基于51单片机的数模转换ADC0809的应用-数字电压表资源-CSDN文库

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数模转换

ADC0809的应用

数字电压表

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57.基于51单片机的数模转换 ADC0809 的应用--数字电压表.rar （19个子文件）

57.基于51单片机的数模转换 ADC0809 的应用--数字电压表

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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 con-

verter, 8-channel multiplexer and microprocessor compatible

control logic. The 8-bit A/D converter uses successive ap-

proximation as the conversion technique. The converter fea-

tures a high impedance chopper stabilized comparator, a

256R voltage divider with analog switch tree and a succes-

sive 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 con-

sumes 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 infor-

mation.)

Features

n Easy interface to all microprocessors

n Operates ratiometrically or with 5 V

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 ADC0808 equivalent to MM74C949

n ADC0809 equivalent to MM74C949-1

Key Specifications

n Resolution 8 Bits

n Total Unadjusted Error

⁄

LSB and

1 LSB

n Single Supply 5 V

n Low Power 15 mW

n Conversion Time 100 µs

Block Diagram

00567201

See Ordering

Information

October 2002

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

Connection Diagrams

Dual-In-Line Package

00567211

Order Number ADC0808CCN or ADC0809CCN

See NS Package J28A or N28A

Molded Chip Carrier Package

00567212

Order Number ADC0808CCV or ADC0809CCV

See NS Package V28A

Ordering Information

TEMPERATURE RANGE −40˚C to +85˚C

Error

⁄

LSB Unadjusted ADC0808CCN ADC0808CCV

1 LSB Unadjusted ADC0809CCN ADC0809CCV

Package Outline N28A Molded DIP V28A Molded Chip Carrier

ADC0808/ADC0809

www.national.com 2

Absolute Maximum Ratings (Notes 2,

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage (V

) (Note 3) 6.5V

Voltage at Any Pin −0.3V to

+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

=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

Operating Conditions (Notes 1, 2)

Temperature Range (Note 1) T

MIN

≤T

MAX

ADC0808CCN,ADC0809CCN −40˚C≤T

≤+85˚C

ADC0808CCV, ADC0809CCV −40˚C≤T

≤+85˚C

Range of V

(Note 1) 4.5 V

to 6.0 V

Electrical Characteristics

Converter Specifications: V

=5 V

REF+

REF(−)

=GND, T

MIN

≤T

MAX

and f

CLK

=640 kHz unless otherwise stated.

Symbol Parameter Conditions Min Typ Max Units

ADC0808

Total Unadjusted Error 25˚C

⁄

LSB

(Note 5) T

MIN

to T

MAX

⁄

LSB

ADC0809

Total Unadjusted Error 0˚C to 70˚C

1 LSB

(Note 5) T

MIN

to T

MAX

⁄

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

+0.10 V

REF(+)

Voltage, Top of Ladder Measured at Ref(+) V

+0.1 V

Voltage, Center of Ladder V

/2-0.1 V

/2 V

/2+0.1 V

REF(−)

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

Comparator Input Current f

=640 kHz, (Note 6) −2

0.5 2 µA

Electrical Characteristics

Digital Levels and DC Specifications: ADC0808CCN, ADC0808CCV, ADC0809CCN and ADC0809CCV, 4.75≤V

≤5.25V,

−40˚C≤T

≤+85˚C unless otherwise noted

Symbol Parameter Conditions Min Typ Max Units

ANALOG MULTIPLEXER

OFF(+)

OFF Channel Leakage Current V

=5V, V

=5V,

=25˚C 10 200 nA

MIN

to T

MAX

1.0 µA

OFF(−)

OFF Channel Leakage Current V

=5V, V

=0,

=25˚C −200 −10 nA

MIN

to T

MAX

−1.0 µA

CONTROL INPUTS

IN(1)

Logical “1” Input Voltage V

−1.5 V

IN(0)

Logical “0” Input Voltage 1.5 V

IN(1)

Logical “1” Input Current V

=15V 1.0 µA

(The Control Inputs)

IN(0)

Logical “0” Input Current V

=0 −1.0 µA

(The Control Inputs)

Supply Current f

CLK

=640 kHz 0.3 3.0 mA

ADC0808/ADC0809

www.national.com3

Electrical Characteristics (Continued)

Digital Levels and DC Specifications: ADC0808CCN, ADC0808CCV, ADC0809CCN and ADC0809CCV, 4.75≤V

≤5.25V,

−40˚C≤T

≤+85˚C unless otherwise noted

Symbol Parameter Conditions Min Typ Max Units

DATA OUTPUTS AND EOC (INTERRUPT)

OUT(1)

Logical “1” Output Voltage V

= 4.75V

OUT

= −360µA

OUT

= −10µA

2.4

4.5

V(min)

OUT(0)

Logical “0” Output Voltage I

=1.6 mA 0.45 V

OUT(0)

Logical “0” Output Voltage EOC I

=1.2 mA 0.45 V

OUT

TRI-STATE Output Current V

=5V 3 µA

=0 −3 µA

Electrical Characteristics

Timing Specifications V

REF(+)

=5V, V

REF(−)

=GND, t

=20 ns and T

=25˚C unless otherwise noted.

Symbol Parameter Conditions MIn Typ Max Units

Minimum Start Pulse Width (Figure 5) 100 200 ns

WALE

Minimum ALE Pulse Width (Figure 5) 100 200 ns

Minimum Address Set-Up Time (Figure 5)2550ns

Minimum Address Hold Time (Figure 5)2550ns

Analog MUX Delay Time R

=0Ω (Figure 5) 1 2.5 µs

From ALE

OE Control to Q Logic State C

=50 pF, R

=10k (Figure 8) 125 250 ns

OE Control to Hi-Z C

=10 pF, R

=10k (Figure 8) 125 250 ns

Conversion Time f

=640 kHz, (Figure 5) (Note 7) 90 100 116 µs

Clock Frequency 10 640 1280 kHz

EOC

EOC Delay Time (Figure 5) 0 8+2 µS Clock

Periods

Input Capacitance At Control Inputs 10 15 pF

OUT

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 V

to GND and has a typical breakdown voltage of 7 V

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

n supply. The spec allows 100 mV forward bias of either diode. This means that as long as the analog V

does not exceed the supply voltage

by more than 100 mV, the output code will be correct. To achieve an absolute 0V

to 5V

input voltage range will therefore require a minimum supply voltage of

4.900 V

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.

ADC0808/ADC0809

www.national.com 4

Functional Description

Multiplexer. The device contains an 8-channel single-ended

analog signal multiplexer. A particular input channel is se-

lected by using the address decoder. Table 1 shows the input

states for the address lines to select any channel. The

address is latched into the decoder on the low-to-high tran-

sition of the address latch enable signal.

TABLE 1.

SELECTED ADDRESS LINE

ANALOG CHANNEL C B A

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. A non-monotonic relationship can cause

oscillations that will be catastrophic for the system. Addition-

ally, the 256R network does not cause load variations on the

reference voltage.

The bottom resistor and the top resistor of the ladder net-

work 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 transi-

tion occurs when the analog signal has reached +

⁄

LSB

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 con-

verter. 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

start 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. Con-

tinuous 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 be-

tween 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 com-

parator drift which has the greatest influence on the repeat-

ability of the device. A chopper-stabilized comparator pro-

vides 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

www.national.com5

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