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PDF AD7575 Data sheet ( Hoja de datos )
| Número de pieza | AD7575 | |
| Descripción | 8-Bit ADC | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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FEATURES
Fast Conversion Time: 5 s
On-Chip Track/Hold
Low Total Unadjusted Error: 1 LSB
Full Power Signal Bandwidth: 50 kHz
Single +5 V Supply
100 ns Data Access Time
Low Power (15 mW typ)
Low Cost
Standard 18-Lead DlPs or 20-Terminal
Surface Mount Packages
LC2MOS
5 s 8-Bit ADC with Track/Hold
AD7575
AIN
AGND
VREF
CLK
FUNCTIONAL BLOCK DIAGRAM
TRACK
AND
HOLD
VDD
COMP
AD7575
CLOCK
OSCILLATOR
DAC
SAR
CS
LATCH AND
DB7
RD
TP
CONTROL
LOGIC
THREE STATE
OUTPUT DRIVERS
DB0
GENERAL DESCRIPTION
The AD7575 is a high speed 8-bit ADC with a built-in track/
hold function. The successive approximation conversion tech-
nique is used to achieve a fast conversion time of 5 µs, while the
built-in track/hold allows full-scale signals up to 50 kHz (386 mV/µs
slew rate) to be digitized. The AD7575 requires only a single +5 V
supply and a low cost, 1.23 V bandgap reference in order to convert
an input signal range of 0 to 2 VREF.
The AD7575 is designed for easy interfacing to all popular 8-bit
microprocessors using standard microprocessor control signals
(CS and RD) to control starting of the conversion and reading of
the data. The interface logic allows the AD7575 to be easily
configured as a memory mapped device, and the part can be
interfaced as SLOW-MEMORY or ROM. All data outputs of
the AD7575 are latched and three-state buffered to allow direct
connection to a microprocessor data bus or I/O port.
The AD7575 is fabricated in an advanced, all ion-implanted high
speed Linear Compatible CMOS (LC2MOS) process and is
available in a small, 0.3" wide, 18-lead DIP, 18-lead SOIC or in
other 20-terminal surface mount packages.
BUSY
DGND
PRODUCT HIGHLIGHTS
1. Fast Conversion Time/Low Power
The fast, 5 µs, conversion time of the AD7575 makes it
suitable for digitizing wideband signals at audio and ultra-
sonic frequencies while retaining the advantage of low
CMOS power consumption.
2. On-Chip Track/Hold
The on-chip track/hold function is completely self-contained
and requires no external hold capacitor. Signals with slew
rates up to 386 mV/µs (e.g., 2.46 V peak-to-peak 50 kHz sine
waves) can be digitized with full accuracy.
3. Low Total Unadjusted Error
The zero, full-scale and linearity errors of the AD7575 are so
low that the total unadjusted error at any point on the trans-
fer function is less than 1 LSB, and offset and gain adjust-
ments are not required.
4. Single Supply Operation
Operation from a single +5 V supply with a low cost +1.23 V
bandgap reference allows the AD7575 to be used in 5 V
microprocessor systems without any additional power
supplies.
5. Fast Digital Interface
Fast interface timing allows the AD7575 to interface easily to
the fast versions of most popular microprocessors such as the
Z80H, 8085A-2, 6502B, 68B09 and the DSP processor, the
TMS32010.
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998
1 page  
AD7575
DIP/SOIC
PIN CONFIGURATIONS
LCCC
PLCC
CS 1
RD 2
TP 3
18 VDD
17 VREF
16 AIN
BUSY 4
15 AGND
AD7575
CLK 5 TOP VIEW 14 DB0 (LSB)
(Not to Scale)
DB7 (MSB) 6
13 DB1
DB6 7
12 DB2
DB5 8
11 DB3
DGND 9
10 DB4
3 2 1 20 19
BUSY 4
CLK 5
DB7 (MSB) 6
DB6 7
DB5 8
AD7575
TOP VIEW
(Not to Scale)
18 AIN
17 AGND
16 DB0 (LSB)
15 DB1
14 DB2
9 10 11 12 13
NC = NO CONNECT
TP 4
BUSY 5
CLK 6
DB7 (MSB) 7
DB6 8
3 2 1 20 19
PIN 1
IDENTIFIER
AD7575
TOP VIEW
(Not to Scale)
18 AIN
17 AGND
16 DB0 (LSB)
15 DB1
14 DB2
9 10 11 12 13
NC = NO CONNECT
ORDERING GUIDE
Model1
Temperature
Range
Relative
Accuracy
(LSB)
Package
Options2
AD7575JR
AD7575JN
AD7575KN
AD7575JP
AD7575KP
AD7575AQ
AD7575BQ
AD7575SQ
AD7575TQ
AD7575SE
AD7575TE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
–25°C to +85°C
–25°C to +85°C
–55°C to +125°C
–55°C to +125°C
–55°C to +125°C
–55°C to +125°C
± 1 max
± 1 max
± 1/2 max
± 1 max
± 1/2 max
± 1 max
± 1/2 max
± 1 max
± 1/2 max
± 1 max
± 1/2 max
R-18
N-18
N-18
P-20A
P-20A
Q-18
Q-18
Q-18
Q-18
E-20A
E-20A
NOTES
1To order MIL-STD-883, Class B process parts, add /883B to part number.
Contact local sales office for military data sheet. For U.S. Standard Military
Drawing (SMD), see DESC drawing #5962-87762.
2E = Leadless Ceramic Chip Carrier; N = Plastic DIP; P = Plastic Leaded Chip
Carrier; Q = Cerdip, R = SOIC.
TERMINOLOGY
LEAST SIGNIFICANT BIT (LSB)
An ADC with 8-bits resolution can resolve 1 part in 28 (i.e.,
256) of full scale. For the AD7575 with +2.46 V full-scale one
LSB is 9.61 mV.
TOTAL UNADJUSTED ERROR
This is a comprehensive specification that includes full-scale
error, relative accuracy and offset error.
RELATIVE ACCURACY
Relative Accuracy is the deviation of the ADC’s actual code
transition points from a straight line drawn between the devices
measured first LSB transition point and the measured full-scale
transition point.
SNR
Signal-to-Noise Ratio (SNR) is the ratio of the desired signal to
the noise produced in the sampled and digitized analog signal.
SNR is dependent on the number of quantization levels used in
the digitization process; the more levels, the smaller the quantiza-
tion noise. The theoretical SNR for a sine wave input is given by
SNR = (6.02 N + 1.76) dB
where N is the number of bits in the ADC.
FULL-SCALE ERROR (GAIN ERROR)
The gain of a unipolar ADC is defined as the difference between
the analog input levels required to produce the first and the last
digital output code transitions. Gain error is a measure of the
deviation of the actual span from the ideal span of FS – 2 LSBs.
ANALOG INPUT RANGE
With VREF = +1.23 V, the maximum analog input voltage range
is 0 V to +2.46 V. The output data in LSBs is related to the
analog input voltage by the integer value of the following
expression:
256 AIN
Data (LSBs) = 2 VREF + 0.5
SLEW RATE
Slew Rate is the maximum allowable rate of change of input
signal such that the digital sample values are not in error. Slew
Rate limitations may restrict the analog signal bandwidth for
full-scale analog signals below the bandwidth allowed from
sampling theorem considerations.
–4– REV. B
5 Page 
AD7575
APPLICATION HINTS
1. NOISE: Both the input signal lead to AIN and the signal
return lead from AGND should be kept as short as possible to
minimize input-noise coupling. In applications where this is
not possible, either a shielded cable or a twisted pair transmis-
sion line between source and ADC is recommended. Also,
since any potential difference in grounds between the signal
source and ADC appears as an error voltage in series with the
input signal, attention should be paid to reducing the ground
circuit impedance as much as possible. In general, the source
resistance should be kept below 2 kΩ. Larger values of source
resistance can cause undesired system noise pickup.
2. PROPER LAYOUT: Layout for a printed circuit board
should ensure that digital and analog lines are kept separated
as much as possible. In particular, care should be taken not to
run any digital track alongside an analog signal track. Both the
analog input and the reference input should be screened by
AGND. A single point analog ground separate from the logic
system ground, should be established at or near the AD7575.
This single point analog ground subsystem should be con-
nected to the digital system ground by a single-track connec-
tion only. Any reference bypass capacitors, analog input filter
capacitors or input signal shielding should be returned to the
analog ground point.
AD7575 WITH AD589 REFERENCE
The AD7575 8-bit A/D converter features a total unadjusted
error specification over its entire operating temperature range.
This total unadjusted error includes all errors in the A/D con-
verter—offset, full scale and linearity. The one feature not pro-
vided on the AD7575 is a voltage reference. This section
discusses the use of the AD589 bandgap reference with the
AD7575, and gives the combined reference and ADC error
budget over the full operating temperature range. This allows
the user to compare the combined AD589/AD7575 errors to
ADCs whose specifications include on-chip references.
Two distinct application areas exist. The first is where the refer-
ence voltage and the analog input voltage are derived from the
same source. In other words, if the reference voltage varies, the
analog input voltage range varies by a ratioed amount. In this
case, the user is not worried about the absolute value of the
reference voltage. The second case is where changes in the refer-
ence voltage are not matched by changes in the analog input
voltage range. Here, the absolute value of the reference voltage,
and its drift over temperature, are of prime importance. Both
applications are discussed below.
If the analog input range varies with the reference voltage, the
part is said to be operating ratiometrically. This is representative
of many applications. If the reference is on-chip, and the user
does not have access to it, it is not possible to get ratiometric
operation. Since the AD7575 uses an external reference, it can
be used in ratiometric applications. However, because the part is
specified with a reference of +1.23 V ± 5%, then the voltage
range for ratiometric operation is limited.
The error analysis over temperature of ratiometric applications
is different from nonratiometric ones. Since the reference and
analog input voltage range are ratioed to each other, tempera-
ture variations in the reference are matched by variations in the
analog input range. Therefore, the AD589 contributes no addi-
tional errors over temperature to the system errors, and the
combined total unadjusted error specification for the AD589
and AD7575 is as per the total unadjusted error specification in
this data sheet.
With nonratiometric applications, however, the analog input
range stays the same if the reference varies and a full-scale error
is introduced. The amount by which the reference varies deter-
mines the amount of error introduced. The AD589 is graded on
temperature coefficient; therefore, selection of different grades
allows the user to tailor the amount of error introduced to suit
the system requirements. The reference voltage from the AD589
can lie between 1.2 V and 1.25 V. This reference voltage can be
adjusted for the desired full-scale voltage range using the circuit
outlined in Figure 19. For example, if an analog input voltage
range of 0 V to +2.46 V is required, the reference should be
adjusted to +1.23 V. Once the reference is adjusted to the de-
sired value at 25°C, the total error is as per the total unadjusted
error specification on the AD7575 specification pages. (To
reduce this still further, offset and full-scale errors of the
AD7575 can be adjusted out using the calibration procedure
outlined in this data sheet.)
+5V
6.8k⍀
10k⍀*
1k⍀*
+5V
AD589
+
–
10k⍀*
TLC271*
*ONLY REQUIRED IF IT IS NECESSARY TO ADJUST
THE ABSOLUTE VALUE OF REFERENCE VOLTAGE.
Figure 19. Reference Adjust Circuit
However, it is as the temperature varies from 25°C that the
AD589 starts to introduce errors. The typical temperature char-
acteristics of the AD589 are shown in Figure 20. The tempera-
ture coefficients (TCs) represent the slopes of the diagonals of
the error band from +25°C to TMIN and +25°C to TMAX. The
AD589 TC is specified in ppm/°C max and is offered in four
different grades.
–10–
REV. B
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet AD7575.PDF ] | |
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