CLK Falling
CL =100 pF
Edge to Output Data Valid
Data MSB First
650
1500
ns
(Note 11)
Data LSB First
250
600
ns
t1H, t0H, — Rising Edge of
CL =10 pF, RL =10k
125
250
ns
CS to Data Output and
(see TRI-STATE ® Test Circuits)
SARS Hi–Z
CL =100 pf, RL =2k
500
CIN, Capacitance of Logic
ns
5
pF
5
pF
Input
COUT, Capacitance of Logic
Outputs
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating
the device beyond its specified operating conditions.
Note 2: All voltages are measured with respect to the ground plugs.
Note 3: Internal zener diodes (6.3 to 8.5V) are connected from V+ to GND and VCC to GND. The zener at V+ can operate as a shunt regulator and is connected
to VCC via a conventional diode. Since the zener voltage equals the A/D’s breakdown voltage, the diode insures that VCC will be below breakdown when the device
is powered from V+. Functionality is therefore guaranteed for V+ operation even though the resultant voltage at VCC may exceed the specified Absolute Max of 6.5V.
It is recommended that a resistor be used to limit the max current into V+. (See Figure 3 in Functional Description Section 6.0)
Note 4: When the input voltage (VIN) at any pin exceeds the power supply rails (VIN < V− or VIN > V+) the absolute value of current at that pin should be limited
to 5 mA or less. The 20 mA package input current limits the number of pins that can exceed the power supply boundaries with a 5 mA current limit to four.
Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 6: Total unadjusted error includes offset, full-scale, linearity, and multiplexer errors.
Note 7: Cannot be tested for ADC0832.
Note 8: For VIN(−)≥VIN(+) the digital output code will be 0000 0000. Two on-chip diodes are tied to each analog input (see Block Diagram) which will forward conduct
for analog input voltages one diode drop below ground or one diode drop greater than the VCC supply. Be careful, during testing at low VCC levels (4.5V), as high
level analog inputs (5V) can cause this input diode to conduct — especially at elevated temperatures, and cause errors for analog inputs near full-scale. The spec
allows 50 mV forward bias of either diode. This means that as long as the analog VIN or VREF does not exceed the supply voltage by more than 50 mV, the output
code will be correct. To achieve an absolute 0 VDC to 5 VDC input voltage range will therefore require a minimum supply voltage of 4.950 VDC over temperature
variations, initial tolerance and loading.
Note 9: Leakage current is measured with the clock not switching.
Note 10: A 40% to 60% clock duty cycle range insures proper operation at all clock frequencies. In the case that an available clock has a duty cycle outside of these
limits, the minimum, time the clock is high or the minimum time the clock is low must be at least 1 µs. The maximum time the clock can be high is 60 µs. The clock
can be stopped when low so long as the analog input voltage remains stable.
Note 11: Since data, MSB first, is the output of the comparator used in the successive approximation loop, an additional delay is built in (see Block Diagram) to allow
for comparator response time.
Note 12: Typicals are at 25˚C and represent most likely parametric norm.
Note 13: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 14: Guaranteed but not 100% production tested. These limits are not used to calculate outgoing quality levels.
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ADC0831/ADC0832/ADC0834/ADC0838
Typical Performance Characteristics
Linearity Error vs. VREF
Voltage
Unadjusted Offset Error vs. VREF Voltage
00558344
00558343
Linearity Error vs. Temperature
Linearity Error vs. fCLK
00558345
00558346
Power Supply Current vs. Temperature (ADC0838,
ADC0831, ADC0834)
Output Current vs. Temperature
00558348
00558347
Note: For ADC0832 add IREF.
7
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ADC0831/ADC0832/ADC0834/ADC0838
Typical Performance Characteristics
(Continued)
Power Supply Current vs. fCLK
00558329
Leakage Current Test Circuit
00558303
TRI-STATE Test Circuits and
Waveforms
t1H
t1H
00558351
t0H
00558349
t0H
00558352
00558350
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Data Input Timing
Data Output Timing
00558324
00558325
ADC0831 Start Conversion Timing
00558326
ADC0831 Timing
00558327
*LSB first output not available on ADC0831.
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ADC0831/ADC0832/ADC0834/ADC0838
Timing Diagrams
ADC0831/ADC0832/ADC0834/ADC0838
Timing Diagrams
(Continued)
ADC0832 Timing
00558328
ADC0834 Timing
00558305
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(Continued)
*Make sure clock edge #18 clocks in the LSB before SE is taken low
Timing Diagrams
ADC0838 Timing
00558306
ADC0831/ADC0832/ADC0834/ADC0838
11
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00558307
Note 1: For the ADC0834, D1 is input directly to the D input of SELECT 1. SELECT 0 is forced to a “1”. For the ADC0832, DI is input directly to the DI input of ODD/SIGN. SELECT 0 is forced to a “0” and SELECT 1 is forced to a
“1”.
*Some of these functions/pins are not available with other options.
ADC0838 Functional Block Diagram
ADC0831/ADC0832/ADC0834/ADC0838
1.0 multiplexer Addressing
The design of these converters utilizes a sample-data comparator structure which provides for a differential analog
input to be converted by a successive approximation routine.
The actual voltage converted is always the difference between an assigned “+” input terminal and a “−” input terminal.
The polarity of each input terminal of the pair being converted indicates which line the converter expects to be the
most positive. If the assigned “+” input is less than the “−”
input the converter responds with an all zeros output code.
The MUX address is shifted into the converter via the DI line.
Because the ADC0831 contains only one differential input
channel with a fixed polarity assignment, it does not require
addressing.
The common input line on the ADC0838 can be used as a
pseudo-differential input. In this mode, the voltage on this pin
is treated as the “−” input for any of the other input channels.
This voltage does not have to be analog ground; it can be
any reference potential which is common to all of the inputs.
This feature is most useful in single-supply application where
the analog circuitry may be biased up to a potential other
than ground and the output signals are all referred to this
potential.
A unique input multiplexing scheme has been utilized to
provide multiple analog channels with software-configurable
single-ended, differential, or a new pseudo-differential option
which will convert the difference between the voltage at any
analog input and a common terminal. The analog signal
conditioning required in transducer-based data acquisition
systems is significantly simplified with this type of input
flexibility. One converter package can now handle ground
referenced inputs and true differential inputs as well as
signals with some arbitrary reference voltage.
A particular input configuration is assigned during the MUX
addressing sequence, prior to the start of a conversion. The
MUX address selects which of the analog inputs are to be
TABLE 1. Multiplexer/Package Options
Part
Number
Number of Analog Channels
Number of
Single-Ended
Differential
Package Pins
ADC0831
1
1
8
ADC0832
2
1
8
ADC0834
4
2
14
ADC0838
8
4
20
13
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ADC0831/ADC0832/ADC0834/ADC0838
enabled and whether this input is single-ended or differential.
In the differential case, it also assigns the polarity of the
channels. Differential inputs are restricted to adjacent channel pairs. For example channel 0 and channel 1 may be
selected as a different pair but channel 0 or 1 cannot act
differentially with any other channel. In addition to selecting
differential mode the sign may also be selected. Channel 0
may be selected as the positive input and channel 1 as the
negative input or vice versa. This programmability is best
illustrated by the MUX addressing codes shown in the following tables for the various product options.
Functional Description
ADC0831/ADC0832/ADC0834/ADC0838
Functional Description
(Continued)
TABLE 2. MUX Addressing: ADC0838
Single-Ended MUX Mode
Analog Single-Ended Channel #
MUX Address
SGL/
ODD/
SELECT
DIF
SIGN
1
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
0
1
1
2
3
4
5
6
7
COM
0
+
−
+
−
+
−
+
−
+
−
+
−
+
−
+
−
TABLE 3. MUX Addressing: ADC0838
Differential MUX Mode
Analog Differential Channel-Pair #
MUX Address
SGL/
ODD/
SELECT
0
DIF
SIGN
1
0
0
1
0
0
0
0
+
−
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
−
1
2
2
3
+
−
3
4
5
+
−
7
+
−
−
+
+
−
+
−
+
TABLE 4. MUX Addressing: ADC0834
Single-Ended MUX Mode
Channel #
MUX Address
SGL/
ODD/
SELECT
DIF
SIGN
1
0
1
0
0
+
1
0
1
1
1
0
1
1
1
1
2
3
+
+
+
COM is internally tied to A GND
TABLE 5. MUX Addressing: ADC0834
Differential MUX Mode
Channel #
MUX Address
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SGL/
ODD/
SELECT
DIF
SIGN
1
0
1
0
0
0
+
−
0
0
1
0
1
0
−
+
0
1
1
14
2
3
+
−
−
+
ADC0831/ADC0832/ADC0834/ADC0838
Functional Description
(Continued)
TABLE 6. MUX Addressing: ADC0832
Single-Ended MUX Mode
MUX Address
Channel #
SGL/
ODD/
0
DIF
SIGN
1
0
1
1
1
+
+
COM is internally tied to A GND
TABLE 7. MUX Addressing: ADC0832
Differential MUX Mode
MUX Address
Channel #
SGL/
ODD/
0
1
DIF
SIGN
0
0
+
−
0
1
−
+
Since the input configuration is under software control, it can
be modified, as required, at each conversion. A channel can
be treated as a single-ended, ground referenced input for
one conversion; then it can be reconfigured as part of a
differential channel for another conversion. Figure 1 illustrates the input flexibility which can be achieved.
The analog input voltages for each channel can range from
50 mV below ground to 50 mV above VCC (typically 5V)
without degrading conversion accuracy.
converter package with no increase in package size and it
can eliminate the transmission of low level analog signals by
locating the converter right at the analog sensor; transmitting
highly noise immune digital data back to the host processor.
To understand the operation of these converters it is best to
refer to the Timing Diagrams and Functional Block Diagram
and to follow a complete conversion sequence. For clarity a
separate diagram is shown of each device.
1. A conversion is initiated by first pulling the CS (chip select)
line low. This line must be held low for the entire conversion.
The converter is now waiting for a start bit and its MUX
assignment word.
2. A clock is then generated by the processor (if not provided
continuously) and output to the A/D clock input.
2.0 THE DIGITAL INTERFACE
A most important characteristic of these converters is their
serial data link with the controlling processor. Using a serial
communication format offers two very significant system
improvements; it allows more function to be included in the
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ADC0831/ADC0832/ADC0834/ADC0838
Functional Description
(Continued)
8 Single-Ended
8 Pseudo-Differential
00558353
00558354
4 Differential
Mixed Mode
00558355
00558356
FIGURE 1. Analog Input Multiplexer Options for the ADC0838
on each falling edge of the clock. This data is the result of the
conversion being shifted out (with the MSB coming first) and
can be read by the processor immediately.
7. After 8 clock periods the conversion is completed. The
SAR status line returns low to indicate this 1⁄2 clock cycle
later.
8. If the programmer prefers, the data can be provided in an
LSB first format [this makes use of the shift enable (SE)
control line]. All 8 bits of the result are stored in an output
shift register. On devices which do not include the SE control
line, the data, LSB first, is automatically shifted out the DO
line, after the MSB first data stream. The DO line then goes
low and stays low until CS is returned high. On the ADC0838
the SE line is brought out and if held high, the value of the
LSB remains valid on the DO line. When SE is forced low,
the data is then clocked out LSB first. The ADC0831 is an
exception in that its data is only output in MSB first format.
9. All internal registers are cleared when the CS line is high.
If another conversion is desired, CS must make a high to low
transition followed by address information.
The DI and DO lines can be tied together and controlled
through a bidirectional processor I/O bit with one wire. This is
3. On each rising edge of the clock the status of the data in
(DI) line is clocked into the MUX address shift register. The
start bit is the first logic “1” that appears on this line (all
leading zeros are ignored). Following the start bit the converter expects the next 2 to 4 bits to be the MUX assignment
word.
4. When the start bit has been shifted into the start location
of the MUX register, the input channel has been assigned
and a conversion is about to begin. An interval of 1⁄2 clock
period (where nothing happens) is automatically inserted to
allow the selected MUX channel to settle. The SAR status
line goes high at this time to signal that a conversion is now
in progress and the DI line is disabled (it no longer accepts
data).
5. The data out (DO) line now comes out of TRI-STATE and
provides a leading zero for this one clock period of MUX
settling time.
6. When the conversion begins, the output of the SAR
comparator, which indicates whether the analog input is
greater than (high) or less than (low) each successive voltage from the internal resistor ladder, appears at the DO line
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16
tied to VCC (done internally on the ADC0832). This technique
relaxes the stability requirements of the system reference as
the analog input and A/D reference move together maintaining the same output code for a given input condition.
For absolute accuracy, where the analog input varies between very specific voltage limits, the reference pin can be
biased with a time and temperature stable voltage source.
The LM385 and LM336 reference diodes are good low current devices to use with these converters.
(Continued)
possible because the DI input is only “looked-at” during the
MUX addressing interval while the DO line is still in a high
impedance state.
3.0 Reference Considerations
The voltage applied to the reference input to these converters defines the voltage span of the analog input (the difference between VIN(MAX) and VIN(MIN)) over which the 256
possible output codes apply. The devices can be used in
either ratiometric applications or in systems requiring absolute accuracy. The reference pin must be connected to a
voltage source capable of driving the reference input resistance of typically 3.5 kΩ. This pin is the top of a resistor
divider string used for the successive approximation conversion.
In a ratiometric system, the analog input voltage is proportional to the voltage used for the A/D reference. This voltage
is typically the system power supply, so the VREF pin can be
The maximum value of the reference is limited to the VCC
supply voltage. The minimum value, however, can be quite
small (see Typical Performance Characteristics) to allow
direct conversions of transducer outputs providing less than
a 5V output span. Particular care must be taken with regard
to noise pickup, circuit layout and system error voltage
sources when operating with a reduced span due to the
increased sensitivity of the converter (1 LSB equals
VREF/256).
00558358
00558357
b) Absolute with a reduced Span
a) Ratiometric
FIGURE 2. Reference Examples
4.0 The Analog Inputs
The most important feature of these converters is that they
can be located right at the analog signal source and through
just a few wires can communicate with a controlling processor with a highly noise immune serial bit stream. This in itself
greatly minimizes circuitry to maintain analog signal accuracy which otherwise is most susceptible to noise pickup.
However, a few words are in order with regard to the analog
inputs should the input be noisy to begin with or possibly
riding on a large common-mode voltage.
The differential input of these converters actually reduces
the effects of common-mode input noise, a signal common
to both selected “+” and “−” inputs for a conversion (60 Hz is
most typical). The time interval between sampling the “+”
input and then the “−” input is 1⁄2 of a clock period. The
change in the common-mode voltage during this short time
interval can cause conversion errors. For a sinusoidal
common-mode signal this error is:
where fCM is the frequency of the common-mode signal,
VPEAK is its peak voltage value
and fCLK, is the A/D clock frequency.
For a 60 Hz common-mode signal to generate a 1⁄4 LSB error
(≈5 mV) with the converter running at 250 kHz, its peak value
would have to be 6.63V which would be larger than allowed
as it exceeds the maximum analog input limits.
Due to the sampling nature of the analog inputs short spikes
of current enter the “+” input and exit the “−” input at the
clock edges during the actual conversion. These currents
decay rapidly and do not cause errors as the internal comparator is strobed at the end of a clock period. Bypass
capacitors at the inputs will average these currents and
cause an effective DC current to flow through the output
17
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ADC0831/ADC0832/ADC0834/ADC0838
Functional Description
ADC0831/ADC0832/ADC0834/ADC0838
Functional Description
(Continued)
resistance of the analog signal source. Bypass capacitors
should not be used if the source resistance is greater than 1
kΩ.
This source resistance limitation is important with regard to
the DC leakage currents of input multiplexer as well. The
worst-case leakage current of ± 1 µA over temperature will
create a 1 mV input error with a 1 kΩ source resistance. An
op amp RC active low pass filter can provide both impedance buffering and noise filtering should a high impedance
signal source be required.
where:
VMAX = the high end of the analog input range
and
VMIN = the low end (the offset zero) of the analog
range.
(Both are ground referenced.)
The VREF (or VCC) voltage is then adjusted to provide a code
change from FEHEX to FFHEX. This completes the adjustment procedure.
5.0 Optional Adjustments
5.1 Zero Error
The zero of the A/D does not require adjustment. If the
minimum analog input voltage value, VIN(MIN), is not ground
a zero offset can be done. The converter can be made to
output 0000 0000 digital code for this minimum input voltage
by biasing any VIN (−) input at this VIN(MIN) value. This
utilizes the differential mode operation of the A/D.
6.0 Power Supply
A unique feature of the ADC0838 and ADC0834 is the inclusion of a zener diode connected from the V+ terminal to
ground which also connects to the VCC terminal (which is the
actual converter supply) through a silicon diode, as shown in
Figure 3. (Note 3)
The zero error of the A/D converter relates to the location of
the first riser of the transfer function and can be measured by
grounding the VIN(−) input and applying a small magnitude
positive voltage to the VIN(+) input. Zero error is the difference between the actual DC input voltage which is necessary to just cause an output digital code transition from 0000
0000 to 0000 0001 and the ideal 1⁄2 LSB value (1⁄2 LSB=9.8
mV for VREF =5.000 VDC).
5.2 Full-Scale
The full-scale adjustment can be made by applying a differential input voltage which is 1 1⁄2 LSB down from the desired
analog full-scale voltage range and then adjusting the magnitude of the VREF input (or VCC for the ADC0832) for a
digital output code which is just changing from 1111 1110 to
1111 1111.
00558311
FIGURE 3. An On-Chip Shunt Regulator Diode
5.3 Adjusting for an Arbitrary Analog Input Voltage
Range
If the analog zero voltage of the A/D is shifted away from
ground (for example, to accommodate an analog input signal
which does not go to ground), this new zero reference
should be properly adjusted first. A VIN (+) voltage which
equals this desired zero reference plus 1⁄2 LSB (where the
LSB is calculated for the desired analog span, using 1 LSB=
analog span/256) is applied to selected “+” input and the
zero reference voltage at the corresponding “−” input should
then be adjusted to just obtain the 00HEX to 01HEX code
transition.
The full-scale adjustment should be made [with the proper
VIN(−) voltage applied] by forcing a voltage to the VIN(+)
input which is given by:
www.national.com
This zener is intended for use as a shunt voltage regulator to
eliminate the need for any additional regulating components.
This is most desirable if the converter is to be remotely
located from the system power source.Figure 4 and Figure 5
illustrate two useful applications of this on-board zener when
an external transistor can be afforded.
An important use of the interconnecting diode between V+
and VCC is shown in Figure 6 and Figure 7. Here, this diode
is used as a rectifier to allow the VCC supply for the converter
to be derived from the clock. The low current requirements of
the A/D and the relatively high clock frequencies used (typically in the range of 10k–400 kHz) allows using the small
value filter capacitor shown to keep the ripple on the VCC line
to well under 1⁄4 of an LSB. The shunt zener regulator can
also be used in this mode. This requires a clock voltage
swing which is in excess of VZ. A current limit for the zener is
needed, either built into the clock generator or a resistor can
be used from the CLK pin to the V+ pin.
18
ADC0831/ADC0832/ADC0834/ADC0838
Applications
00558312
00558335
*4.5V ≤ VCC ≤ 6.3V
FIGURE 4. Operating with a Temperature
Compensated Reference
FIGURE 6. Generating VCC from the Converter Clock
00558336
*4.5V ≤ VCC ≤ 6.3V
00558334
FIGURE 5. Using the A/D as
the System Supply Regulator
FIGURE 7. Remote Sensing —
Clock and Power on 1 Wire
Digital Link and Sample Controlling Software for theSerially Oriented COP420 and the Bit Programmable I/O INS8048
00558313
19
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ADC0831/ADC0832/ADC0834/ADC0838
Applications
8048 CODING EXAMPLE
(Continued)
Mnemonic
Cop Coding Example
Mnemonic
START:
Instruction
LEI
ENABLES SIO’s INPUT AND OUTPUT
SC
C=1
OGI
G0=0 (CS =0)
CLR A
CLEARS ACCUMULATOR
AISC 1
LOADS ACCUMULATOR WITH 1
XAS
EXCHANGES SIO WITH ACCUMULATOR
B, #5
MOV
A, #ADDR
RRC
A
;A←MUX ADDRESS
;CY←ADDRESS BIT
JC
ONE
;TEST BIT
ANL
P1, #0FEH ;DI←0
JMP
CONT
;CONTINUE
ONE:
ORL
P1, #1
;BIT=1
;DI←1
CONT:
CALL
PULSE
;PULSE SK 0→1→0
DJNZ
B, LOOP 1 ;CONTINUE UNTIL
DONE
CALL
PULSE
MOV
B, #8
LOOP 1:
;BIT=0
ZERO:
LOADS MUX ADDRESS FROM RAM
INTO ACCUMULATOR
NOP
—
XAS
LOADS MUX ADDRESS FROM
P1, #0F7H ;SELECT A/D (CS =0)
;BIT COUNTER←5
MOV
AND STARTS SK CLOCK
LDD
ANL
Instruction
ACCUMULATOR TO SIO REGISTER
↑
8 INSTRUCTIONS
↓
;PULSE SK 0→1→0
;CY←DO
CALL
PULSE
READS HIGH ORDER NIBBLE (4 BITS)
IN
A, P1
INTO ACCUMULATOR
RRC
A
XIS
PUTS HIGH ORDER NIBBLE INTO RAM
RRC
A
CLR A
CLEARS ACCUMULATOR
MOV
A, C
RC
C=0
RLC
A
XAS
READS LOW ORDER NIBBLE INTO
MOV
C, A
ACCUMULATOR AND STOPS SK
DJNZ
B, LOOP 2 ;CONTINUE UNTIL
DONE
XAS
XIS
PUTS LOW ORDER NIBBLE INTO RAM
OGI
G0=1 (CS =1)
LEI
DISABLES SIO’s INPUT AND OUTPUT
LOOP 2:
;EXTRA CLOCK FOR
SYNC
;BIT COUNTER←8
RETR
PULSE:
ORL
20
P1, #04
;PULSE SUBROUTINE
;SK←1
NOP
;DELAY
ANL
P1, #0FBH ;SK←0
RET
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;A←RESULT
;A(0)←BIT AND SHIFT
;C←RESULT
ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
A “Stand-Alone” Hook-Up for ADC0838 Evaluation
00558359
*Pinouts shown for ADC0838.
For all other products tie to
pin functions as shown.
Low-Cost Remote Temperature Sensor
00558360
21
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ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Digitizing a Current Flow
00558315
Operating with Ratiometric Transducers
00558337
*VIN(−) = 0.15 VCC
15% of VCC ≤ VXDR ≤ 85% of VCC
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22
ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Span Adjust: 0V≤VIN≤3V
00558361
Zero-Shift and Span Adjust: 2V≤VIN≤5V
00558362
23
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ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Obtaining Higher Resolution
00558363
a) 9-Bit A/D
00558364
Controller performs a routine to determine which input polarity (9-bit example) or which channel pair (10-bit example) provides a non-zero output code. This
information provides the extra bits.
b) 10-Bit A/D
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24
ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Protecting the Input
00558318
Diodes are 1N914
High Accuracy Comparators
00558338
DO = all 1s if +VIN > −VIN
DO = all 0s if +VIN < −VIN
25
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ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Digital Load Cell
00558319
• Uses one more wire than load cell itself
• Two mini-DIPs could be mounted inside load cell for digital output transducer
• Electronic offset and gain trims relax mechanical specs for gauge factor and offset
• Low level cell output is converted immediately for high noise immunity
4 mA-20 mA Current Loop Converter
00558320
• All power supplied by loop
• 1500V isolation at output
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26
ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Isolated Data Converter
00558339
• No power required remotely
• 1500V isolation
27
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ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Two Wire Interface for 8 Channels
00558321
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28
ADC0831/ADC0832/ADC0834/ADC0838
Applications
(Continued)
Two Wire 1-Channels Interface
00558322
29
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ADC0831/ADC0832/ADC0834/ADC0838
Physical Dimensions
inches (millimeters)
unless otherwise noted
Wide Body Molded Small-Outline Package (WM)
NS Package Number M14B
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30
ADC0831/ADC0832/ADC0834/ADC0838
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Wide Body Molded Small-Outline Package (WM)
NS Package Number M20B
Molded Dual-In-Line Package (N)
NS Package Number N08E
31
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ADC0831/ADC0832/ADC0834/ADC0838
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
NS Package Number N14A
Molded-Dual-In-Line Package (N)
NS Package Number N20A
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32
inches (millimeters) unless otherwise noted (Continued)
Molded Chip Carrier Package (V)
Order Number ADC0838BCV or ADC0838CCV
NS Package Number V20A
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ADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer Options
Physical Dimensions
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