TI ADS1282IPWRG4 High-resolution analog-to-digital converter Datasheet

ADS1282
AD
S1
282
www.ti.com ................................................................................................................................................. SBAS418D – SEPTEMBER 2007 – REVISED JULY 2008
High-Resolution Analog-to-Digital Converter
FEATURES
DESCRIPTION
1
• High Resolution:
130dB SNR (250SPS, High-Resolution Mode)
127dB SNR (250SPS, Low-Power Mode)
• High Accuracy:
THD: –122dB
INL: 0.5ppm
• 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: 250SPS to 4kSPS
• Filter Bypass Option
• Low Power Consumption:
High-Resolution Mode: 25mW
Low-Power Mode: 17mW
Shutdown: 10µW
• Offset and Gain Calibration Engine
• SYNC Input
• Analog Supply:
Unipolar (+5V) or Bipolar (±2.5V)
• Digital Supply: 1.8V to 3.3V
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.
2
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.
APPLICATIONS
•
•
•
Two operating modes allow optimization of noise and
power. Together, the amplifier, modulator, and filter
dissipate 25mW and only 17mW in low-power mode.
The ADS1282 is available in a compact TSSOP-28
package and is fully specified from –40°C to +85°C,
with a maximum operating range to +125°C.
Energy Exploration
Seismic Monitoring
High-Accuracy Instrumentation
AVDD
VREFN
VREFP
DVDD
CLK
ADS1282
MUX
Input 1
Input 2
PGA
4th-Order
DS
Modulator
Programmable
Digital Filter
Calibration
SPI
Interface
SCLK
DOUT
DIN
DRDY
Control
SYNC
RESET
PWDN
VCOM
Over-Range
Modulator Output
3
AVSS
DGND
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
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 © 2007–2008, Texas Instruments Incorporated
ADS1282
SBAS418D – SEPTEMBER 2007 – REVISED JULY 2008 ................................................................................................................................................. www.ti.com
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.
ORDERING INFORMATION
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.
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
Digital input voltage to DGND
–0.3 to DVDD + 0.3
V
+150
°C
Operating temperature range
–40 to +125
°C
Storage temperature range
–60 to +150
°C
Maximum junction temperature
(1)
2
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.
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ELECTRICAL CHARACTERISTICS
Limit specifications at –40°C to +85°C. Typical specifications at +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK (1) = 4.096MHz, VREFP = +2.5V,
VREFN = –2.5V, DVDD = +3.3V, CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
ADS1282
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUTS
Full-scale input voltage
VIN = (AINP – AINN)
Absolute input range
AINP or AINN
±VREF/2 × PGA
AVSS + 0.7
PGA input voltage noise density
V
AVDD – 1.25
V
5
Differential input impedance (2)
Common-mode input impedance
Input bias current
Crosstalk
f = 31.25Hz
MUX on-resistance
nV/√Hz
1
GΩ
100
MΩ
1
nA
–135
dB
30
Ω
PGA OUTPUT (CAPP, CAPN)
Absolute output range
AVSS + 0.4
AVDD – 0.4
PGA differential output impedance
600
Output impedance tolerance
±10
External bypass capacitance
10
Modulator differential input impedance
V
Ω
%
100
nF
High-resolution mode
55
kΩ
Low-power mode
110
kΩ
AC PERFORMANCE
Signal-to-noise ratio (3)
SNR
High-resolution mode
120
124
Low-power mode
117
121
dB
High-resolution mode
Total harmonic distortion (4)
Spurious-free dynamic
range
THD
PGA = 1...16
–122
–114
PGA = 32
–117
–110
PGA = 64
–115
dB
Low-power mode
PGA = 1...16
–122
–114
PGA = 32
–113
–108
PGA = 64
–109
SFDR
dB
dB
123
DC PERFORMANCE
Resolution
Data rate
Integral nonlinearity (INL)
fDATA
(5)
No missing codes
31
FIR filter mode
250
4000
SPS
Sinc filter mode
8000
128,000
SPS
0.00005
0.0004
% FSR (6)
50
200
µV
Differential input
Offset error
Offset error after calibration (7)
Shorted input
Offset drift
Gain error (8)
1
µV
0.02
µV/°C
High-resolution mode
–1.5
–1.0
–0.5
%
Low-power mode
–1
–0.5
0
%
Gain error after calibration (7)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Bits
0.0002
%
fCLK = system clock.
Input impedance is improved by disabling input chopping (CHOP bit = 0).
VIN = 20mVDC/PGA, see Table 1.
VIN = 31.25Hz, –0.5dBFS.
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).
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).
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ELECTRICAL CHARACTERISTICS (continued)
Limit specifications at –40°C to +85°C. Typical specifications at +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V,
VREFN = –2.5V, DVDD = +3.3V, CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
ADS1282
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
DC PERFORMANCE (continued)
Gain drift
PGA = 1
2
PGA = 16
9
Gain matching (9)
0.3
fCM = 60Hz (10)
Common-mode rejection
Power-supply rejection
AVDD, AVSS
DVDD
fPS = 60Hz (10)
95
ppm/°C
ppm/°C
0.8
110
80
90
90
115
0.5
5
%
dB
dB
VOLTAGE REFERENCE INPUTS
Reference input voltage
(VREF = VREFP – VREFN)
(AVDD – AVSS)
+ 0.2
V
V
Negative reference input
VREFN
AVSS – 0.1
VREFP – 0.5
Positive reference input
VREFP
VREFN + 0.5
AVDD + 0.1
Reference input impedance
V
High-resolution mode
85
kΩ
Low-power mode
170
kΩ
DIGITAL FILTER RESPONSE
Passband ripple
±0.003
Passband (–0.01dB)
0.375 × fDATA
Bandwidth (–3dB)
0.413 × fDATA
High-pass filter corner
0.1
Stop band attenuation (11)
135
Hz
Hz
10
0.500 × fDATA
Settling time (latency)
Hz
dB
Stop band
Group delay
dB
Minimum phase filter
5/fDATA
Linear phase filter
31/fDATA
Minimum phase filter
10/fDATA
Linear phase filter
62/fDATA
Hz
s
s
DIGITAL INPUT/OUTPUT
VIH
0.8 × DVDD
DVDD
V
VIL
DGND
0.2 × DVDD
V
VOH
IOH = 1mA
VOL
IOL = 1mA
0.2 × DVDD
V
0 < VDIGITAL IN < DVDD
±10
µA
4.096
MHz
fCLK/2
MHz
Input leakage
Clock input
Serial clock rate
fCLK
0.8 × DVDD
1
fSCLK
V
(9) Gain match relative to PGA = 1.
(10) fCM is the input common-mode frequency. fPS is the power-supply frequency.
(11) 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 = 120dB, typ.
4
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ELECTRICAL CHARACTERISTICS (continued)
Limit specifications at –40°C to +85°C. Typical specifications at +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V,
VREFN = –2.5V, DVDD = +3.3V, CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
ADS1282
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
POWER SUPPLY
AVSS
–2.6
0
V
AVDD
AVSS + 4.75
AVSS + 5.25
V
DVDD
1.65
3.6
V
AVDD, AVSS current
DVDD current
Power dissipation
High-resolution mode
4.5
6.5
|mA|
Low-power mode
3
4.2
|mA|
Standby mode
1
15
|µA|
Power-down mode
1
15
|µA|
All modes
0.6
0.8
mA
Modulator mode
0.1
Standby mode
25
50
µA
Power-down mode (12)
1
15
µA
High-reolution mode
25
35
mW
Low-power mode
17
25
mW
Standby mode
90
250
µW
Power-down mode
10
125
µW
mA
(12) CLK input stopped.
TIMING DIAGRAM
tSCDL
tSCLK
tSPWH
SCLK
tDIST
tSPWL
tSCDL
DIN
tDIHD
tDOHD
DOUT
tDOPD
TIMING REQUIREMENTS
At TA = –40°C to +85°C and DVDD = 1.65V to 3.6V, unless otherwise noted.
PARAMETER DESCRIPTION
tSCLK
tSPWH,
(1)
(2)
MIN
MAX
UNITS
2
16
1/fCLK
SCLK pulse width, high and low (1)
0.8
10
1/fCLK
SCLK period
L
tDIST
DIN valid to SCLK rising edge: setup time
50
tDIHD
Valid DIN to SCLK rising edge: hold time
50
ns
tDOPD
SCLK falling edge to valid new DOUT: propagation delay (2)
tDOHD
SCLK falling edge to DOUT invalid: hold time
0
ns
tSCDL
Final SCLK rising edge of command to first SCLK rising edge for register read/write
data. (Also between consecutive commands.)
24
1/fCLK
ns
100
ns
Holding SCLK low for 64 DRDY falling edges resets the serial interface.
Load on DOUT = 20pF || 100kΩ.
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DEVICE INFORMATION
TSSOP-28
Top View
CLK
1
28
BYPAS
SCLK
2
27
DGND
DRDY
3
26
DVDD
DOUT
4
25
DGND
DIN
5
24
RESET
DGND
6
23
PWDN
MCLK
7
22
VREFP
M1
8
21
VREFN
ADS1282
M0
9
20
AVSS
SYNC
10
19
AVDD
MFLAG
11
18
AINN1
DGND
12
17
AINP1
CAPN
13
16
AINN2
CAPP
14
15
AINP2
TERMINAL FUNCTIONS
6
NAME
NO.
FUNCTION
DESCRIPTION
Master clock input
CLK
1
Digital input
SCLK
2
Digital input
Serial clock input
DRDY
3
Digital output
Data ready output: read data on falling edge
DOUT
4
Digital output
Serial data output
DIN
5
Digital input
Serial data input
MCLK
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).
M1
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).
M0
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).
SYNC
10
Digital input
Synchronize input
MFLAG
11
Digital output
Modulator Over-Range flag: 0 = normal, 1 = modulator over-range
DGND
6, 12, 25, 27
Digital ground
Digital ground, pin 12 is the key ground point
CAPN
13
Analog
PGA outputs: Connect 10nF capacitor from CAPP to CAPN
PGA outputs: Connect 10nF capacitor from CAPP to CAPN
CAPP
14
Analog
AINP2
15
Analog input
Positive analog input 2
AINN2
16
Analog input
Negative analog input 2
AINP1
17
Analog input
Positive analog input 1
AINN1
18
Analog input
Negative analog input 1
AVDD
19
Analog supply
Positive analog power supply
AVSS
20
Analog supply
Negative analog power supply
VREFN
21
Analog input
Negative reference input
VREFP
22
Analog input
Positive reference input
PWDN
23
Digital input
Power-down input, active low
RESET
24
Digital input
Reset input, active low
DVDD
26
Digital supply
Digital power supply: +1.8V to +3.3V
BYPAS
28
Analog
Sub-regulator output: Connect 1µF capacitor to DGND
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TYPICAL CHARACTERISTICS
At +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V, VREFN = –2.5V, DVDD = +3.3V,
CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
OUTPUT SPECTRUM
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
High-Resolution Mode
PGA = 1
THD = -124.0dB
-20
-40
Amplitude (dB)
OUTPUT SPECTRUM
-60
-80
-100
-120
0
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
Low-Power Mode
PGA = 1
THD = -123.0dB
-20
-40
Amplitude (dB)
0
-60
-80
-100
-120
-140
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
Figure 1.
-60
-80
-100
-120
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
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
Figure 3.
-60
-80
-100
-120
0
-40
-60
-80
-100
-120
-140
-140
-160
-160
-180
8192-Point FFT
VIN = -0.5dBFS, 31.25Hz
Low-Power Mode
PGA = 16
THD = -121.4dB
-20
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 4.
OUTPUT SPECTRUM
0
Amplitude (dB)
500
Figure 2.
OUTPUT SPECTRUM
0
100 150 200 250 300 350 400 450
Frequency (Hz)
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
Figure 5.
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
Figure 6.
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TYPICAL CHARACTERISTICS (continued)
At +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V, VREFN = –2.5V, DVDD = +3.3V,
CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
OUTPUT SPECTRUM
0
-20
-60
-80
-100
-120
8192-Point FFT
Shorted Input
Low-Power Mode
SNR = 121.0dB
-20
-40
Amplitude (dB)
-40
Amplitude (dB)
OUTPUT SPECTRUM
0
8192-Point FFT
Shorted Input
High-Resolution Mode
SNR = 124.0dB
-60
-80
-100
-120
-140
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
Figure 7.
Figure 8.
OUTPUT SPECTRUM
0
-60
-80
-100
-120
8192-Point FFT
20mVDC
Low-Power Mode
SNR = 121.3dB
-20
-40
Amplitude (dB)
-40
Amplitude (dB)
OUTPUT SPECTRUM
0
8192-Point FFT
20mVDC
High-Resolution Mode
SNR = 124.2dB
-20
-60
-80
-100
-120
-140
-140
-160
-160
-180
-180
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
500
0
50
100 150 200 250 300 350 400 450
Frequency (Hz)
Figure 9.
SNR vs TEMPERATURE
126
-105
High-Resolution Mode, PGA = 1
Low-Power Mode, PGA = 1
High-Resolution Mode, PGA = 8
Low-Power Mode, PGA = 8
-115
-120
-125
Signal-to-Noise Ratio (dB)
THD Limited by
Signal Generator
-110
500
Figure 10.
THD vs INPUT FREQUENCY
-100
Total Harmonic Distortion (dB)
500
VIN = 20mVDC
125
High-Resolution Mode
124
123
122
Low-Power Mode
121
VIN = -0.5dBFS
-130
10
20
30
40
50
60
70
Input Frequency (Hz)
80
90
100
120
-55
Figure 11.
8
-35
-15
5
25
45
65
Temperature (°C)
85
105
125
Figure 12.
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TYPICAL CHARACTERISTICS (continued)
At +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V, VREFN = –2.5V, DVDD = +3.3V,
CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
THD vs TEMPERATURE
SNR vs REFERENCE VOLTAGE
130
PGA = 8
VIN = 31.25Hz, -0.5dBFS
High-Resolution Mode, PGA = 1
Signal-to-Noise Ratio (dB)
Total Harmonic Distortion (dB)
-110
-115
Low-Power Mode
-120
-125
High-Resolution Mode
125
High-Resolution Mode, PGA = 8
120
115
Low-Power Mode, PGA = 1
110
105
Low-Power Mode, PGA = 8
-130
-55
100
-35
-15
5
25
45
65
Temperature (°C)
85
105
0
125
1
2
Figure 13.
3
VREF (V)
4
5
5.5
Figure 14.
THD vs REFERENCE VOLTAGE
SNR vs CLOCK FREQUENCY
125
-110
Signal-to-Noise Ratio (dB)
Total Harmonic Distortion (dB)
High-Resolution Mode, PGA = 8
-115
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
4
5
0.5
6
1.0
1.5
VREF (V)
Figure 15.
4.0
4.5
-120
High-Resolution Mode
130
Common-Mode Rejection (dB)
Total Harmonic Distortion (dB)
Low-Power Mode
-125
3.5
CMR vs INPUT FREQUENCY
PGA = 8
VIN = 31.25Hz, -0.5dBFS
Data Rate = fCLK/4096
-115
2.5
3.0
fCLK (MHz)
Figure 16.
THD vs CLOCK FREQUENCY
-110
2.0
120
110
100
90
Low-Power Mode
80
High-Resolution Mode
-130
70
0.5
1.0
1.5
2.0
2.5
3.0
fCLK (MHz)
3.5
4.0
4.5
10
Figure 17.
100
1k
10k
Input Frequency (Hz)
100k
1M
Figure 18.
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TYPICAL CHARACTERISTICS (continued)
At +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V, VREFN = –2.5V, DVDD = +3.3V,
CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
POWER-SUPPLY REJECTION
vs FREQUENCY
INL vs INPUT AMPLITUDE
4
140
AVDD
3
Integral Nonlinearity (ppm)
Power-Supply Rejection (dB)
DVDD
120
100
80
AVSS
60
40
20
2
PGA = 2
1
0
-1
PGA = 8
-3
0
10
100
1k
10k
100k
Power-Supply Frequency (Hz)
-4
-100
1M
-50
-25
0
25
50
Input Amplitude (% Full-Scale)
-75
Figure 19.
75
100
Figure 20.
INL vs TEMPERATURE
CROSSTALK OUTPUT SPECTRUM
4
0
Shorted Input
8192-Point FFT
Adjacent Channel VIN = -0.5dBFS, 31.25Hz
-20
-40
3
Amplitude (dB)
Integral Nonlinearity (ppm)
PGA = 32
-2
2
1
-60
-80
-100
-120
-140
-160
0
-55
-180
-35
-15
5
25
45
65
Temperature (°C)
85
105
125
0
100 150 200 250 300 350 400 450
Frequency (Hz)
50
Figure 21.
500
Figure 22.
POWER vs TEMPERATURE
POWER vs CLOCK FREQUENCY
30
30
High-Resolution Mode
High-Resolution Mode
25
Power (mW)
Power (mW)
25
20
Low-Power Mode
20
Low-Power Mode
15
10
15
5
10
-55
0
-35
-15
5
25
45
65
Temperature (°C)
85
105
125
1.0
Figure 23.
10
1.5
2.0
2.5
3.0
fCLK (MHz)
3.5
4.0
4.5
Figure 24.
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TYPICAL CHARACTERISTICS (continued)
At +25°C, AVDD = +2.5V, AVSS = –2.5V, fCLK = 4.096MHz, VREFP = +2.5V, VREFN = –2.5V, DVDD = +3.3V,
CAPN – CAPP = 10nF, PGA = 1, High-Resolution Mode, and fDATA = 1000SPS, unless otherwise noted.
OFFSET HISTOGRAM
GAIN ERROR HISTOGRAM
30
10
25 Units
25 Units
25
8
High-Resolution Mode
20
Occurrences
Occurrences
PGA = 8
15
10
6
4
PGA = 1
Low-Power Mode
2
5
0
-100 -80 -60 -40 -20
0
20
Offset (mV)
40
60
80
0
-1.2
100
-1.1 -1.0
-0.9
Figure 25.
80
Occurrences
30
60
50
PGA = 8, 64
30
20
PGA =1
-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
0
-0.02
10
-0.04
PGA = 16
40
10
-0.08
PGA = 1, 2, 4
PGA = 32
40
-0.10
-0.3
70
50
20
25 Units Based on +20°C Intervals
Over the Range of -40°C to +85°C
80
PGA = 8
60
-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
-0.5
Figure 26.
OFFSET DRIFT HISTOGRAM
90
-0.8 -0.7 -0.6
Gain Error (%)
Gain Drift (ppm/°C)
Offset Drift (mV/°C)
Figure 27.
Figure 28.
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 29.
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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 250SPS to
4000SPS. Figure 30 shows the block diagram of the
ADS1282.
The
two-channel
input
MUX
allows
five
configurations: Input 1; Input 2; Input 1 and Input 2
shorted together; shorted with 400Ω 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.
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.
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.
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).
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.
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.
ADS1282
AINP2
AINN2
AINP1
AINN1
BYPAS
CLK
+1.8V
(Digital core)
DVDD
LDO
MUX
300W
400W
PGA
4th-Order
DS
Modulator
300W
400W
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 30. ADS1282 Block Diagram
12
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The device features unipolar and bipolar analog
power supplies (AVDD and AVSS, respectively) for
input range flexibility and a digital supply accepting
1.8V to 3.3V. The analog supplies may be set to +5V
to accept unipolar signals (with input offset) or set
lower in the range of ±2.5V 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 1µF 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 3dB for each
setting. Table 1 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
–137dB 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
(1)
FSRRMS = Full-scale range RMS = VREF/2 × √2 ×
PGA
NRMS = Noise RMS (input-referred)
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 17mW (from 25mW) and SNR
decreases an average of 3dB. The default mode is
high-resolution.
Table 1. Signal-to-Noise Ratio (dB) (1)
(1)
PGA (High-Resolution Mode)
PGA (Low-Power Mode)
DATA RATE
(SPS)
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
500
127
127
126
125
122
116
111
124
124
123
122
119
113
108
1000
124
124
123
122
119
113
108
121
121
120
119
116
110
105
2000
121
121
120
119
116
111
106
118
118
117
116
113
108
103
4000
118
118
117
116
113
108
103
115
115
114
113
110
105
100
VIN = 20mVDC/PGA.
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Table 2. Multiplexer Modes
ANALOG INPUTS AND MULTIPLEXER
A diagram of the input multiplexer is shown in
Figure 31.
MUX[2:0]
ESD diodes protect the multiplexer inputs. If either
input is taken below AVSS – 0.3V or above AVDD +
0.3V, 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).
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.
AVDD
S1
ESD Diodes
S2
AINP2
400W
2
To PGA
400W
S4
S5
AINN1
ESD Diodes
AINN2
S1, S5
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
S3
AVDD + AVSS
AVDD
000
(+)
S7
AVSS
DESCRIPTION
AINP1 and AINN1 connected to
preamplifer
The typical on-resistance (RON) of the multiplexer
switch is 30Ω. 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 32 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 33 with MUX[2:0] = 011.
(-)
S6
Total Harmonic Distortion (dB)
AINP1
SWITCHES
PGA = 1
PGA = 2
PGA = 4
PGA = 8
PGA = 16
PGA = 32
PGA = 64
-20
-40
-60
-80
-100
-120
-140
0.1k
1k
10k
100k
1M
10M
RLOAD (W)
AVSS
Figure 31. Analog Inputs and Multiplexer
Figure 32. THD versus External Load and Signal
Magnitude (PGA) (see Figure 33)
The specified input operating range of the PGA is
shown in Equation 2:
AVSS + 0.7V < (AINN or AINP) < AVDD - 1.25V (2)
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 2 summarizes the multiplexer
configurations for Figure 31.
RLOAD
14
ADS1282
Input 1
Input 2
Figure 33. Driving an External Load Through the
MUX
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PGA (Programmable Gain Amplifier)
AVDD
Referring to Figure 34, amplifiers A1 and A2 are
chopped to remove the offset, offset drift, and the 1/f
noise. Chopping moves the effects to fCLK/128 (8kHz),
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 (>> 1GΩ). As shown in
Figure 35, 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 3 shows the register bit setting for the PGA and
resulting full-scale differential range.
The specified output operating range of the PGA is
shown in Equation 4:
AVSS + 0.4V < (CAPN or CAPP) < AVDD - 0.4V (4)
PGA output levels (signal plus common-mode) should
be maintained within these limits for best operation.
MUX (+)
Gain Control
PGA[2:0] Bits
GAIN
000
1
±2.5
001
2
±1.25
010
4
±0.625
011
8
±0.312
100
16
±0.156
101
32
±0.078
110
64
±0.039
10nF
(1)
300W
CAPN
A2
(55kW, typ )
Modulator
Effective
Impedance
MUX (-)
Chopping Control CHOP Bit
AVSS
(1) Low-power mode = 110kΩ.
Figure 34. PGA Block Diagram
100
PGA CHOP Off
10
PGA CHOP On
1
DIFFERENTIAL
INPUT RANGE
(V)(1)
PGA[2:0]
CAPP
CHOP
10
Table 3. PGA Gain Settings
300W
A1
PGA Noise (nV/ÖHz)
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 300Ω 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)
100
Frequency (Hz)
1k
Figure 35. PGA Noise
(1) VREF = 5V.
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The ADC block of the ADS1282 is composed of two
sections: a high-accuracy modulator and a
programmable digital filter.
MODULATOR
The
high-performance
modulator
is
an
inherently-stable, fourth-order, ΔΣ, 2 + 2 pipelined
structure, as Figure 36 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.
fCLK/4
MCLK
passband. The noise moves out of the passband and
appears at the chopping frequency (fCLK/512 = 8kHz).
The component at 5.8kHz is the tone frequency,
shifted out of band by an external 20mV/PGA offset.
The frequency of the tone is proportional to the
applied dc input and is given by PGA × VIN/0.003 (in
kHz).
0
1Hz Resolution
VIN = 20mVDC
-20
-40
Magnitude (dB)
ADC
-60
-80
-100
-120
-140
Analog Input (VIN)
2nd-Order
DS
1st-Stage
M0
-160
-180
1
10
100
1k
10k
100k
Frequency (Hz)
2nd-Order
DS
2nd-Stage
M1
Figure 37. Modulator Output Spectrum
4th-Order Modulator
MODULATOR OVER-RANGE
Figure 36. 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
4kHz passband. As Figure 37 shows, the noise
shaping of the modulator results in a sharp increase
in noise above 6kHz. The modulator has a chopped
input structure that further reduces noise within the
16
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 (that is, all 1s, all 0s, or
±110%FSR), 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
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the input returns to 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).
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 100mA peak or 10mA
continuous if an overvoltage condition is possible.
MODULATOR OVER-RANGE DETECTION
(MFLAG)
The ADS1282 has a fast-responding over-range
detection that indicates when the differential input
exceeds approximately 100% over-range. The
threshold tolerance is ±2.5%.The MFLAG output
asserts high when in an over-range condition. As
Figure 38 and Figure 39 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.
AINP
MODULATOR INPUT IMPEDANCE
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).
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 =
4.096MHz is 55kΩ (110kΩ 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% or
more over production lots, affecting the gain error.
å
IABSI
P
100% FS
AINN
Q
MFLAG
Pin
fMOD/2
Figure 38. Modulator Over-Range Block Diagram
+100%
(AINP - AINN)
0%
Time
-100%
MFLAG
Pin
Figure 39. Modulator Over-Range Flag Operation
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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 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 40. 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.
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.
VOLTAGE REFERENCE INPUTS
(VREFP, VREFN)
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 41.
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.
AVDD
ESD
Diodes
VREFP
VREFN
ESD
Diodes
tCSHD
CLK
tCMD
tSYMD
MCLK
REFF =
1
fMOD ´ CX
AVSS
tSCSU
SYNC
REFF = 85kW
(170kW Low-Power Mode)
(fMOD = 1.024MHz)
11.5pF
Figure 41. Simplified Reference Input Circuit
(1)
tMCD0, 1
M0
M1
(1) High-resolution mode: MCLK = fCLK/4; low-power mode:
MCLK = fCLK/8.
Figure 40. Modulator Mode Timing
Modulator Output Timing for Figure 40
PARAMETER
tMCD0,
(1)
18
1
DESCRIPTION
MIN
TYP
MCLK rising edge to M0, M1 valid propagation delay (1)
MAX
UNIT
100
ns
tCMD
CLK rising edge (after SYNC rising edge) to MCLK rising edge
reset time
tCSHD
CLK to SYNC hold time to not latch on CLK edge
10
ns
tSCSU
SYNC to CLK setup time to latch on CLK edge
10
ns
tSYMD
SYNC to stable bit stream
5
1/fCLK
16
1/fMOD
Load on M0 and M1 = 20pF || 100kΩ.
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Table 4. 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:
FILTR[1:0] BITS
DIGITAL FILTERS SELECTED
00
Bypass; modulator output mode
01
Sinc
10
Sinc + FIR
11
Sinc + FIR + HPF
(low-pass and high-pass)
AVSS - 300mV < (VREFP or VREFN) < AVDD + 300mV
(6)
Note that the minimum valid input for VREFN is
AVSS – 0.1V and maximum valid input for VREFP is
AVDD + 0.1V.
A high-quality +5V 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
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 5.
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 42.
The output can be taken from one of the three filter
blocks, as Figure 42 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 4 shows the
filter options.
N
H(Z) =
1-Z
-1
1-Z
5
(7)
Table 5. 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 42. Digital Filter and Output Code Processing
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Equation 8 shows the frequency domain transfer
function of the sinc filter.
0
-0.5
5
-1.0
½H(f)½ =
N sin
Gain (dB)
2pN ´ f
sin
fMOD
2p ´ f
fMOD
-2.0
(8)
where:
N = decimation ratio (see Table 5)
0
0
-20
Gain (dB)
-40
-60
-80
-100
-120
-140
1
-2.5
-3.0
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 43 shows
the frequency response of the sinc filter and
Figure 44 shows the roll-off of the sinc filter.
0
-1.5
2
3
4
Normalized Frequency (fIN/fDATA)
5
0.05
0.10
0.15
0.20
Normalized Frequency (fIN/fDATA)
Figure 44. Sinc Filter Roll-Off
FIR Stage
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 45. 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 22
(in the Appendix section at the end of this document)
lists the FIR stage coefficients. Table 6 lists the data
rates and overall decimation ratio of the FIR stage.
Table 6. FIR Filter Data Rates
Figure 43. 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 4
Decimate by 2
FIR Stage 3
Decimate by 4
Output
Coefficients
Linear
Minimum
PHASE Select
Figure 45. FIR Filter Sub-Stages
20
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As shown in Figure 46, the FIR frequency response
provides a flat passband to 0.375 of the data rate
(±0.003dB passband ripple). Figure 47 shows the
transition from passband to stop band.
0.003
Magnitude (dB)
0.002
GROUP DELAY AND STEP RESPONSE
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.
Linear Phase Response
0.001
0
-0.001
-0.002
-0.003
0
0.08
0.16
0.24
0.32
Normalized Input Frequency (fIN/fDATA)
0.40
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 48.
Figure 46. FIR Passband Magnitude Response
(fDATA = 500Hz)
1.4
Minimum Phase Filter
1.2
0
Amplitude (dB)
1.0
Magnitude (dB)
-20
-40
-60
0.8
0.6
0.4
0.2
Linear Phase Filter
-80
0
-100
-0.2
0
-120
-140
0.35
0.40
0.45
0.50
0.55
0.60
Normalized Input Frequency (fIN/fDATA)
0.65
5
10 15 20 25 30 35 40 45 50 55 60 65
Time Index (1/fDATA)
Figure 48. FIR Step Response
Figure 47. FIR Transition Band Magnitude
Response
Although not shown in Figure 47, 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
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.
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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 49. The filter phase is selected by
the PHS bit, as Table 7 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 9:
1 - Z-1
2-a
´
HPF(Z) =
-1
2
1 - bZ
(9)
35
Linear Phase Filter
Group Delay (1/fDATA)
30
where b is calculated as shown in Equation 10:
25
2 2
b=
20
(1 + (1 - a) )
2
(10)
The high-pass corner frequency is programmed by
registers HPF[1:0], in hexadecimal. Equation 11 is
used to set the high-pass corner frequency. Table 8
lists example values for the high-pass filter.
15
10
Minimum Phase Filter
5
0
20
40
60
80 100 120
Frequency (Hz)
140 160 180
200
HPF[1:0] = 65,536 1 -
1-2
cos wN + sin wN - 1
cos wN
Figure 49. FIR Group Delay (fDATA = 500Hz)
Table 7. FIR Phase Selection
PHS BIT
FILTER PHASE
0
Linear
1
Minimum
(11)
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 8. High-Pass Filter Value Examples
22
fHP (Hz)
DATA RATE (SPS)
HPF[1:0]
0.5
250
0337h
1.0
500
0337h
1.0
1000
019Ah
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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 50 shows the gain
error of the HPF. The gain error factor is illustrated in
Equation 15 (see the Appendix at the end of this
document).
Gain Error (dB)
-0.10
-0.20
SYNCHRONIZATION
(SYNC PIN AND SYNC COMMAND)
-0.30
The ADS1282 can be synchronized to an external
event, as well as synchronized to other ADS1282
devices if the sync event is applied simultaneously.
-0.40
-0.50
0.0001
0.001
0.01
0.1
Frequency Ratio (fHP/fDATA)
Figure 50. HPF Gain Error
0
90
-7.5
75
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.
60
Amplitude
45
-22.5
Phase
-30.0
30
-37.5
15
Phase (°)
Amplitude (dB)
Figure 51 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.
-45.0
0.01
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 50Ω series resistor close to the source.
0
-15.0
MASTER CLOCK INPUT (CLK)
0
0.1
1
10
Normalized Frequency (f/fC)
100
Figure 51. HPF Amplitude and Phase Response
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PULSE-SYNC MODE
tCSHD
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 52 and Table 9.
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.
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 52).
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. 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
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 53 shows the timing for
Continuous-Sync mode.
System Clock
(fCLK)
tSCSU
SYNC Command
tSPWH
SYNC Pin
New Data
Ready
tSPWL
tDR
DRDY
(Pulse-Sync)
New Data
Ready
tDR
DRDY
(Continuous-Sync)
DOUT
Figure 52. Pulse-Sync Timing, Continuous-Sync
Timing with Single Sync
tSCSU
tCSHD
System Clock
(fCLK)
tSPWL
tSPWH
SYNC
tSYNC
DRDY
1/fDATA
Figure 53. Continuous-Sync Timing with Sync
Clock
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.
Table 9. Pulse-Sync Timing for Figure 52 and Figure 53
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)
24
L
Time for data ready (SINC filter)
ns
See Appendix, Table 23
Time for data ready (FIR filter)
62.98046875/fDATA + 466/fCLK
Continuous-Sync mode; a free-running SYNC clock input without causing re-synchronization.
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RESET (RESET Pin and Reset Command)
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 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 54 and Table 10.
Settled
Data
DRDY
tDR
tCRHD
Wakeup
Command
DRDY
tDR
Figure 55. PWDN Pin and Wake-Up Command
Timing
(Table 11 shows tDR)
The ADS1282 has three power supplies: AVDD,
AVSS, and DVDD. Figure 56 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 56 and Table 11.
tRCSU
RESET Pin
or
RESET Command
Figure 54. Reset Timing
Table 10. Reset Timing for Figure 54
PARAMETER DESCRIPTION
PWDN Pin
POWER-ON SEQUENCE
System Clock
(fCLK)
tRST
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 55 and
Table 11 show the timing.
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)
Internal Reset
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.
2
fCLK
DRDY
tDR
Figure 56. Power-On Sequence
Table 11. 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
See Appendix, Table 23
SINC (1)
62.98046875/fDATA + 468/fCLK (2)
FIR
Supply power-on and PWDN pin default is 1000SPS 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.
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DVDD POWER SUPPLY
Serial Clock (SCLK)
The DVDD supply operates over the range of +1.65V
to +3.6V. If DVDD is operated at less than 2.25V,
connect the DVDD pin to the BYPAS pin. If DVDD is
greater than or equal to 2.25V, do not connect DVDD
to the BYPAS pin. Figure 57 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.
1.65V to 3.6V
DVDD
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
1m F
Figure 57. DVDD Power
Data Input (DIN)
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 58 shows the connection when
multiple converters are used.
FPGA or Processor
SCLK
DOUT1
ADS1282
DIN2
DRDY1
SCLK
DOUT2
ADS1282
DIN2
DRDY2
SCLK
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.
DOUT1
DIN1
IRQ
SCLK (optional)
DOUT2
DIN2
IRQ (optional)
Figure 58. Interface for Multiple Devices
26
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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 59. 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 12. 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.
Table 12. 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 59. DRDY with Data Retrieval
2 x PGA
DRDY resets high on the first falling edge of SCLK.
Figure 59 and Figure 60 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 60.
4/fCLK
VREF
2PGA ´ (230 - 1)
0
-VREF
2PGA ´ (230 - 1)
Data Updating
-VREF
2PGA
DRDY
Figure 60. DRDY With No Data Retrieval
<
-VREF
2PGA
´
230
230 - 1
´
230
230 - 1
SINC
FILTER
7FFFFFFFh
(2)
7FFFFFFEh
3FFFFFFFh
00000002h
00000001h
00000000h
00000000h
FFFFFFFFh
FFFFFFFFh
80000001h
C0000000h
80000000h
(2)
(1) Excludes effects of noise, linearity, offset, and gain errors.
(2) In sinc filter mode, the output does not clip at half-scale code
when the full-scale range is exceeded.
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READING DATA
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.
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 61. 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 62). 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.
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 61. Read Data Continuous
Table 13. Timing Data for Figure 61
PARAMETER
DESCRIPTION
(1)
MIN
TYP
DRDY to valid MSB on DOUT propagation delay (1)
tDDPD
MAX
UNITS
100
ns
Load on DOUT = 20pF || 100kΩ.
DRDY
tDR
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
33 34 35 36 37 38
39 40
SCLK
DOUT
Don't Care
DIN
Data Byte 1 (MSB)
Date Byte 4 (LSB)
tDDPD
Command Byte (0001 0010)
Figure 62. Read Data By Command, RDATA (tDDPD timing is given in Table 13)
Table 14. Read Data Timing for Figure 62
PARAMETER
tDR
28
DESCRIPTION
MIN
Time for new data after data read command
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0
TYP
MAX
UNITS
1
fDATA
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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 63 shows this
sequence. First, issue the STANDBY command to set
the Standby mode.
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
The conversion data can be scaled for offset and gain
before yielding the final output code. As shown in
Figure 64, the output of the digital filter is first
subtracted by the offset register (OFC) and then
multiplied by the full-scale register (FSC).
Equation 12 shows the scaling:
FSC[2:0]
Final Output Data = (Input - OFC[2:0]) ´
400000h
(12)
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
Performing One-Shot Conversion
Standby
DRDY
DIN
(1)
STANDBY
STANDBY
WAKEUP
Settled
Data
DOUT
(1) See Figure 55 and Table 11 for time to new data.
Figure 63. 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 64. Calibration Block Diagram
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OFC[2:0] Registers
FSC[2:0] Registers
The offset calibration is a 24-bit word, composed of
three 8-bit registers, as shown in Table 17. 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 15), 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 18. The
full-scale calibration value is 24-bit, straight offset
binary, normalized to 1.0 at code 400000h. Table 16
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.
Table 16. Full-Scale Calibration Register Values
Table 15. 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 17. Offset Calibration Word
REGISTER
BYTE
OFC0
LSB
B7
B6
B5
B4
BIT ORDER
B3
B2
B1
OFC1
MID
B15
B14
B13
B12
B11
B10
B9
B8
OFC2
MSB
B23 (MSB)
B22
B21
B20
B19
B18
B17
B16
B0 (LSB)
B0 (LSB)
Table 18. Full-Scale Calibration Word
30
REGISTER
BYTE
FSC0
LSB
B7
B6
B5
B4
BIT ORDER
B3
B2
B1
FSC1
MID
B15
B14
B13
B12
B11
B10
B9
B8
FSC2
MSB
B23 (MSB)
B22
B21
B20
B19
B18
B17
B16
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CALIBRATION COMMANDS
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.
Figure 65 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
RDATAC
16 Data
Periods
64 Data Periods
Calibration
Complete
SYNC
Figure 65. Offset/Gain Calibration Timing
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USER CALIBRATION
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
average the n output readings.
32
The value written to the FSC registers is calculated
by Equation 13.
DC signal calibration is shown in Equation 13. The
expected output code is based on 31-bit output data.
FSC[2:0] = 400000h ´
Expected Output Code
Actual Output Code
(13)
For ac signal calibration, use an RMS value of
collected data (as shown in Equation 14).
Expected RMS Value
FSC[2:0] = 400000h ´
Actual RMS Value
(14)
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COMMANDS
The commands listed in Table 19 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.
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 66.
Command
Byte
DIN
Command
Byte
SCLK
(1)
tSCLKDLY
(1)
tSCLKDLY = 24/fCLK (min).
Figure 66. Consecutive Commands
Table 19. Command Descriptions
COMMAND
TYPE
DESCRIPTION
1st COMMAND BYTE (1) (2)
WAKEUP
Control
Wake-up from Standby mode
0000 000X (00h or 01h)
STANDBY
Control
Enter Standby mode
0000 001X (02h or 03h)
SYNC
Control
Synchronize the A/D conversion
0000 010X (04h or 5h)
RESET
Control
Reset registers to default values
0000 011X (06h or 07h)
RDATAC
Control
Read data continuous
0001 0000 (10h)
SDATAC
Control
Stop read data continuous
0001 0001 (11h)
RDATA
Data
RREG
Register
Read nnnnn register(s) at address rrrrr (4)
001r rrrr (20h + 000r rrrr)
000n nnnn (00h + n nnnn)
WREG
Register
Write nnnnn register(s) at address rrrrr
010r rrrr (40h + 000r rrrr)
000n nnnn (00h + n nnnn)
OFSCAL
Calibration
Offset calibration
0110 0000 (60h)
GANCAL
Calibration
Gain calibration
0110 0001 (61h)
(1)
(2)
(3)
(4)
Read data by command
(4)
2nd COMMAND BYTE (3)
0001 0010 (12h)
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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WAKEUP: Wake-Up From Standby Mode
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 55
and Table 12. 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 67.
Description: This command reads the conversion
data. See the Read Data By Command section for
more details.
DIN
0000 001X
(STANDBY)
0000 000X
(WAKEUP)
Standby Mode
Operating
Figure 67. 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 54 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.
34
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.
SCLK
Operating
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 68. 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 69 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.
tDLY
1
2
3
4
5
6
7
8
9
tDLY
10 11 12 13 14 15 16
tDLY
17 18 19 20 21 22 23 24
25 26
SCLK
DIN
Command Byte 1
DOUT
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 68. Read Register Data (Table 20 shows tDLY)
tDLY
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
tDLY
tDLY
17 18 19 20 21 22 23 24
25 26
SCLK
DIN
Command Byte 1
Command Byte 2
Register Data 5
Register Data 6
Example: Write six registers, starting at register 05h (OFC0)
Command Byte 1 = 0100 0101
Command Byte 2 = 0000 0101
Figure 69. Write Register Data (Table 20 shows tDLY)
Table 20. 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.
Table 21. Register Map
ADDRESS
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
HPF1
03h
HPF15
HPF14
HPF13
HPF12
HPF11
HPF10
HPF09
HPF08
05h
OFC0
00h
OFC07
OFC06
OFC05
OFC04
OFC03
OFC02
OFC01
OFC00
06h
OFC1
00h
OFC15
OFC14
OFC13
OFC12
OFC11
OFC10
OFC09
OFC08
07h
OFC2
00h
OFC23
OFC22
OFC21
OFC20
OFC19
OFC18
OFC17
OFC16
08h
FSC0
00h
FSC07
FSC06
FSC05
FSC04
FSC03
FSC02
FSC01
FSC00
09h
FSC1
00h
FSC15
FSC14
FSC13
FSC12
FSC11
FSC10
FSC09
FSC08
0Ah
FSC2
40h
FSC23
FSC22
FSC21
FSC20
FSC19
FSC18
FSC17
FSC16
BIT 0
ID : ID REGISTER (ADDRESS 00h)
7
6
5
4
3
2
1
0
ID3
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'
36
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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
Bit[6]
MODE
0: Low-power mode
1: High-resolution mode (default)
Bit[5:3]
Data Rate Select
DR[2:0]
000: 250SPS
001: 500SPS
010: 1000SPS (default)
011: 2000SPS
100: 4000SPS
Bit[2]
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
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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]
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: G
001: G
010: G
011: G
100: G
101: G
110: G
38
=
=
=
=
=
=
=
1 (default)
2
4
8
16
32
64
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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)
7
6
5
4
3
2
1
0
HP15
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
6
5
4
3
2
1
0
OC07
OC06
OC05
OC04
OC03
OC02
OC01
OC00
Reset value = 00h.
OFC1: Offset Calibration, Mid Byte (Address 06h)
7
6
5
4
3
2
1
0
OC15
OC14
OC13
OC12
OC11
OC10
OC09
OC08
Reset value = 00h.
OFC2: Offset Calibration, High Byte (Address 07h)
7
6
5
4
3
2
1
0
OC23
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
6
5
4
3
2
1
0
FSC07
FSC06
FSC05
FSC04
FSC03
FSC02
FSC01
FSC00
Reset value = 00h.
FSC1: Full-Scale Calibration, Mid Byte (Address 09h)
7
6
5
4
3
2
1
0
FSC15
FSC14
FSC13
FSC12
FSC11
FSC10
FSC09
FSC08
Reset value = 00h.
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ADS1282
SBAS418D – SEPTEMBER 2007 – REVISED JULY 2008 ................................................................................................................................................. www.ti.com
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.
CONFIGURATION GUIDE
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.
40
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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APPLICATION INFORMATION
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 70. The application shows the ADS1282
operation with dual ±2.5V analog supplies. The
ADS1282 can also operate with a single +5V 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 +2.5V
(AVDD/2). Resistors R5 and R6 can also influence
common-mode attenuation. To maintain good CMR
performance, resistors R5 and R6 may require
matching.
The REF02 +5V reference provides the reference to
the ADS1282. The reference output is filtered by R7
and C5. 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).
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 +5.2V minimum power
supply. The noise filter is also required on these
references.
Optional components R8, and R9 provides a 20mV
offset to the ADS1282. The internal 300Ω 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 (10nF) 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 ≈25kHz.
Diode clamps protect the ADS1282 inputs from
voltage transients and overloads.
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ADS1282
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+2.5V
15
+2.5V
Test
Source
-2.5V
19
20
AVDD
AVSS
AINP2
16
AINN2
R1
100W
R3
100W
C2
1nF, COG
Geophone
R2
100W
C3
1nF, COG
R4
100W
17
AINP1
R5
20kW
C4
10nF
COG
R6
20kW
18
AINN1
ADS1282
-2.5V
R8
(1)
75kW
+6.5V
(+2.8V REF5050)
1m F
14
C6
10nF
COG 13
CAPN
R9
R7
1kW
REF02
(REF5050)
CAPP
(1)
75kW
22
VREFP
1m F
+
C5
100mF
C7
0.1mF
21
-2.5V
VREFN
DGND
6, 12, 25, 27
(1) Optional 20mV offset. Match to 0.1% to maintain CMR.
Figure 70. Geophone Interface Application
42
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Figure 71 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.
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. 47Ω 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
DIN1
47W
2
SCLK1
47W
10
SYNC
47W
11
CLK Input
MFLAG1
4, 12, 23
+3.3V
26
(1)
1mF
CLK
DVDD
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 < 2.25V, see the DVDD Power Supply section.
Figure 71. Microcontroller Interface with Dual ADS1282s
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ADS1282
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APPENDIX
Table 22. 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
b0
–10944
–774
–73
819
–132
11767
b1
0
0
–874
8211
–432
133882
b2
103807
8994
–4648
44880
–75
769961
b3
0
0
–16147
174712
2481
2940447
b4
–507903
–51663
–41280
536821
6692
8262605
b5
0
0
–80934
1372637
7419
17902757
b6
2512192
199523
–120064
3012996
–266
30428735
b7
4194304
0
–118690
5788605
–10663
40215494
b8
2512192
–629120
–18203
9852286
–8280
39260213
b9
0
0
224751
14957445
10620
23325925
b10
–507903
2570188
580196
20301435
22008
–1757787
b11
0
4194304
893263
24569234
348
–21028126
b12
103807
2570188
891396
26260385
–34123
–21293602
b13
0
0
293598
24247577
–25549
–3886901
b14
–10944
–629120
–987253
18356231
33460
14396783
b15
0
–2635779
9668991
61387
16314388
b16
199523
–3860322
327749
–7546
1518875
b17
0
–3572512
–7171917
–94192
–12979500
b18
–51663
–822573
–10926627
–50629
–11506007
b19
0
4669054
–10379094
101135
2769794
b20
8994
12153698
–6505618
134826
12195551
b21
0
19911100
–1333678
–56626
6103823
b22
–774
25779390
2972773
–220104
–6709466
b23
27966862
5006366
–56082
–9882714
b24
Only half shown;
symmetric starting
with b22.
4566808
263758
–353347
2505652
231231
8629331
126331
–215231
5597927
b27
–1496514
–430178
–4389168
b28
–1933830
34715
–7594158
b29
–1410695
580424
–428064
b30
–502731
283878
6566217
b31
245330
–588382
4024593
b32
565174
–693209
–3679749
b33
492084
366118
–5572954
b34
231656
1084786
332589
5136333
b25
b26
44
SECTION 2
b35
–9196
132893
b36
–125456
–1300087
2351253
b37
–122207
–878642
–3357202
b38
–61813
1162189
–3767666
b39
–4445
1741565
1087392
b40
22484
–522533
3847821
b41
22245
–2490395
919792
b42
10775
–688945
–2918303
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Table 22. 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
b44
–2953
2425494
1493873
b45
–2599
–2338095
2595051
b46
–1052
–4511116
–79991
b47
–43
641555
–2260106
b48
214
6661730
–963855
b49
132
2950811
1482337
b50
33
–8538057
1480417
COEFFICIENT
Scaling = 1/8388608
LINEAR
PHASE
b51
–10537298
–586408
b52
9818477
–1497356
b53
41426374
–168417
b54
56835776
1166800
b55
Only half shown;
symmetric starting
with b53.
644405
b56
b57
–675082
–806095
b58
211391
b59
740896
b60
141976
b61
–527673
b62
–327618
b63
278227
b64
363809
b65
–70646
b66
–304819
b67
–63159
b68
205798
b69
124363
b70
–107173
b71
–131357
b72
31104
b73
107182
b74
15644
b75
–71728
b76
–36319
b77
38331
b78
38783
b79
–13557
b80
–31453
b81
–1230
b82
20983
b83
7729
b84
–11463
b85
–8791
b86
4659
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ADS1282
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Table 22. FIR Stage Coefficients (continued)
SECTION 1
SECTION 2
SECTION 3
SECTION 4
Scaling = 134217728
COEFFICIENT
LINEAR
PHASE
Scaling = 1/8388608
MINIMUM PHASE
Scaling = 134217728
LINEAR
PHASE
b87
MINIMUM PHASE
7126
b88
–732
b89
–4687
b90
–976
b91
2551
b92
1339
b93
–1103
b94
–1085
b95
314
b96
681
b97
16
b98
–349
b99
–96
b100
144
b101
78
b102
–46
b103
–42
b104
9
b105
16
b106
0
b107
–4
1-
1-2
HPF Gain Error Factor =
2-
cos wN + sin wN - 1
cos wN
cos wN + sin wN - 1
cos wN
(15)
See the HPF Stage section for an example of how to use this equation.
Table 23. tDR Time for Data Ready (Sinc Filter)
(1)
fDATA
fCLK (1)
128k
440
64k
616
32k
968
16k
1672
8k
2824
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.
Table 23 is referenced by Table 9 and Table 11.
46
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Revision History
Changes from Revision C (May 2008) to Revision D ...................................................................................................... Page
•
•
•
•
•
•
•
Changed fCLK/128 to fCLK/512 in last paragraph of Modulator section .................................................................................
Updated second paragraph of Modulator Input Impedance section....................................................................................
Updated second paragraph in Modulator Output Mode section ..........................................................................................
Updated Figure 40 and added footnote 1............................................................................................................................
Updated Figure 42 ...............................................................................................................................................................
Updated Table 12 and added footnote 2 .............................................................................................................................
Updated Figure 70 ...............................................................................................................................................................
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16
17
18
18
19
27
42
47
PACKAGE OPTION ADDENDUM
www.ti.com
11-Jul-2008
PACKAGING INFORMATION
Orderable Device
Status (1)
Package
Type
Package
Drawing
Pins Package Eco Plan (2)
Qty
ADS1282IPW
ACTIVE
TSSOP
PW
28
50
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
ADS1282IPWG4
ACTIVE
TSSOP
PW
28
50
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
ADS1282IPWR
ACTIVE
TSSOP
PW
28
2000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
ADS1282IPWRG4
ACTIVE
TSSOP
PW
28
2000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
Lead/Ball Finish
MSL Peak Temp (3)
(1)
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 continues to take
reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on
incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited
information may not be available for release.
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.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
10-Jun-2008
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
ADS1282IPWR
Package Package Pins
Type Drawing
TSSOP
PW
28
SPQ
Reel
Reel
Diameter Width
(mm) W1 (mm)
2000
330.0
16.4
Pack Materials-Page 1
A0 (mm)
B0 (mm)
K0 (mm)
P1
(mm)
6.95
8.3
1.6
8.0
W
Pin1
(mm) Quadrant
16.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
10-Jun-2008
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1282IPWR
TSSOP
PW
28
2000
346.0
346.0
33.0
Pack Materials-Page 2
MECHANICAL DATA
MTSS001C – JANUARY 1995 – REVISED FEBRUARY 1999
PW (R-PDSO-G**)
PLASTIC SMALL-OUTLINE PACKAGE
14 PINS SHOWN
0,30
0,19
0,65
14
0,10 M
8
0,15 NOM
4,50
4,30
6,60
6,20
Gage Plane
0,25
1
7
0°– 8°
A
0,75
0,50
Seating Plane
0,15
0,05
1,20 MAX
PINS **
0,10
8
14
16
20
24
28
A MAX
3,10
5,10
5,10
6,60
7,90
9,80
A MIN
2,90
4,90
4,90
6,40
7,70
9,60
DIM
4040064/F 01/97
NOTES: A.
B.
C.
D.
All linear dimensions are in millimeters.
This drawing is subject to change without notice.
Body dimensions do not include mold flash or protrusion not to exceed 0,15.
Falls within JEDEC MO-153
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
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