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ADS1245
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
Low-Power, 24-Bit
Analog-to-Digital Converter
FEATURES
D20-Bit Effective Resolution
DHigh-Impedance Buffered Input
D±2.5V Differential Input Range
DPin-Compatible with ADS1244
D0.0006% INL (typ), 0.0015% INL (max)
DSimple Two-Wire Serial Interface
DSimultaneous 50Hz and 60Hz Rejection
DSingle Conversions with Sleep Mode
DSingle-Cycle Settling
DSelf-Calibration
DWell Suited for Multi-Channel Systems
DEasily Connects to the MSP430
DCurrent Consumption: 158µA
DAnalog Supply: 2.5V to 5.25V
DDigital Supply: 1.8V to 3.6V
APPLICATIONS
DHand-Held Instrumentation
DPortable Medical Equipment
DIndustrial Process Control
DTest and Measurement Systems
DESCRIPTION
The ADS1245 is a 24-bit, delta-sigma analog-to-digital
converter (ADC). It offers excellent performance and very
low power in an MSOP-10 package and is well suited for
demanding high-resolution measurements, especially in
portable and other space- and power-constrained
systems.
The buffered input presents an impedance of 3GΩ, mini-
mizing measurement errors when using high-impedance
sources. The ADS1245 is compatible with ADS1244 and
offers a direct upgrade path for designs requiring higher input impedance.
A third-order delta-sigma (∆Σ) modulator and digital filter
form the basis of the ADC. The analog modulator has a
±2.5V differential input range. The digital filter rejects both
50Hz and 60Hz signals, completely settles in one cycle,
and outputs data at 15 samples per second (SPS).
A simple, two-wire serial interface provides all the
necessary control. Data retrieval, self-calibration, and
Sleep mode are handled with a few simple waveforms.
When only single conversions are needed, the ADS1245
can be shut down (Sleep mode) while idle between
measurements to dramatically reduce the overall power
dissipation. Multiple ADS1245s can be connected
together to create a synchronously sampling multichannel
measurement system. The ADS1245 is designed to easily
connect to microcontrollers, such as the MSP430.
The ADS1245 supports 2.5V to 5.25V analog supplies and
1.8V to 3.6V digital supplies. Power is typically less than
470µW in normal operation and less than 1µW during
Sleep mode.
VREFP VREFNAVDD
AINP
AINN
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For the most current specifications and package information, refer to our web site at www.ti.com.
PACKAGE
DESIGNATOR
(1)
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
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ORDERING
NUMBER
ADS1245IDGSTTape and Reel, 250
ADS1245IDGSRTape and Reel, 2500
TRANSPORT
MEDIA, QUANTITY
ABSOLUTE MAXIMUM RATINGS
over operat i n g f ree-air temperature range unless otherwise noted
ADS1245UNIT
AVDD to GND−0.3 to +6V
DVDD to GND−0.3 to +3.6V
Input Current100, momentarymA
Input Current10, continuousmA
Analog Input Voltage to GND−0.5 to AVDD + 0.5V
Analog Input Voltage to GND−0.3 to DVDD + 0.3V
Digital Output Voltage to GND−0.3 to DVDD + 0.3V
Maximum Junction Temperature+150°C
Operating Temperature Range−40 to +85°C
Storage Temperature Range−60 to +150°C
Lead Tem perature (soldering, 10s)+300°C
(1)
Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods
may degrade device reliability. These are stress ratings only , an d
functional operation of the device at these or any other conditions
beyond those specified is not implied.
This integrated circuit can be damaged by ESD. Texas
Instruments recommends that all integrated circuits be
handled with appropriate precautions. Failure to observe
proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to
complete device failure. Precision integrated circuits may be more
susceptible t o damage because very small parametric changes could
cause the device not to meet its published specifications.
(1)
PIN ASSIGNMENTS
DGS PACKAGE
MSOP
(TOP VIEW)
ADS1245
GND
VREFP
VREFN
AINN
AINP
1
2
3
4
5
10
9
8
7
6
CLK
SCLK
DRDY/DOUT
DVDD
AVDD
Terminal Functions
TERMINAL
NAMENO.DESCRIPTION
GND1Analog and digital ground
VREFP2Positive reference input
VREFN3Negative reference input
AINN4Negative analog input
AINP5Positive analog input
AVDD6Analog power supply, 2.5V to 5.25V
DVDD7Digital power supply, 1.8V to 3.6V
DRDY/DOUT8Dual-purpose output:
Data ready: indicates valid data by going low.
Data output: outputs data, MSB first, on the
first rising edge of SCLK.
SCLK9Serial clock input: clocks out data on the
rising edge. Used to initiate calibration and
Sleep mode (see text for more details).
CLK10System clock input: typically 2.4576MHz
2
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Common-mode rejection
Normal-mode rejection
Logic levels
AVDD current
DVDD current
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
"#$%&
ELECTRICAL CHARACTERISTICS
All specifications at TA = −40°C to +85°C, AVDD = +5V, DVDD = +3V, f
PARAMETERTEST CONDITIONSMINTYPMAXUNIT
Analog Input
Full-scale input voltage rangeAINP − AINN±2V
Absolute input rangeAINP, AINN with respect to GNDGND + 0.1AVDD − 1.25V
Differential input impedancef
System Performance
ResolutionNo missing codes24Bits
Data ratef
Integral nonlinearity (INL)Differential input signal, end point fit±0.0006±0.0015%FSR
Offset error114ppm of FSR
Offset error drift
Gain error
Gain error drift
Common-mode rejection
Input referred noise2
Analog power-supply rejectionAt DC, ∆AVDD = 5%100dB
Digital power-supply rejectionAt DC, ∆AVDD = 5%100dB
Voltage Reference Input
Reference input voltage (V
Negative reference input (VREFN)GND − 0.1VREFP − 0.5V
Positive reference input (VREFP)VREFN + 0.5AVDD + 0.1V
Voltage reference impedancef
Recalibration can reduce these errors to the level of the noise.
(4)
Achieving specified gain error performance requires that calibration be performed with reference voltage input between (GND + 0.1V) and
(AVDD − 1.25V). See Voltage Reference Inputs section.
(5)
fCM is the frequency of the common-mode input.
(6)
f
SIG
(7)
It will not be possible to reach the digital output full-scale code when VIN > 2V