ADC0808/ADC0809 8-Bit μP Compatible A/D Converters with 8-Channel Multiplexer

July 8, 2009

ADC0808/ADC0809

8-Bit μP Compatible A/D Converters with 8-Channel

Multiplexer
General Description Features
The ADC0808, ADC0809 data acquisition component is a ■ Easy interface to all microprocessors
monolithic CMOS device with an 8-bit analog-to-digital con- ■ Operates ratiometrically or with 5 VDC or analog span
verter, 8-channel multiplexer and microprocessor compatible adjusted voltage reference
control logic. The 8-bit A/D converter uses successive ap-
■ No zero or full-scale adjust required
proximation as the conversion technique. The converter fea-
tures a high impedance chopper stabilized comparator, a ■ 8-channel multiplexer with address logic
256R voltage divider with analog switch tree and a successive ■ 0V to VCC input range
approximation register. The 8-channel multiplexer can direct- ■ Outputs meet TTL voltage level specifications
ly access any of 8-single-ended analog signals. ■ ADC0808 equivalent to MM74C949
The device eliminates the need for external zero and full-scale ■ ADC0809 equivalent to MM74C949-1
adjustments. Easy interfacing to microprocessors is provided
by the latched and decoded multiplexer address inputs and
latched TTL TRI-STATE outputs.
Key Specifications
The design of the ADC0808, ADC0809 has been optimized ■ Resolution 8 Bits
by incorporating the most desirable aspects of several A/D ■ Total Unadjusted Error ±½ LSB and ±1 LSB
conversion techniques. The ADC0808, ADC0809 offers high ■ Single Supply 5 VDC
speed, high accuracy, minimal temperature dependence, ex- ■ Low Power 15 mW
cellent long-term accuracy and repeatability, and consumes ■ Conversion Time 100 μs
minimal power. These features make this device ideally suit-
ed to applications from process and machine control to con-
sumer and automotive applications. For 16-channel multi-
plexer with common output (sample/hold port) see ADC0816
data sheet. (See AN-247 for more information.)

Block Diagram

567201
See Ordering Information

© 2009 National Semiconductor Corporation 5672 www.national.com

ADC0808/ADC0809
Connection Diagrams
Dual-In-Line Package Molded Chip Carrier Package

567211
Order Number ADC0808CCN or ADC0809CCN 567212
See NS Package NA28E Order Number ADC0808CCV or ADC0809CCV
See NS Package V28A

Ordering Information
Temperature Range −40°C to +85°C
V28A Molded Chip Carrier
Package Outline NA28E Molded DIP V28A Molded Chip Carrier
(Tape and Reel)
±½ LSB Unadjusted ADC0808CCN ADC0808CCV ADC0808CCVX
Error
±1 LSB Unadjusted ADC0809CCN ADC0809CCV ADC0809CCVX

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 ADC0808/ADC0809
Absolute Maximum Ratings Operating Conditions
(Notes 2, 1) (Notes 1, 2)
If Military/Aerospace specified devices are required, Temperature Range TMIN≤TA≤TMAX
please contact the National Semiconductor Sales Office/   −40°C≤TA≤+85°C
Distributors for availability and specifications.
Range of VCC 4.5 VDC to 6.0 VDC
Supply Voltage (VCC) (Note 3) 6.5V
Voltage at Any Pin −0.3V to (VCC
+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 TA=25°C 875 mW
Lead Temp. (Soldering, 10 seconds)
Dual-In-Line Package (plastic) 260°C
Molded Chip Carrier Package
Vapor Phase (60 seconds) 215°C
Infrared (15 seconds) 220°C
ESD Susceptibility (Note 8) 400V

Electrical Characteristics – Converter Specifications

Converter Specifications: VCC=5 VDC=VREF+, VREF(−)=GND, TMIN≤TA≤TMAX and fCLK=640 kHz unless otherwise stated.
Symbol Parameter Conditions Min Typ Max Units
ADC0808
Total Unadjusted Error 25°C ±½ LSB
 (Note 5) TMIN to TMAX ±¾ LSB
ADC0809
Total Unadjusted Error 0°C to 70°C ±1 LSB
 (Note 5) TMIN to TMAX ±1¼ LSB
Input Resistance From Ref(+) to Ref(−) 1.0 2.5 kΩ
Analog Input Voltage Range (Note 4) V(+) or V(−) GND − 0.1 VCC + 0.1 VDC
VREF(+) Voltage, Top of Ladder Measured at Ref(+) VCC VCC + 0.1 V

Voltage, Center of Ladder (VCC/2) − 0.1 VCC/2 (VCC/2) + 0.1 V

VREF(−) Voltage, Bottom of Ladder Measured at Ref(−) −0.1 0 V

IIN Comparator Input Current fc=640 kHz, (Note 6) −2 ±0.5 2 μA

Electrical Characteristics – Digital Levels and DC Specifications

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
VCC=5V, VIN=5V,
IOFF(+) OFF Channel Leakage Current TA=25°C 10 200 nA
TMIN to TMAX 1.0 μA
VCC=5V, VIN=0,
IOFF(−) OFF Channel Leakage Current TA=25°C −200 −10 nA
TMIN to TMAX −1.0 μA
CONTROL INPUTS
VIN(1) Logical “1” Input Voltage (VCC − 1.5) V
VIN(0) Logical “0” Input Voltage 1.5 V

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ADC0808/ADC0809 Symbol Parameter Conditions Min Typ Max Units
Logical “1” Input Current (The Control
IIN(1) VIN=15V 1.0 μA
Inputs)
Logical “0” Input Current (The Control
IIN(0) VIN=0 −1.0 μA
Inputs)
ICC Supply Current fCLK=640 kHz 0.3 3.0 mA
DATA OUTPUTS AND EOC (INTERRUPT)
VCC = 4.75V
VOUT(1) Logical “1” Output Voltage IOUT = −360µA 2.4 V
IOUT = −10µA 4.5 V
VOUT(0) Logical “0” Output Voltage IO=1.6 mA 0.45 V
VOUT(0) Logical “0” Output Voltage EOC IO=1.2 mA 0.45 V
VO=5V 3 μA
IOUT TRI-STATE Output Current
VO=0 −3 μA

Electrical Characteristics – Timing Specifications

Timing Specifications VCC=VREF(+)=5V, VREF(−)=GND, tr=tf=20 ns and TA=25°C unless otherwise noted.
Symbol Parameter Conditions MIn Typ Max Units
tSTCLK Start Time Delay from Clock (Figure 5) 300 900 ns
tWS Minimum Start Pulse Width (Figure 5) 100 200 ns
tWALE Minimum ALE Pulse Width (Figure 5) 100 200 ns
ts Minimum Address Set-Up Time (Figure 5) 25 50 ns
tH Minimum Address Hold Time (Figure 5) 25 50 ns
tD Analog MUX Delay Time From ALE RS=0Ω (Figure 5) 1 2.5 μs
tH1, tH0 OE Control to Q Logic State CL=50 pF, RL=10k (Figure 8) 125 250 ns
t1H, t0H OE Control to Hi-Z CL=10 pF, RL=10k (Figure 8) 125 250 ns
tc Conversion Time fc=640 kHz, (Figure 5) (Note 7) 90 100 116 μs
fc Clock Frequency 10 640 1280 kHz
Clock
tEOC EOC Delay Time (Figure 5) 0 8 + 2 μS
Periods
CIN Input Capacitance At Control Inputs 10 15 pF
COUT TRI-STATE Output Capacitance At TRI-STATE Outputs 10 15 pF

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 GND, unless otherwise specified.
Note 3: A Zener diode exists, internally, from VCC 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 VCCn supply. The spec allows 100 mV forward bias of either diode. This means that as long as the analog VIN does not exceed the supply voltage
by more than 100 mV, the output code will be correct. To achieve an absolute 0VDC to 5VDC input voltage range will therefore require a minimum supply voltage
of 4.900 VDC 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: Comparator input 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.

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 ADC0808/ADC0809
The bottom resistor and the top resistor of the ladder network
Functional Description in Figure 1 are not the same value as the remainder of the
MULTIPLEXER network. The difference in these resistors causes the output
characteristic to be symmetrical with the zero and full-scale
The device contains an 8-channel single-ended analog signal
points of the transfer curve. The first output transition occurs
multiplexer. A particular input channel is selected by using the
when the analog signal has reached +½ LSB and succeeding
address decoder. Table 1 shows the input states for the ad-
output transitions occur every 1 LSB later up to full-scale.
dress lines to select any channel. The address is latched into
the decoder on the low-to-high transition of the address latch The successive approximation register (SAR) performs 8 it-
enable signal. erations to approximate the input voltage. For any SAR type
converter, n-iterations are required for an n-bit converter. Fig-
TABLE 1. Analog Channel Selection ure 2 shows a typical example of a 3-bit converter. In the
ADC0808, ADC0809, the approximation technique is extend-
SELECTED ANALOG ADDRESS LINE
ed to 8 bits using the 256R network.
CHANNEL C B A
The A/D converter's successive approximation register (SAR)
IN0 L L L is reset on the positive edge of the start conversion start pulse.
IN1 L L H The conversion is begun on the falling edge of the start con-
IN2 L H L version pulse. A conversion in process will be interrupted by
receipt of a new start conversion pulse. Continuous conver-
IN3 L H H
sion may be accomplished by tying the end-of-conversion
IN4 H L L (EOC) output to the SC input. If used in this mode, an external
IN5 H L H start conversion pulse should be applied after power up. End-
IN6 H H L of-conversion will go low between 0 and 8 clock pulses after
the rising edge of start conversion.
IN7 H H H
The most important section of the A/D converter is the com-
CONVERTER CHARACTERISTICS parator. It is this section which is responsible for the ultimate
accuracy of the entire converter. It is also the comparator drift
The Converter which has the greatest influence on the repeatability of the
The heart of this single chip data acquisition system is its 8- device. A chopper-stabilized comparator provides the most
bit analog-to-digital converter. The converter is designed to effective method of satisfying all the converter requirements.
give fast, accurate, and repeatable conversions over a wide The chopper-stabilized comparator converts the DC input sig-
range of temperatures. The converter is partitioned into 3 ma- nal into an AC signal. This signal is then fed through a high
jor sections: the 256R ladder network, the successive ap- gain AC amplifier and has the DC level restored. This tech-
proximation register, and the comparator. The converter's nique limits the drift component of the amplifier since the drift
digital outputs are positive true. is a DC component which is not passed by the AC amplifier.
The 256R ladder network approach (Figure 1) was chosen This makes the entire A/D converter extremely insensitive to
over the conventional R/2R ladder because of its inherent temperature, long term drift and input offset errors.
monotonicity, which guarantees no missing digital codes. Figure 4 shows a typical error curve for the ADC0808 as
Monotonicity is particularly important in closed loop feedback measured using the procedures outlined in AN-179.
control systems. A non-monotonic relationship can cause os-
cillations that will be catastrophic for the system. Additionally,
the 256R network does not cause load variations on the ref-
erence voltage.

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ADC0808/ADC0809

567202

FIGURE 1. Resistor Ladder and Switch Tree

567213
567214

FIGURE 2. 3-Bit A/D Transfer Curve

FIGURE 3. 3-Bit A/D Absolute Accuracy Curve

567215

FIGURE 4. Typical Error Curve

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 ADC0808/ADC0809
Timing Diagram

567204

FIGURE 5.

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ADC0808/ADC0809
Typical Performance Characteristics

567216

FIGURE 6. Comparator IIN vs. VIN

(VCC=VREF=5V)

567217

FIGURE 7. Multiplexer RON vs. VIN

(VCC=VREF=5V)

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 ADC0808/ADC0809
TRI-STATE Test Circuits and Timing Diagrams
t1H, tH1 t0H, tH0

567218 567221

t1H, CL = 10 pF t0H, CL = 10 pF

567222
567219

tH1, CL = 50 pF tH0, CL = 50 pF

567223
567220
FIGURE 8. TRI-STATE Test Circuits and Timing Diagrams

proportion of full-scale, reference requirements are greatly

Applications Information reduced, eliminating a large source of error and cost for many
OPERATION applications. A major advantage of the ADC0808, ADC0809
is that the input voltage range is equal to the supply range so
1.0 RATIOMETRIC CONVERSION the transducers can be connected directly across the supply
The ADC0808, ADC0809 is designed as a complete Data and their outputs connected directly into the multiplexer in-
Acquisition System (DAS) for ratiometric conversion systems. puts, (Figure 9).
In ratiometric systems, the physical variable being measured Ratiometric transducers such as potentiometers, strain
is expressed as a percentage of full-scale which is not nec- gauges, thermistor bridges, pressure transducers, etc., are
essarily related to an absolute standard. The voltage input to suitable for measuring proportional relationships; however,
the ADC0808 is expressed by the equation many types of measurements must be referred to an absolute
standard such as voltage or current. This means a system
reference must be used which relates the full-scale voltage to
the standard volt. For example, if VCC=VREF=5.12V, then the
(1) full-scale range is divided into 256 standard steps. The small-
VIN= Input voltage into the ADC0808 est standard step is 1 LSB which is then 20 mV.
Vfs= Full-scale voltage 2.0 RESISTOR LADDER LIMITATIONS
VZ= Zero voltage The voltages from the resistor ladder are compared to the
DX= Data point being measured selected into 8 times in a conversion. These voltages are
DMAX= Maximum data limit coupled to the comparator via an analog switch tree which is
DMIN= Minimum data limit referenced to the supply. The voltages at the top, center and
A good example of a ratiometric transducer is a potentiometer bottom of the ladder must be controlled to maintain proper
used as a position sensor. The position of the wiper is directly operation.
proportional to the output voltage which is a ratio of the full- The top of the ladder, Ref(+), should not be more positive than
scale voltage across it. Since the data is represented as a the supply, and the bottom of the ladder, Ref(−), should not
be more negative than ground. The center of the ladder volt-

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ADC0808/ADC0809 age must also be near the center of the supply because the Figure 10 shows a ground referenced system with a separate
analog switch tree changes from N-channel switches to P- supply and reference. In this system, the supply must be
channel switches. These limitations are automatically satis- trimmed to match the reference voltage. For instance, if a
fied in ratiometric systems and can be easily met in ground 5.12V is used, the supply should be adjusted to the same
referenced systems. voltage within 0.1V.

567207

FIGURE 9. Ratiometric Conversion System

The ADC0808 needs less than a milliamp of supply current The top and bottom ladder voltages cannot exceed VCC and
so developing the supply from the reference is readily ac- ground, respectively, but they can be symmetrically less than
complished. In Figure 11 a ground referenced system is VCC and greater than ground. The center of the ladder voltage
shown which generates the supply from the reference. The should always be near the center of the supply. The sensitivity
buffer shown can be an op amp of sufficient drive to supply of the converter can be increased, (i.e., size of the LSB steps
the milliamp of supply current and the desired bus drive, or if decreased) by using a symmetrical reference system. In Fig-
a capacitive bus is driven by the outputs a large capacitor will ure 13, a 2.5V reference is symmetrically centered about
supply the transient supply current as seen in Figure 12. The VCC/2 since the same current flows in identical resistors. This
LM301 is overcompensated to insure stability when loaded by system with a 2.5V reference allows the LSB bit to be half the
the 10 μF output capacitor. size of a 5V reference system.

567224

FIGURE 10. Ground Referenced

Conversion System Using Trimmed Supply

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 ADC0808/ADC0809
567225

FIGURE 11. Ground Referenced Conversion System with

Reference Generating VCC Supply

567226

FIGURE 12. Typical Reference and Supply Circuit

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ADC0808/ADC0809

567227

RA=RB
*Ratiometric transducers
FIGURE 13. Symmetrically Centered Reference

3.0 CONVERTER EQUATIONS VREF(+)÷512)

The transition between adjacent codes N and N+1 is given
by: 4.0 ANALOG COMPARATOR INPUTS
The dynamic comparator input current is caused by the peri-
odic switching of on-chip stray capacitances. These are con-
(2) nected alternately to the output of the resistor ladder/switch
tree network and to the comparator input as part of the oper-
The center of an output code N is given by: ation of the chopper stabilized comparator.
The average value of the comparator input current varies di-
rectly with clock frequency and with VIN as shown in
(3)
Figure 6.
The output code N for an arbitrary input are the integers within If no filter capacitors are used at the analog inputs and the
the range: signal source impedances are low, the comparator input cur-
rent should not introduce converter errors, as the transient
created by the capacitance discharge will die out before the
(4) comparator output is strobed.
Where: VIN=Voltage at comparator input If input filter capacitors are desired for noise reduction and
VREF(+)=Voltage at Ref(+) signal conditioning they will tend to average out the dynamic
VREF(−)=Voltage at Ref(−) comparator input current. It will then take on the characteris-
tics of a DC bias current whose effect can be predicted
VTUE=Total unadjusted error voltage (typically
conventionally.

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 ADC0808/ADC0809
Typical Application

567210
*Address latches needed for 8085 and SC/MP interfacing the ADC0808 to a microprocessor

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)

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ADC0808/ADC0809
Physical Dimensions inches (millimeters) unless otherwise noted

Molded Dual-In-Line Package (N)

Order Number ADC0808CCN or ADC0809CCN
NS Package Number NA28E

Molded Chip Carrier (V)

Order Number ADC0808CCV or ADC0809CCV
NS Package Number V28A

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 ADC0808/ADC0809

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ADC0808/ADC0809 8-Bit μP Compatible A/D Converters with 8-Channel Multiplexer
Notes

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