NSC ADC0831CCJ, ADC0831BCN, ADC0831BCJ, ADC0831CMWC, ADC0831CMDC Datasheet

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 proces-

sors, 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 Operates ratiometrically or with 5 V

DC

voltage reference

n No zero or full-scale adjust required
n 2-, 4- or 8-channel multiplexer options with address logic
n Shunt regulator allows operation with high voltage

supplies

n 0V to 5V input range with single 5V power supply
n Remote operation with serial digital data link
n TTL/MOS input/output compatible
n 0.3" standard width, 8-, 14- or 20-pin DIP package
n 20 Pin Molded Chip Carrier Package (ADC0838 only)
n Surface-Mount Package

Key Specifications

n Resolution 8 Bits
n Total Unadjusted Error

±

1

⁄2LSB and±1 LSB

n Single Supply 5 V

DC

n Low Power 15 mW
n Conversion Time 32 µs

Typical Application

00558301

TRI-STATE®is a registered trademark of National Semiconductor Corporation.
COPS

™

and MICROWIRE™are trademarks of National Semiconductor Corporation.

July 2002

ADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer Options

© 2002 National Semiconductor Corporation DS005583 www.national.com

Connection Diagrams

ADC0838 8-Channel Mux

Small Outline/Dual-In-Line Package (WM and N)

00558308

Top View

ADC0834 4-Channel MUX

Small Outline/Dual-In-Line Package (WM and N)

00558330

COM internally connected to A GND

Top View

Top View

ADC0832 2-Channel MUX

Dual-In-Line Package (N)

00558331

COM internally connected to GND.

V

REF

internally connected to VCC.

Top View

Top View

ADC0832 2-Channel MUX

Small Outline Package (WM)

00558341

Top View

ADC0831 Single

Differential Input

Dual-In-Line Package (N)

00558332

Top View

ADC0831 Single Differential Input

Small Outline Package (WM)

00558342

Top View

ADC0838 8-Channel MUX

Molded Chip Carrier (PCC) Package (V)

00558333

ADC0831/ADC0832/ADC0834/ADC0838

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Ordering Information

Part Number Analog Input Total Package Temperature

Channels Unadjusted Error Range

ADC0831CCN 1

±

1 Molded (N) 0˚C to +70˚C

ADC0831CCWM SO(M) 0˚C to +70˚C

ADC0832CIWM 2

±

1 SO(M) −40˚C to +85˚C

ADC0832CCN Molded (N) 0˚C to +70˚C

ADC0832CCWM SO(M) 0˚C to +70˚C

ADC0834BCN 4

±

1

⁄

2

Molded (N) 0˚C to +70˚C

ADC0834CCN

±

1 Molded (N) 0˚C to +70˚C

ADC0834CCWM SO(M) 0˚C to +70˚C

ADC0838BCV 8

±

1

⁄

2

PCC (V) 0˚C to +70˚C

ADC0838CCV

±

1 PCC (V) 0˚C to +70˚C

ADC0838CCN 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

ADC0831/ADC0832/ADC0834/ADC0838

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Absolute Maximum Ratings (Notes 1,

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) 15 mA

Supply Voltage, V

CC

(Note 3) 6.5V

Voltage

Logic Inputs −0.3V to V

CC

+

0.3V

Analog Inputs −0.3V to V

CC

+

0.3V

Input Current per Pin (Note 4)

±

5mA

Package

±

20 mA

Storage Temperature −65˚C to +150˚C

Package Dissipation

at T

A

=25˚C (Board Mount) 0.8W

Lead Temperature (Soldering 10
sec.)

Dual-In-Line Package (Plastic) 260˚C

Molded Chip Carrier Package

Vapor Phase (60 sec.) 215˚C

Infrared (15 sec.) 220˚C

ESD Susceptibility (Note 5) 2000V

Operating Ratings (Notes 1, 2)

Supply Voltage, V

CC

4.5 VDCto 6.3 V

DC

Temperature Range T

MIN≤TA≤TMAX

ADC0832/8CIWM −40˚C to +85˚C

ADC0834BCN,

ADC0838BCV,

ADC0831/2/4/8CCN,

ADC0838CCV,

ADC0831/2/4/8CCWM 0˚C to +70˚C

Converter and Multiplexer Electrical Characteristics The following specifications apply for

V

CC

=V+=V

REF

= 5V, V

REF

≤ VCC+0.1V, TA=Tj= 25˚C, and f

CLK

= 250 kHz unless otherwise specified. Boldface limits

apply from T

MIN

to T

MAX

.

Parameter

Conditions CIWM Devices BCV, CCV, CCWM, BCN

and CCN Devices

Typ Tested Design Typ Tested Design Units

(Note 12) Limit Limit (Note 12) Limit Limit

(Note 13) (Note 14) (Note 13) (Note 14)

CONVERTER AND MULTIPLEXER CHARACTERISTICS

Total Unadjusted Error V

REF

=5.00 V

ADC0838BCV (Note 6)

±

1

⁄

2

±

1

⁄

2

ADC0834BCN

±

1

⁄

2

±

1

⁄

2

LSB

(Max)

ADC0838CCV

±

1

±

1

ADC0831/2/4/8CCN

±

1

±

1

ADC0831/2/4/8CCWM

±

1

±

1

ADC0832/8CIWM

±

1

Minimum Reference 3.5 1.3 3.5 1.3 1.3 kΩ

Input Resistance (Note 7)
Maximum Reference 3.5 5.9 3.5 5.4 5.9 kΩ

Input Resistance (Note 7)

Maximum Common-Mode
Input Range (Note 8)

V

CC

+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

DC Common-Mode Error

±

1/16

±

1

⁄

4

±

1/16

±

1

⁄

4

±

1

⁄

4

LSB

Change in zero 15 mA into V+

error from V

CC

=5V VCC=N.C.

to internal zener V

REF

=5V

operation (Note 3) 1 1 1 LSB

V

Z

, internal MIN 15 mA into V+ 6.3 6.3 6.3

diode breakdown MAX 8.5 8.5 8.5 V

(at V

+

) (Note 3)

ADC0831/ADC0832/ADC0834/ADC0838

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Converter and Multiplexer Electrical Characteristics The following specifications apply for

V

CC

=V+=V

REF

= 5V, V

REF

≤ VCC+0.1V, TA=Tj= 25˚C, and f

CLK

= 250 kHz unless otherwise specified. Boldface limits

apply from T

MIN

to T

MAX

. (Continued)

Parameter

Conditions CIWM Devices BCV, CCV, CCWM, BCN

and CCN Devices

Typ Tested Design Typ Tested Design Units

(Note 12) Limit Limit (Note 12) Limit Limit

(Note 13) (Note 14) (Note 13) (Note 14)

CONVERTER AND MULTIPLEXER CHARACTERISTICS

Power Supply Sensitivity V

CC

=5V±5%

±

1/16

±

1

⁄

4

±

1

⁄

4

±

1/16

±

1

⁄

4

±

1

⁄

4

LSB

I

OFF

, Off Channel Leakage On

Channel=5V,

−0.2 −0.2 −1 µA

Current (Note 9) Off

Channel=0V

−1

On
Channel=0V,

+0.2 +0.2 +1 µA

Off
Channel=5V

+1

I

ON

, On Channel Leakage On

Channel=0V,

−0.2 −0.2 −1 µA

Current (Note 9) Off

Channel=5V

−1

On
Channel=5V,

+0.2 +0.2 +1 µA

Off
Channel=0V

+1

DIGITAL AND DC CHARACTERISTICS

V

IN(1)

, Logical “1” Input VCC=5.25V 2.0 2.0 2.0 V

Voltage (Min)

V

IN(0)

, Logical “0” Input VCC=4.75V 0.8 0.8 0.8 V

Voltage (Max)

I

IN(1)

, Logical “1” Input VIN=5.0V 0.005 1 0.005 1 1 µA

Current (Max)

I

IN(0)

, Logical “0” Input VIN=0V −0.005 −1 −0.005 −1 −1 µA

Current (Max)

V

OUT(1)

, Logical “1” Output VCC=4.75V

Voltage (Min) I

OUT

=−360 µA 2.4 2.4 2.4 V

I

OUT

=−10 µA 4.5 4.5 4.5 V

V

OUT(0)

, Logical “0” Output VCC=4.75V 0.4 0.4 0.4 V

Voltage (Max) I

OUT

=1.6 mA

I

OUT

, TRI-STATE Output V

OUT

=0V −0.1 −3 −0.1 −3 −3 µA

Current (Max) V

OUT

=5V 0.1 3 0.1 +3 +3 µA

I

SOURCE

, Output Source V

OUT

=0V −14 −6.5 −14 −7.5 −6.5 mA

Current (Min)

I

SINK

, Output Sink Current (Min) V

OUT=VCC

16 8.0 16 9.0 8.0 mA

I

CC

, Supply Current (Max)

ADC0831, ADC0834, 0.9 2.5 0.9 2.5 2.5 mA

ADC0838

ADC0832 Includes

Ladder

2.3 6.5 2.3 6.5 6.5 mA

Current

ADC0831/ADC0832/ADC0834/ADC0838

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AC Characteristics

The following specifications apply for VCC= 5V, tr=tf= 20 ns and 25˚C unless otherwise specified.

Typ Tested Design Limit

Parameter Conditions (Note 12) Limit Limit Units

(Note 13) (Note 14)

f

CLK

, Clock Frequency Min 10 kHz

Max 400 kHz

t

C

, Conversion Time Not including MUX Addressing Time 8 1/f

CLK

Clock Duty Cycle Min 40 %

(Note 10) Max 60 %

t

SET-UP

, CS Falling Edge or 250 ns

Data Input Valid to CLK

Rising Edge

t

HOLD

, Data Input Valid 90 ns

after CLK Rising Edge

t

pd1,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

t

1H,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 C

L

=100 pf, RL=2k 500 ns

C

IN

, Capacitance of Logic 5 pF

Input

C

OUT

, Capacitance of Logic 5 pF

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 V

CC

to GND. The zener at V+ can operate as a shunt regulator and is connected

to V

CC

via a conventional diode. Since the zener voltage equals the A/D’s breakdown voltage, the diode insures that VCCwill be below breakdown when the device

is powered from V+. Functionality is therefore guaranteed for V+ operation even though the resultant voltage at V

CC

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 (V

IN

) at any pin exceeds the power supply rails (V

IN

<

V−or V

IN

>

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 witha5mAcurrent 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 V

IN

(−)≥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 V

CC

supply. Be careful, during testing at low VCClevels (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 V

IN

or V

REF

does not exceed the supply voltage by more than 50 mV, the output

code will be correct. To achieve an absolute 0 V

DC

to5VDCinput voltage range will therefore require a minimum supply voltage of 4.950 VDCover 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.

ADC0831/ADC0832/ADC0834/ADC0838

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Typical Performance Characteristics

Unadjusted Offset Error vs. V

REF

Voltage

Linearity Error vs. V

REF

Voltage

00558343

00558344

Linearity Error vs. Temperature Linearity Error vs. f

CLK

00558345

00558346

Power Supply Current vs. Temperature (ADC0838,

ADC0831, ADC0834) Output Current vs. Temperature

00558347

Note: For ADC0832 add I

REF

.

00558348

ADC0831/ADC0832/ADC0834/ADC0838

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Typical Performance Characteristics (Continued)

Power Supply Current vs. f

CLK

00558329

Leakage Current Test Circuit

00558303

TRI-STATE Test Circuits and
Waveforms

t

1H

00558349

t

0H

00558350

t

1H

00558351

t

0H

00558352

ADC0831/ADC0832/ADC0834/ADC0838

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Timing Diagrams

Data Input Timing Data Output Timing

00558324

00558325

ADC0831 Start Conversion Timing

00558326

ADC0831 Timing

00558327

*LSB first output not available on ADC0831.

ADC0831/ADC0832/ADC0834/ADC0838

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Timing Diagrams (Continued)

ADC0832 Timing

00558328

ADC0834 Timing

00558305

ADC0831/ADC0832/ADC0834/ADC0838

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Timing Diagrams (Continued)

ADC0838 Timing

00558306

*Make sure clock edge

#

18 clocks in the LSB before SE is taken low

ADC0831/ADC0832/ADC0834/ADC0838

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ADC0838 Functional Block Diagram

00558307

*Some of these functions/pins are not available with other options.

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”.

ADC0831/ADC0832/ADC0834/ADC0838

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Functional Description

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.

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

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.

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.

TABLE 1. Multiplexer/Package Options

Part Number of Analog Channels Number of

Number Single-Ended Differential Package Pins

ADC0831 1 1 8

ADC0832 2 1 8

ADC0834 4 2 14

ADC0838 8 4 20

ADC0831/ADC0832/ADC0834/ADC0838

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Functional Description (Continued)

TABLE 2. MUX Addressing: ADC0838

Single-Ended MUX Mode

MUX Address Analog Single-Ended Channel

#

SGL/ ODD/ SELECT 01234567COM

DIF

SIGN 1 0

1000+ −

1001 + −

1010 + −

1011 + −

1100 + −

1101 + −

1110 + −

1111 +−

TABLE 3. MUX Addressing: ADC0838

Differential MUX Mode

MUX Address Analog Differential Channel-Pair

#

SGL/ ODD/ SELECT 0 1 2 3

DIF

SIGN 1 0 01234567

0000+−

0001 +−

0010 +−

0011 +−

0100−+

0101 −+

0110 −+

0111 −+

TABLE 4. MUX Addressing: ADC0834

Single-Ended MUX Mode

MUX Address Channel

#

SGL/ ODD/ SELECT

DIF SIGN 1 0 1 2 3

10 0+

10 1 +

11 0 +

11 1 +

COM is internally tied to A GND

TABLE 5. MUX Addressing: ADC0834

Differential MUX Mode

MUX Address Channel

#

SGL/ ODD/ SELECT

DIF SIGN 1 0 1 2 3

00 0+−

00 1 +−

01 0−+

01 1 −+

ADC0831/ADC0832/ADC0834/ADC0838

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Functional Description (Continued)

TABLE 6. MUX Addressing: ADC0832

Single-Ended MUX Mode

MUX Address Channel

#

SGL/ ODD/ 0 1

DIF

SIGN

10+

11 +

COM is internally tied to A GND

TABLE 7. MUX Addressing: ADC0832

Differential MUX Mode

MUX Address Channel

#

SGL/ ODD/ 0 1

DIF

SIGN

00+ −

01− +

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 V

CC

(typically 5V)

without degrading conversion accuracy.

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

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.

ADC0831/ADC0832/ADC0834/ADC0838

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Functional Description (Continued)

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

⁄2clock
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

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

⁄2clock 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

8 Single-Ended 8 Pseudo-Differential

00558353

00558354

4 Differential Mixed Mode

00558355

00558356

FIGURE 1. Analog Input Multiplexer Options for the ADC0838

ADC0831/ADC0832/ADC0834/ADC0838

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Functional Description (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 V

IN(MAX)

and V

IN(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 V

REF

pin can be

tied to V

CC

(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.

The maximum value of the reference is limited to the V

CC

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
V

REF

/256).

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

⁄2of 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 fCMis the frequency of the common-mode signal,

V

PEAK

is its peak voltage value

and f

CLK

, is the A/D clock frequency.

For a 60 Hz common-mode signal to generate a

1

⁄4LSB 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

00558357

a) Ratiometric

00558358

b) Absolute with a reduced Span

FIGURE 2. Reference Examples

ADC0831/ADC0832/ADC0834/ADC0838

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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

createa1mVinput error witha1kΩ 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.

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, V

IN(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 V

IN

(−) input at this V

IN(MIN)

value. This

utilizes the differential mode operation of the A/D.
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 V

IN

(−) input and applying a small magnitude

positive voltage to the V

IN

(+) 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

⁄2LSB value (1⁄2LSB=9.8

mV for V

REF

=5.000 VDC).

5.2 Full-Scale

The full-scale adjustment can be made by applying a differ­ential input voltage which is 1

1

⁄2LSB down from the desired
analog full-scale voltage range and then adjusting the mag­nitude of the V

REF

input (or VCCfor the ADC0832) for a
digital output code which is just changing from 1111 1110 to
1111 1111.

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 V

IN

(+) voltage which

equals this desired zero reference plus

1

⁄2LSB (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 00

HEX

to 01

HEX

code

transition.
The full-scale adjustment should be made [with the proper

V

IN

(−) voltage applied] by forcing a voltage to the VIN(+)

input which is given by:

where:

V

MAX

= the high end of the analog input range

and

V

MIN

= the low end (the offset zero) of the analog

range.
(Both are ground referenced.)

The V

REF

(or VCC) voltage is then adjusted to provide a code

change from FE

HEX

to FF

HEX

. This completes the adjust-

ment procedure.

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 V

CC

terminal (which is the
actual converter supply) through a silicon diode, as shown in
Figure 3. (Note 3)

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 VCCis shown in Figure 6 and Figure 7. Here, this diode
is used as a rectifier to allow the V

CC

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 V

CC

line

to well under

1

⁄4of an LSB. The shunt zener regulator can
also be used in this mode. This requires a clock voltage
swing which is in excess of V

Z

. 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.

00558311

FIGURE 3. An On-Chip Shunt Regulator Diode

ADC0831/ADC0832/ADC0834/ADC0838

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Applications

Digital Link and Sample Controlling Software for theSerially Oriented COP420 and the Bit Programmable I/O INS8048

00558313

00558312

FIGURE 4. Operating with a Temperature

Compensated Reference

00558334

FIGURE 5. Using the A/D as

the System Supply Regulator

00558335

*4.5V ≤ VCC≤ 6.3V

FIGURE 6. Generating VCCfrom the Converter Clock

00558336

*4.5V ≤ VCC≤ 6.3V

FIGURE 7. Remote Sensing —

Clock and Power on 1 Wire

ADC0831/ADC0832/ADC0834/ADC0838

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Applications (Continued)

Cop Coding Example

Mnemonic 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

AND STARTS SK CLOCK

LDD LOADS MUX ADDRESS FROM RAM

INTO ACCUMULATOR

NOP —

XAS LOADS MUX ADDRESS FROM

ACCUMULATOR TO SIO REGISTER

↑

8 INSTRUCTIONS

↓

XAS READS HIGH ORDER NIBBLE (4 BITS)

INTO ACCUMULATOR

XIS PUTS HIGH ORDER NIBBLE INTO RAM

CLR A CLEARS ACCUMULATOR

RC C=0

XAS READS LOW ORDER NIBBLE INTO

ACCUMULATOR AND STOPS SK

XIS PUTS LOW ORDER NIBBLE INTO RAM

OGI G0=1 (CS =1)

LEI DISABLES SIO’s INPUT AND OUTPUT

8048 CODING EXAMPLE

Mnemonic Instruction

START: ANL P1,

#

0F7H ;SELECT A/D (CS =0)

MOV B,#5 ;BIT COUNTER←5

MOV A,

#

ADDR ;A←MUX ADDRESS

LOOP 1: RRC A ;CY←ADDRESS BIT

JC ONE ;TEST BIT

;BIT=0

ZERO: ANL P1,

#

0FEH ;DI←0

JMP CONT ;CONTINUE

;BIT=1

ONE: ORL P1,

#

1 ;DI←1

CONT: CALL PULSE ;PULSE SK 0→1→0

DJNZ B, LOOP 1 ;CONTINUE UNTIL

DONE

CALL PULSE ;EXTRA CLOCK FOR

SYNC

MOV B,

#

8 ;BIT COUNTER←8

LOOP 2: CALL PULSE ;PULSE SK 0→1→0

IN A, P1 ;CY←DO

RRC A

RRC A

MOV A, C ;A←RESULT

RLC A ;A(0)←BIT AND SHIFT

MOV C, A ;C←RESULT

DJNZ B, LOOP 2 ;CONTINUE UNTIL

DONE

RETR

;PULSE SUBROUTINE

PULSE: ORL P1,

#

04 ;SK←1

NOP ;DELAY

ANL P1,

#

0FBH ;SK←0

RET

ADC0831/ADC0832/ADC0834/ADC0838

www.national.com 20

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

ADC0831/ADC0832/ADC0834/ADC0838

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Applications (Continued)

Digitizing a Current Flow

00558315

Operating with Ratiometric Transducers

00558337

*VIN(−) = 0.15 V

CC

15% of VCC≤ V

XDR

≤ 85% of V

CC

ADC0831/ADC0832/ADC0834/ADC0838

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Applications (Continued)

Span Adjust: 0V≤V

IN

≤3V

00558361

Zero-Shift and Span Adjust: 2V≤VIN≤5V

00558362

ADC0831/ADC0832/ADC0834/ADC0838

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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

ADC0831/ADC0832/ADC0834/ADC0838

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Applications (Continued)

Protecting the Input

00558318

Diodes are 1N914

High Accuracy Comparators

00558338

DO = all 1s if +V

IN

>

−V

IN

DO = all 0s if +V

IN

<

−V

IN

ADC0831/ADC0832/ADC0834/ADC0838

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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

ADC0831/ADC0832/ADC0834/ADC0838

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Applications (Continued)

Isolated Data Converter

00558339

•

No power required remotely

•

1500V isolation

ADC0831/ADC0832/ADC0834/ADC0838

www.national.com27

Applications (Continued)

Two Wire Interface for 8 Channels

00558321

ADC0831/ADC0832/ADC0834/ADC0838

www.national.com 28

Applications (Continued)

Two Wire 1-Channels Interface

00558322

ADC0831/ADC0832/ADC0834/ADC0838

www.national.com29

Physical Dimensions inches (millimeters)

unless otherwise noted

Wide Body Molded Small-Outline Package (WM)

NS Package Number M14B

ADC0831/ADC0832/ADC0834/ADC0838

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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

ADC0831/ADC0832/ADC0834/ADC0838

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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

ADC0831/ADC0832/ADC0834/ADC0838

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Molded Chip Carrier Package (V)

Order Number ADC0838BCV or ADC0838CCV

NS Package Number V20A

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www.national.com

ADC0831/ADC0832/ADC0834/ADC0838 8-Bit Serial I/O A/D Converters with Multiplexer Options

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.