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Teilenummer | ADC0808CJ |
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Beschreibung | 8-Bit uP Compatible A/D Converters with 8-Channel Multiplexer | |
Hersteller | National Semiconductor | |
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Gesamt 14 Seiten October 1999
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, ex-
cellent 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 mul-
tiplexer 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 VDC 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
n Total Unadjusted Error
n Single Supply
n Low Power
n Conversion Time
8 Bits
±1⁄2 LSB and ±1 LSB
5 VDC
15 mW
100 µs
Block Diagram
See Ordering
Information
TRI-STATE® is a registered trademark of National Semiconductor Corp.
© 1999 National Semiconductor Corporation DS005672
DS005672-1
www.national.com
Functional Description (Continued)
FIGURE 1. Resistor Ladder and Switch Tree
DS005672-2
DS005672-13
FIGURE 2. 3-Bit A/D Transfer Curve
DS005672-14
FIGURE 3. 3-Bit A/D Absolute Accuracy Curve
FIGURE 4. Typical Error Curve
DS005672-15
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6
6 Page Applications Information (Continued)
4.0 ANALOG COMPARATOR INPUTS
The dynamic comparator input current is caused by the pe-
riodic 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 di-
rectly with clock frequency and with VIN as shown in
Figure 6.
Typical Application
If no filter capacitors are used at the analog inputs and the
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
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 characteris-
tics of a DC bias current whose effect can be predicted con-
ventionally.
*Address latches needed for 8085 and SC/MP interfacing the ADC0808 to a microprocessor
DS005672-10
PROCESSOR
8080
8085
Z-80
SC/MP
6800
TABLE 2. Microprocessor Interface Table
READ
MEMR
RD
RD
NRDS
VMA•φ2•R/W
WRITE
MEMW
WR
WR
NWDS
VMA•φ•R/W
INTERRUPT (COMMENT)
INTR (Thru RST Circuit)
INTR (Thru RST Circuit)
INT (Thru RST Circuit, Mode 0)
SA (Thru Sense A)
IRQA or IRQB (Thru PIA)
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12
12 Page | ||
Seiten | Gesamt 14 Seiten | |
PDF Download | [ ADC0808CJ Schematic.PDF ] |
Teilenummer | Beschreibung | Hersteller |
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