TEXAS INSTRUMENTS ADS1245 Technical data

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ADS1245
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
Low-Power, 24-Bit
Analog-to-Digital Converter
FEATURES
D 20-Bit Effective Resolution D High-Impedance Buffered Input D ±2.5V Differential Input Range D Pin-Compatible with ADS1244 D 0.0006% INL (typ), 0.0015% INL (max) D Simple Two-Wire Serial Interface D Simultaneous 50Hz and 60Hz Rejection D Single Conversions with Sleep Mode D Single-Cycle Settling D Self-Calibration D Well Suited for Multi-Channel Systems D Easily Connects to the MSP430 D Current Consumption: 158µA D Analog Supply: 2.5V to 5.25V D Digital Supply: 1.8V to 3.6V
APPLICATIONS
D Hand-Held Instrumentation D Portable Medical Equipment D Industrial Process Control D Test 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 VREFN AVDD
AINP
AINN
semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
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Buffer
3rd−Order Modulator
Digital
Filter
GND
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DVDD
Serial
Interface
CLK
DRDY/DOUT
SCLK
Copyright 2003, Texas Instruments Incorporated
"#$%&
ADS1245
MSOP-10
DGS
−40°C to +85°C
BHI
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
ORDERING INFORMATION
PRODUCT PACKAGE−LEAD
(1)
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
ADS1245IDGST Tape and Reel, 250 ADS1245IDGSR Tape and Reel, 2500
TRANSPORT
MEDIA, QUANTITY
ABSOLUTE MAXIMUM RATINGS
over operat i n g f ree-air temperature range unless otherwise noted
ADS1245 UNIT
AVDD to GND −0.3 to +6 V DVDD to GND −0.3 to +3.6 V Input Current 100, momentary mA Input Current 10, continuous mA Analog Input Voltage to GND −0.5 to AVDD + 0.5 V Analog Input Voltage to GND −0.3 to DVDD + 0.3 V Digital Output Voltage to GND −0.3 to DVDD + 0.3 V 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
NAME NO. DESCRIPTION
GND 1 Analog and digital ground VREFP 2 Positive reference input VREFN 3 Negative reference input AINN 4 Negative analog input AINP 5 Positive analog input AVDD 6 Analog power supply, 2.5V to 5.25V DVDD 7 Digital power supply, 1.8V to 3.6V DRDY/DOUT 8 Dual-purpose output:
Data ready: indicates valid data by going low. Data output: outputs data, MSB first, on the first rising edge of SCLK.
SCLK 9 Serial clock input: clocks out data on the
rising edge. Used to initiate calibration and Sleep mode (see text for more details).
CLK 10 System 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
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Analog Input
Full-scale input voltage range AINP − AINN ±2V Absolute input range AINP, AINN with respect to GND GND + 0.1 AVDD − 1.25 V Differential input impedance f
System Performance
Resolution No missing codes 24 Bits Data rate f Integral nonlinearity (INL) Differential input signal, end point fit ±0.0006 ±0.0015 %FSR Offset error 1 14 ppm of FSR Offset error drift Gain error Gain error drift
Common-mode rejection
Input referred noise 2 Analog power-supply rejection At DC, AVDD = 5% 100 dB
Digital power-supply rejection At DC, AVDD = 5% 100 dB
Voltage Reference Input
Reference input voltage (V Negative reference input (VREFN) GND − 0.1 VREFP − 0.5 V Positive reference input (VREFP) VREFN + 0.5 AVDD + 0.1 V Voltage reference impedance f
Digital Input/Output
Input leakage (CLK, SCLK) 0 < (CLK, SCLK) < DVDD ±10 µA CLK frequency (f CLK duty cycle 30 70 %
Power Supply
AVDD 2.7 5.25 V DVDD 1.8 3.6 V
AVDD current
DVDD current
Total power dissipation AVDD = DVDD = 3V 0.47 mW (1)
SPS = samples per second.
(2)
FSR = full-scale range = 4V
(3)
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
(3)
(4)
(3)
) V
REF
VIH (CLK, SCLK) 0.8 DVDD 5.25 V VIL (CLK, SCLK) GND 0.2 DVDD V VOH (DRDY, DOUT) IOH = 1mA DVDD − 0.4 DVDD V VOL (DRDY, DOUT) IOL = 1mA GND DVDD + 0.4 V
) 6 MHz
CLK
.
REF
is the frequency of the input signal.
= 2.4576MHz 3 G
CLK
= 2.4576MHz 15 SPS
CLK
At DC 90 100 dB
(5)
f
= 50 ± 1Hz, f
CM
fCM = 60 ± 1Hz, f
(6)
f
= 50 ± 1Hz, f
SIG
f
= 60 ± 1Hz, f
SIG
VREFP − VREFN 0.5 1.25 AVDD
REF
= 2.4576MHz 1 M
CLK
Sleep mode 0.1 1 µA AVDD = 3V 152 µA AVDD = 5V 158 250 µA Sleep mode, CLK stopped 0.1 µA Sleep mode, 2.4576MHZ CLK running 1.6 5 µA DVDD = 3V 5 10 µA
CLK
= 2.4576MHz 100 dB
CLK
CLK
= 2.4576MHz 70 dB
CLK
= 2.4576MHz, and V
CLK
= 2.4576MHz 100 dB
= 2.4576MHz 60 dB
.
REF
= +1.25V , unless otherwise noted.
REF
REF
0.01 ppm of FSR/°C
0.005 0.1 %
0.5 ppm/°C
(7)
ppm of FSR,
RMS
V
(1)
V
(2)
3
"#$%&
ANALOG CURRENT vs ANALOG SUPPLY
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
TYPICAL CHARACTERISTICS
At TA = +25°C, AVDD = +5V, DVDD = +3V, f
CLK
= 2.4576MHz, and V
= +1.25V , unless otherwise specified.
REF
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220 210 200 190 180
A)
µ
170 160 150
Current (
140 130 120 110 100
ANALOG CURRENT vs TEMPERATURE
AVDD = +5V, f
45
5
25 35 55 75 95
= 4.9152MHz
CLK
AVDD = +3V, f
15
Temp erature (_C)
CLK
=2.4576MHz
12
10
8
A)
µ
6
Current (
4
2
0
45
Figure 1
164 162 160
A)
158
µ
156 154
Current(
152 150 148
f
=4.9152Hz
CLK
f
=2.4576MHz
CLK
Analog Supply (V)
4.03.53.0 4.5 5.0 5.52.5
16 14 12
A)
10
µ
8 6
Current (
4 2 0
DIGITALCURRENT vs TEMPERATURE
DVDD = +3V, f
DVDD = +1.8V, f
25 35 55 75 95
15
5
Temperature (_C)
= 4.9152MHz
CLK
CLK
Figure 2
DIGITALCURRENT vs DIGITALSUPPLY
f
= 4.9152MHz
CLK
f
= 2.4576MHz
CLK
25 35 55 75 95
45
15
5
Digital Supply (V)
= 2.4576MHz
Figure 3
INTEGRAL NONLINEARITY vs ANALOG SUPPLY
= 2.4 or (( 1.8)/2 + 0.3), whichever is smaller
V
CM
30
25
20
15
10
INL (ppm of FSR)
5
0
T=+85_C
V
REF
AVDD
= 1.25; f
AVDD
Figure 5
4
= 2.4576MHz
OSC
T= 40_C
T=+25_C
4.03.53.0 4.5 5.0 5.52.5 (V)
Figure 4
12.5
10.0
7.5
5.0
2.5 0
2.5
INL (ppm of FSR)
5.0
7.5
10.0
12.5
2.5
INTEGRAL NONLINEARITY vs V
T=+25_C
T=+85_C
T=−40_C
1.5
0.5 0.5 1.5 2.5 VIN(V)
IN
Figure 6
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OFFSET vs TEMPERATURE
GAIN vs TEMPERATURE
Gain (Normalized)
HISTOGRAM OF OUTPUT DATA
TYPICAL CHARACTERISTICS
At TA = +25°C, AVDD = +5V, DVDD = +3V, f
= 2.4576MHz, and V
CLK
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
= +1.25V , unless otherwise specified.
REF
"#$%&
5 4 3 2 1 0
1
2
3
Normalized Offset (ppm of FSR)
4
5
45
25 35 55 75 95
15
5
Temperat ure (_C)
Figure 7
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
Noise (ppm of FSR, RMS)
1.6
1.4
1.2
2.5
NOISE vs INPUT SIGNAL
1.5
0.5 0.5 1.5 2.5 VIN(V)
1.00006
1.00005
1.00004
1.00003
1.00002
1.00001
1.00000
0.99999
0.99998
0.99997
0.99996
0.99995
0.99994
3.0
2.5
2.0
1.5
1.0
Noise (ppm of FSR, RMS)
0.5
25 35 55 75 95
45
15
5
Temperature (_C)
Figure 8
NOISE vs TEMPERATURE
0
45
25 35 55 75 95
15
5
Temperature (_C)
Figure 9
COMMON−MODE REJECTION RATIO
900 800 700 600 500 400 300
Number of Occurences
200 100
0
10
−9−8−7−6−5−4−3−2−
−14−12−
1
012345678
ppmof FSR
Figure 11
9
101112
160 140 120 100
80
CMRR (dB)
60 40 20
0
Figure 10
vs FREQUENCY
1k10010 10k 100k1
Frequency (Hz)
Figure 12
5
"#$%&
ANALOGPOWER−SUPPLY REJECTION RATIO
SBAS287A − JUNE 2003 − REVISED SEPTEMBER 2003
TYPICAL CHARACTERISTICS
At TA = +25°C, AVDD = +5V, DVDD = +3V, f
CLK
= 2.4576MHz, and V
= +1.25V , unless otherwise specified.
REF
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DIGITALPOWER−SUPPLYREJECTION RATIO
140
120
100
80
60
PSRR (dB)
40
20
0
vs FREQUENCY
1k10010 10k 100k1
Frequency (Hz)
140
120
100
80
60
PSRR (dB)
40
20
0
Figure 13
vs FREQUENCY
1k10010 10k 100k1
Frequency (Hz)
Figure 14
6
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