Document Outline
- FEATURES
- DESCRIPTION
- APPLICATIONS
- ABSOLUTE MAXIMUM RATINGS(
- PACKAGE/ORDERING INFORMATION
- PRODUCT FAMILY
- ELECTRICAL CHARACTERISTICS
- PIN CONFIGURATION
- PIN DESCRIPTIONS
- TYPICAL CHARACTERISTICS
- THEORY OF OPERATION
- ANALOG INPUT
- BIPOLAR INPUT
- DELTA-SIGMA MODULATOR
- REFERENCE INPUT
- DIGITAL FILTER
- CONTROL LOGIC
- DOUT/DRDY\
- SYNCHRONIZING MULTIPLE CONVERTERS
- POWER-DOWN MODE
- SERIAL INTERFACE
- ISOLATION
- LAYOUT
- POWER SUPPLY
- GROUNDING
- DECOUPLING
- SYSTEM CONSIDERATIONS
ADS1
251
24-Bit, 20kHz, Low-Power
ANALOG-TO-DIGITAL CONVERTER
FEATURES
q
24 BITS--NO MISSING CODES
q
19 BITS EFFECTIVE RESOLUTION UP TO
20kHz DATA RATE
q
LOW NOISE: 1.5ppm
q
DIFFERENTIAL INPUTS
q
INL: 15ppm (max)
q
EXTERNAL REFERENCE (0.5V to 5V)
q
POWER-DOWN MODE
q
SYNC MODE
q
LOW POWER: 8mW at 20kHz
5mW at 10kHz
DESCRIPTION
The ADS1251 is a precision, wide dynamic range, delta-
sigma, Analog-to-Digital (A/D) converter with 24-bit resolu-
tion operating from a single +5V supply. The delta-sigma
architecture features wide dynamic range, and 24 bits of no
missing code performance. Effective resolution of 19 bits
(1.5ppm of rms noise) is achieved at conversion rates up to
20kHz.
The ADS1251 is designed for high-resolution measurement
applications in cardiac diagnostics, smart transmitters, indus-
trial process control, weigh scales, chromatography, and
portable instrumentation. The converter includes a flexible,
2-wire synchronous serial interface for low-cost isolation.
The ADS1251 is a single-channel converter and is offered in
an SO-8 package. It is pin-compatible with the faster ADS1252
(41.7kHz data rate).
APPLICATIONS
q
CARDIAC DIAGNOSTICS
q
DIRECT THERMOCOUPLE INTERFACES
q
BLOOD ANALYSIS
q
INFRARED PYROMETERS
q
LIQUID/GAS CHROMATOGRAPHY
q
PRECISION PROCESS CONTROL
4th-Order
Modulator
Digital
Filter
Serial
Interface
Control
+V
IN
CLK
V
REF
SCLK
DOUT/DRDY
+V
DD
GND
V
IN
ADS1251
ADS1251
SBAS184A MARCH 2001 REVISED SEPTEMBER 2003
www.ti.com
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright 2001-2003, Texas Instruments Incorporated
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
ADS1251
2
SBAS184A
www.ti.com
Analog Input: Current ...............................................
100mA, Momentary
10mA, Continuous
Voltage .................................... GND 0.3V to V
DD
+ 0.3V
V
DD
to GND ............................................................................ 0.3V to 6V
V
REF
Voltage to GND ............................................... 0.3V to V
DD
+ 0.3V
Digital Input Voltage to GND ................................... 0.3V to V
DD
+ 0.3V
Digital Output Voltage to GND ................................. 0.3V to V
DD
+ 0.3V
Operating Temperature ...................................................... 40
C to 85
C
Lead Temperature (soldering, 10s) .............................................. +300
C
Power Dissipation .......................................................................... 500mW
ABSOLUTE MAXIMUM RATINGS
(1)
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Texas
Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper han-
dling and installation procedures can cause damage.
ESD damage can range from subtle performance degrada-
tion to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
NOTE: (1) Stresses above those listed under "Absolute Maximum Ratings"
may cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.
SPECIFIED
PACKAGE
TEMPERATURE
PACKAGE
ORDERING
TRANSPORT
PRODUCT
PACKAGE-LEAD
DESIGNATOR
(1)
RANGE
MARKING
NUMBER
MEDIA, QUANTITY
ADS1251
SO-8
D
40
C to +85
C
ADS1251U
ADS1251U
Rails, 100
"
"
"
"
"
ADS1251U/2K5
Tape and Reel, 2500
NOTE: (1) For the most current specifications and package information, refer to our web site at www.ti.com.
PACKAGE/ORDERING INFORMATION
ELECTRICAL CHARACTERISTICS
All specifications at T
MIN
to T
MAX
, V
DD
= +5V, CLK = 8MHz, and V
REF
= 4.096, unless otherwise specified.
ADS1251U
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ANALOG INPUT
Full-Scale Input Voltage
+V
IN
(V
IN
)
V
REF
V
Absolute Input Voltage
+V
IN
or V
IN
to GND
0.3
V
DD
V
Differential Input Impedance
CLK = 3.84kHz
430
M
CLK = 1MHz
1.7
M
CLK = 8MHz
210
k
Input Capacitance
6
pF
Input Leakage
At +25
C
5
50
pA
At T
MIN
to T
MAX
1
nA
DYNAMIC CHARACTERISTICS
Data Rate
20.8
kHz
Bandwidth
3dB, CLK = 8MHz
4.24
kHz
Serial Clock (SCLK)
8
MHz
System Clock Input (CLK)
8
MHz
ACCURACY
Integral Nonlinearity
Differential Input
0.0002
0.0015
% of FSR
THD
1kHz Input; 0.1dB below FS
105
dB
Noise
1.5
2.5
ppm of FSR, rms
Resolution
24
Bits
No Missing Codes
24
Bits
Common-Mode Rejection
60Hz, AC
90
98
dB
Gain Error
0.1
1
% of FSR
Offset Error
30
100
ppm of FSR
Gain Sensitivity to V
REF
1:1
Power-Supply Rejection Ratio
70
80
dB
PERFORMANCE OVER TEMPERATURE
Offset Drift
0.07
ppm/
C
Gain Drift
0.4
ppm/
C
PRODUCT
# OF INPUTS
MAXIMUM DATA RATE
COMMENTS
ADS1250
1 Differential
25.0kHz
Includes PGA from 1 to 8
ADS1251
1 Differential
26.8kHz
ADS1252
1 Differential
41.7kHz
ADS1253
4 Differential
20.8kHz
ADS1254
4 Differential
20.8kHz
Includes Separate Analog and Digital Supplies
PRODUCT FAMILY
ADS1251
3
SBAS184A
www.ti.com
ELECTRICAL CHARACTERISTICS
(Cont.)
All specifications at T
MIN
to T
MAX
, V
DD
= +5V, CLK = 8MHz, and V
REF
= 4.096, unless otherwise specified.
ADS1251U
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VOLTAGE REFERENCE
V
REF
0.5
4.096
V
DD
V
Load Current
32
A
DIGITAL INPUT/OUTPUT
Logic Family
CMOS
Logic Level: V
IH
+4.0
+V
DD
+ 0.3
V
V
IL
0.3
+0.8
V
V
OH
I
OH
= 500
A
+4.5
V
V
OL
I
OL
= 500
A
0.4
V
Input (SCLK, CLK) Hysteresis
0.6
V
Data Format
Offset Binary Two's Complement
POWER-SUPPLY REQUIREMENTS
Operation
+4.75
+5
+5.25
VDC
Quiescent Current
V
DD
= +5VDC
1.5
2
mA
Operating Power
7.5
10
mW
Power-Down Current
0.4
1
A
TEMPERATURE RANGE
Operating
40
+85
C
Storage
60
+100
C
PIN CONFIGURATION
Top View
SO
PIN DESCRIPTIONS
PIN
NAME
PIN DESCRIPTION
1
+V
IN
Analog Input: Positive Input of the Differen-
tial Analog Input
2
V
IN
Analog Input: Negative Input of the Differ-
ential Analog Input.
3
+V
DD
Input: Power-Supply Voltage, +5V
4
CLK
Digital Input: Device System Clock. The
system clock is in the form of a CMOS-
compatible clock. This is a Schmitt-Trigger
input.
5
DOUT/DRDY
Digital Output: Serial Data Output/Data
Ready. This output indicates that a new
output word is available from the ADS1251
data output register. The serial data is
clocked out of the serial data output shift
register using SCLK.
6
SCLK
Digital Input: Serial Clock. The serial clock
is in the form of a CMOS-compatible clock.
The serial clock operates independently
from the system clock, therefore, it is pos-
sible to run SCLK at a higher frequency
than CLK. The normal state of SCLK is
LOW. Holding SCLK HIGH will either ini-
tiate a modulator reset for synchronizing
multiple converters or enter power-down
mode. This is a Schmitt-Trigger input.
7
GND
Input: Ground
8
V
REF
Analog Input: Reference Voltage Input
+V
IN
ADS1251U
GND
V
IN
V
REF
+V
DD
SCLK
DOUT/DRDY
CLK
1
2
3
4
8
7
6
5
ADS1251
4
SBAS184A
www.ti.com
TYPICAL CHARACTERISTICS
At T
A
= +25
C, V
DD
= +5V, CLK = 8MHz, and V
REF
= 4.096, unless otherwise specified.
RMS NOISE vs DATA RATE
Data Rate (Hz)
100
10
10k
1k
100k
RMS Noise (ppm of FS)
2.0
1.6
1.2
0.8
0.4
0
EFFECTIVE RESOLUTION vs DATA OUTPUT RATE
Data Output Rate (Hz)
1k
100
10k
100k
Ef
fective Resolution (Bits)
20.0
19.5
19.0
18.5
18.0
2.0
1.8
1.6
1.4
1.2
1.0
RMS NOISE vs TEMPERATURE
Temperature (
C)
40
20
0
20
40
60
80
100
RMS Noise (ppm of FS)
19.5
19.0
18.5
18.0
EFFECTIVE RESOLUTION vs TEMPERATURE
Temperature (
C)
40
20
0
20
40
60
80
100
Effective Resolution (Bits)
18
16
14
12
10
8
6
4
2
0
V
REF
Voltage (V)
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
RMS Noise (
V)
RMS NOISE vs V
REF
VOLTAGE
14
12
10
8
6
4
2
0
V
REF
Voltage (V)
0
1
2
3
4
5
RMS Noise (ppm of FS)
RMS NOISE vs V
REF
VOLTAGE
ADS1251
5
SBAS184A
www.ti.com
TYPICAL CHARACTERISTICS
(Cont.)
At T
A
= +25
C, V
DD
= +5V, CLK = 8MHz, and V
REF
= 4.096, unless otherwise specified.
2.0
1.5
1.0
0.5
0
Input Voltage (V)
5
4
3
2
1
0
1
2
3
4
5
RMS Noise (ppm of FS)
RMS NOISE vs INPUT VOLTAGE
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
INTEGRAL NONLINEARITY vs TEMPERATURE
Temperature (
C)
40
20
0
20
40
60
80
100
INL (ppm of FS)
5
4
3
2
1
0
INTEGRAL NONLINEARITY vs DATA OUTPUT RATE
Data Output Rate (Hz)
100
1k
10k
100k
INL (ppm of FS)
40
35
30
25
20
15
10
5
0
OFFSET vs TEMPERATURE
Temperature (
C)
40
20
0
20
40
60
80
100
Offset (ppm of FS)
650
625
600
575
550
525
500
GAIN ERROR vs TEMPERATURE
Temperature (
C)
40
20
0
20
40
60
80
100
Gain Error (ppm of FS)
60
65
70
75
80
85
90
95
100
POWER-SUPPLY REJECTION RATIO
vs CLK FREQUENCY
Clock Frequency (MHz)
1
2
3
4
5
6
7
8
PSRR (dB)
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