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ADS574KE Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer ADS574KE
Beschreibung Microprocessor-Compatible Sampling CMOS ANALOG-TO-DIGITAL CONVERTER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 13 Seiten
ADS574KE Datasheet, Funktion
®
ADS574
ADS574
ADS574
ADS574
Microprocessor-Compatible Sampling
CMOS ANALOG-TO-DIGITAL CONVERTER
FEATURES
q REPLACES ADC574 FOR NEW DESIGNS
q COMPLETE SAMPLING A/D WITH
REFERENCE, CLOCK AND
MICROPROCESSOR INTERFACE
q FAST ACQUISITION AND CONVERSION:
25µs max
q ELIMINATES EXTERNAL SAMPLE/HOLD
IN MOST APPLICATIONS
q GUARANTEED AC AND DC PERFORMANCE
q SINGLE +5V SUPPLY OPERATION
q LOW POWER: 100mW max
q PACKAGE OPTIONS: 0.6" and 0.3" DIPs,
SOIC
DESCRIPTION
The ADS574 is a 12-bit successive approximation
analog-to-digital converter using an innovative
capacitor array (CDAC) implemented in low-power
CMOS technology. This is a drop-in replacement for
ADC574 models in most applications, with internal
sampling, much lower power consumption, and capa-
bility to operate from a single +5V supply.
The ADS574 is complete with internal clock, micro-
processor interface, three-state outputs, and internal
scaling resistors for input ranges of 0V to +10V, 0V to
+20V, ±5V, or ±10V. The maximum throughput time
for 12-bit conversions is 25µs over the full operating
temperature range, including both acquisition and con-
version.
Complete user control over the internal sampling func-
tion facilitates elimination of external sample/hold
amplifiers in most existing designs.
The ADS574 requires +5V, with –12V or –15V op-
tional, depending on usage. No +15V supply is re-
quired. Available packages include 0.3" or 0.6" wide
28-pin plastic DIPs and 28-lead SOICs.
Control
Inputs
Bipolar Offset
20V Range
10V Range
2.5V Reference
Input
2.5V Reference
Output
CDAC
Control Logic
Clock
+
Comparator
Successive
Approximation
Register
2.5V
Reference
Status
Parallel
Data
Output
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
© 1991 Burr-Brown Corporation
PDS-1104F
Printed in U.S.A. July, 1993






ADS574KE Datasheet, Funktion
THEORY OF OPERATION
In the ADS574, the advantages of advanced CMOS technol-
ogy—high logic density, stable capacitors, precision analog
switches—and Burr-Brown’s state of the art laser trimming
techniques are combined to produce a fast, low power
analog-to-digital converter with internal sample/hold.
The charge-redistribution successive-approximation circuitry
converts analog input voltages into digital words.
A simple example of a charge-redistribution A/D converter
with only 3 bits is shown in Figure 1.
Analog
Input
Signal
SC Comparator
4C
S
S1
2C
S2
C
S3
RG RG RG
L
o
g
i
c
Out
Reference
Input
+
FIGURE 1. 3-Bit Charge Redistribution A/D.
INPUT SCALING
Precision laser-trimmed scaling resistors at the input divide
standard input ranges (0V to +10V, 0V to +20V, ±5V or
±10V) into levels compatible with the CMOS characteristics
of the internal capacitor array.
SAMPLING
While sampling, the capacitor array switch for the MSB
capacitor (S1) is in position “S”, so that the charge on the
MSB capacitor is proportional to the voltage level of the
analog input signal. The remaining array switches (S2 and
S3) are set to position “G”. Switch SC is closed, setting the
comparator input offset to zero.
CONVERSION
When a conversion command is received, switch S1 is opened
to trap a charge on the MSB capacitor proportional to the
analog input level at the time of the sampling command, and
switch SC is opened to float the comparator input. The charge
trapped in the capacitor array can now be moved between the
three capacitors in the array by connecting switches S1, S2, and
S3 to positions “R” (to connect to the reference) or “G” (to
connect to GND), thus changing the voltage generated at the
comparator input.
During the first approximation, the MSB capacitor is con-
nected through switch S1 to the reference, while switches S2
and S3 are connected to GND. Depending on whether the
comparator output is HIGH or LOW, the logic will then
latch S1 in position “R” or “G”. Similarly, the second
approximation is made by connecting S2 to the reference and
S3 to GND, and latching S2 according to the output of the
comparator. After three successive approximation steps have
been made the voltage level at the comparator will be within
1/2LSB of GND, and a digital word which represents the
analog input can be determined from the positions of S1, S2
and S3.
OPERATION
BASIC OPERATION
Figure 2 shows the minimum circuit required to operate the
ADS574 in a basic ±10V range in the Control Mode (dis-
cussed in detail in a later section.) The falling edge of a
Convert Command (a pulse taking pin 5 LOW for a mini-
mum of 25ns) both switches the ADS574 input to the hold
state and initiates the conversion. Pin 28 (STATUS) will
output a HIGH during the conversion, and falls only after the
conversion is completed and the data has been latched on the
data output pins (pins 16 to 27.) Thus, the falling edge of
STATUS on pin 28 can be used to read the data from the
conversion. Also, during conversion, the STATUS signal
puts the data output pins in a High-Z state and inhibits the
input lines. This means that pulses on pin 5 are ignored, so
that new conversions cannot be initiated during the conver-
sion, either as a result of spurious signals or to short-cycle
the ADS574.
The ADS574 will begin acquiring a new sample as soon as
the conversion is completed, even before the STATUS
output falls, and will track the input signal until the next
conversion is started. The ADS574 is designed to complete
a conversion and accurately acquire a new signal in 25µs
max over the full operating temperature range, so that
conversions can take place at a full 40kHz.
CONTROLLING THE ADS574
The Burr-Brown ADS574 can be easily interfaced to most
microprocessor systems and other digital systems. The
microprocessor may take full control of each conversion, or
the converter may operate in a stand-alone mode, controlled
only by the R/C input. Full control consists of selecting an
8- or 12-bit conversion cycle, initiating the conversion, and
reading the output data when ready—choosing either 12 bits
all at once, or the 8 MSB bits followed by the 4 LSB bits in
a left-justified format. The five control inputs (12/8, CS, A0,
R/C, and CE) are all TTL/CMOS-compatible. The functions
of the control inputs are described in Table II. The control
function truth table is shown in Table III.
STAND-ALONE OPERATION
For stand-alone operation, control of the converter is accom-
plished by a single control line connected to R/C. In this
mode CS and A0 are connected to digital common and CE
and 12/8 are connected to +5V. The output data are pre-
sented as 12-bit words. The stand-alone mode is used in
systems containing dedicated input ports which do not
require full bus interface capability.
®
ADS574
6

6 Page









ADS574KE pdf, datenblatt
+VCC
R1
100k
Unipolar
Offset
Adjust
Full-Scale
Adjust
R2
100k
–VCC
100
2.5V
10
8
Ref In
Ref Out
ADS574
100
R3
Analog
Input
10V
Range
12 Bipolar Offset
13
Analog
Common
20V
Range
14
9
FIGURE 10. Unipolar Configuration.
Full-Scale Adjust
R2
100
10 Ref In
2.5V 8 Ref Out
ADS574
Bipolar
Offset
Adjust
100
R1
12 Bipolar Offset
Analog
Input
10V
Range
20V
Range
Analog
Common
13
14
9
FIGURE 11. Bipolar Configuration.
If the 10V analog input range is used (either bipolar or
unipolar), the 20V range input (pin 14) should be shielded
with ground plane to reduce noise pickup.
Coupling between analog input and digital lines should be
minimized by careful layout. For instance, if the lines must
cross, they should do so at right angles. Parallel analog and
digital lines should be separated from each other by a pattern
connected to common.
If external full scale and offset potentiometers are used, the
potentiometers and associated resistors should be as close as
possible to the ADS574.
POWER SUPPLY DECOUPLING
On the ADS574, +5V (to Pin 1) is the only power supply
required for correct operation. Pin 7 is not connected inter-
nally, so there is no problem in existing ADC574 sockets
where this is connected to +15V. Pin 11 (VEE) is only used
as a logic input to select modes of control over the sampling
function as described above. When used in an existing
ADC574 socket, the –15V on pin 11 selects the ADC574
Emulation Mode. Since pin 11 is used as a logic input, it is
immune to typical supply variations.
The +5V supply should be bypassed with a 10µF tantalum
capacitor located close to the converter to promote noise-
free operations, as shown in Figure 2. Noise on the power
supply lines can degrade the converter’s performance. Noise
and spikes from a switching power supply are especially
troublesome.
RANGE CONNECTIONS
The ADS574 offers four standard input ranges: 0V to +10V,
0V to +20V, ±5V, or ±10V. Figures 10 and 11 show the
necessary connections for each of these ranges, along with
the optional gain and offset trim circuits. If a 10V input
range is required, the analog input signal should be con-
nected to pin 13 of the converter. A signal requiring a 20V
range is connected to pin 14. In either case the other pin of
the two is left unconnected. Pin 12 (Bipolar Offset) is
connected either to Pin 9 (Analog Common) for unipolar
operation, or to Pin 8 (2.5V Ref Out), or the external
reference, for bipolar operation. Full-scale and offset adjust-
ments are described below.
The input impedance of the ADS574 is typically 84kin the
20V ranges and 21kin the 10V ranges. This is signifi-
cantly higher than that of traditional ADC574 architectures,
reducing the load on the input source in most applications.
INPUT STRUCTURE
Figure 12 shows the resistor divider input structure of the
ADS574. Since the input is driving a capacitor in the CDAC
during acquisition, the input is looking into a high imped-
Pin 14
20V Range
68k
Pin 13
10V Range
34k
34k
Capacitor
Array
Bipolar
Offset
Pin 12
17k
10k
®
ADS574
FIGURE 12. ADS574 Input Structure.
12

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