TI ADS1282SJDJ

ADS1282-HT
AD
S1
282
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
HIGH-RESOLUTION ANALOG-TO-DIGITAL CONVERTER
Check for Samples: ADS1282-HT
FEATURES
1
•
•
•
•
•
•
•
•
•
•
Analog Supply:
Unipolar (5 V) or Bipolar (±2.5 V)
Digital Supply: 1.75 V to 3.3 V
SUPPORTS EXTREME TEMPERATURE
APPLICATIONS
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•
High Resolution:
122-dB SNR
(250 SPS, High-Resolution Mode, 210°C)
119-dB SNR
(250 SPS, Low-Power Mode, 210°C)
High Accuracy:
THD: –102 dB (210°C)
INL: 0.5 ppm
Low-Noise PGA
Two-Channel Input MUX
Inherently-Stable Modulator with Fast
Responding Over-Range Detection
Flexible Digital Filter:
Sinc + FIR + IIR (Selectable)
Linear or Minimum Phase Response
Programmable High-Pass Filter
Selectable FIR Data Rates: 250 SPS to 4 kSPS
Filter Bypass Option
Low Power Consumption:
High-Resolution Mode: 30 mW (210°C)
Low-Power Mode: 22 mW (210°C)
Offset and Gain Calibration Engine
SYNC Input
•
•
•
•
•
•
•
•
•
Controlled Baseline
One Assembly/Test Site
One Fabrication Site
Available in Extreme (–55°C to 210°C)
Temperature Range
Extended Product Life Cycle
Extended Product-Change Notification
Product Traceability
Texas Instruments high temperature products
utilize highly optimized silicon (die) solutions
with design and process enhancements to
maximize performance over extended
temperatures.
APPLICATIONS
•
•
•
•
•
Energy Exploration
Seismic Monitoring
High-Accuracy Instrumentation
Down-Hole Drilling
High Temperature Environments
DESCRIPTION
The ADS1282 is an extremely high-performance, single-chip analog-to-digital converter (ADC) with an integrated,
low-noise programmable gain amplifier (PGA) and two-channel input multiplexer (MUX). The ADS1282 is
suitable for the demanding needs of energy exploration and seismic monitoring environments.
The converter uses a fourth-order, inherently stable, delta-sigma (ΔΣ) modulator that provides outstanding noise
and linearity performance. The modulator is used either in conjunction with the on-chip digital filter, or can be
bypassed for use with post processing filters.
The flexible input MUX provides an additional external input for measurement, as well as internal self-test
connections. The PGA features outstanding low noise (5nV/√Hz) and high input impedance, allowing easy
interfacing to geophones and hydrophones over a wide range of gains.
The digital filter provides selectable data rates from 250 to 4000 samples per second (SPS). The high-pass filter
(HPF) features an adjustable corner frequency. On-chip gain and offset scaling registers support system
calibration.
The synchronization input (SYNC) can be used to synchronize the conversions of multiple ADS1282s. The
SYNC input also accepts a clock input for continuous alignment of conversions from an external source.
1
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.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Two operating modes allow optimization of noise and power. Together, the amplifier, modulator, and filter
dissipate 30 mW and only 22 mW in low-power mode. The ADS1282 is fully specified from –55°C to 210°C or
from –55°C to 175°C for the PW package.
AVDD
VREFN
VREFP
DVDD
CLK
ADS1282
MUX
Input 1
Input 2
4th-Order
DS
Modulator
PGA
Programmable
Digital Filter
SCLK
DOUT
DIN
DRDY
SPI
Interface
Calibration
VCOM
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Over-Range
Modulator Output
Control
3
AVSS
SYNC
RESET
PWDN
DGND
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 to damage because very small parametric changes could cause the device not to meet its published specifications.
Table 1. ORDERING INFORMATION (1)
TA
–55°C to 210°C
–55°C to 175°C
(1)
(2)
PACKAGE (2)
ORDERABLE PART NUMBER
TOP-SIDE MARKING
KGD
ADS1282SKGDA
NA
JDJ
ADS1282SJDJ
ADS1282SJDJ
PW (Preview only)
ADS1282HPW
ADS1282HPW
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
Web site at www.ti.com.
Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines are available at
www.ti.com/sc/package.
BARE DIE INFORMATION
DIE THICKNESS
BACKSIDE FINISH
BACKSIDE
POTENTIAL
BOND PAD
METALLIZATION COMPOSITION
15 mils.
Silicon with backgrind
GND
Al-Si-Cu (0.5%)
Origin
a
c
b
d
2
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Table 2. Bond Pad Coordinates in Microns - Rev A
DISCRIPTION
PAD NUMBER
a
b
c
d
CLK
1
1512.6
31.45
1588.6
107.45
SCLK
2
1827.6
31.45
1903.6
107.45
DRDY
3
2127.3
31.05
2203.3
107.05
DOUT
4
2310.6
214.35
2386.6
290.35
DIN
5
2310.25
502.25
2386.25
578.25
DGND
6
2310.25
910.05
2386.25
986.05
MCLK
7
2310.6
1199.15
2386.6
1275.15
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M1
8
2310.6
1488.35
2386.6
1564.35
M0
9
2310.6
1776.35
2386.6
1852.35
SYNC
10
2310.25
2834.9
2386.25
2910.9
MFLAG
11
2310.65
3233.7
2386.65
3309.7
DGND
12
2084.3
3455.35
2160.3
3531.35
CAPN
13
1655.95
3467.6
1731.95
3543.6
CAPP
14
1386.05
3467.6
1462.05
3543.6
AINP2
15
715.95
3467.6
791.95
3543.6
AINN2
16
526.05
3467.6
602.05
3543.6
AINP1
17
356.05
3467.6
432.05
3543.6
AINN1
18
166.05
3467.6
242.05
3543.6
AVDD
19
25.7
2705.15
101.7
2781.15
AVDD
20
25.7
2609.6
101.7
2685.6
AVSS
21
25.7
2481.2
101.7
2557.2
AVSS
22
25.8
2329.1
101.8
2405.1
VREFN
23
19.2
2220.4
95.2
2296.4
VREFP
24
19.2
2110.4
95.2
2186.4
PWDN
25
31.45
927.5
107.45
1003.5
RESET
26
31.45
630.5
107.45
706.5
DGND
27
31.45
214.1
107.45
290.1
DVDD
28
190.3
31.35
266.3
107.35
DGND
29
389.1
31.35
465.1
107.35
BYPAS
30
503.4
31.35
579.4
107.35
Copyright © 2009–2011, Texas Instruments Incorporated
3
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
½
2417.7 mm
¾
DRDY
SCLK
DGND
CLK
½
½
www.ti.com
DVDD
BYPAS
DGND
DOUT
¾
RESET
DIN
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¾
PWDN
M1
M0
3564.55 mm
MCLK
PAD #1
DGND
VREFP
38 mm
VREFN
AVSS
AVSS
AVDD
AVDD
SYNC
MFLAG
4
CAPN
CAPP
AINP2
½
DGND
½
0.0
0.0
AINN1
AINP1
½
AINN2
39 mm
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
DEVICE INFORMATION
JDJ OR PW PACKAGE
(TOP VIEW)
1
28
BYPAS
2
27
DGND
¾
DRDY
3
26
DVDD
DOUT
4
25
DGND
DIN
5
24
¾
RESET
DGND
6
23
¾
PWDN
MCLK
7
22
VREFP
M1
8
21
VREFN
M0
9
20
AVSS
SYNC
10
19
AVDD
MFLAG
11
18
AINN1
DGND
12
17
AINP1
CAPN
13
16
AINN2
CAPP
14
15
AINP2
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CLK
SCLK
TERMINAL FUNCTIONS
NO.
NAME
CLK
SCLK
DRDY
DOUT
DIN
MCLK
M1
M0
SYNC
MFLAG
DGND
CAPN
DESCRIPTION
KGD
JDJ/PW
FUNCTION
1
1
Digital input
Master clock input
2
2
Digital input
Serial clock input
3
3
Digital output
Data ready output: read data on falling edge
4
4
Digital output
Serial data output
5
5
Digital input
Serial data input
7
7
Digital I/O
Modulator clock output; if in modulator mode:
MCLK: Modulator clock output
Otherwise, the pin is an unused input (must be tied).
8
8
Digital I/O
Modulator data output 1; if in modulator mode:
M1: Modulator data output 1
Otherwise, the pin is an unused input (must be tied).
9
9
Digital I/O
Modulator data output 0; if in modulator mode:
M0: Modulator data output 0
Otherwise, the pin is an unused input (must be tied).
10
10
Digital input
11
11
Digital output
Synchronize input
Modulator Over-Range flag: 0 = normal, 1 = modulator over-range
6, 12,
27, 29
6, 12,
25, 27
Digital ground
Digital ground, pin 12 is the key ground point
13
13
Analog
PGA outputs: Connect 10-nF capacitor from CAPP to CAPN
14
14
Analog
PGA outputs: Connect 10-nF capacitor from CAPP to CAPN
15
15
Analog input
Positive analog input 2
16
16
Analog input
Negative analog input 2
17
17
Analog input
Positive analog input 1
AINN1
18
18
Analog input
AVDD
19, 20
19
Analog supply
Positive analog power supply
Negative analog power supply
CAPP
AINP2
AINN2
AINP1
Negative analog input 1
AVSS
21, 22
20
Analog supply
VREFN
23
21
Analog input
Negative reference input
VREFP
24
22
Analog input
Positive reference input
PWDN
25
23
Digital input
Power-down input, active low
RESET
26
24
Digital input
DVDD
28
26
Digital supply
BYPAS
30
28
Analog
Copyright © 2009–2011, Texas Instruments Incorporated
Reset input, active low
Digital power supply: 1.8 V to 3.3 V
Sub-regulator output: Connect 1-μF capacitor to DGND
5
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range (unless otherwise noted).
ADS1282
UNIT
AVDD to AVSS
–0.3 to 5.5
V
AVSS to DGND
–2.8 to 0.3
V
DVDD to DGND
–0.3 to 3.9
V
100, momentary
mA
10, continuous
mA
AVSS – 0.3 to AVDD + 0.3
V
Input current
Input current
Analog input voltage
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–0.3 to DVDD + 0.3
Digital input voltage to DGND
Operating temperature range
KGD and JDJ packages
–55 to 210
PW package
–55 to 175
–60 to 210
Storage temperature range
(1)
V
°C
°C
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, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
THERMAL INFORMATION
ADS1282
THERMAL METRIC
θJA
θJCtop
θJB
ψJT
θJCbot
(1)
(2)
(3)
(4)
(5)
(6)
6
PW
28 PINS
28 PINS
Junction-to-ambient thermal resistance (1)
43.1
54.6
Junction-to-case (top) thermal resistance (2)
14.03
11.3
Junction-to-board thermal resistance (3)
23.2
13
n/a
0.5
Junction-to-board characterization parameter (5)
n/a
12.7
Junction-to-case (bottom) thermal resistance (6)
4.98
n/a
Junction-to-top characterization parameter
ψJB
JDJ
(4)
UNITS
°C/W
The junction-to-ambient thermal resistance under natural convection is obtained in a simulation on a JEDEC-standard, high-K board, as
specified in JESD51-7, in an environment described in JESD51-2a.
The junction-to-case (top) thermal resistance is obtained by simulating a cold plate test on the package top. No specific
JEDEC-standard test exists, but a close description can be found in the ANSI SEMI standard G30-88.
The junction-to-board thermal resistance is obtained by simulating in an environment with a ring cold plate fixture to control the PCB
temperature, as described in JESD51-8.
The junction-to-top characterization parameter, ψJT, estimates the junction temperature of a device in a real system and is extracted
from the simulation data for obtaining θJA, using a procedure described in JESD51-2a (sections 6 and 7).
The junction-to-board characterization parameter, ψJB, estimates the junction temperature of a device in a real system and is extracted
from the simulation data for obtaining θJA , using a procedure described in JESD51-2a (sections 6 and 7).
The junction-to-case (bottom) thermal resistance is obtained by simulating a cold plate test on the exposed (power) pad. No specific
JEDEC standard test exists, but a close description can be found in the ANSI SEMI standard G30-88.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ELECTRICAL CHARACTERISTICS
Limit specifications at –55°C to 210°C. Typical specifications at 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK (1) = 4.096 MHz, VREFP = 2.5 V,
VREFN = –2.5 V, DVDD = 3.3 V, CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
PARAMETER
CONDITIONS
TA = 210°C (2)
TA = –55°C to 125°C
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
ANALOG INPUTS
±VREF/(2 ×
PGA)
VIN = (AINP – AINN)
Full-scale input voltage
Absolute input range
AINP
or AINN
AVDD –
1.25
AVSS +
0.7
5
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Differential input impedance
(3)
Common-mode input impedance
Input bias current
Crosstalk
AVDD –
1.25
AVSS +
0.7
PGA input voltage noise density
V
f = 31.25 Hz
MUX on-resistance
V
nV/√Hz
1
GΩ
100
MΩ
1
1000
nA
–128
–123
dB
30
45
Ω
PGA OUTPUT (CAPP, CAPN)
AVDD – 0.4
AVSS +
0.4
Absolute output range
AVSS +
0.4
AVDD – 0.4
V
PGA differential output impedance
600
600
Ω
Output impedance tolerance
±10
±10
%
External bypass capacitance
10
Modulator differential input
impedance
100
10
nF
High-resolution mode
55
kΩ
Low-power mode
110
kΩ
AC PERFORMANCE
Signal-to-noise ratio (4)
SNR
High-resolution mode
112
124
110
122
Low-power mode
109
121
107
119
dB
High-resolution mode
Total harmonic
distortion (5)
THD
Spurious-free dynamic
range
PGA = 1...16
–122
–99
–102
–99
PGA = 32
–117
–99
–98
–94
PGA = 64
–115
dB
–93
Low-power mode
PGA = 1...16
–122
–99
–108
–90
PGA = 32
–113
–99
–95
–91
PGA = 64
–109
SFDR
dB
–87
dB
123
DC PERFORMANCE
Resolution
Data rate
Integral nonlinearity (INL)
Offset error
fDATA
(6)
Offset error after calibration (8)
Offset drift
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
No missing codes
31
FIR filter mode
250
4000
250
4000
SPS
Sinc filter mode
8000
128,000
8000
128,000
SPS
Differential input
Shorted input
31
Bits
0.00005
0.0090
0.002
0.0100
%
FSR (7)
50
200
99
250
μV
1
2
μV
0.02
0.19
μV/°C
fCLK = system clock.
Minimum and maximum parameters are characterized for operation at TA = 210°C, but may not be production tested at that
temperature. Production test limits with statistical guardbands are used to ensure high temperature performance.
Input impedance is improved by disabling input chopping (CHOP bit = 0).
VIN = 20mVDC/PGA, see Table 3.
VIN = 31.25 Hz, –0.5 dBFS.
Best-fit method.
FSR: Full-scale range = ±VREF/(2 × PGA).
Calibration accuracy is on the level of noise reduced by 4 (calibration averages 16 readings).
Copyright © 2009–2011, Texas Instruments Incorporated
7
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Limit specifications at –55°C to 210°C. Typical specifications at 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK (1) = 4.096 MHz,
VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V, CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000
SPS, unless otherwise noted.
PARAMETER
CONDITIONS
Gain error (9)
MIN
TYP
MAX
MIN
High-resolution mode
–1.5
–1.0
–0.5
Low-power mode
–1
–0.5
0
Gain error after calibration (8)
TYP
MAX
–1.5
–1
–0.5
–1
–0.48
0
0.0002
PGA = 1
2
PGA = 16
9
Gain matching (10)
0.3
fCM = 60Hz (11)
Common-mode rejection
Power-supply rejection
AVDD,
AVSS
fPS = 60Hz (11)
DVDD
%
%
%
3
ppm/°C
11
0.8
82
UNIT
0.0002
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Gain drift
TA = 210°C (2)
TA = –55°C to 125°C
82
110
80
90
83
90
115
101
0.5
5
ppm/°C
0.8
137
%
dB
dB
VOLTAGE REFERENCE INPUTS
(VREF = VREFP –
VREFN)
Reference input voltage
(AVDD –
AVSS) +
0.2
0.5
(AVDD –
AVSS) +
0.2
Negative reference input
VREFN
AVSS –
0.1
VREFP –
0.5
AVSS –
0.1
VREFP –
0.5
Positive reference input
VREFP
VREFN +
0.5
AVDD + 0.1
VREFN +
0.5
AVDD + 0.1
Reference input impedance
V
V
V
High-resolution mode
85
85
kΩ
Low-power mode
170
170
kΩ
DIGITAL FILTER RESPONSE
Passband ripple
±0.003
dB
Passband (–0.01 dB)
0.375 × fDATA
Hz
Bandwidth (–3 dB)
0.413 × fDATA
Hz
High-pass filter corner
0.1
Stop band attenuation (12)
135
Stop band
Group delay
10
Hz
dB
0.500 × fDATA
Settling time (latency)
Minimum phase filter (13)
5/fDATA
Linear phase filter
31/fDATA
Minimum phase filter
62/fDATA
Linear phase filter
62/fDATA
Hz
s
s
DIGITAL INPUT/OUTPUT
VIH
VIL
IOH = 1mA
VOH
VOL
Input leakage
Clock input
Serial clock rate
(9)
(10)
(11)
(12)
(13)
8
fCLK
fSCLK
0.8 ×
DVDD
DVDD
0.8 X
DVDD
DVDD
DGND
0.2 × DVDD
DGND
0.2 × DVDD
0.8 ×
DVDD
0.8 X
DVDD
V
V
V
IOL = 1mA
0.2 × DVDD
0.2 × DVDD
V
0 < VDIGITAL IN < DVDD
±10
±10
μA
1
4.096
fCLK/2
1
4.096
MHz
fCLK/2
MHz
The PGA output impedance and the modulator input impedance results in –1% systematic gain error (high-resolution mode) and –0.5%
error (low-power mode).
Gain match relative to PGA = 1.
fCM is the input common-mode frequency. fPS is the power-supply frequency.
Input frequencies in the range of NfCLK/512 ± fDATA/2 (N = 1, 2, 3...) can mix with the modulator chopping clock. In these frequency
ranges intermodulation = 120 dB, typ.
At dc. See Figure 49.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Limit specifications at –55°C to 210°C. Typical specifications at 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK (1) = 4.096 MHz,
VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V, CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000
SPS, unless otherwise noted.
PARAMETER
CONDITIONS
TA = 210°C (2)
TA = –55°C to 125°C
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
POWER SUPPLY
AVSS
–2.6
0
–2.6
0
V
AVDD
AVSS +
4.75
AVSS +
5.25
AVSS +
4.75
AVSS +
5.25
V
3.6
1.75
1.75
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DVDD
High-resolution mode
AVDD, AVSS current
DVDD current
Power dissipation
4.5
7.2
5.2
3.6
V
10
|mA|
Low-power mode
3
4.6
3.5
8
|mA|
Standby mode
68
110
3000
3700
|μA|
Power-down mode
68
110
3000
3700
|μA|
All modes
0.6
1.5
1.2
2
Modulator mode
0.1
1.1
mA
mA
μA
Standby mode
73
175
576
950
Power-down mode (14)
32
120
186
240
μA
High-reolution mode
25
41
29.7
56.1
mW
Low-power mode
17
28
21.5
46.1
mW
Standby mode
0.58
1.1
16.9
21.6
mW
Power-down mode
0.45
0.95
15.6
19.3
mW
(14) CLK input stopped.
Copyright © 2009–2011, Texas Instruments Incorporated
9
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (PW PACKAGE)
Limit specifications at –55°C to 175°C. Typical specifications at 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK (1) = 4.096 MHz, VREFP = 2.5 V,
VREFN = –2.5 V, DVDD = 3.3 V, CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
PARAMETER
CONDITIONS
TA = 175°C (2)
TA = –55°C to 125°C
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
ANALOG INPUTS
±VREF/(2 ×
PGA)
VIN = (AINP – AINN)
Full-scale input voltage
Absolute input range
AINP
or AINN
5
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Differential input impedance
Input bias current
f = 31.25 Hz
MUX on-resistance
V
AVDD –
1.25
AVSS +
0.7
5
(3)
Common-mode input impedance
Crosstalk
AVDD –
1.25
AVSS +
0.7
PGA input voltage noise density
±VREF/(2 ×
PGA)
V
nV/√Hz
1
1
GΩ
100
100
MΩ
1
1000
nA
–128
–123
dB
30
45
Ω
PGA OUTPUT (CAPP, CAPN)
AVDD – 0.4
AVSS +
0.4
Absolute output range
AVSS +
0.4
AVDD – 0.4
V
PGA differential output impedance
600
600
Ω
Output impedance tolerance
±10
±10
%
External bypass capacitance
10
Modulator differential input
impedance
10
nF
High-resolution mode
55
100
55
kΩ
Low-power mode
110
110
kΩ
AC PERFORMANCE
Signal-to-noise ratio (4)
SNR
High-resolution mode
112
124
112
122
Low-power mode
109
121
109
119
dB
High-resolution mode
Total harmonic
distortion (5)
THD
Spurious-free dynamic
range
PGA = 1...16
–122
–99
–112
–99
PGA = 32
–117
–99
–106
–94
PGA = 64
–115
dB
–102
Low-power mode
PGA = 1...16
–122
–99
–109
–90
PGA = 32
–113
–99
–103
–99
PGA = 64
–109
SFDR
dB
–98
dB
123
DC PERFORMANCE
Resolution
Data rate
Integral nonlinearity (INL)
Offset error
fDATA
(6)
Offset error after calibration (8)
Offset drift
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
10
No missing codes
31
FIR filter mode
250
4000
250
4000
SPS
Sinc filter mode
8000
128,000
8000
128,000
SPS
Differential input
Shorted input
31
Bits
0.00005
0.0090
0.00004
0.0090
%
FSR (7)
50
200
50
200
μV
1
2
μV
0.02
0.19
μV/°C
fCLK = system clock.
Minimum and maximum parameters are characterized for operation at TA = 175°C, but may not be production tested at that
temperature. Production test limits with statistical guardbands are used to ensure high temperature performance.
Input impedance is improved by disabling input chopping (CHOP bit = 0).
VIN = 20mVDC/PGA, see Table 3.
VIN = 31.25 Hz, –0.5 dBFS.
Best-fit method.
FSR: Full-scale range = ±VREF/(2 × PGA).
Calibration accuracy is on the level of noise reduced by 4 (calibration averages 16 readings).
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (PW PACKAGE) (continued)
Limit specifications at –55°C to 175°C. Typical specifications at 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK (1) = 4.096 MHz,
VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V, CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000
SPS, unless otherwise noted.
PARAMETER
CONDITIONS
Gain error (9)
MIN
TYP
MAX
MIN
High-resolution mode
–1.5
–1.0
–0.5
Low-power mode
–1
–0.5
0
Gain error after calibration (8)
TYP
MAX
–1.5
–1
–0.5
–1
–0.5
0
0.0002
PGA = 1
2
PGA = 16
9
Gain matching (10)
0.3
fCM = 60Hz (11)
Common-mode rejection
Power-supply rejection
AVDD,
AVSS
fPS = 60Hz (11)
DVDD
%
2
ppm/°C
0.4
82
%
%
11
0.8
UNIT
0.0002
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Gain drift
TA = 175°C (2)
TA = –55°C to 125°C
82
110
80
90
84
90
115
106
0.5
5
ppm/°C
0.8
114
%
dB
dB
VOLTAGE REFERENCE INPUTS
(VREF = VREFP –
VREFN)
Reference input voltage
(AVDD –
AVSS) +
0.2
0.5
(AVDD –
AVSS) +
0.2
Negative reference input
VREFN
AVSS –
0.1
VREFP –
0.5
AVSS –
0.1
VREFP –
0.5
Positive reference input
VREFP
VREFN +
0.5
AVDD + 0.1
VREFN +
0.5
AVDD + 0.1
Reference input impedance
V
V
V
High-resolution mode
85
85
kΩ
Low-power mode
170
170
kΩ
DIGITAL FILTER RESPONSE
Passband ripple
±0.003
±0.003
dB
Passband (–0.01 dB)
0.375 × fDATA
0.375 ×
fDATA
Hz
Bandwidth (–3 dB)
0.413 × fDATA
0.413 ×
fDATA
Hz
High-pass filter corner
0.1
Stop band attenuation (12)
135
Stop band
Group delay
10
0.1
0.500 × fDATA
Settling time (latency)
10
135
0.500 ×
fDATA
Minimum phase filter (13)
5/fDATA
5/fDATA
Linear phase filter
31/fDATA
31/fDATA
Minimum phase filter
62/fDATA
62/fDATA
Linear phase filter
62/fDATA
62/fDATA
Hz
dB
Hz
s
s
DIGITAL INPUT/OUTPUT
VIH
VIL
IOH = 1mA
VOH
VOL
Input leakage
Clock input
Serial clock rate
(9)
(10)
(11)
(12)
(13)
0.8 ×
DVDD
DVDD
0.8 X
DVDD
DVDD
DGND
0.2 × DVDD
DGND
0.2 × DVDD
0.8 ×
DVDD
0.8 X
DVDD
V
V
V
IOL = 1mA
0.2 × DVDD
0.2 × DVDD
V
0 < VDIGITAL IN < DVDD
±10
±10
μA
fCLK
fSCLK
1
4.096
fCLK/2
1
4.096
MHz
fCLK/2
MHz
The PGA output impedance and the modulator input impedance results in –1% systematic gain error (high-resolution mode) and –0.5%
error (low-power mode).
Gain match relative to PGA = 1.
fCM is the input common-mode frequency. fPS is the power-supply frequency.
Input frequencies in the range of NfCLK/512 ± fDATA/2 (N = 1, 2, 3...) can mix with the modulator chopping clock. In these frequency
ranges intermodulation = 120 dB, typ.
At dc. See Figure 49.
Copyright © 2009–2011, Texas Instruments Incorporated
11
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (PW PACKAGE) (continued)
Limit specifications at –55°C to 175°C. Typical specifications at 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK (1) = 4.096 MHz,
VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V, CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000
SPS, unless otherwise noted.
PARAMETER
CONDITIONS
TA = 175°C (2)
TA = –55°C to 125°C
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
POWER SUPPLY
AVSS
–2.6
0
–2.6
0
V
AVDD
AVSS +
4.75
AVSS +
5.25
AVSS +
4.75
AVSS +
5.25
V
3.6
1.75
1.75
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DVDD
High-resolution mode
7.2
5.2
3.6
V
9.2
|mA|
Low-power mode
3
4.6
3.4
6
|mA|
Standby mode
68
110
52
900
|μA|
Power-down mode
68
110
52
900
|μA|
All modes
0.6
1.5
0.7
1.5
mA
Modulator mode
0.1
Standby mode
73
175
255
600
Power-down mode (14)
32
120
118
220
μA
High-reolution mode
25
41
31
41
mW
mW
AVDD, AVSS current
DVDD current
4.5
Power dissipation
1.05
mA
μA
Low-power mode
17
28
22
28
Standby mode
0.58
1.1
2.5
5
mW
Power-down mode
0.45
0.95
2.06
4.5
mW
(14) CLK input stopped.
1000000
Estimated Life (Hours)
100000
Electromigration Fail Mode
10000
1000
110
130
150
170
190
210
230
Continuous TJ (°C)
A.
Device is qualified to ensure reliable operation for 1000 hours at maximum rated temperature. This includes, but is
not limited to temperature bake, temperature cycle, electromigration, bond intermetallic life, and mold compound life.
Such qualification testing should not be viewed as justifying use of this component beyond specified performance and
environmental limits. For plastic package only.
Figure 1. ADS1282SKGD1/ADS1282SJDJ/ADS1282HPW
Operating Life Derating Chart
12
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TIMING DIAGRAM
tSCLK
tSCDL
tSPWH
SCLK
tDIST
tSPWL
tSCDL
DIN
tDIHD
tDOHD
DOUT
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tDOPD
TIMING REQUIREMENTS
At TA = –55°C to 210°C and DVDD = 1.65 V to 3.6 V, unless otherwise noted.
PARAMETER
tSCLK
tSPWH,
tDIST
tDIHD
tDOPD
tDOHD
tSCDL
(1)
(2)
DESCRIPTION
SCLK period
L
TA = –55°C to 125°C
MIN
MAX
TA = 175°C
MIN
MAX
TA = 210°C
MIN
MAX
UNITS
2
16
2
16
2
16
1/fCLK
SCLK pulse width, high and low (1)
0.8
10
0.8
10
0.8
10
1/fCLK
DIN valid to SCLK rising edge: setup time
50
50
50
ns
Valid DIN to SCLK rising edge: hold time
50
50
50
ns
SCLK falling edge to valid new DOUT:
propagation delay (2)
100
100
100
ns
SCLK falling edge to DOUT invalid: hold time
0
0
0
ns
Final SCLK rising edge of command to first
SCLK rising edge for register read/write data
24
24
24
1/fCLK
Holding SCLK low for 64 DRDY falling edges resets the serial interface.
Load on DOUT = 20 pF || 100 kΩ.
Copyright © 2009–2011, Texas Instruments Incorporated
13
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TYPICAL CHARACTERISTICS
At 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V,
CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
OUTPUT SPECTRUM
OUTPUT SPECTRUM
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
High-Resolution Mode
PGA = 1
THD = -124.0dB
-60
-80
-100
-120
-140
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
Low-Power Mode
PGA = 1
THD = -123.0dB
-40
-60
-80
-100
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Amplitude (dB)
-40
0
-20
Amplitude (dB)
0
-20
-120
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
Figure 2.
-60
-80
-100
-120
-140
0
8192-Point FFT
VIN = -20dBFS, 31.25Hz
Low-Power Mode
PGA = 1
THD = -117.0dB
-20
-40
Amplitude (dB)
-40
Amplitude (dB)
OUTPUT SPECTRUM
8192-Point FFT
VIN = -20dBFS, 31.25Hz
High-Resolution Mode
PGA = 1
THD = -120.1dB
-20
-60
-80
-100
-120
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
Figure 4.
-60
-80
-100
-120
-140
0
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
Low-Power Mode
PGA = 16
THD = -121.4dB
-20
-40
Amplitude (dB)
Amplitude (dB)
-40
500
OUTPUT SPECTRUM
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
High-Resolution Mode
PGA = 16
THD = -122.4dB
-20
100 150 200 250 300 350 400 450
Frequency (Hz)
Figure 5.
OUTPUT SPECTRUM
0
-60
-80
-100
-120
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
Figure 6.
14
500
Figure 3.
OUTPUT SPECTRUM
0
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
Figure 7.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V,
CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
OUTPUT SPECTRUM
0
8192-Point FFT
Shorted Input
High-Resolution Mode
SNR = 124.0dB
-20
-60
-80
-40
-120
-140
-60
-80
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-100
8192-Point FFT
Shorted Input
Low-Power Mode
SNR = 121.0dB
-20
Amplitude (dB)
-40
Amplitude (dB)
OUTPUT SPECTRUM
0
-100
-120
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
Figure 8.
-20
-40
Amplitude (dB)
-60
-80
-100
-120
-140
8192-Point FFT
20mVDC
Low-Power Mode
SNR = 121.3dB
-60
-80
-100
-120
-140
-160
-160
-180
-180
0
-100
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
100 150 200 250 300 350 400 450
Frequency (Hz)
Figure 11.
THD
vs
INPUT FREQUENCY
SNR (1000 SPS)
vs
TEMPERATURE
500
126
THD Limited by
Signal Generator
-105
50
Figure 10.
125
High-Resolution Mode
124
-110
High-Resolution Mode, PGA = 1
Low-Power Mode, PGA = 1
High-Resolution Mode, PGA = 8
Low-Power Mode, PGA = 8
-115
-120
SN R (d B)
Amplitude (dB)
-40
Total Harmonic Distortion (dB)
OUTPUT SPECTRUM
0
8192-Point FFT
20mVDC
High-Resolution Mode
SNR = 124.2dB
-20
500
Figure 9.
OUTPUT SPECTRUM
0
100 150 200 250 300 350 400 450
Frequency (Hz)
123
122
121
120
119
Low-Power Mode
118
-125
VIN = -0.5dBFS
-130
10
20
30
40
50
60
70
Input Frequency (Hz)
Figure 12.
Copyright © 2009–2011, Texas Instruments Incorporated
80
90
100
117
-55 -35 -15 5 25 45 65 85 105 125 145 165 185 205
Temperature (°C)
Figure 13.
15
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V,
CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
THD (G = 8)
vs
TEMPERATURE
SNR
vs
REFERENCE VOLTAGE
-100
130
-105
125
Signal-to-Noise Ratio (dB)
-110
-115
Low-Power Mode
-120
-125
High-Resolution Mode, PGA = 8
120
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T H D (d B )
High-Resolution Mode, PGA = 1
High-ResolutionMode
115
Low-Power Mode, PGA = 1
110
105
Low-Power Mode, PGA = 8
-130
100
-55 -35 -15
5
25 45 65 85 105 125 145 165 185 205
0
1
2
3
VREF (V)
Temperature(°C)
Figure 14.
Figure 15.
THD
vs
REFERENCE VOLTAGE
SNR
vs
CLOCK FREQUENCY
4
5
5.5
125
-110
-115
Signal-to-Noise Ratio (dB)
Total Harmonic Distortion (dB)
High-Resolution Mode, PGA = 8
Low-Power Mode, PGA = 8
-120
-125
Low-Power Mode, PGA = 1
124
High-Resolution Mode
123
122
121
Low-Power Mode
120
VIN = 20mVDC
Data Rate = fCLK/4096
High-Resolution Mode, PGA = 1
119
-130
0
1
2
3
VREF (V)
Figure 16.
16
4
5
6
0.5
1.0
1.5
2.0
2.5
3.0
fCLK (MHz)
3.5
4.0
4.5
Figure 17.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V,
CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
THD
vs
CLOCK FREQUENCY
-115
Low-Power Mode
-120
-125
130
Common-Mode Rejection (dB)
PGA = 8
VIN = 31.25Hz, -0.5dBFS
Data Rate = fCLK/4096
120
110
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Total Harmonic Distortion (dB)
-110
CMR
vs
INPUT FREQUENCY
High-Resolution Mode
100
90
Low-Power Mode
80
High-Resolution Mode
-130
70
0.5
1.0
2.0
2.5
3.0
fCLK (MHz)
3.5
4.0
4.5
10
100
1k
10k
Input Frequency (Hz)
Figure 18.
Figure 19.
POWER-SUPPLY REJECTION
vs
FREQUENCY
INL
vs
INPUT AMPLITUDE
100k
1M
4
140
DVDD
AVDD
3
120
100
80
Integral Nonlinearity (ppm)
Power-Supply Rejection (dB)
1.5
AVSS
60
40
20
2
PGA = 2
1
0
-1
PGA = 8
PGA = 32
-2
-3
0
10
100
1k
10k
100k
Power-Supply Frequency (Hz)
Figure 20.
Copyright © 2009–2011, Texas Instruments Incorporated
1M
-4
-100
-75
-50
-25
0
25
50
Input Amplitude (% Full-Scale)
75
100
Figure 21.
17
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V,
CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
INL
vs
TEMPERATURE
CROSSTALK OUTPUT SPECTRUM
0
30
Shorted Input
8192-Point FFT
Adjacent Channel VIN = -0.5dBFS, 31.25Hz
-20
-40
0
Amplitude (dB)
10
-60
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IN L ( p p m )
20
-80
-100
-120
-140
-160
-10
-55 -35 -15
-180
5
0
25 45 65 85 105 125 145 165 185 205
100 150 200 250 300 350 400 450
Frequency (Hz)
50
Temperature (°C)
35
Figure 22.
Figure 23.
POWER
vs
TEMPERATURE
POWER
vs
CLOCK FREQUENCY
500
30
High-Resolution Mode
25
20
15
High-ResolutionMode
Power (mW)
P W R (m W )
30
25
Low-PowerMode
10
-55 -35 -15 5 25 45 65 85 105125 145165185205
20
Low-Power Mode
15
10
5
0
1.0
1.5
2.0
2.5
3.0
fCLK (MHz)
3.5
4.0
4.5
Temperature(°C)
Figure 24.
18
Figure 25.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At 25°C, AVDD = 2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREFP = 2.5 V, VREFN = –2.5 V, DVDD = 3.3 V,
CAPN – CAPP = 10 nF, PGA = 1, High-Resolution Mode, and fDATA = 1000 SPS, unless otherwise noted.
OFFSET HISTOGRAM
GAIN ERROR HISTOGRAM
30
10
25 Units
25 Units
25
8
High-Resolution Mode
Occurrences
20
15
10
6
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Occurrences
PGA = 8
4
PGA = 1
Low-Power Mode
2
5
0
-100 -80 -60 -40 -20
0
20
Offset (mV)
40
60
0
-1.2
100
80
-1.1 -1.0
-0.9
Figure 26.
80
PGA = 8
50
40
30
20
25 Units Based on +20°C Intervals
Over the Range of -40°C to +85°C
PGA = 1, 2, 4
PGA = 32
60
50
PGA = 16
PGA = 8, 64
40
30
20
PGA =1
10
-0.3
70
Occurrences
60
10
0
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
0.10
0.08
0.06
0.04
0.02
0
-0.02
-0.04
-0.10
0
-0.06
Occurrences
70
-0.4
GAIN DRIFT HISTOGRAM
90
25 Units Based on
+20°C Intervals
Over the Range of
-40°C to +85°C
-0.08
80
-0.5
Figure 27.
OFFSET DRIFT HISTOGRAM
90
-0.8 -0.7 -0.6
Gain Error (%)
Gain Drift (ppm/°C)
Offset Drift (mV/°C)
Figure 28.
Figure 29.
GAIN MATCH HISTOGRAM
8
Worst-Case Gain Match Relative PGA = 1 (25 Units)
Occurrences
6
4
2
0.02
0.06
0.10
0.14
0.18
0.22
0.26
0.30
0.34
0.38
0.42
0.46
0.50
0
Gain Error (%)
Figure 30.
Copyright © 2009–2011, Texas Instruments Incorporated
19
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
OVERVIEW
The ADS1282 is a high-performance analog-to-digital
converter (ADC) intended for energy exploration,
seismic monitoring, chomatography, and other
exacting applications. The converter provides 24- or
32-bit output data in data rates from 250 SPS to 4000
SPS. Figure 31 shows the block diagram of the
ADS1282.
The SYNC input resets the operation of both the
digital
filter
and
the
modulator,
allowing
synchronization conversions of multiple ADS1282
devices to an external event. The SYNC input
supports a continuously-toggled input mode that
accepts an external data frame clock locked to the
conversion rate.
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The
two-channel
input
MUX
allows
five
configurations: Input 1; Input 2; Input 1 and Input 2
shorted together; shorted with 400-Ω test; and
common-mode test. The input MUX is followed by a
continuous time PGA, featuring very low noise of
5nV/√Hz. The PGA is controlled by register settings,
allowing gains of 1 to 64.
Gain and offset registers scale the digital filter output
to produce the final code value. The scaling feature
can be used for calibration and sensor gain matching.
The output data word is provided as either a 24-bit
word or a full 32-bit word, allowing complete
utilization of the inherently high resolution.
The inherently-stable, fourth-order, delta-sigma
modulator measures the differential input signal
VIN = (AINP – AINN) PGA against the differential
reference VREF = (VREFP – VREFN). A digital output
(MFLAG) indicates that the modulator is in overload
as a result of an overdrive condition. The modulator
output is available directly on the MCLK, M0, and M1
output pins. The modulator connects to an on-chip
digital filter that provides the output code readings.
Noise-immune Schmitt-trigger and clock-qualified
inputs (RESET and SYNC) provide increased
reliability in high-noise environments. The serial
interface is used to read conversion data, in addition
to reading from and writing to the configuration
registers.
VREFP
VREFN
AVDD
CAPN
CAPP
The digital filter consists of a variable decimation rate,
fifth-order sinc filter followed by a variable phase,
decimate-by-32,
finite-impulse
response
(FIR)
low-pass filter with programmable phase, and then by
an adjustable high-pass filter for dc removal of the
output reading. The output of the digital filter can be
taken from the sinc, the FIR low-pass, or the infinite
impulse response (IIR) high-pass sections.
The RESET input resets the register settings and
also restarts the conversion process. The PWDN
input sets the device into a micro-power state. Note
that register settings are not retained in PWDN mode.
Use the STANDBY command in its place if it is
desired to retain register settings (the quiescent
current in the Standby mode is slightly higher).
ADS1282
+1.8V
(Digital core)
DVDD
LDO
300W
MUX
AINP2
AINN2
AINP1
AINN1
BYPAS
CLK
400W
400W
PGA
4th-Order
DS
Modulator
300W
Programmable
Digital Filter
Calibration
Serial
Interface
Over-Range
Detection
SYNC
Control
RESET
PWDN
AVDD + AVSS
2
AVSS
DRDY
SCLK
DIN
DOUT
MFLAG
MCLK
M0
DGND
M1
Figure 31. ADS1282 Block Diagram
20
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
The device features unipolar and bipolar analog
power supplies (AVDD and AVSS, respectively) for
input range flexibility and a digital supply accepting
1.8 V to 3.3 V. The analog supplies may be set to 5 V
to accept unipolar signals (with input offset) or set
lower in the range of ±2.5 V to accept true bipolar
input signals (ground referenced).
INPUT-REFERRED NOISE
An internal sub-regulator is used to supply the digital
core from DVDD. The BYPAS pin (pin 28) is the
sub-regulator output and requires a 1-μF capacitor for
noise reduction. BYPAS should not be used to drive
external circuitry.
where:
NOISE PERFORMANCE
IDLE TONES
The ADS1282 offers outstanding noise performance
(SNR). SNR depends on the data rate, the PGA
setting, and the mode (high-resolution or low-power).
As the bandwidth is reduced by decreasing the data
rate, the SNR improves correspondingly. Similarly, as
the PGA gain is increased, the SNR decreases. In
low-power mode, the SNR decreases 3 dB for each
setting. Table 3 summarizes the noise performance
versus data rate, PGA setting, and mode.
The ADS1282 modulator incorporates an internal
dither signal that randomizes the idle tone energy.
Low-level idle tones may still be present,
typically –137 dB below full-scale. The low-level idle
tones can be shifted out of the passband with an
external offset = 20mV/PGA. See the Application
Information section for the recommended offset
circuit.
The input-referred noise is related to SNR by
Equation 1:
FSRRMS
SNR = 20log
NRMS
FSRRMS = Full-scale range RMS = VREF/(2 × √2 ×
PGA)
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NRMS = Noise RMS (input-referred)
(1)
OPERATING MODE
For applications where minimal power consumption is
important, the low-power mode can be selected
(register bit MODE = 0). In low-power mode, the
power is reduced to 17 mW (from 25 mW) and SNR
decreases an average of 3 dB. The default mode is
high-resolution.
Table 3. Signal-to-Noise Ratio (dB) (1)
PGA (Low-Power Mode)
1
2
4
8
16
32
64
1
2
4
8
16
32
64
250
130
130
129
128
125
119
114
127
127
126
125
122
116
111
127
127
126
125
122
116
111
124
124
123
122
119
113
108
124
124
123
122
119
113
108
121
121
120
119
116
110
105
121
121
120
119
116
111
106
118
118
117
116
113
108
103
118
118
117
116
113
108
103
115
115
114
113
110
105
100
500
1000
2000
4000
(1)
PGA (High-Resolution Mode)
DATA RATE
(SPS)
VIN = 20mVDC/PGA.
Copyright © 2009–2011, Texas Instruments Incorporated
21
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Table 4. Multiplexer Modes
ANALOG INPUTS AND MULTIPLEXER
A diagram of the input multiplexer is shown in
Figure 32.
MUX[2:0]
ESD diodes protect the multiplexer inputs. If either
input is taken below AVSS – 0.3 V or above AVDD +
0.3 V, the ESD protection diodes may turn on. If
these conditions are possible, external Schottky
clamp diodes and/or series resistors may be required
to limit the input current to safe values (see the
Absolute Maximum Ratings table).
AVDD
S1
S2
400W
001
S2, S6
AINP2 and AINN2 connected to
preamplifier
010
S3, S4
Preamplifier inputs shorted together
through 400Ω internal resistors
011
S1, S5, S2, S6
AINP1, AINN1 and AINP2, AINN2
connected together and to the preamplifier
100
S6, S7
External short, preamplifier inputs shorted
to AINN2 (common-mode test)
0
To PGA
AVDD + AVSS
AVDD
2
400W
S4
S5
ESD Diodes
AINN2
S1, S5
(+)
S3
S7
AVSS
AINN1
000
The typical on-resistance (RON) of the multiplexer
switch is 30 Ω. When the multiplexer is used to drive
an external load on one input by a signal generator
on the other input, on-resistance and on-resistance
amplitude dependency can lead to measurement
errors. Figure 33 shows THD versus load resistance
and amplitude. Note that THD improves with
high-impedance loads and with lower amplitude drive
signals. The data are measured with the circuit from
Figure 34 with MUX[2:0] = 011.
(-)
S6
Total Harmonic Distortion (dB)
ESD Diodes
AINP2
DESCRIPTION
AINP1 and AINN1 connected to
preamplifer
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Also, overdriving one unused input may affect the
conversions of the other input. If overdriven inputs
are possible, it is recommended to clamp the signal
with external Schottky diodes.
AINP1
SWITCHES
-20
-40
-60
-80
-100
-120
-140
0.1k
1k
10k
The specified input operating range of the PGA is
shown in Equation 2:
AVSS + 0.7V < (AINN or AINP) < AVDD - 1.25V (2)
1M
10M
Figure 33. THD versus External Load and Signal
Magnitude (PGA) (see Figure 34)
500W
Absolute input levels (input signal level and
common-mode level) should be maintained within
these limits for best operation.
500W
The multiplexer connects one of the two external
differential inputs to the preamplifier inputs, in
addition to internal connections for various self-test
modes. Table 4 summarizes the multiplexer
configurations for Figure 32.
RLOAD
22
100k
RLOAD (W)
AVSS
Figure 32. Analog Inputs and Multiplexer
PGA = 1
PGA = 2
PGA = 4
PGA = 8
PGA = 16
PGA = 32
PGA = 64
ADS1282
Input 1
Input 2
Figure 34. Driving an External Load Through the
MUX
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
PGA (Programmable Gain Amplifier)
Table 5. PGA Gain Settings (continued)
Referring to Figure 35, amplifiers A1 and A2 are
chopped to remove the offset, offset drift, and the 1/f
noise. Chopping moves the effects to fCLK/128 (8
kHz), which is safely out of the passband. Chopping
can be disabled by setting the CHOP register bit = 0.
With chopping disabled, the impedance of the PGA
increases substantially (>> 1 GΩ). As shown in
Figure 36, chopping maintains flat noise density; if
chopping is disabled, however, it results in a rising 1/f
noise profile.
The PGA has programmable gains from 1 to 64.
Table 5 shows the register bit setting for the PGA and
resulting full-scale differential range.
Table 5. PGA Gain Settings
DIFFERENTIAL
INPUT RANGE
(V)(1)
PGA[2:0]
GAIN
000
1
±2.5
2
±1.25
4
±0.625
8
±0.312
16
±0.156
32
±0.078
011
100
101
64
±0.039
AVDD
MUX (+)
300W
A1
CHOP
Copyright © 2009–2011, Texas Instruments Incorporated
CAPP
Gain Control
PGA[2:0] Bits
300W
10nF
CAPN
A2
(1)
(55kW, typ )
Modulator
Effective
Impedance
MUX (-)
Chopping Control CHOP Bit
AVSS
(1) Low-power mode = 110 kΩ.
Figure 35. PGA Block Diagram
100
PGA Noise (nV/ÖHz)
PGA output levels (signal plus common-mode) should
be maintained within these limits for best operation.
010
GAIN
110
(1) VREF = 5 V.
The specified output operating range of the PGA is
shown in Equation 4:
AVSS + 0.4V < (CAPN or CAPP) < AVDD - 0.4V (4)
001
PGA[2:0]
DIFFERENTIAL
INPUT RANGE
(V)(1)
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The PGA of the ADS1282 is a low-noise,
continuous-time, differential-in/differential-out CMOS
amplifier. The gain is programmable from 1 to 64, set
by register bits, PGA[2:0]. The PGA differentially
drives the modulator through 300-Ω internal resistors.
A COG capacitor (10nF typical) must be connected to
CAPP and CAPN to filter modulator sampling
glitches. The external capacitor also serves as an
anti-alias filter. The corner frequency is given in
Equation 3:
1
fP =
6.3 ´ 600 ´ C
(3)
PGA CHOP Off
10
PGA CHOP On
1
10
100
Frequency (Hz)
1k
Figure 36. PGA Noise
23
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
The ADC block of the ADS1282 is composed of two
sections: a high-accuracy modulator and a
programmable digital filter.
MODULATOR
0
1Hz Resolution
VIN = 20mVDC
-20
-40
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The
high-performance
modulator
is
an
inherently-stable, fourth-order, ΔΣ, 2 + 2 pipelined
structure, as Figure 37 shows. It shifts the
quantization noise to a higher frequency (out of the
passband) where digital filtering can easily remove it.
The modulator can be filtered either by the on-chip
digital filter or by use of post-processing filters.
appears at the chopping frequency (fCLK/512 = 8
kHz). The component at 5.8 kHz is the tone
frequency, shifted out of band by an external 20
mV/PGA offset. The frequency of the tone is
proportional to the applied dc input and is given by
PGA × VIN/0.003 (in kHz).
Magnitude (dB)
ADC
fCLK/4
Analog Input (VIN)
MCLK
-60
-80
-100
-120
-140
-160
2nd-Order
DS
1st-Stage
M0
-180
1
10
100
1k
10k
100k
Frequency (Hz)
2nd-Order
DS
2nd-Stage
M1
4th-Order Modulator
Figure 37. Fourth-Order Modulator
The modulator first stage converts the analog input
voltage into a pulse-code modulated (PCM) stream.
When the level of differential analog input (AINP –
AINN) is near one-half the level of the reference
voltage 1/2 × (VREFP – VREFN), the ‘1’ density of
the PCM data stream is at its highest. When the level
of the differential analog input is near zero, the PCM
‘0’ and ‘1’ densities are nearly equal. At the two
extremes of the analog input levels (+FS and –FS),
the ‘1’ density of the PCM streams is approximately
+90% and +10%, respectively.
The modulator second stage produces a '1' density
data stream designed to cancel the quantization
noise of the first stage. The data streams of the two
stages are then combined before the digital filter
stage, as shown in Equation 5.
Y[n] = 3M0[n - 2] - 6M0[n - 3] + 4M0[n - 4]
+ 9(M1[n] - 2M1[n - 1] + M1[n - 2])
(5)
M0[n] represents the most recent first-stage output
while M0[n – 1] is the previous first-stage output.
When the modulator output is enabled, the digital
filter shuts down to save power.
The modulator is optimized for input signals within a
4-kHz passband. As Figure 38 shows, the noise
shaping of the modulator results in a sharp increase
in noise above 6 kHz. The modulator has a chopped
input structure that further reduces noise within the
passband. The noise moves out of the passband and
24
Figure 38. Modulator Output Spectrum
MODULATOR OVER-RANGE
The ADS1282 modulator is inherently stable, and
therefore, has predictable recovery behavior resulting
from an input overdrive condition. The modulator
does not exhibit self-resetting behavior, which often
results in an unstable output data stream.
The ADS1282 modulator outputs a 1s density data
stream at 90% duty cycle with the positive full-scale
input signal applied (10% duty cycle with the negative
full-scale signal). If the input is overdriven past 90%
modulation, but below 100% modulation (10% and
0% for negative overdrive, respectively), the
modulator remains stable and continues to output the
1s density data stream. The digital filter may or may
not clip the output codes to +FS or –FS, depending
on the duration of the overdrive. When the input
returns to the normal range from a long duration
overdrive (worst case), the modulator returns
immediately to the normal range, but the group delay
of the digital filter delays the return of the conversion
result to within the linear range (31 readings for linear
phase FIR). 31 additional readings (62 total) are
required for completely settled data.
If the inputs are sufficiently overdriven to drive the
modulator to full duty cycle, all 1s or all 0s, the
modulator enters a stable saturated state. The digital
output code may clip to +FS or –FS, again depending
on the duration. A small duration overdrive may not
always clip the output code. When the input returns to
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
the normal range, the modulator requires up to 12
modulator clock cycles (fMOD) to exit saturation and
return to the linear region. The digital filter requires an
additional 62 conversions for fully settled data (linear
phase FIR).
The ADS1282 has a fast-responding over-range
detection that indicates when the differential input
exceeds ±100% full scale. The threshold tolerance is
±2.5%.The MFLAG output asserts high when in an
over-range condition. As Figure 39 and Figure 40
illustrate, the absolute differential input is compared
to 100% of range. The output of the comparator is
sampled at the rate of fMOD/2, yielding the MFLAG
output. The minimum MFLAG pulse width is fMOD/2.
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In the extreme case of over-range, either input is
overdriven, exceeding the voltage of either analog
supply voltage plus an internal ESD diode drop. The
internal diodes begin to conduct and the signal on the
input is clipped. When the input overdrive is removed,
the diodes recover quickly. Keep in mind that the
input current must be limited to 100-mA peak or 10
mA continuous if an overvoltage condition is possible.
MODULATOR OVER-RANGE DETECTION
(MFLAG)
AINP
MODULATOR INPUT IMPEDANCE
Where:
fMOD = Modulator sample frequency
(High-resolution mode = CLK/4)
(Low-power mode = CLK/8)
CS = Input sampling capacitor (17pF, typ)
The resulting modulator input impedance for CLK =
4.096 MHz is 55 kΩ (110 kΩ low-power mode). The
modulator input impedance and the PGA output
resistors result in a systematic gain error of –1%
(–0.5% in low-power mode). CS can vary ±20% over
production lots, affecting the gain error.
Copyright © 2009–2011, Texas Instruments Incorporated
IABSI
P
100% FS
AINN
Q
MFLAG
Pin
fMOD/2
Figure 39. Modulator Over-Range Block Diagram
VIN (% of Full-Scale)
The modulator samples the buffered input voltage
with an internal capacitor to perform conversions. The
charging of the input sampling capacitor draws a
transient current from the PGA output. The average
value of the current can be used to calculate an
effective input impedance of REFF = 1/(fMOD × CS).
å
+100
(AINP - AINN)
0
Time
-100
MFLAG
Pin
Figure 40. Modulator Over-Range Flag Operation
25
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
MODULATOR OUTPUT MODE
The modulator digital stream output is accessible
directly, bypassing and disabling the internal digital
filter. The modulator output mode is activated by
setting the CONFIG0 register bits FILTR[1:0] = 00.
Pins M0 and M1 then become the modulator data
outputs and the MCLK becomes the modulator clock
output. When not in the modulator mode, these pins
are inputs and must be tied.
The modulator output data are two bits wide, which
must be merged together before being filtered. Use
the time domain equation of Equation 5 to merge the
data outputs.
tCSHD
CLK
The voltage reference for the ADS1282 is the
differential voltage between VREFP and VREFN:
VREF = VREFP – VREFN. The reference inputs use a
structure similar to that of the analog inputs with the
circuitry of the reference inputs shown in Figure 42.
The average load presented by the switched
capacitor reference input can be modeled with an
effective differential impedance of REFF = tSAMPLE/CIN
(tSAMPLE = 1/fMOD). Note that the effective impedance
of the reference inputs loads the external reference.
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The modulator output is composed of three signals:
one output for the modulator clock (MCLK) and two
outputs for the modulator data (M0 and M1). The
modulator clock output rate is fMOD (fCLK/4 for
high-resolution mode, fCLK/8 for low-power mode).
The SYNC input resets the MCLK phase, as shown in
Figure 41. The SYNC input is latched on the rising
edge of CLK. The MCLK resets and the next rising
edge of MCLK occurs five CLK periods later.
VOLTAGE REFERENCE INPUTS
(VREFP, VREFN)
AVDD
ESD
Diodes
VREFP
VREFN
ESD
Diodes
tCMD
REFF =
1
fMOD ´ CX
tSCSU
SYNC
tSYMD
MCLK
REFF = 85kW
(170kW Low-Power Mode)
(fMOD = 1.024MHz)
11.5pF
(1)
AVSS
tMCD0, 1
M0
M1
Figure 42. Simplified Reference Input Circuit
(1) High-resolution mode: MCLK = fCLK/4; low-power mode:
MCLK = fCLK/8.
Figure 41. Modulator Mode Timing
Table 6. Modulator Output Timing for Figure 41
PARAMETER
tMCD0,
tCMD
tCSHD
tSCSU
tSYMD
(1)
26
1
DESCRIPTION
MIN
TYP
MCLK rising edge to M0, M1 valid propagation delay (1)
CLK rising edge (after SYNC rising edge) to MCLK rising edge
reset time
UNIT
100
ns
5
CLK to SYNC hold time to not latch on CLK edge
10
SYNC to CLK setup time to latch on CLK edge
10
SYNC to stable bit stream
MAX
16
1/fCLK
ns
ns
1/fMOD
Load on M0 and M1 = 20 pF || 100 kΩ.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Table 7. Digital Filter Selection
The ADS1282 reference inputs are protected by ESD
diodes. In order to prevent these diodes from turning
on, the voltage on either input must stay within the
range shown in Equation 6:
AVSS - 300mV < (VREFP or VREFN) < AVDD + 300mV
(6)
DIGITAL FILTERS SELECTED
00
Bypass; modulator output mode
01
Sinc
10
Sinc + FIR
11
Sinc + FIR + HPF
(low-pass and high-pass)
Sinc Filter Stage (sinx/x)
The sinc filter is a variable decimation rate, fifth-order,
low-pass filter. Data are supplied to this section of the
filter from the modulator at the rate of fMOD (fCLK/4).
The sinc filter attenuates the high-frequency noise of
the modulator, then decimates the data stream into
parallel data. The decimation rate affects the overall
data rate of the converter; it is set by the DR[2:0]
register bits, as shown in Table 8.
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Note that the minimum valid input for VREFN is
AVSS – 0.1 V and maximum valid input for VREFP is
AVDD + 0.1 V.
FILTR[1:0] BITS
A high-quality +5 V reference voltage is necessary for
achieving the best performance from the ADS1282.
Noise and drift on the reference degrade overall
system performance, and it is critical that special care
be given to the circuitry generating the reference
voltages in order to achieve full performance. See the
Application Information section for reference
recommendations.
DIGITAL FILTER
Equation 7 shows the scaled Z-domain transfer
function of the sinc filter.
The digital filter receives the modulator output and
decimates the data stream. By adjusting the amount
of filtering, tradeoffs can be made between resolution
and data rate: filter more for higher resolution, filter
less for higher data rate.
The digital filter is comprised of three cascaded filter
stages: a variable-decimation, fifth-order sinc filter; a
fixed-decimation FIR, low-pass filter (LPF) with
selectable phase; and a programmable, first-order,
high-pass filter (HPF), as shown in Figure 43.
The output can be taken from one of the three filter
blocks, as Figure 43 shows. To implement the digital
filter completely off-chip, select the filter bypass
setting (modulator output). For partial filtering by the
ADS1282, select the sinc filter output. For complete
on-chip filtering, activate both the sinc and FIR
stages. The HPF can then be included to remove dc
and low frequencies from the data. Table 7 shows the
filter options.
5
1 - Z-N
H(Z) =
-1
N(1 - Z )
(7)
Table 8. Sinc Filter Data Rates (CLK = 4.096MHz)
DR[2:0] REGISTER
DECIMATION
RATIO (N)
SINC DATA RATE
(SPS)
000
128
8,000
001
64
16,000
010
32
32,000
011
16
64,000
100
8
128,000
3
Direct Modulator
Bit Stream
Filter Mode
(Register Select)
30
Filter
MUX
From Modulator
Sinc Filter
(Decimate by
8 to 128)
Coefficient Filter
(FIR)
(Decimate by 32)
High-Pass Filter
(IIR)
CAL
Block
Code
Clip
To Output Register
31
Figure 43. Digital Filter and Output Code Processing
Copyright © 2009–2011, Texas Instruments Incorporated
27
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Equation 8 shows the frequency domain transfer
function of the sinc filter.
0
-0.5
5
pN ´ f
fMOD
½H(f)½ =
-1.0
Gain (dB)
sin
p´f
fMOD
N sin
-1.5
-2.0
(8)
-2.5
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where:
N = decimation ratio (see Table 8)
-3.0
0
The sinc filter has notches (or zeroes) that occur at
the output data rate and multiples thereof. At these
frequencies, the filter has zero gain. Figure 44 shows
the frequency response of the sinc filter and
Figure 45 shows the roll-off of the sinc filter.
0.05
0.10
0.15
0.20
Normalized Frequency (fIN/fDATA)
Figure 45. Sinc Filter Roll-Off
FIR Stage
0
-20
Gain (dB)
-40
-60
-80
-100
-120
-140
0
1
2
3
4
Normalized Frequency (fIN/fDATA)
5
The second stage of the ADS1282 digital filter is an
FIR low-pass filter. Data are supplied to this stage
from the sinc filter. The FIR stage is segmented into
four sub-stages, as shown in Figure 46. The first two
sub-stages are half-band filters with decimation ratios
of 2. The third sub-stage decimates by 4 and the
fourth sub-stage decimates by 2. The overall
decimation of the FIR stage is 32. Note that two
coefficient sets are used for the third and fourth
sections, depending on the phase selection. Table 25
(in the Appendix section at the end of this document)
lists the FIR stage coefficients. Table 9 lists the data
rates and overall decimation ratio of the FIR stage.
Table 9. FIR Filter Data Rates
Figure 44. Sinc Filter Frequency Response
Sinc
Filter
FIR Stage 1
Decimate by 2
FIR Stage 2
Decimate by 2
DR[2:0] REGISTER
DECIMATION
RATIO (N)
FIR DATA RATE
(SPS)
000
4096
250
001
2048
500
010
1024
1000
011
512
2000
100
256
4000
FIR Stage 3
Decimate by 4
FIR Stage 4
Decimate by 2
Output
Coefficients
Linear
Minimum
PHASE Select
Figure 46. FIR Filter Sub-Stages
28
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
As shown in Figure 47, the FIR frequency response
provides a flat passband to 0.375 of the data rate
(±0.003 dB passband ripple). Figure 48 shows the
transition from passband to stop band.
2.0
1.0
GROUP DELAY AND STEP RESPONSE
0.5
The FIR block is implemented as a multi-stage FIR
structure with selectable linear or minimum phase
response. The passband, transition band, and stop
band responses of the filters are nearly identical but
differ in the respective phase responses.
0
-0.5
-1.0
-1.5
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Linear Phase Response
-2.0
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Normalized Input Frequency (fIN/fDATA)
Figure 47. FIR Passband Magnitude Response
(fDATA = 500Hz)
20
0
Magnitude (dB)
-20
-40
Linear phase filters exhibit constant delay time versus
input frequency (that is, constant group delay). Linear
phase filters have the property that the time delay
from any instant of the input signal to the same
instant of the output data is constant and is
independent of the signal nature. This filter behavior
results in essentially zero phase error when analyzing
multi-tone signals. However, the group delay and
settling time of the linear phase filter are somewhat
larger than the minimum phase filter, as shown in
Figure 49.
1.4
-60
Minimum Phase Filter
1.2
-80
1.0
-100
-120
-140
-160
0
0.1
0.2 0.3 0.4 0.5 0.6 0.7 0.8
Normalized Input Frequency (fIN/fDATA)
0.9
1.0
Amplitude (dB)
Magnitude (mdB)
1.5
present in the signal and not externally filtered, fold
back (or alias) into the passband and cause errors. A
low-pass signal filter reduces the effect of aliasing.
Often, the RC low-pass filter provided by the PGA
output resistors and the external capacitor connected
to CAPP and CAPN provides sufficient signal
attenuation.
0.8
0.6
0.4
0.2
Linear Phase Filter
0
Figure 48. FIR Transition Band Magnitude
Response
Although not shown in Figure 48, the passband
response repeats at multiples of the modulator
frequency (NfMOD – f0 and NfMOD + f0, where N = 1, 2,
etc. and f0 = passband). These image frequencies, if
Copyright © 2009–2011, Texas Instruments Incorporated
-0.2
0
5
10 15 20 25 30 35 40 45 50 55 60 65
Time Index (1/fDATA)
Figure 49. FIR Step Response
29
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Minimum Phase Response
HPF Stage
The minimum phase filter provides a short delay from
the arrival of an input signal to the output, but the
relationship (phase) is not constant versus frequency,
as shown in Figure 50. The filter phase is selected by
the PHS bit, as Table 10 shows.
The last stage of the ADS1282 filter block is a
first-order HPF implemented as an IIR structure. This
filter stage blocks dc signals and rolls off
low-frequency components below the cut-off
frequency. The transfer function for the filter is shown
in Equation 14 of the APPENDIX.
35
The high-pass corner frequency is programmed by
registers HPF[1:0], in hexadecimal. Equation 9 is
used to set the high-pass corner frequency. Table 11
lists example values for the high-pass filter.
Linear Phase Filter
25
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Group Delay (1/fDATA)
30
HPF[1:0] = 65,536 1 -
20
15
10
Minimum Phase Filter
5
0
20
40
60
80 100 120
Frequency (Hz)
140 160 180
200
Figure 50. FIR Group Delay (fDATA = 500Hz)
Table 10. FIR Phase Selection
30
PHS BIT
FILTER PHASE
0
Linear
1
Minimum
1-2
cos wN + sin wN - 1
cos wN
(9)
Where:
HPF = High-pass filter register value (converted
to hexadecimal)
ωN = 2πfHP/fDATA (normalized frequency,
radians)
fHP = High-pass corner frequency (Hz)
fDATA = Data rate (Hz)
Table 11. High-Pass Filter Value Examples
fHP (Hz)
DATA RATE (SPS)
HPF[1:0]
0.5
250
0337h
1.0
500
0337h
1.0
1000
019Ah
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
The HPF causes a small gain error, in which case the
magnitude of the error depends on the ratio of
fHP/fDATA. For many common values of (fHP/fDATA), the
gain error is negligible. Figure 51 shows the gain
error of the HPF. The gain error factor is illustrated in
Equation 13 (see the Appendix at the end of this
document).
Gain Error (dB)
-0.30
-0.40
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-0.20
SYNCHRONIZATION
(SYNC PIN AND SYNC COMMAND)
The ADS1282 can be synchronized to an external
event, as well as synchronized to other ADS1282
devices if the sync event is applied simultaneously.
-0.50
0.0001
0.001
0.01
0.1
Frequency Ratio (fHP/fDATA)
Figure 51. HPF Gain Error
Figure 52 shows the first-order amplitude and phase
response of the HPF. Note that in the case of
applying step inputs or synchronizing, the settling
time of the filter should be taken into account.
Amplitude (dB)
-7.5
-15.0
-22.5
90
75
60
Amplitude
45
Phase
-30.0
-37.5
-45.0
0.01
The ADS1282 has two sources for synchronization:
the SYNC input pin and the SYNC command. The
ADS1282 also has two synchronizing modes:
Pulse-sync and Continuous-sync. In Pulse-sync
mode, the ADS1282 synchronizes to a single sync
event. In Continuous-sync mode, either a single
SYNC event is used to synchronize conversions or a
continuous clock is applied to the pin with a period
equal to integer multiples of the data rate. When the
periods of the sync input and the DRDY output do not
match,
the
ADS1282
re-synchronizes
and
conversions are restarted.
Phase (°)
0
The ADS1282 requires a clock input for operation.
The clock is applied to the CLK pin. The data
conversion rate scales directly with the CLK
frequency. Power consumption versus CLK frequency
is relatively constant (see the Typical Characteristics).
As with any high-speed data converter, a high-quality,
low-jitter clock is essential for optimum performance.
Crystal clock oscillators are the recommended clock
source. Make sure to avoid excess ringing on the
clock input; keep the clock trace as short as possible
and use a 50-Ω series resistor close to the source.
0
-0.10
MASTER CLOCK INPUT (CLK)
30
15
0
0.1
1
10
Normalized Frequency (f/fC)
100
Figure 52. HPF Amplitude and Phase Response
Copyright © 2009–2011, Texas Instruments Incorporated
31
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
PULSE-SYNC MODE
In Pulse-sync mode, the ADS1282 stops and restarts
the conversion process when a sync event occurs (by
pin or command). When the sync event occurs, the
device resets the internal memory; DRDY goes high
(pulse SYNC mode) otherwise in Continuous SYNC
mode, DRDY continues to toggle, and after the digital
filter has settled, new conversion data are available,
as shown in Figure 53 and Table 12.
www.ti.com
re-synchronization. Note that the phase of the applied
clock and output data rate (DRDY) are not matched
because of the initial delay of DRDY after SYNC is
first applied. Figure 54 shows the timing for
Continuous-Sync mode.
Note that a SYNC clock input should be applied after
the Continuous-Sync mode is set. The first rising
edge of SYNC then causes a synchronization.
tCSHD
Note that resynchronization occurs on the next rising
CLK edge after the rising edge of the SYNC pin or
after the eighth rising SCLK edge for opcode SYNC
commands. To be effective, the SYNC opcode should
be broadcast to all devices simultaneously.
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System Clock
(fCLK)
tSCSU
SYNC Command
tSPWH
SYNC Pin
CONTINUOUS-SYNC MODE
In Continuous-sync mode, either a single sync pulse
or a continuous clock may be applied. When a single
sync pulse is applied (rising edge), the device
behaves similar to the Pulse-sync mode. However, in
this mode, DRDY continues to toggle unaffected but
the DOUT output is held low until data are ready, 63
DRDY periods later. When the conversion data are
non-zero, new conversion data are ready (as shown
in Figure 53).
When a continuous clock is applied to the SYNC pin,
the period must be an integral multiple of the output
data rate or the device re-synchronizes. Note that
synchronization results in the restarting of the digital
filter and an interruption of 63 readings (refer to
Table 12).
tSPWL
New Data
Ready
tDR
DRDY
(Pulse-Sync)
New Data
Ready
tDR
DRDY
(Continuous-Sync)
DOUT
Figure 53. Pulse-Sync Timing, Continuous-Sync
Timing with Single Sync
When the sync input is first applied, the device
re-synchronizes (under the condition tSYNC ≠ N/fDATA).
DRDY continues to output but DOUT is held low until
the new data are ready. Then, if SYNC is applied
again and the period matches an integral multiple of
the output data rate, the device freely runs without
tSCSU
tCSHD
System Clock
(fCLK)
tSPWL
SYNC
tSPWH
tSYNC
DRDY
1/fDATA
Figure 54. Continuous-Sync Timing with Sync
Clock
Table 12. Pulse-Sync Timing for Figure 53 and Figure 54
PARAMETER
DESCRIPTION
MIN
MAX
UNITS
tSYNC
SYNC period (1)
1
Infinite
n/fDATA
tCSHD
CLK to SYNC hold time to not latch on CLK edge
10
tSCSU
SYNC to CLK setup time to latch on CLK edge
10
ns
SYNC pulse width, high or low
2
1/fCLK
tSPWH,
tDR
(1)
32
L
Time for data ready (SINC filter)
ns
See Appendix, Table 26
Time for data ready (FIR filter)
62.98046875/fDATA + 466/fCLK
Continuous-Sync mode; a free-running SYNC clock input without causing re-synchronization.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
RESET (RESET Pin and Reset Command)
In reset, registers are set to default and the
conversions are synchronized on the next rising edge
of CLK. New conversion data are available, as shown
in Figure 55 and Table 13.
DRDY
Settled
Data
tDR
tCRHD
System Clock
(fCLK)
tRST
RESET Pin
or
RESET Command
PWDN Pin
Wakeup
Command
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The ADS1282 may be reset in two ways: toggle the
RESET pin low or send a Reset command. When
using the RESET pin, take it low and hold for at least
2/fCLK to force a reset. The ADS1282 is held in reset
until the pin is released. By command, RESET takes
effect on the next rising edge of fCLK after the eighth
rising edge of SCLK of the command. Note that in
order to ensure the Reset command can function, the
SPI interface may require resetting itself; see the
Serial Interface section.
In power-down, note that the device outputs remain
active and the device inputs must not float. When the
Standby command is sent, the SPI port and the
configuration registers are kept active. Figure 56 and
Table 14 show the timing.
tDR
Figure 56. PWDN Pin and Wake-Up Command
Timing
(Table 14 shows tDR)
POWER-ON SEQUENCE
The ADS1282 has three power supplies: AVDD,
AVSS, and DVDD. Figure 57 shows the power-on
sequence of the ADS1282. The power supplies can
be sequenced in any order. The supplies [the
difference of (AVDD – AVSS) and DVDD] generate
an internal reset whose outputs are summed to
generate a global internal reset. After the supplies
have crossed the minimum thresholds, 216 fCLK cycles
are counted before releasing the internal reset. After
the internal reset is released, new conversion data
are available, as shown in Figure 57 and Table 14.
tRCSU
Figure 55. Reset Timing
Table 13. Reset Timing for Figure 55
PARAMETER DESCRIPTION
DRDY
MIN
UNITS
tCRHD
CLK to RESET hold time
10
ns
tRCSU
RESET to CLK setup time
10
ns
tRST
RESET low
2
1/fCLK
tDR
Time for data ready
62.98046875/
fDATA + 468/fCLK
AVDD - AVSS
DVDD
3.5V nom
1V nom
CLK
16
POWER-DOWN
(PWDN Pin and Standby Command)
There are two ways to power-down the ADS1282:
take the PWDN pin low or send a Standby command.
When the PWDN pin is pulled low, the internal
circuitry is disabled to minimize power and the
contents of the register settings are reset.
Internal Reset
2
fCLK
DRDY
tDR
Figure 57. Power-On Sequence
Table 14. Power-On, PWDN Pin, and Wake-Up Command Timing for New Data
PARAMETER
DESCRIPTION
FILTER MODE
16
tDR
(1)
(2)
Time for data ready 2 CLK cycles after power-on;
and new data ready after PWDN pin or Wake-Up command
SINC (1)
See Appendix, Table 26
62.98046875/fDATA + 468/fCLK
(2)
FIR
Supply power-on and PWDN pin default is 1000 SPS FIR.
Subtract two CLK cycles for the Wake-Up command. The Wake-Up command is timed from the next rising edge of CLK to after the
eighth rising edge of SCLK during command to DRDY falling.
Copyright © 2009–2011, Texas Instruments Incorporated
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ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
DVDD POWER SUPPLY
Serial Clock (SCLK)
The DVDD supply operates over the range of 1.75 V
to 3.6 V. If DVDD is operated at less than 2.25 V,
connect the DVDD pin to the BYPAS pin. If DVDD is
greater than or equal to 2.25 V, do not connect
DVDD to the BYPAS pin. Figure 58 shows this
connection.
The serial clock (SCLK) is an input that is used to
clock data into (DIN) and out of (DOUT) the
ADS1282. This input is a Schmitt-trigger input that
has a high degree of noise immunity. However, it is
recommended to keep SCLK as clean as possible to
prevent possible glitches from inadvertently shifting
the data.
1.75V to 3.6V
DVDD
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Data are shifted into DIN on the rising edge of SCLK
and data are shifted out of DOUT on the falling edge
of SCLK. If SCLK is held low for 64 DRDY cycles,
data transfer or commands in progress terminate and
the SPI interface resets. The next SCLK pulse starts
a new communication cycle. This timeout feature can
be used to recover the interface when a transmission
is interrupted or SCLK inadvertently glitches. SCLK
should remain low when not active.
ADS1282
Tie DVDD to BYPAS if
DVDD power is < 2.25V.
Otherwise float BYPAS.
BYPAS
1mF
Figure 58. DVDD Power
SERIAL INTERFACE
A serial interface is used to read the conversion data
and access the configuration registers. The interface
consists of three basic signals: SCLK, DIN, and
DOUT. An additional output, DRDY, transitions low in
Read Data Continuous mode when data are ready for
retrieval. Figure 59 shows the connection when
multiple converters are used.
FPGA or Processor
SCLK
DOUT1
ADS1282
DIN2
DRDY1
SCLK
DOUT2
ADS1282
DIN2
DRDY2
Data Input (DIN)
The data input pin (DIN) is used to input register data
and commands to the ADS1282. Keep DIN low when
reading conversion data in the Read Data Continuous
mode (except when issuing a STOP Read Data
Continuous command). Data on DIN are shifted into
the converter on the rising edge of SCLK. In Pin
mode, DIN is not used.
Data Output (DOUT)
The data output pin (DOUT) is used to output data
from the ADS1282. Data are shifted out on DOUT on
the falling edge of SCLK.
SCLK
DOUT1
DIN1
IRQ
SCLK (optional)
DOUT2
DIN2
IRQ (optional)
Figure 59. Interface for Multiple Devices
34
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Data Ready (DRDY)
DATA FORMAT
DRDY is an output; when it transitions low, this
transition indicates new conversion data are ready, as
shown in Figure 60. When reading data by the
continuous mode, the data must be read within four
CLK periods before DRDY goes low again or the data
are overwritten with new conversion data. When
reading data by the command mode, the read
operation can overlap the occurrence of the next
DRDY without data corruption.
The ADS1282 provides 32 bits of conversion data in
binary twos complement format, as shown in
Table 15. The LSB of the data is a redundant sign bit:
'0' for positive numbers and '1' for negative numbers.
However, when the output is clipped to +FS, the
LSB = 1; when the output is clipped to –FS, the
LSB = 0. If desired, the data readback may be
stopped at 24 bits. Note that in sinc filter mode, the
output data are scaled by 1/2.
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Table 15. Ideal Output Code versus Input Signal
DRDY
INPUT SIGNAL VIN
(AINP – AINN)
DOUT
Bit 31
Bit 30
32-BIT IDEAL OUTPUT
CODE(1)
Bit 29
FIR FILTER
SCLK
VREF
>
2 x PGA
VREF
Figure 60. DRDY with Data Retrieval
2 x PGA
DRDY resets high on the first falling edge of SCLK.
Figure 60 and Figure 61 show the function of DRDY
with and without data readback, respectively.
If data are not retrieved (no SCLK provided), DRDY
pulses high for four fCLK periods during the update
time, as shown in Figure 61.
4/fCLK
VREF
2PGA ´ (230 - 1)
0
-VREF
2PGA ´ (230 - 1)
Data Updating
DRDY
<
Figure 61. DRDY With No Data Retrieval
´
230 - 1
(3)
7FFFFFFEh
3FFFFFFFh
00000002h
00000001h
00000000h
00000000h
FFFFFFFFh
FFFFFFFFh
80000001h
C0000000h
80000000h
(3)
230
-VREF
2PGA
7FFFFFFFh
230
-VREF
2PGA
SINC
FILTER(2)
´
230 - 1
(1) Excludes effects of noise, linearity, offset, and gain errors.
(2) Due to the reduction in oversampling ratio (OSR) related to
the sinc filter high data rates, full 32-bit available resolution is
reduced.
(3) In sinc filter mode, the output does not clip at half-scale code
when the full-scale range is exceeded.
Copyright © 2009–2011, Texas Instruments Incorporated
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ADS1282-HT
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www.ti.com
READING DATA
Read Data Continuous
Read Data By Command
In the Read Data Continuous mode, the conversion
data are shifted out directly from the device without
the need for sending a read command. This mode is
the default mode at power-on. This mode is also
enabled by the RDATAC command. When DRDY
goes low, indicating that new data are available, the
MSB of data appears on DOUT, as shown in
Figure 62. The data are normally read on the rising
edge of SCLK, at the occurrence of the first falling
edge of SCLK, DRDY returns high. After 32 bits of
data have been shifted out, further SCLK transitions
cause DOUT to go low. If desired, the read operation
may be stopped at 24 bits. The data shift operation
must be completed within four CLK periods before
DRDY falls again or the data may be corrupted.
The Read Data Continuous mode is stopped by the
SDATAC command. In this mode, conversion data
are read by command. In the Read Data By
Command mode, a read data command must be sent
to the device for each data conversion (as shown in
Figure 63). When the read data command is received
(on the eighth SCLK rising edge), data are available
to read only when DRDY goes low (tDR). When DRDY
goes low, conversion data appear on DOUT. The
data may be read on the rising edge of SCLK.
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The ADS1282 has two ways to read conversion data:
Read Data Continuous and Read Data By Command.
When a Stop Read Data Continuous command is
issued, the DRDY output is blocked but the ADS1282
continues conversions. In stop continuous mode, the
data can only be read by command.
DRDY
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
25 26 27 28 29 30
31 32
SCLK
DOUT
Data Byte 1 (MSB)
Data Byte 2 (MSB - 1)
Data Byte 4 (LSB)
tDDPD
DIN
Figure 62. Read Data Continuous
Table 16. Timing Data for Figure 62
PARAMETER
tDDPD
(1)
DESCRIPTION
MIN
TYP
DRDY to valid MSB on DOUT propagation delay (1)
MAX
UNITS
100
ns
Load on DOUT = 20 pF || 100 kΩ.
DRDY
tDR
1
SCLK
DOUT
DIN
2
3
4
5
6
7
8
9
Don't Care
10 11 12 13 14 15 16
33 34 35 36 37 38
Data Byte 1 (MSB)
Command Byte (0001 0010)
39 40
Date Byte 4 (LSB)
tDDPD
Figure 63. Read Data By Command, RDATA (tDDPD timing is given in Table 16)
Table 17. Read Data Timing for Figure 63
PARAMETER
tDR
36
DESCRIPTION
Time for new data after data read command
MIN
0
TYP
MAX
UNITS
1
fDATA
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ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
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ONE-SHOT OPERATION
The ADS1282 can perform very power-efficient,
one-shot conversions using the STANDBY command
while under software control. Figure 64 shows this
sequence. First, issue the STANDBY command to set
the Standby mode.
The conversion data can be scaled for offset and gain
before yielding the final output code. As shown in
Figure 65, the output of the digital filter is first
subtracted by the offset register (OFC) and then
multiplied by the full-scale register (FSC).
Equation 10 shows the scaling:
FSC[2:0]
Final Output Data = (Input - OFC[2:0]) ´
400000h
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When ready to make a measurement, issue the
WAKEUP command. Monitor DRDY; when it goes
low, the fully settled conversion data are ready and
may be read directly in Read Data Continuous mode.
Afterwards, issue another STANDBY command.
When ready for the next measurement, repeat the
cycle starting with another WAKEUP command.
OFFSET AND FULL-SCALE CALIBRATION
REGISTERS
(10)
The values of the offset and full-scale registers are
set by writing to them directly, or they are set
automatically by calibration commands.
Note that the offset and full-scale calibrations apply to
specific PGA settings. When the PGA changes, the
contents of these registers may have to be
recalculated. Calibration is bypassed in the sinc filter
mode.
Standby
ADS1282 Status
DRDY
DIN
DOUT
Performing One-Shot Conversion
(1)
STANDBY
Standby
STANDBY
WAKEUP
Settled
Data
(1) See Figure 56 and Table 14 for time to new data.
Figure 64. One-Shot Conversions Using the STANDBY Command
AINP
Modulator
AINN
Digital
Filter
+
S
´
OFC
Register
FSC Register
400000h
-
Output Data
Clipped to 32 Bits
Final Output
Figure 65. Calibration Block Diagram
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ADS1282-HT
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www.ti.com
FSC[2:0] Registers
The offset calibration is a 24-bit word, composed of
three 8-bit registers, as shown in Table 20. The offset
register is left-justified to align with the 32-bits of
conversion data. The offset is in twos complement
format with a maximum positive value of 7FFFFFh
and a maximum negative value of 800000h. This
value is subtracted from the conversion data. A
register value of 00000h has no offset correction
(default value). Note that while the offset calibration
register value can correct offsets ranging from –FS to
+FS (as shown in Table 18), to avoid input overload,
the analog inputs cannot exceed the full-scale range.
The full-scale calibration is a 24-bit word, composed
of three 8-bit registers, as shown in Table 21. The
full-scale calibration value is 24-bit, straight offset
binary, normalized to 1.0 at code 400000h. Table 19
summarizes the scaling of the full-scale register. A
register value of 400000h (default value) has no gain
correction (gain = 1). Note that while the gain
calibration register value corrects gain errors above 1
(gain correction < 1), the full-scale range of the
analog inputs cannot be exceeded to avoid input
overload.
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OFC[2:0] Registers
Table 19. Full-Scale Calibration Register Values
Table 18. Offset Calibration Values
FSC REGISTER
GAIN CORRECTION
OFC REGISTER
FINAL OUTPUT CODE(1)
800000h
2.0
7FFFFFh
80000000h
400000h
1.0
000001h
FFFFFF00h
200000h
0.5
000000h
00000000h
000000h
0
FFFFFFh
00000100h
800000h
7FFFFF00h
(1) Full 32-bit final output code with zero code input.
Table 20. Offset Calibration Word
REGISTER
OFC0
OFC1
OFC2
BYTE
BIT ORDER
LSB
B7
B6
B5
B4
B3
B2
B1
MID
B15
B14
B13
B12
B11
B10
B9
B0 (LSB)
B8
MSB
B23 (MSB)
B22
B21
B20
B19
B18
B17
B16
B0 (LSB)
Table 21. Full-Scale Calibration Word
REGISTER
FSC0
FSC1
FSC2
38
BYTE
BIT ORDER
LSB
B7
B6
B5
B4
B3
B2
B1
MID
B15
B14
B13
B12
B11
B10
B9
B8
MSB
B23 (MSB)
B22
B21
B20
B19
B18
B17
B16
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OFSCAL Command
Calibration commands may be sent to the ADS1282
to calibrate the conversion data. The values of the
offset and gain calibration registers are internally
written to perform calibration. The appropriate input
signals must be applied to the ADS1282 inputs
before sending the commands. Use slower data rates
to achieve more consistent calibration results; this
effect is a byproduct of the lower noise that these
data rates provide. Also, if calibrating at power-on, be
sure the reference voltage is fully settled.
The OFSCAL command performs an offset
calibration. Before sending the offset calibration
command, a zero input signal must be applied to the
ADS1282 and the inputs allowed to stabilize. When
the command is sent, the ADS1282 averages 16
readings and then writes this value to the OFC
register. The contents of the OFC register may be
subsequently read or written. During offset
calibration, the full-scale correction is bypassed.
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CALIBRATION COMMANDS
Figure 66 shows the calibration command sequence.
After the analog input voltage (and reference) have
stabilized, send the Stop Data Continuous command
followed by the SYNC and Read Data Continuous
commands. 64 data periods later, DRDY goes low.
After DRDY goes low, send the Stop Data
Continuous, then the Calibrate command followed by
the Read Data Continuous command. After 16 data
periods, calibration is complete and conversion data
may be read at this time. The SYNC input must
remain high during the calibration sequence.
Note that the calibration commands apply to specific
PGA settings. If the PGA is changed, recalibration is
necessary. Calibration is bypassed in the sinc filter
mode.
GANCAL Command
The GANCAL command performs a gain calibration.
Before sending the GANCAL command, a dc input
signal must be applied that is in the range of, but not
exceeding, positive or negative full-scale. After the
signal has stabilized, the command can be sent. The
ADS1282 averages 16 readings, then computes the
value that compensates for the gain error. The gain
correction value is then written to the FSC register.
The contents of the GANCAL register may be
subsequently read or written. Note that while the gain
calibration command corrects for gain errors above 1
(gain correction < 1), to avoid input overload, the
analog inputs cannot exceed full-scale range. The
gain calibration should be performed after the offset
calibration.
VIN
Fully stable input and reference voltage.
Commands
SDATAC
DRDY
SYNC
RDATAC
SDATAC
OFSCAL or
GANCAL
64 Data Periods
RDATAC
16 Data
Periods
Calibration
Complete
SYNC
Figure 66. Offset/Gain Calibration Timing
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ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
USER CALIBRATION
average the n output readings.
The value written to the FSC registers is calculated
by Equation 11.
DC signal calibration is shown in Equation 11. The
expected output code is based on 31-bit output data.
FSC[2:0] = 400000h ´
Expected Output Code
Actual Output Code
(11)
For ac signal calibration, use an RMS value of
collected data (as shown in Equation 12).
Expected RMS Value
FSC[2:0] = 400000h ´
Actual RMS Value
(12)
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System calibration of the ADS1282 can be performed
without using the calibration commands. This
procedure requires the calibration values to be
externally calculated and then written to the
calibration registers. The steps for this procedure are:
1. Set the OFSCAL[2:0] register = 0h and
GANCAL[2:0] = 400000h. These values set the
offset and gain registers to 0 and 1, respectively.
2. Apply a zero differential input to the input of the
system. Wait for the system to settle and then
average n output readings. Higher numbers of
averaged readings result in more consistent
calibration. Write the averaged value to the OFC
register.
3. Apply a differential positive or negative dc signal,
or an ac signal, less than the full-scale input to
the system. Wait for the system to settle and then
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Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
COMMANDS
The commands listed in Table 22 control the
operation of the ADS1282. Most commands are
stand-alone (that is, 1 byte in length); the register
reads and writes require a second command byte in
addition to the actual data bytes.
In Read Data Continuous mode, the ADS1282 places
conversion data on the DOUT pin as SCLK is
applied. As a consequence of the potential conflict of
conversion data on DOUT and data placed on DOUT
resulting from a register or Read Data By Command
operation, it is necessary to send a STOP Read Data
Continuous command before Register or Data Read
By Command. The STOP Read Data Continuous
command disables the direct output of conversion
data on the DOUT pin.
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A delay of 24 fCLK cycles between commands and
between bytes within a command is required, starting
from the last SCLK rising edge of one command to
the first SCLK rising edge of the following command.
This delay is shown in Figure 67.
Command
Byte
DIN
Command
Byte
SCLK
(1)
tSCLKDLY
(1)
tSCLKDLY = 24/fCLK (min).
Figure 67. Consecutive Commands
Table 22. Command Descriptions
COMMAND
WAKEUP
STANDBY
SYNC
RESET
RDATAC
SDATAC
RDATA
RREG
WREG
OFSCAL
GANCAL
(1)
(2)
(3)
(4)
1st COMMAND BYTE (1)
(2)
TYPE
DESCRIPTION
Control
Wake-up from Standby mode
0000 000X (00h or 01h)
Control
Enter Standby mode
0000 001X (0 h or 03h)
Control
Synchronize the A/D conversion
0000 010X (04h or 5h)
Control
Reset registers to default values
0000 011X (06h or 07h)
Control
Read data continuous
0001 0000 (10h)
Control
Stop read data continuous
0001 0001 (11h)
Data
Read data by command (4)
Register
Read nnnnn register(s) at address rrrrr
2nd COMMAND BYTE (3)
0001 0010 (12h)
(4)
00r rrrr (20h + 000r rrrr)
000n nnnn (00h + n nnnn)
000n nnnn (00h + n nnnn)
Register
Write nnnnn register(s) at address rrrrr
010r rrrr (40h + 000r rrrr)
Calibration
Offset calibration
0110 0000 (60h)
Calibration
Gain calibration
0110 0001 (61h)
X = don't care.
rrrrr = starting address for register read and write commands.
nnnnn = number of registers to be read/written – 1. For example, to read/write three registers, set nnnnn = 2 (00010).
Required to cancel Read Data Continuous mode before sending a command.
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SDATAC: Stop Read Data Continuous
Description: This command is used to exit the
standby mode. Upon sending the command, the time
for the first data to be ready is illustrated in Figure 56
and Table 15. Sending this command during normal
operation has no effect; for example, reading data by
the Read Data Continuous method with DIN held low.
Description: This command stops the Read Data
Continuous mode. Exiting the Read Data Continuous
mode is required before sending Register and Data
read commands. This command suppresses the
DRDY output, but the ADS1282 continues
conversions.
STANDBY: Standby Mode
RDATA: Read Data By Command
Description: This command places the ADS1282
into Standby mode. In Standby, the device enters a
reduced power state where a low quiescent current
remains to keep the register settings and SPI
interface active. For complete device shutdown, take
the PWDN pin low (register settings are not saved).
To exit Standby mode, issue the WAKEUP command.
The operation of Standby mode is shown in
Figure 68.
Description: This command reads the conversion
data. See the Read Data By Command section for
more details.
DIN
SCLK
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WAKEUP: Wake-Up From Standby Mode
0000 001X
(STANDBY)
Operating
0000 000X
(WAKEUP)
Standby Mode
Description: This command is used to read single or
multiple register data. The command consists of a
two-byte op-code argument followed by the output of
register data. The first byte of the op-code includes
the starting address, and the second byte specifies
the number of registers to read – 1.
First command byte: 001r rrrr, where rrrrr is the
starting address of the first register.
Operating
Figure 68. STANDBY Command Sequence
SYNC: Synchronize the A/D Conversion
Description: This command synchronizes the A/D
conversion. Upon receipt of the command, the
reading in progress is cancelled and the conversion
process is re-started. In order to synchronize multiple
ADS1282s,
the
command
must
be
sent
simultaneously to all devices. Note that the SYNC pin
must be high for this command.
RESET: Reset the Device
Description: The RESET command resets the
registers to default values, enables the Read Data
Continuous mode, and restarts the conversion
process; the RESET command is functionally the
same as the RESET pin. See Figure 55 for the
RESET command timing.
RDATAC: Read Data Continuous
Description: This command enables the Read Data
Continuous mode (default mode). In this mode,
conversion data can be read from the device directly
without the need to supply a data read command.
Each time DRDY falls low, new data are available to
read. See the Read Data Continuous section for
more details.
42
RREG: Read Register Data
Second command byte: 000n nnnn, where nnnnn is
the number of registers – 1 to read.
Starting with the 16th falling edge of SCLK, the
register data appear on DOUT.
The RREG command is illustrated in Figure 69. Note
that a delay of 24 fCLK cycles is required between
each byte transaction.
WREG: Write to Register
Description: This command writes single or multiple
register data. The command consists of a two-byte
op-code argument followed by the input of register
data. The first byte of the op-code contains the
starting address and the second byte specifies the
number of registers to write – 1.
First command byte: 001r rrrr, where rrrrr is the
starting address of the first register.
Second command byte: 000n nnnn, where nnnnn is
the number of registers – 1 to write.
Data byte(s): one or more register data bytes,
depending on the number of registers specified.
Figure 70 illustrates the WREG command.
Note that a delay of 24 fCLK cycles is required
between each byte transaction.
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OFSCAL: Offset Calibration
GANCAL: Gain Calibration
Description: This command performs an offset
calibration. The inputs to the converter (or the inputs
to the external pre-amplifier) should be zeroed and
allowed to stabilize before sending this command.
The offset calibration register updates after this
operation. See the Calibration Commands section for
more details.
Description: This command performs a gain
calibration. The inputs to the converter should have a
stable dc input, preferably close to (but not
exceeding) positive full-scale. The gain calibration
register updates after this operation. See the
Calibration Commands section for more details.
SCLK
DIN
DOUT
tDLY
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tDLY
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Command Byte 1
17 18 19 20 21 22 23 24
tDLY
25 26
Command Byte 2
Don't Care
Register Data 5
Register Data 6
Example: Read six registers, starting at register 05h (OFC0)
Command Byte 1 = 0010 0101
Command Byte 2 = 0000 0101
Figure 69. Read Register Data (Table 23 shows tDLY)
tDLY
1
SCLK
DIN
2
3
4
5
6
7
Command Byte 1
8
9
10 11 12 13 14 15 16
Command Byte 2
tDLY
17 18 19 20 21 22 23 24
Register Data 5
tDLY
25 26
Register Data 6
Example: Write six registers, starting at register 05h (OFC0)
Command Byte 1 = 0100 0101
Command Byte 2 = 0000 0101
Figure 70. Write Register Data (Table 23 shows tDLY)
Table 23. tDRY Value
PARAMETER
MIN
tDLY
24/fCLK
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REGISTER MAP
Collectively, the registers contain all the information needed to configure the part, such as data rate, filter
selection, calibration, etc. The registers are accessed by the RREG and WREG commands. The registers can be
accessed individually or as a block of registers by sending or receiving consecutive bytes. Note that after a
register write operation the ADC resets, resulting in an interruption of 63 readings.
Table 24. Register Map
REGISTER
RESET
VALUE
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
00h
ID
X0h
ID3
ID2
ID1
ID0
0
0
0
0
01h
CONFIG0
52h
SYNC
MODE
DR2
DR1
DR0
PHS
FILTR1
FILTR0
02h
CONFIG1
08h
0
MUX2
MUX1
MUX0
CHOP
PGA2
PGA1
PGA0
03h
HPF0
32h
HPF07
HPF06
HPF05
HPF04
HPF03
HPF02
HPF01
HPF00
04h
05h
06h
07h
08h
09h
0Ah
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ADDRESS
BIT 0
HPF1
03h
HPF15
HPF14
HPF13
HPF12
HPF11
HPF10
HPF09
HPF08
OFC0
00h
OFC07
OFC06
OFC05
OFC04
OFC03
OFC02
OFC01
OFC00
OFC1
00h
OFC15
OFC14
OFC13
OFC12
OFC11
OFC10
OFC09
OFC08
OFC2
00h
OFC23
OFC22
OFC21
OFC20
OFC19
OFC18
OFC17
OFC16
FSC0
00h
FSC07
FSC06
FSC05
FSC04
FSC03
FSC02
FSC01
FSC00
FSC1
00h
FSC15
FSC14
FSC13
FSC12
FSC11
FSC10
FSC09
FSC08
FSC2
40h
FSC23
FSC22
FSC21
FSC20
FSC19
FSC18
FSC17
FSC16
ID : ID REGISTER (ADDRESS 00h)
7
ID3
6
5
4
3
2
1
0
ID2
ID1
ID0
0
0
0
0
Reset value = X0h.
Bit[7:4]
ID[3:0]
Factory-programmed identification bits (read-only)
Bit[3:0]
Reserved
Always write '0'
44
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
CONFIG0 : CONFIGURATION REGISTER 0 (ADDRESS 01h)
7
6
5
4
3
2
1
0
SYNC
MODE
DR2
DR1
DR0
PHASE
FILTR1
FILTR0
Reset value = 52h.
Bit[7]
SYNC
Synchronization mode
0: Pulse SYNC mode (default)
1: Continuous SYNC mode
MODE
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Bit[6]
0: Low-power mode
1: High-resolution mode (default)
Bit[5:3]
Data Rate Select
DR[2:0]
000:
001:
010:
011:
100:
Bit[2]
250SPS
500SPS
1000SPS (default)
2000SPS
4000SPS
FIR Phase Response
PHASE
0: Linear phase (default)
1: Minimum phase
Bit[1:0]
Digital Filter Select
FILTR[1:0]
Digital filter configuration
00: On-chip filter bypassed, modulator output mode
01: Sinc filter block only
10: Sinc + LPF filter blocks (default)
11: Sinc + LPF + HPF filter blocks
Copyright © 2009–2011, Texas Instruments Incorporated
45
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
CONFIG1 : CONFIGURATION REGISTER 1 (ADDRESS 02h)
7
6
5
4
3
2
1
0
0
MUX2
MUX1
MUX0
CHOP
PGA2
PGA1
PGA0
Reset value = 08h.
Bit[7]
Reserved
Always write '0'
Bit[6:4]
MUX Select
MUX[2:0]
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000: AINP1 and AINN1 (default)
001: AINP2 and AINN2
010: Internal short via 400Ω
011:AINP1 and AINN1 connected to AINP2 and AINN2
100: External short to AINN2
Bit[3]
PGA Chopping Enable
CHOP
0: PGA chopping disabled
1: PGA chopping enabled (default)
Bit[2:0]
PGA Gain Select
PGA[2:0]
000:
001:
010:
011:
100:
101:
110:
46
G
G
G
G
G
G
G
=
=
=
=
=
=
=
1 (default)
2
4
8
16
32
64
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
HPF1 and HPF0
These two bytes (high-byte and low-byte, respectively) set the corner frequency of the high-pass filter.
HPF0: High-Pass Filter Corner Frequency, Low Byte (Address 03h)
7
6
5
4
3
2
1
0
HP07
HP06
HP05
HP04
HP03
HP02
HP01
HP00
Reset value = 32h.
HPF1: High-Pass Filter Corner Frequency, High Byte (Address 04h)
HP15
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7
6
5
4
3
2
1
0
HP14
HP13
HP12
HP11
HP10
HP09
HP08
Reset value = 03h.
OFC2, OFC1, OFC0
These three bytes set the offset calibration value.
OFC0: Offset Calibration, Low Byte (Address 05h)
7
OC07
6
5
4
3
2
1
0
OC06
OC05
OC04
OC03
OC02
OC01
OC00
Reset value = 00h.
OFC1: Offset Calibration, Mid Byte (Address 06h)
7
OC15
6
5
4
3
2
1
0
OC14
OC13
OC12
OC11
OC10
OC09
OC08
Reset value = 00h.
OFC2: Offset Calibration, High Byte (Address 07h)
7
OC23
6
5
4
3
2
1
0
OC22
OC21
OC20
OC19
OC18
OC17
OC16
Reset value = 00h.
FSC2, FSC1, FSC0
These three bytes set the full-scale calibration value.
FSC0: Full-Scale Calibration, Low Byte (Address 08h)
7
FSC07
6
5
4
3
2
1
0
FSC06
FSC05
FSC04
FSC03
FSC02
FSC01
FSC00
Reset value = 00h.
FSC1: Full-Scale Calibration, Mid Byte (Address 09h)
7
FSC15
6
5
4
3
2
1
0
FSC14
FSC13
FSC12
FSC11
FSC10
FSC09
FSC08
Reset value = 00h.
FSC2: Full-Scale Calibration, High Byte (Address 0Ah)
7
6
5
4
3
2
1
0
FSC23
FSC22
FSC21
FSC20
FSC19
FSC18
FSC17
FSC16
Reset value = 40h.
Copyright © 2009–2011, Texas Instruments Incorporated
47
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
CONFIGURATION GUIDE
4. Set the data mode. After register configuration,
the device may be configured for Read Data
Continuous mode, either by the Read Data
Continuous command or configured in Read Data
By Register mode using SDATAC command.
5. Synchronize readings. Whenever SYNC is high,
the ADS1282 freely runs the data conversions.
To stop and re-sync the conversions, take SYNC
low and then high.
6. Read data. If the Read Data Continuous mode is
active, the data are read directly after DRDY falls
by applying SCLK pulses. If the Read Data
Continuous mode is inactive, the data can only
be read by Read Data By Command. The Read
Data opcode command must be sent in this mode
to read each conversion result (note that DRDY
only asserts after each read data command is
sent).
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After RESET or power-on, the registers can be
configured using the following procedure:
1. Reset the serial interface. Before using the
serial interface, it may be necessary to recover
the serial interface (undefined I/O power-up
sequencing may cause false SCLK detection). To
reset the SPI interface, toggle the RESET pin or,
when in Read Data Continuous mode, hold SCLK
low for 64 DRDY periods.
2. Configure the registers. The registers are
configured by either writing to them individually or
as a group. Software may be configured in either
mode. The SDATAC command must be sent
before register read/write operations to cancel the
Read Data Continuous mode.
3. Verify register data. The register may be read
back for verification of device communications.
48
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
APPLICATION INFORMATION
Diode clamps protect the ADS1282 inputs from
voltage transients and overloads.
The REF02 +5-V reference provides the reference to
the ADS1282. The reference output is filtered by the
optional R7 and C5 filter network. The filter requires
several seconds to settle after power-on. Capacitor
C7 provides high-frequency bypassing of the
reference inputs and should be placed close to the
ADS1282 pins. Note that R7 (1kΩ) results in a
systematic gain error (–1.2% in high-resolution mode,
and –0.6% in low-power mode).
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The ADS1282 is a very high-resolution ADC. Optimal
performance requires giving special attention to the
support circuitry and printed circuit board (PCB)
design. Locate noisy digital components, such as
microcontrollers, oscillators, etc, in an area of the
PCB away from the converter or front-end
components. Locating the digital components close to
the power-entry point keeps the digital current path
short and separate from sensitive analog
components.
A typical geophone front-end application is shown in
Figure 71. The application shows the ADS1282
operation with dual ±2.5-V analog supplies. The
ADS1282 can also operate with a single 5-V analog
supply.
The geophone input signal is filtered both
differentially, by components C4 and R1 to R4 and
filtered independently by components C2, C3 and R1,
R2. The differential filter removes high-frequency
normal mode components from the input signal. The
independent
filters
remove
high-frequency
components that are common to both input signals
leads (common-mode filter). The recommended input
filters may not be required for all applications
depending on the system requirements.
Resistors R5 and R6 bias the signals inputs to
midsupply (ground), and also provide the bias current
return path for the ADS1282 inputs. For single-supply
operation, set the bias to a low impedance 2.5 V
(AVDD/2). Resistors R5 and R6 can also influence
common-mode attenuation. To maintain good CMR
performance, resistors R5 and R6 may require
matching.
Copyright © 2009–2011, Texas Instruments Incorporated
Alternatively, the REF5050 (5V) or REF5045 (4.5V)
reference can be used. The REF5045 reference has
the advantage of operating from the +5V power
supply. The REF5050 requires 5.2-V minimum power
supply.
Optional components R8, and R9 provides a 20mV
offset to the ADS1282. The internal 300-Ω resistors
form a voltage divider with the external resistors to
provide the offset. The offset moves the low level idle
tones out of the passsband. Note that the offset is
independent of the PGA setting. To maintain good
CMR performance, R10 and R11 should be matched to
0.1%, and the traces routed back directly to the
reference.
Capacitor C6 (10 nF) filters the PGA output glitches
caused by sampling of the modulator. The capacitor
also forms a low-pass filter on the input signal with a
cut-off frequency ≉ 25 kHz.
49
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
+2.5V
15
+2.5V
Test
Source
-2.5V
19
20
AVDD
AVSS
AINP2
16
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AINN2
R1
100W
Geophone
R3
100W
17
C2
1nF, COG
R5
20kW
R6
20kW
(2)
R2
100W
C3
1nF, COG
AINP1
C4
10nF
COG
R4
100W
18
AINN1
ADS1282
-2.5V
R8
(1)
75kW
+6.5V
(+2.8V REF5050)
1 mF
14
C6
10nF
COG 13
CAPN
R9
R7
1kW
REF02
(REF5050)
CAPP
(1)
75kW
22
VREFP
1mF
+
C5
100mF
C7
0.1mF
21
-2.5V
VREFN
DGND
6, 12, 25, 27
(1) Optional 20 mV offset. Match to 0.1% to maintain CMR.
Figure 71. Geophone Interface Application
50
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Figure 72 shows the digital connection to a field
programmable gate array (FPGA) device. In this
example, two ADS1282s are shown connected. The
DRDY output from each ADS1282 can be used;
however, when the devices are synchronized, the
DRDY output from only one device is sufficient. A
shared SCLK line between the devices is optional.
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The modulator over-range flag (MFLAG) from each
device ties to the FPGA. For synchronization, one
SYNC control line connects all ADS1282 devices.
The RESET line also connects to all ADS1282
devices.
For best performance, the FPGA and the ADS1282s
should operate from the same clock. Avoid ringing on
the digital inputs. 47-Ω resistors in series with the
digital traces can help to reduce ringing by controlling
impedances. Place the resistors at the source (driver)
end of the trace. Unused digital inputs should not
float; tie them to DVDD or GND. This includes the
modulator data pins, M0, M1, and MCLK.
4.096MHz Clock
47W
+3.3V
26
(1)
DVDD
1mF
28
CLK
1
ADS1282
24
RESET
BYPAS
DOUT
DIN
1mF
SCLK
SYNC
DGND
MFLAG
4
47W
RESET
47W
DOUT1
47W
5
CLK Input
DIN1
47W
2
SCLK1
47W
10
SYNC
47W
11
MFLAG1
4, 12, 23
+3.3V
26
(1)
1mF
DVDD
CLK
ADS1282
RESET
28
BYPAS
DOUT
DIN
1mF
SCLK
SYNC
MFLAG
DGND
DRDY
1
FPGA
24
4
47W
DOUT2
5
DIN2
2
SCLK2
47W
10
47W
11
3
47W
MFLAG2
DRDY
6, 12, 25
NOTE: Dashed line is optional.
(1) For DVDD < 2.25 V, see the DVDD Power Supply section.
Figure 72. Microcontroller Interface with Dual ADS1282s
Copyright © 2009–2011, Texas Instruments Incorporated
51
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
APPENDIX
Table 25. FIR Stage Coefficients
SECTION 1
COEFFICIENT
Scaling = 1/8388608
SECTION 3
SECTION 4
Scaling = 134217728
Scaling = 134217728
LINEAR
PHASE
MINIMUM PHASE
LINEAR
PHASE
MINIMUM PHASE
–10944
–774
–73
819
–132
11767
b1
0
0
–874
8211
–432
133882
b2
103807
8994
–4648
44880
–75
769961
2940447
b4
b5
b6
b7
b8
b9
b10
b11
b12
b13
b14
b15
b16
b17
b18
b19
b20
b21
b22
b23
b24
b25
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b0
b3
0
0
–16147
174712
2481
–507903
–51663
–41280
536821
6692
8262605
0
0
–80934
1372637
7419
17902757
2512192
199523
–120064
3012996
–266
30428735
4194304
0
–118690
5788605
–10663
40215494
2512192
–629120
–18203
9852286
–8280
39260213
23325925
0
0
224751
14957445
10620
–507903
2570188
580196
20301435
22008
–1757787
0
4194304
893263
24569234
348
–21028126
103807
2570188
891396
26260385
–34123
–21293602
0
0
293598
24247577
–25549
–3886901
–10944
–629120
–987253
18356231
33460
14396783
0
–2635779
9668991
61387
16314388
199523
–3860322
327749
–7546
1518875
0
–3572512
–7171917
–94192
–12979500
–51663
–822573
–10926627
–50629
–11506007
0
4669054
–10379094
101135
2769794
8994
12153698
–6505618
134826
12195551
0
19911100
–1333678
–56626
6103823
–774
25779390
2972773
–220104
–6709466
27966862
5006366
–56082
–9882714
Only half shown;
symmetric starting
with b22.
4566808
263758
–353347
2505652
231231
8629331
126331
–215231
5597927
–1496514
–430178
–4389168
–1933830
34715
–7594158
–1410695
580424
–428064
–502731
283878
6566217
245330
–588382
4024593
565174
–693209
–3679749
492084
366118
–5572954
231656
1084786
332589
b35
–9196
132893
5136333
b36
–125456
–1300087
2351253
b37
–122207
–878642
–3357202
b38
–61813
1162189
–3767666
b26
b27
b28
b29
b30
b31
b32
b33
b34
52
SECTION 2
b39
–4445
1741565
1087392
b40
22484
–522533
3847821
b41
22245
–2490395
919792
b42
10775
–688945
–2918303
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Table 25. FIR Stage Coefficients (continued)
SECTION 1
SECTION 2
SECTION 3
SECTION 4
Scaling = 134217728
Scaling = 134217728
MINIMUM PHASE
LINEAR
PHASE
MINIMUM PHASE
b43
940
2811738
–2193542
COEFFICIENT
Scaling = 1/8388608
LINEAR
PHASE
–2953
2425494
1493873
–2599
–2338095
2595051
b46
–1052
–4511116
–79991
b47
–43
641555
–2260106
214
6661730
–963855
132
2950811
1482337
33
–8538057
1480417
b48
b49
b50
b51
b52
b53
b54
b55
b56
b57
b58
b59
b60
b61
b62
b63
b64
b65
b66
b67
b68
b69
b70
b71
b72
b73
b74
b75
b76
b77
b78
b79
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b44
b45
–10537298
–586408
9818477
–1497356
41426374
–168417
56835776
1166800
Only half shown;
symmetric starting
with b53.
–675082
644405
–806095
211391
740896
141976
–527673
–327618
278227
363809
–70646
–304819
–63159
205798
124363
–107173
–131357
31104
107182
15644
–71728
–36319
38331
38783
–13557
b80
–31453
b81
–1230
b82
20983
b83
7729
b84
–11463
b85
–8791
b86
4659
b87
7126
Copyright © 2009–2011, Texas Instruments Incorporated
53
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Table 25. FIR Stage Coefficients (continued)
SECTION 1
COEFFICIENT
SECTION 2
Scaling = 1/8388608
SECTION 3
SECTION 4
Scaling = 134217728
Scaling = 134217728
LINEAR
PHASE
LINEAR
PHASE
MINIMUM PHASE
MINIMUM PHASE
b88
–732
b89
–4687
b90
–976
b91
2551
b93
b94
b95
b96
b97
b98
b99
b100
b101
b102
b103
b104
b105
b106
b107
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b92
1+
HPF Gain =
–1085
314
681
16
–349
–96
144
78
–46
–42
9
16
0
–4
cos wN + sin wN - 1
1-2
2-
1339
–1103
cos wN
cos wN + sin wN - 1
cos wN
(13)
See the HPF Stage section for an example of how to use this equation.
HPF Transfer Function
-1
2-a
1-Z
´
HPF(Z) =
-1
1 - bZ
2
(14)
where b is calculated as shown in Equation 15:
2 2
b=
(1 + (1 - a) )
2
(15)
Table 26. tDR Time for Data Ready (Sinc Filter)
fDATA
(1)
54
fCLK
(1)
128k
440
64k
616
32k
968
16k
1672
For SYNC and Wake-Up commands, fCLK = number of CLK cycles from next rising CLK edge directly after eighth rising SCLK edge to
DRDY falling edge. For Wake-Up command only, subtract two fCLK cycles.
Copyright © 2009–2011, Texas Instruments Incorporated
ADS1282-HT
SBAS446F – DECEMBER 2009 – REVISED AUGUST 2011
www.ti.com
Table 26. tDR Time for Data Ready (Sinc Filter) (continued)
fDATA
8k
fCLK
(1)
2824
Table 26 is referenced by Table 12 and Table 14.
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Copyright © 2009–2011, Texas Instruments Incorporated
55
PACKAGE OPTION ADDENDUM
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29-Aug-2011
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PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
(2)
Pins
Package Qty
PW
28
50
Green (RoHS
& no Sb/Br)
Eco Plan
Lead/
Ball Finish
MSL Peak Temp
ADS1282HPW
ACTIVE
TSSOP
ADS1282SJDJ
ACTIVE
CDIP SB
JDJ
28
13
TBD
Call TI
N / A for Pkg Type
ADS1282SKGDA
ACTIVE
XCEPT
KGD
0
80
TBD
Call TI
N / A for Pkg Type
(1)
(3)
Samples
(Requires Login)
CU NIPDAU Level-3-260C-168 HR
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
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In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
OTHER QUALIFIED VERSIONS OF ADS1282-HT :
• Catalog: ADS1282
NOTE: Qualified Version Definitions:
Addendum-Page 1
PACKAGE OPTION ADDENDUM
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• Catalog - TI's standard catalog product
Addendum-Page 2
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