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

November 1995

ADC0808/ADC0809
8-Bit µP Compatible A/D Converters with 8-Channel
Multiplexer
General Description Features
The ADC0808, ADC0809 data acquisition component is a n Easy interface to all microprocessors
monolithic CMOS device with an 8-bit analog-to-digital con- n 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- n No zero or full-scale adjust required
proximation as the conversion technique. The converter fea- n 8-channel multiplexer with address logic
tures a high impedance chopper stabilized comparator, a n 0V to 5V input range with single 5V power supply
256R voltage divider with analog switch tree and a succes-
n Outputs meet TTL voltage level specifications
sive approximation register. The 8-channel multiplexer can
directly access any of 8-single-ended analog signals. n Standard hermetic or molded 28-pin DIP package
n 28-pin molded chip carrier package
The device eliminates the need for external zero and
full-scale adjustments. Easy interfacing to microprocessors n ADC0808 equivalent to MM74C949
is provided by the latched and decoded multiplexer address n ADC0809 equivalent to MM74C949-1
inputs and latched TTL TRI-STATE ® outputs.
The design of the ADC0808, ADC0809 has been optimized Key Specifications
by incorporating the most desirable aspects of several A/D n Resolution: 8 Bits
conversion techniques. The ADC0808, ADC0809 offers high n Total Unadjusted Error: ± 1⁄2 LSB and ± 1 LSB
speed, high accuracy, minimal temperature dependence, ex- n Single Supply: 5 VDC
cellent long-term accuracy and repeatability, and consumes n Low Power: 15 mW
minimal power. These features make this device ideally
n Conversion Time: 100 µs
suited to applications from process and machine control to
consumer and automotive applications. For 16-channel mul-
tiplexer with common output (sample/hold port) see
ADC0816 data sheet. (See AN-247 for more information.)

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

© 1997 National Semiconductor Corporation DS005672 www.national.com

 Block Diagram

DS005672-1

See Ordering
Information

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 Absolute Maximum Ratings (Notes 1, Dual-In-Line Package (ceramic) 300˚C
2) Molded Chip Carrier Package
If Military/Aerospace specified devices are required, Vapor Phase (60 seconds) 215˚C
please contact the National Semiconductor Sales Office/ Infrared (15 seconds) 220˚C
Distributors for availability and specifications. ESD Susceptibility (Note 8) 400V
Supply Voltage (VCC) (Note 3) 6.5V
Voltage at Any Pin −0.3V to (VCC+0.3V) Operating Conditions (Notes 1, 2)
Except Control Inputs Temperature Range (Note 1) TMIN≤TA≤TMAX
Voltage at Control Inputs −0.3V to +15V ADC0808CJ −55˚C≤TA≤+125˚C
(START, OE, CLOCK, ALE, ADD A, ADD B, ADD C) ADC0808CCJ, ADC0808CCN,
Storage Temperature Range −65˚C to +150˚C ADC0809CCN −40˚C≤TA≤+85˚C
Package Dissipation at TA = 25˚C 875 mW ADC0808CCV, ADC0809CCV −40˚C ≤ TA ≤ +85˚C
Lead Temp. (Soldering, 10 seconds) Range of VCC (Note 1) 4.5 VDC to 6.0 VDC
Dual-In-Line Package (plastic) 260˚C

Electrical Characteristics
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 ± 1⁄2 LSB
(Note 5) TMIN to TMAX ± 3⁄4 LSB
ADC0809
Total Unadjusted Error 0˚C to 70˚C ±1 LSB
(Note 5) TMIN to TMAX ± 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 VCC+0.10 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: ADC0808CJ 4.5V≤VCC≤5.5V, −55˚C≤TA≤+125˚C unless otherwise noted
ADC0808CCJ, 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
IOFF(+) OFF Channel Leakage Current VCC = 5V, VIN = 5V,
TA = 25˚C 10 200 nA
TMIN to TMAX 1.0 µA
IOFF(−) OFF Channel Leakage Current VCC = 5V, VIN = 0,
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
IIN(1) Logical “1” Input Current VIN = 15V 1.0 µA
(The Control Inputs)
IIN(0) Logical “0” Input Current VIN = 0 −1.0 µA
(The Control Inputs)
ICC Supply Current fCLK = 640 kHz 0.3 3.0 mA

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 Electrical Characteristics (Continued)

Digital Levels and DC Specifications: ADC0808CJ 4.5V≤VCC≤5.5V, −55˚C≤TA≤+125˚C unless otherwise noted
ADC0808CCJ, 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)
VOUT(1) Logical “1” Output Voltage IO = −360 µA VCC−0.4 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
IOUT TRI-STATE Output Current VO = 5V 3 µA
VO = 0 −3 µA

Electrical Characteristics
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
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 RS = 0Ω (Figure 5) 1 2.5 µS
From ALE
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
tEOC EOC Delay Time (Figure 5) 0 8+2 µS Clock
Periods
CIN Input Capacitance At Control Inputs 10 15 pF
COUT TRI-STATE Output At TRI-STATE Outputs 10 15 pF
Capacitance
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 othewise 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 2. None of these A/Ds requires a zero or full-scale adjust. How-
ever, 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 *NO TGT: fig NS0592*). 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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Functional Description The bottom resistor and the top resistor of the ladder net-
work in Figure 1 are not the same value as the remainder of
Multiplexer. The device contains an 8-channel single-ended the network. The difference in these resistors causes the
analog signal multiplexer. A particular input channel is se- output characteristic to be symmetrical with the zero and
lected by using the address decoder. Table 1 shows the input full-scale points of the transfer curve. The first output transi-
states for the address lines to select any channel. The ad- tion occurs when the analog signal has reached +1⁄2 LSB
dress is latched into the decoder on the low-to-high transition and succeeding output transitions occur every 1 LSB later up
of the address latch enable signal. to full-scale.
The successive approximation register (SAR) performs 8 it-
TABLE 1. erations to approximate the input voltage. For any SAR type
converter, n-iterations are required for an n-bit converter.
SELECTED ADDRESS LINE
Figure 2 shows a typical example of a 3-bit converter. In the
ANALOG C B A ADC0808, ADC0809, the approximation technique is ex-
CHANNEL tended to 8 bits using the 256R network.
IN0 L L L The A/D converter’s successive approximation register
IN1 L L H (SAR) is reset on the positive edge of the start conversion
(SC) pulse. The conversion is begun on the falling edge of
IN2 L H L the start conversion pulse. A conversion in process will be in-
IN3 L H H terrupted by receipt of a new start conversion pulse. Con-
IN4 H L L tinuous conversion may be accomplished by tying the
end-of-conversion (EOC) output to the SC input. If used in
IN5 H L H
this mode, an external start conversion pulse should be ap-
IN6 H H L plied after power up. End-of-conversion will go low between
IN7 H H H 0 and 8 clock pulses after the rising edge of start conversion.
The most important section of the A/D converter is the com-
parator. It is this section which is responsible for the ultimate
CONVERTER CHARACTERISTICS
accuracy of the entire converter. It is also the comparator
drift which has the greatest influence on the repeatability of
The Converter
the device. A chopper-stabilized comparator provides the
The heart of this single chip data acquisition system is its most effective method of satisfying all the converter require-
8-bit analog-to-digital converter. The converter is designed to ments.
give fast, accurate, and repeatable conversions over a wide
The chopper-stabilized comparator converts the DC input
range of temperatures. The converter is partitioned into 3
signal into an AC signal. This signal is then fed throught a
major sections: the 256R ladder network, the successive ap-
high gain AC amplifier and has the DC level restored. This
proximation register, and the comparator. The converter’s
technique limits the drift component of the amplifier since the
digital outputs are positive true.
drift is a DC component which is not passed by the AC am-
The 256R ladder network approach (Figure 1) was chosen plifier. This makes the entire A/D converter extremely insen-
over the conventional R/2R ladder because of its inherent sitive to 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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 Functional Description (Continued)

DS005672-2

FIGURE 1. Resistor Ladder and Switch Tree

DS005672-13
DS005672-14
FIGURE 2. 3-Bit A/D Transfer Curve
FIGURE 3. 3-Bit A/D Absolute Accuracy Curve

DS005672-15

FIGURE 4. Typical Error Curve

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Connection Diagrams
Dual-In-Line Package Molded Chip Carrier Package

DS005672-11

Order Number ADC0808CCN, ADC0809CCN, DS005672-12

ADC0808CCJ or ADC0808CJ Order Number ADC0808CCV or ADC0809CCV

See NS Package J28A or N28A See NS Package V28A

Timing Diagram

DS005672-4

FIGURE 5.

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 Typical Performance Characteristics

DS005672-16 DS005672-17

FIGURE 6. Comparator IIN vs VIN FIGURE 7. Multiplexer RON vs VIN

(VCC = VREF = 5V) (VCC = VREF = 5V)

TRI-STATE Test Circuits and Timing Diagrams

t1H, tH1 t1H, CL = 10 pF tH1, CL = 50 pF

DS005672-18 DS005672-20
DS005672-19

t0H, tH0 t0H, CL = 10 pF tH0, CL = 50 pF

DS005672-23
DS005672-22
DS005672-21

FIGURE 8.

Applications Information VZ = Zero voltage

DX = Data point being measured
OPERATION DMAX = Maximum data limit
DMIN = Minimum data limit
1.0 RATIOMETRIC CONVERSION
A good example of a ratiometric transducer is a potentiom-
The ADC0808, ADC0809 is designed as a complete Data eter used as a position sensor. The position of the wiper is di-
Acquisition System (DAS) for ratiometric conversion sys- rectly proportional to the output voltage which is a ratio of the
tems. In ratiometric systems, the physical variable being full-scale voltage across it. Since the data is represented as
measured is expressed as a percentage of full-scale which is a proportion of full-scale, reference requirements are greatly
not necessarily related to an absolute standard. The voltage reduced, eliminating a large source of error and cost for
input to the ADC0808 is expressed by the equation many applications. A major advantage of the ADC0808,
ADC0809 is that the input voltage range is equal to the sup-
ply range so the transducers can be connected directly
across the supply and their outputs connected directly into
(1) the multiplexer inputs, (Figure 9).
VIN = Input voltage into the ADC0808 Ratiometric transducers such as potentiometers, strain
Vfs = Full-scale voltage gauges, thermistor bridges, pressure transducers, etc., are

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Applications Information (Continued) The top of the ladder, Ref(+), should not be more positive
than the supply, and the bottom of the ladder, Ref(−), should
suitable for measuring proportional relationships; however, not be more negative than ground. The center of the ladder
many types of measurements must be referred to an abso- voltage must also be near the center of the supply because
lute standard such as voltage or current. This means a sys- the analog switch tree changes from N-channel switches to
tem reference must be used which relates the full-scale volt- P-channel switches. These limitations are automatically sat-
age to the standard volt. For example, if VCC = VREF = 5.12V, isfied in ratiometric systems and can be easily met in ground
then the full-scale range is divided into 256 standard steps. referenced systems.
The smallest standard step is 1 LSB which is then 20 mV. Figure 10 shows a ground referenced system with a sepa-
rate supply and reference. In this system, the supply must be
2.0 RESISTOR LADDER LIMITATIONS trimmed to match the reference voltage. For instance, if a
The voltages from the resistor ladder are compared to the 5.12V is used, the supply should be adjusted to the same
selected into 8 times in a conversion. These voltages are voltage within 0.1V.
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.

DS005672-7

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 volt-
shown which generates the supply from the reference. The age should always be near the center of the supply. The sen-
buffer shown can be an op amp of sufficient drive to supply sitivity of the converter can be increased, (i.e., size of the
the milliamp of supply current and the desired bus drive, or if LSB steps decreased) by using a symmetrical reference sys-
a capacitive bus is driven by the outputs a large capacitor will tem. In Figure 13, a 2.5V reference is symmetrically cen-
supply the transient supply current as seen in Figure 12. The tered about VCC/2 since the same current flows in identical
LM301 is overcompensated to insure stability when loaded resistors. This system with a 2.5V reference allows the LSB
by the 10 µF output capacitor. bit to be half the size of a 5V reference system.

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 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 VCC Supply

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Applications Information (Continued)

DS005672-26

FIGURE 12. Typical Reference and Supply Circuit

DS005672-27

RA = RB
*Ratiometric transducers

FIGURE 13. Symmetrically Centered Reference

3.0 CONVERTER EQUATIONS
The transition between adjacent codes N and N+1 is given
by:
(4)
where: VIN = Voltage at comparator input
VREF(+) = Voltage at Ref(+)
(2) VREF(−) = Voltage at Ref(−)
The center of an output code N is given by: VTUE = Total unadjusted error voltage (typically
VREF(+)÷512)

(3)
The output code N for an arbitrary input are the integers
within the range:

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 Applications Information (Continued) If no filter capacitors are used at the analog inputs and the
signal source impedances are low, the comparator input cur-
4.0 ANALOG COMPARATOR INPUTS rent should not introduce converter errors, as the transient
The dynamic comparator input current is caused by the pe- created by the capacitance discharge will die out before the
riodic switching of on-chip stray capacitances. These are comparator output is strobed.
connected alternately to the output of the resistor ladder/ If input filter capacitors are desired for noise reduction and
switch tree network and to the comparator input as part of signal conditioning they will tend to average out the dynamic
the operation of the chopper stabilized comparator. comparator input current. It will then take on the characteris-
The average value of the comparator input current varies di- tics of a DC bias current whose effect can be predicted con-
rectly with clock frequency and with VIN as shown in ventionally.
Figure 6.

Typical Application

DS005672-10

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

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)

Ordering Information
TEMPERATURE RANGE −40˚C to +85˚C −55˚C to +125˚C
Error ± 1⁄2 LSB 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

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Physical Dimensions inches (millimeters) unless otherwise noted

Ceramic Dual-In-Line Package (J)

Order Number ADC0808CCJ or ADC0808CJ
NS Package Number J28A

Molded Dual-In-Line Package (N)

Order Number ADC0808CCN or ADC0809CCN
NS Package Number N28B

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ADC0808/ADC0809 8-Bit µP Compatible A/D Converters with 8-Channel Multiplexer
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Molded Chip Carrier (V)

Order Number ADC0808CCV or ADC0809CCV
NS Package Number V28A

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with instructions for use provided in the labeling, can
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