Page 1
ADC0808/ADC0809
8-Bit µP Compatible A/D Converters with 8-Channel
Multiplexer
General Description
The ADC0808, ADC0809 data acquisition component is a
monolithic CMOS device with an 8-bit analog-to-digital converter,8-channelmultiplexerand microprocessor compatible
control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a
256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can
directly access any of 8-single-ended analog signals.
The device eliminates the need for external zero and
full-scale adjustments. Easy interfacing to microprocessors
is provided by the latched and decoded multiplexer address
inputs and latched TTL TRI-STATE
®
outputs.
The design of the ADC0808, ADC0809 has been optimized
by incorporating the most desirable aspects of several A/D
conversion techniques. The ADC0808, ADC0809 offers high
speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes
minimal power. These features make this device ideally
suited to applications from process and machine control to
consumer and automotive applications. For 16-channel multiplexer with common output (sample/hold port) see
ADC0816 data sheet. (See AN-247 for more information.)
Features
n Easy interface to all microprocessors
n Operates ratiometrically or with 5 V
DC
or analog span
adjusted voltage reference
n No zero or full-scale adjust required
n 8-channel multiplexer with address logic
n 0V to 5V input range with single 5V power supply
n Outputs meet TTL voltage level specifications
n Standard hermetic or molded 28-pin DIP package
n 28-pin molded chip carrier package
n ADC0808 equivalent to MM74C949
n ADC0809 equivalent to MM74C949-1
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 100 µs
Block Diagram
TRI-STATE®is a registered trademark of National Semiconductor Corp.
DS005672-1
See Ordering
Information
October 1999
ADC0808/ADC0809 8-Bit µP Compatible A/D Converters with 8-Channel Multiplexer
© 1999 National Semiconductor Corporation DS005672 www.national.com
Page 2
Connection Diagrams
Ordering Information
TEMPERATURE RANGE −40˚C to +85˚C −55˚C to +125˚C
Error
±
1
⁄2LSB Unadjusted ADC0808CCN ADC0808CCV ADC0808CCJ ADC0808CJ
±
1 LSB Unadjusted ADC0809CCN ADC0809CCV
Package Outline N28A Molded DIP V28A Molded Chip Carrier J28A Ceramic DIP J28A Ceramic DIP
Dual-In-Line Package
DS005672-11
Order Number ADC0808CCN or ADC0809CCN
See NS Package J28A or N28A
Molded Chip Carrier Package
DS005672-12
Order Number ADC0808CCV or ADC0809CCV
See NS Package V28A
ADC0808/ADC0809
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Page 3
Absolute Maximum Ratings (Notes 2, 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
CC
) (Note 3) 6.5V
Voltage at Any Pin −0.3V to (V
CC
+0.3V)
Except Control Inputs
Voltage at Control Inputs −0.3V to +15V
(START, OE, CLOCK, ALE, ADD A, ADD B, ADD C)
Storage Temperature Range −65˚C to +150˚C
Package Dissipation at T
A
=
25˚C 875 mW
Lead Temp. (Soldering, 10 seconds)
Dual-In-Line Package (plastic) 260˚C
Dual-In-Line Package (ceramic) 300˚C
Molded Chip Carrier Package
Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C
ESD Susceptibility (Note 8) 400V
Operating Conditions (Notes 1, 2)
Temperature Range (Note 1) T
MIN≤TA≤TMAX
ADC0808CCN,ADC0809CCN −40˚C≤TA≤+85˚C
ADC0808CCV, ADC0809CCV −40˚C ≤ T
A
≤ +85˚C
Range of V
CC
(Note 1) 4.5 VDCto 6.0 V
DC
Electrical Characteristics
Converter Specifications: V
CC
=
5V
DC
=
V
REF+,VREF(−)
=
GND, T
MIN≤TA≤TMAX
and f
CLK
=
640 kHz unless otherwise stated.
Symbol Parameter Conditions Min Typ Max Units
ADC0808
Total Unadjusted Error 25˚C
±
1
⁄
2
LSB
(Note 5) T
MIN
to T
MAX
±
3
⁄
4
LSB
ADC0809
Total Unadjusted Error 0˚C to 70˚C
±
1 LSB
(Note 5) T
MIN
to T
MAX
±
11⁄
4
LSB
Input Resistance From Ref(+) to Ref(−) 1.0 2.5 kΩ
Analog Input Voltage Range (Note 4) V(+) or V(−) GND−0.10 V
CC
+0.10 V
DC
V
REF(+)
Voltage, Top of Ladder Measured at Ref(+) V
CC
VCC+0.1 V
Voltage, Center of Ladder VCC/2-0.1 VCC/2 VCC/2+0.1 V
V
REF(−)
Voltage, Bottom of Ladder Measured at Ref(−) −0.1 0 V
I
IN
Comparator Input Current f
c
=
640 kHz, (Note 6) −2
±
0.5 2 µA
Electrical Characteristics
Digital Levels and DC Specifications: ADC0808CCN, ADC0808CCV, ADC0809CCN and ADC0809CCV, 4.75≤VCC≤5.25V,
−40˚C≤TA≤+85˚C unless otherwise noted
Symbol Parameter Conditions Min Typ Max Units
ANALOG MULTIPLEXER
I
OFF(+)
OFF Channel Leakage Current V
CC
=
5V, V
IN
=
5V,
T
A
=
25˚C 10 200 nA
T
MIN
to T
MAX
1.0 µA
I
OFF(−)
OFF Channel Leakage Current V
CC
=
5V, V
IN
=
0,
T
A
=
25˚C −200 −10 nA
T
MIN
to T
MAX
−1.0 µA
CONTROL INPUTS
V
IN(1)
Logical “1” Input Voltage VCC−1.5 V
V
IN(0)
Logical “0” Input Voltage 1.5 V
I
IN(1)
Logical “1” Input Current V
IN
=
15V 1.0 µA
(The Control Inputs)
I
IN(0)
Logical “0” Input Current V
IN
=
0 −1.0 µA
(The Control Inputs)
I
CC
Supply Current f
CLK
=
640 kHz 0.3 3.0 mA
ADC0808/ADC0809
www.national.com3
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Electrical Characteristics (Continued)
Digital Levels and DC Specifications: ADC0808CCN, ADC0808CCV, ADC0809CCN and ADC0809CCV, 4.75≤VCC≤5.25V,
−40˚C≤TA≤+85˚C unless otherwise noted
Symbol Parameter Conditions Min Typ Max Units
DATA OUTPUTS AND EOC (INTERRUPT)
V
OUT(1)
Logical “1” Output Voltage V
CC
=
4.75V
I
OUT
=
−360µA
I
OUT
=
−10µA
2.4
4.5
V(min)
V(min)
V
OUT(0)
Logical “0” Output Voltage I
O
=
1.6 mA 0.45 V
V
OUT(0)
Logical “0” Output Voltage EOC I
O
=
1.2 mA 0.45 V
I
OUT
TRI-STATE Output Current V
O
=
5V 3 µA
V
O
=
0−3 µA
Electrical Characteristics
Timing Specifications V
CC
=
V
REF(+)
=
5V, V
REF(−)
=
GND, t
r
=
t
f
=
20 ns and T
A
=
25˚C unless otherwise noted.
Symbol Parameter Conditions MIn Typ Max Units
t
WS
Minimum Start Pulse Width (
Figure 5
) 100 200 ns
t
WALE
Minimum ALE Pulse Width (
Figure 5
) 100 200 ns
t
s
Minimum Address Set-Up Time (
Figure 5
)2550ns
t
H
Minimum Address Hold Time (
Figure 5
)2550ns
t
D
Analog MUX Delay Time R
S
=
0Ω (
Figure 5
) 1 2.5 µs
From ALE
t
H1,tH0
OE Control to Q Logic State C
L
=
50 pF, R
L
=
10k (
Figure 8
) 125 250 ns
t
1H,t0H
OE Control to Hi-Z C
L
=
10 pF, R
L
=
10k (
Figure 8
) 125 250 ns
t
c
Conversion Time f
c
=
640 kHz, (
Figure 5
) (Note 7) 90 100 116 µs
f
c
Clock Frequency 10 640 1280 kHz
t
EOC
EOC Delay Time (
Figure 5
) 0 8+2 µS Clock
Periods
C
IN
Input Capacitance At Control Inputs 10 15 pF
C
OUT
TRI-STATE Output At TRI-STATE Outputs 10 15 pF
Capacitance
Note 1: AbsoluteMaximum 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 GND, unless othewise specified.
Note 3: Azener diode exists, internally, from V
CC
to GND and has a typical breakdown voltage of 7 VDC.
Note 4: Two on-chip diodes are tied to each analog input which will forward conduct for analog input voltages one diode drop below ground or one diode drop greater
than the V
CC
n supply. The spec allows 100 mV forward bias of either diode. This means that as long as the analog VINdoes not exceed the supply voltage by more
than 100 mV,the output code will be correct. To achieve an absolute 0V
DC
to 5VDCinput voltage range will therefore require a minimum supply voltage of 4.900 V
DC
over temperature variations, initial tolerance and loading.
Note 5: Total unadjusted error includes offset, full-scale, linearity, and multiplexer errors. See
Figure 3
. None of these A/Ds requires a zero or full-scale adjust. However,if an all zero code is desired for an analog input other than 0.0V, or if a narrow full-scale span exists (for example: 0.5V to 4.5V full-scale) the reference voltages
can be adjusted to achieve this. See
Figure 13
.
Note 6: Comparatorinput current is a bias current into or out of the chopper stabilized comparator. The bias current varies directly with clock frequency and has little
temperature dependence (
Figure 6
). See paragraph 4.0.
Note 7: The outputs of the data register are updated one clock cycle before the rising edge of EOC.
Note 8: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
ADC0808/ADC0809
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Functional Description
Multiplexer. The device contains an 8-channel single-ended
analog signal multiplexer. A particular input channel is selected by using the address decoder.
Table1
shows the input
states for the address lines to select any channel. The address is latched into the decoder on the low-to-high transition
of the address latch enable signal.
TABLE 1.
SELECTED ADDRESS LINE
ANALOG
CHANNEL
CBA
IN0 L L L
IN1 L L H
IN2 L H L
IN3 L H H
IN4 H L L
IN5 H L H
IN6 H H L
IN7 H H H
CONVERTER CHARACTERISTICS
The Converter
The heart of this single chip data acquisition system is its
8-bit analog-to-digital converter.The converter is designed to
give fast, accurate, and repeatable conversions over a wide
range of temperatures. The converter is partitioned into 3
major sections: the 256R ladder network, the successive approximation register, and the comparator. The converter’s
digital outputs are positive true.
The 256R ladder network approach (
Figure 1
) was chosen
over the conventional R/2R ladder because of its inherent
monotonicity, which guarantees no missing digital codes.
Monotonicity is particularly important in closed loop feedback
control systems. Anon-monotonic relationship can cause oscillations that will be catastrophic for the system. Additionally,
the 256R network does not cause load variations on the reference voltage.
The bottom resistor and the top resistor of the ladder network in
Figure 1
are not the same value as the remainder of
the network. The difference in these resistors causes the
output characteristic to be symmetrical with the zero and
full-scale points of the transfer curve. The first output transition occurs when the analog signal has reached +
1
⁄2LSB
and succeeding output transitions occur every 1 LSB later up
to full-scale.
The successive approximation register (SAR) performs 8 iterations to approximate the input voltage. For any SAR type
converter, n-iterations are required for an n-bit converter.
Figure 2
shows a typical example of a 3-bit converter. In the
ADC0808, ADC0809, the approximation technique is extended to 8 bits using the 256R network.
The A/D converter’s successive approximation register
(SAR) is reset on the positive edge of the start conversion
(SC) pulse. The conversion is begun on the falling edge of
the start conversion pulse. A conversion in process will be interrupted by receipt of a new start conversion pulse. Continuous conversion may be accomplished by tying the
end-of-conversion (EOC) output to the SC input. If used in
this mode, an external start conversion pulse should be applied after power up. End-of-conversion will go low between
0 and 8 clock pulses after the rising edge of start conversion.
The most important section of the A/D converter is the comparator. It is this section which is responsible for the ultimate
accuracy of the entire converter. It is also the comparator
drift which has the greatest influence on the repeatability of
the device. A chopper-stabilized comparator provides the
most effective method of satisfying all the converter requirements.
The chopper-stabilized comparator converts the DC input
signal into an AC signal. This signal is then fed through a
high gain AC amplifier and has the DC level restored. This
technique limits the drift component of the amplifier since the
drift is a DC component which is not passed by the AC amplifier. This makes the entire A/D converter extremely insensitive to temperature, long term drift and input offset errors.
Figure 4
shows a typical error curve for the ADC0808 as
measured using the procedures outlined in AN-179.
ADC0808/ADC0809
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Page 6
Functional Description (Continued)
DS005672-2
FIGURE 1. Resistor Ladder and Switch Tree
DS005672-13
FIGURE 2. 3-Bit A/D Transfer Curve
DS005672-14
FIGURE 3. 3-Bit A/D Absolute Accuracy Curve
DS005672-15
FIGURE 4. Typical Error Curve
ADC0808/ADC0809
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Page 7
Timing Diagram
DS005672-4
FIGURE 5.
ADC0808/ADC0809
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Typical Performance Characteristics
TRI-STATE Test Circuits and Timing Diagrams
Applications Information
OPERATION
1.0 RATIOMETRIC CONVERSION
The ADC0808, ADC0809 is designed as a complete Data
Acquisition System (DAS) for ratiometric conversion systems. In ratiometric systems, the physical variable being
measured is expressed as a percentage of full-scale which is
not necessarily related to an absolute standard. The voltage
input to the ADC0808 is expressed by the equation
(1)
V
IN
=
Input voltage into the ADC0808
V
fs
=
Full-scale voltage
V
Z
=
Zero voltage
D
X
=
Data point being measured
D
MAX
=
Maximum data limit
D
MIN
=
Minimum data limit
A good example of a ratiometric transducer is a potentiometer used as a position sensor. The position of the wiper is directly proportional to the output voltage which is a ratio of the
full-scale voltage across it. Since the data is represented as
a proportion of full-scale, reference requirements are greatly
reduced, eliminating a large source of error and cost for
many applications. A major advantage of the ADC0808,
ADC0809 is that the input voltage range is equal to the supply range so the transducers can be connected directly
across the supply and their outputs connected directly into
the multiplexer inputs, (
Figure 9
).
Ratiometric transducers such as potentiometers, strain
gauges, thermistor bridges, pressure transducers, etc., are
suitable for measuring proportional relationships; however,
many types of measurements must be referred to an absolute standard such as voltage or current. This means a sys-
DS005672-16
FIGURE 6. Comparator IINvs V
IN
(V
CC
=
V
REF
=
5V)
DS005672-17
FIGURE 7. Multiplexer RONvs V
IN
(V
CC
=
V
REF
=
5V)
t
1H,tH1
DS005672-18
t1H,C
L
=
10 pF
DS005672-19
tH1,C
L
=
50 pF
DS005672-20
t0H,t
H0
DS005672-21
t0H,C
L
=
10 pF
DS005672-22
tH0,C
L
=
50 pF
DS005672-23
FIGURE 8.
ADC0808/ADC0809
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Page 9
Applications Information (Continued)
tem reference must be used which relates the full-scale voltage to the standard volt. For example, if V
CC
=
V
REF
=
5.12V,
then the full-scale range is divided into 256 standard steps.
The smallest standard step is 1 LSB which is then 20 mV.
2.0 RESISTOR LADDER LIMITATIONS
The voltages from the resistor ladder are compared to the
selected into 8 times in a conversion. These voltages are
coupled to the comparator via an analog switch tree which is
referenced to the supply.The voltages at the top, center and
bottom of the ladder must be controlled to maintain proper
operation.
The top of the ladder, Ref(+), should not be more positive
than the supply, and the bottom of the ladder,Ref(−), should
not be more negative than ground. The center of the ladder
voltage must also be near the center of the supply because
the analog switch tree changes from N-channel switches to
P-channel switches. These limitations are automatically satisfied in ratiometric systems and can be easily met in ground
referenced systems.
Figure 10
shows a ground referenced system with a separate supply and reference. In this system, the supply must be
trimmed to match the reference voltage. For instance, if a
5.12V is used, the supply should be adjusted to the same
voltage within 0.1V.
The ADC0808 needs less than a milliamp of supply current
so developing the supply from the reference is readily accomplished. In
Figure 11
a ground referenced system is
shown which generates the supply from the reference. The
buffer shown can be an op amp of sufficient drive to supply
the milliamp of supply current and the desired bus drive, or if
a capacitive bus is driven by the outputs a large capacitor will
supply the transient supply current as seen in
Figure 12
. The
LM301 is overcompensated to insure stability when loaded
by the 10 µF output capacitor.
The top and bottom ladder voltages cannot exceed V
CC
and
ground, respectively, but they can be symmetrically less than
V
CC
and greater than ground. The center of the ladder voltage should always be near the center of the supply.The sensitivity of the converter can be increased, (i.e., size of the
LSB steps decreased) by using a symmetrical reference system. In
Figure 13
, a 2.5V reference is symmetrically cen-
tered about V
CC
/2 since the same current flows in identical
resistors. This system with a 2.5V reference allows the LSB
bit to be half the size of a 5V reference system.
DS005672-7
FIGURE 9. Ratiometric Conversion System
ADC0808/ADC0809
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Page 10
Applications Information (Continued)
DS005672-24
FIGURE 10. Ground Referenced
Conversion System Using Trimmed Supply
DS005672-25
FIGURE 11. Ground Referenced Conversion System with
Reference Generating V
CC
Supply
ADC0808/ADC0809
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Page 11
Applications Information (Continued)
3.0 CONVERTER EQUATIONS
The transition between adjacent codes N and N+1 is given
by:
(2)
The center of an output code N is given by:
(3)
The output code N for an arbitrary input are the integers
within the range:
(4)
Where: V
IN
=
Voltage at comparator input
V
REF(+)
=
Voltage at Ref(+)
V
REF(−)
=
Voltage at Ref(−)
V
TUE
=
Total unadjusted error voltage (typically
V
REF(+)
÷
512)
DS005672-26
FIGURE 12. Typical Reference and Supply Circuit
DS005672-27
R
A
=
R
B
*
Ratiometric transducers
FIGURE 13. Symmetrically Centered Reference
ADC0808/ADC0809
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Page 12
Applications Information (Continued)
4.0 ANALOG COMPARATOR INPUTS
The dynamic comparator input current is caused by the periodic switching of on-chip stray capacitances. These are
connected alternately to the output of the resistor ladder/
switch tree network and to the comparator input as part of
the operation of the chopper stabilized comparator.
The average value of the comparator input current varies directly with clock frequency and with V
IN
as shown in
Figure 6
.
If no filter capacitors are used at the analog inputs and the
signal source impedances are low, the comparator input current should not introduce converter errors, as the transient
created by the capacitance discharge will die out before the
comparator output is strobed.
If input filter capacitors are desired for noise reduction and
signal conditioning they will tend to average out the dynamic
comparator input current. It will then take on the characteristics of a DC bias current whose effect can be predicted conventionally.
Typical Application
TABLE 2. Microprocessor Interface Table
PROCESSOR READ WRITE INTERRUPT (COMMENT)
8080 MEMR
MEMW INTR (Thru RST Circuit)
8085 RD
WR INTR (Thru RST Circuit)
Z-80 RD
WR INT (Thru RST Circuit, Mode 0)
SC/MP NRDS NWDS SA (Thru Sense A)
6800 VMA
•φ2•
R/W VMA•φ•R/W IRQA or IRQB (Thru PIA)
DS005672-10
*Address latches needed for 8085 and SC/MP interfacing the ADC0808 to a microprocessor
ADC0808/ADC0809
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Page 13
Physical Dimensions inches (millimeters) unless otherwise noted
Molded Dual-In-Line Package (N)
Order Number ADC0808CCN or ADC0809CCN
NS Package Number N28B
Molded Chip Carrier (V)
Order Number ADC0808CCV or ADC0809CCV
NS Package Number V28A
ADC0808/ADC0809
www.national.com13
Page 14
Notes
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
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Tel: 65-2544466
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Email: sea.support@nsc.com
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Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
ADC0808/ADC0809 8-Bit µP Compatible A/D Converters with 8-Channel Multiplexer
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.
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