TI ADS7280IRSAR Low-power, 14-bit, 1mhz, single/dual unipolar input, analog-to-digital converters with serial interface Datasheet

ADS7279
ADS7280
www.ti.com........................................................................................................................................................................................................ SBAS436 – MAY 2008
LOW-POWER, 14-BIT, 1MHz, SINGLE/DUAL UNIPOLAR INPUT,
ANALOG-TO-DIGITAL CONVERTERS WITH SERIAL INTERFACE
FEATURES
APPLICATIONS
• 2.7V to 5.5V Analog Supply, Low Power:
– 13.7mW (1MHz, +VA = 3V, +VBD = 1.8V)
• 1MHz Sampling Rate 3V ≤ +VA ≤ 5.5V,
900kHz Sampling Rate 2.7V ≤ +VA ≤ 3V
• Excellent DC Performance:
– ±0.4LSB Typ, ±1.0LSB Max INL
– ±0.4LSB Typ, ±1.0LSB Max DNL
– ±0.8mV Max Offset Error at 3V
– ±1.25mV Max Offset Error at 5V
• Excellent AC Performance at fi = 10kHz with
85.9dB SNR, 105.3dB SFDR, –100.1dB THD
• Built-In Conversion Clock (CCLK)
• 1.65V to 5.5V I/O Supply:
– SPI™/DSP-Compatible Serial Interface
– SCLK up to 50MHz
• Comprehensive Power-Down Modes:
– Deep Power-Down
– Nap Power-Down
– Auto Nap Power-Down
• Unipolar Input Range: 0V to VREF
• Software Reset
• Global CONVST (Independent of CS)
• Programmable Status/Polarity EOC/INT
• 4 × 4 QFN-16 and TSSOP-16 Packages
• Multi-Chip Daisy-Chain Mode
• Programmable TAG Bit Output
• Auto/Manual Channel Select Mode (ADS7280)
•
•
•
•
•
•
•
1
23
Communications
Transducer Interface
Medical Instruments
Magnetometers
Industrial Process Control
Data Acquisition Systems
Automatic Test Equipment
DESCRIPTION
The ADS7279 is a low-power, 14-bit, 1MSPS
analog-to-digital converter (ADC) with a unipolar
input. The device includes a 14-bit, capacitor-based
successive approximation register (SAR) ADC with
inherent sample-and-hold.
The ADS7280 is based on the same core and
includes a 2-to-1 input MUX with a programmable
TAG bit output option. Both the ADS7279 and
ADS7280 offer a high-speed, wide voltage serial
interface, and are capable of daisy-chain mode
operation when multiple converters are used.
These converters are available in 4 × 4 QFN and
TSSOP-16 packages, and are fully specified for
operation over the industrial –40°C to +85°C
temperature range.
Low Power, High-Speed SAR Converter Family
Type/Speed
16-bit single-ended
14-bit single-ended
12-bit single-ended
ADS7280
ADS7279
+IN1
NC
+IN0
COM
+IN
-IN
REF+
REF
OUTPUT
LATCH
and
3-STATE
DRIVER
SAR
+
_
OSC
1 MSPS
ADS8327
ADS8329
Dual
ADS8328
ADS8330
Single
ADS7279
Dual
ADS7280
Single
ADS7229
Dual
ADS7230
SDO
CDAC
COMPARATOR
500 kSPS
Single
CONVERSION
and
CONTROL
LOGIC
FS/CS
SCLK
SDI
CONVST
EOC/INT/CDI
1
2
3
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.
SPI is a trademark of Motorola, Inc.
All other 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 © 2008, Texas Instruments Incorporated
ADS7279
ADS7280
SBAS436 – MAY 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 (1)
MAXIMUM
INTEGRAL
LINEARITY
(LSB)
MODEL
ADS7279I
MAXIMUM
DIFFERENTIAL
LINEARITY
(LSB)
±1
MAXIMUM
OFFSET
ERROR
(mV)
±1
PACKAGE
TYPE
PACKAGE
DESIGNATOR
4 × 4 QFN-16
RSA
±1.25
4 × 4 QFN-16
±1
±1
TRANSPORT
MEDIA,
QUANTITY
ADS7279IRSAT
Small tape and reel, 250
ADS7279IRSAR
Tape and reel, 3000
ADS7279IPW
Tube, 90
ADS7279IPWR
Tape and reel, 2000
ADS7280IRSAT
Small tape and reel, 250
ADS7280IRSAR
Tape and reel, 3000
PW
RSA
±1.25
–40°C to +85°C
TSSOP-16
(1)
ORDERING
INFORMATION
–40°C to +85°C
TSSOP-16
ADS7280I
TEMPERATURE
RANGE
ADS7280IPW
Tube, 90
ADS7280IPWR
Tape and reel, 2000
PW
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.
Voltage
Voltage range
ADS7279, ADS7280
UNIT
+IN to AGND
–0.3 to +VA + 0.3
V
–IN to AGND
–0.3 to +VA + 0.3
V
+VA to AGND
–0.3 to 7
V
+VBD to BDGND
–0.3 to 7
V
–0.3 to 0.3
V
Digital input voltage to BDGND
AGND to BDGND
–0.3 to +VBD + 0.3
V
Digital output voltage to BDGND
–0.3 to +VBD + 0.3
V
TA
Operating free-air temperature range
–40 to +85
°C
Tstg
Storage temperature range
–65 to +150
°C
TJ max
Junction temperature
+150
°C
Vapor phase (60 sec)
+215
°C
Infrared (15 sec)
+220
°C
4 × 4 QFN-16
package
Lead temperature,
soldering
Power dissipation
(TJmax – TA)/θJA
θJA thermal impedance
TSSOP-16
package
Lead temperature,
soldering
47
°C/W
Vapor phase (60 sec)
+215
°C
Infrared (15 sec)
+220
°C
Power dissipation
θJA thermal impedance
(1)
2
(TJmax – TA)/θJA
86
°C/W
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
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ADS7279
ADS7280
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ELECTRICAL CHARACTERISTICS: VREF = 5V
At TA = –40°C to +85°C, +VA = 5V, +VBD = +1.65V to +5.5V, VREF = 5V, and fSAMPLE = 1MHz, unless otherwise noted.
ADS7279, ADS7280
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
V
ANALOG INPUT
Full-scale input voltage (1)
FSR
Absolute input voltage
+IN – (–IN) or (+INx – COM)
0
VREF
+IN, +IN0, +IN1
AGND – 0.2
+VA + 0.2
–IN or COM
AGND – 0.2
AGND + 0.2
Input capacitance
Input leakage current
Input channel isolation, ADS7280 only
45
No ongoing conversion,
dc input
50
At dc
109
VI = ±1.25VPP at 50kHz
101
V
pF
nA
dB
SYSTEM PERFORMANCE
Resolution
14
NMC
No missing codes
14
INL
Integral linearity
–1
±0.4
DNL
Differential linearity
–1
EO
Offset error (3)
–1.25
Offset error drift
EG
FSR = 5V
Gain error
Common-mode rejection ratio
–0.25
Power-supply rejection ratio
LSB (2)
±0.4
1
LSB (2)
±0.3
1.25
±0.05
At dc
70
VI = 0.4VPP at 1MHz
50
At FFFFh output code (3)
mV
ppm/°C
0.25
±0.5
Noise
PSRR
Bits
1
±0.2
Gain error drift
CMRR
Bits
%FSR
ppm/°C
dB
33
µVRMS
78
dB
18
CCLK
SAMPLING DYNAMICS
tCONV
tSAMPLE1
tSAMPLE2
Conversion time
Acquisition time
Manual trigger
Auto trigger
3
Throughput rate
(1)
(2)
(3)
CCLK
3
1
MHz
Aperture delay
5
ns
Aperture jitter
10
ps
Step response
100
ns
Overvoltage recovery
100
ns
Ideal input span; does not include gain or offset error.
LSB means least significant bit.
Measured relative to an ideal full-scale input [(+IN) – (–IN)] of 4.096V when +VA = 5V.
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ADS7279
ADS7280
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ELECTRICAL CHARACTERISTICS: VREF = 5V (continued)
At TA = –40°C to +85°C, +VA = 5V, +VBD = +1.65V to +5.5V, VREF = 5V, and fSAMPLE = 1MHz, unless otherwise noted.
ADS7279, ADS7280
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DYNAMIC CHARACTERISTICS
THD
Total harmonic distortion (4)
SNR
Signal-to-noise ratio
SINAD
Signal-to-noise + distortion
SFDR
Spurious-free dynamic range
VIN = 5VPP at 10kHz
–100.1
VIN = 5VPP at 100kHz
–89.1
VIN = 5VPP at 10kHz
dB
85.9
VIN = 5VPP at 100kHz
81.0
VIN = 5VPP at 10kHz
85.7
VIN = 5VPP at 100kHz
82.7
VIN = 5VPP at 10kHz
105.3
VIN = 5VPP at 100kHz
91.3
–3dB small-signal bandwidth
dB
84.3
dB
dB
30
MHz
CLOCK
Internal conversion clock frequency
SCLK external serial clock
21
23
Used as I/O clock only
24.5
50
As I/O clock and conversion clock
1
42
MHz
MHz
EXTERNAL VOLTAGE REFERENCE INPUT
VREF
Input
reference
range
VREF[REF+ – (REF–)]
0.3
(REF–) – AGND
Resistance (5)
5
–0.1
Reference input
+VA
0.1
40
V
kΩ
DIGITAL INPUT/OUTPUT
Logic family—CMOS
VIH
High-level input voltage
5.5V ≥ +VBD ≥ 4.5V
0.65 × (+VBD)
+VBD + 0.3
VIL
Low-level input voltage
5.5V ≥ +VBD ≥ 4.5V
–0.3
0.35 × (+VBD)
V
II
Input current
VI = +VBD or BDGND
–50
50
nA
Ci
Input capacitance
5
VOH
High-level output voltage
5.5V ≥ +VBD ≥ 4.5V,
IO = 100µA
VOL
Low-level output voltage
5.5V ≥ +VBD ≥ 4.5V,
IO = 100µA
CO
Output capacitance
CL
Load capacitance
V
pF
+VBD – 0.6
+VBD
V
0
0.4
V
5
pF
30
pF
Data format—straight binary
POWER-SUPPLY REQUIREMENTS
Power-supply
voltage
+VBD
1.65
3.3
5.5
V
4.5
5
5.5
V
1MHz Sample rate
5.7
7.0
Nap or Auto Nap mode
0.3
0.5
+VA
Supply current
PD Mode
Buffer I/O supply current
Power dissipation
0.004
1
1MSPS, BVDD = 1.8V
0.1
0.5
1MSPS, BVDD = 3V
0.5
1.2
AVDD = 5V, BVDD = 1.8V
28.7
35.9
AVDD = 5V, BVDD = 3V
30.0
38.6
mA
µA
mA
mW
TEMPERATURE RANGE
TA
(4)
(5)
4
Operating free-air temperature
–40
+85
°C
Calculated on the first nine harmonics of the input frequency.
Can vary ±30%.
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Product Folder Link(s): ADS7279 ADS7280
ADS7279
ADS7280
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ELECTRICAL CHARACTERISTICS: VREF = 2.5V
At TA = –40°C to +85°C, +VA = 2.7V to 3.6V, +VBD = 1.65V to 1.5x(+VA), VREF = 2.5V, fSAMPLE = 1MHz for 3V ≤ +VA ≤ 3.6V,
and fSAMPLE = 900kHz for 3V < +VA ≤ 2.7V using external clock, unless otherwise noted.
ADS7279, ADS7280
PARAMETER
TEST CONDITIONS
MIN
+IN – (–IN) or (+INx – COM)
0
TYP
MAX
UNIT
VREF
V
ANALOG INPUT
Full-scale input voltage (1)
FSR
Absolute input voltage
+IN, +IN0, +IN1
AGND – 0.2
+VA + 0.2
–IN or COM
AGND – 0.2
AGND + 0.2
Input capacitance
Input leakage current
Input channel isolation, ADS7280 only
45
No ongoing conversion,
dc Input
50
At dc
108
VIN = ±1.25VPP at 50kHz
101
V
pF
nA
dB
SYSTEM PERFORMANCE
Resolution
14
Bits
No missing codes
14
INL
Integral linearity
–1
±0.4
1
LSB (2)
DNL
Differential linearity
–1
±0.4
1
LSB (2)
–0.8
±0.05
0.8
EO
Offset error
(3)
Offset error drift
EG
FSR = 2.5V
Gain error
±0.1
–0.25
Gain error drift
CMRR
Common-mode rejection ratio
Power-supply rejection ratio
±0.06
At dc
70
VIN = 0.4VPP at 1MHz
50
At FFFFh output code (3)
mV
ppm/°C
0.25
±0.5
Noise
PSRR
Bits
%FSR
ppm/°C
dB
33
µVRMS
78
dB
18
CCLK
SAMPLING DYNAMICS
tCONV
tSAMPLE1
tSAMPLE2
Conversion time
Acquisition time
Throughput rate
(1)
(2)
(3)
Manual trigger
Auto trigger
3
CCLK
3
2.7V ≤ +VA < 3.0V
0.9
3.0V ≤ +VA < 3.64V
1
MHz
Aperture delay
5
ns
Aperture jitter
10
ps
Step response
100
ns
Overvoltage recovery
100
ns
Ideal input span; does not include gain or offset error.
LSB means least significant bit.
Measured relative to an ideal full-scale input [(+IN) – (–IN)] of 2.5V when +VA = 3V.
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ADS7279
ADS7280
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ELECTRICAL CHARACTERISTICS: VREF = 2.5V (continued)
At TA = –40°C to +85°C, +VA = 2.7V to 3.6V, +VBD = 1.65V to 1.5x(+VA), VREF = 2.5V, fSAMPLE = 1MHz for 3V ≤ +VA ≤ 3.6V,
and fSAMPLE = 900kHz for 3V < +VA ≤ 2.7V using external clock, unless otherwise noted.
ADS7279, ADS7280
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DYNAMIC CHARACTERISTICS
THD
Total harmonic distortion (4)
SNR
Signal-to-noise ratio
SINAD
Signal-to-noise + distortion
SFDR
Spurious-free dynamic range
VIN = 2.5VPP at 10kHz
–100.8
VIN = 2.5VPP at 100kHz
–88.4
VIN = 2.5VPP at 10kHz
81
VIN = 2.5VPP at 100kHz
dB
83.1
dB
82
VIN = 2.5VPP at 10kHz
83
VIN = 2.5VPP at 100kHz
81.4
VIN = 2.5VPP at 10kHz
102.6
VIN = 2.5VPP at 100kHz
89.8
–3dB small-signal bandwidth
dB
dB
30
MHz
CLOCK
Internal conversion clock frequency
SCLK external serial clock
21
22
Used as I/O clock only
23.5
42
As I/O clock and conversion clock
1
42
MHz
MHz
EXTERNAL VOLTAGE REFERENCE INPUT
VREF
Input reference
range
VREF [REF+ –
(REF–)]
3.6V ≥ +VA ≥ 2.7V
2.475
(REF–) – AGND
Resistance (5)
2.5
–0.1
Reference input
2.525
V
0.1
40
kΩ
DIGITAL INPUT/OUTPUT
Logic family—CMOS
VIH
High-level input voltage
(+VA × 1.5)V ≥ +VBD ≥ 1.65V
0.65 × (+VBD)
+VBD + 0.3
VIL
Low-level input voltage
(+VA × 1.5)V ≥ +VBD ≥ 1.65V
–0.3
0.35 × (+VBD)
V
II
Input current
VI = +VBD or BDGND
–50
50
nA
Ci
Input capacitance
5
VOH
High-level output voltage
(+VA × 1.5)V ≥ +VBD ≥ 1.65V,
IO = 100µA
VOL
Low-level output voltage
(+VA × 1.5)V ≥ +VBD ≥ 1.65V,
IO = 100µA
CO
Output capacitance
CL
Load capacitance
V
pF
+VBD – 0.6
+VBD
V
0
0.4
V
5
pF
30
pF
1.5 × (+VA)
V
Data format—straight binary
POWER SUPPLY REQUIREMENTS
+VBD
Power-supply
voltage
+VA
Supply current
1.65
fs ≤ 1MHz
fs ≤ 900kHz
3.6
2.7
3.6
1MHz sample rate,
3V ≤ +VA ≤ 3.6V
4.5
900kHz sample rate,
2.7V ≤ +VA ≤ 3V
4.2
Nap or Auto Nap mode
0.25
PD Mode
Buffer I/O supply current
Power dissipation
+VA
3
V
6.0
mA
0.4
0.001
1
1MSPS, BVDD = 1.8V
0.1
0.5
1MSPS, BVDD = 3V
0.5
1.2
AVDD = 3V, BVDD = 1.8V
13.7
18.9
AVDD = 3V, BVDD = 3V
15.0
21.6
µA
mA
mW
TEMPERATURE RANGE
TA
(4)
(5)
6
Operating free-air temperature
–40
+85
°C
Calculated on the first nine harmonics of the input frequency.
Can vary ±30%.
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ADS7279
ADS7280
www.ti.com........................................................................................................................................................................................................ SBAS436 – MAY 2008
TIMING CHARACTERISTICS (1) (2): 5V
All specifications typical at –40°C to +85°C and +VA = +VBD = 5V, unless otherwise noted.
ADS7279, ADS7280
PARAMETER
fCCLK
Frequency, conversion clock, CCLK
MIN
External,
fCCLK = 1/2 fSCLK
0.5
Internal,
fCCLK = 1/2 fSCLK
21
TYP
MAX
UNIT
21
MHz
23
24.5
t1
Setup time, falling edge of CS to EOC
1
CCLK
t2
Hold time, falling edge of CS to EOC
0
ns
tCL
Pulse duration, CONVST low
40
ns
t3
Hold time, falling edge of CS to EOS
20
ns
t4
Setup time, rising edge of CS to EOS
20
ns
t5
Hold time, rising edge of CS to EOS
20
ns
t6
Setup time, falling edge of CS to first falling
SCLK
5
ns
tSCLKL
Pulse duration, SCLK low
8
tSCLK – 8
ns
tSCLKH
Pulse duration, SCLK high
8
tSCLK – 8
ns
I/O clock only
I/O and conversion clock
tSCLK
Cycle time, SCLK
I/O clock, chain mode
I/O and conversion clock,
chain mode
20
23.8
2000
ns
20
23.8
2000
tH2
Hold time, falling edge of SCLK to SDO
invalid
10pF load
tD1
Delay time, falling edge of SCLK to SDO
valid
10pF load
10
ns
tD2
Delay time, falling edge of CS to SDO
valid, SDO MSB output
10pF load
8.5
ns
tS1
Setup time, SDI to falling edge of SCLK
8
ns
tH1
Hold time, SDI to falling edge of SCLK
4
ns
tD3
Delay time, rising edge of CS/FS to SDO
tD3 3-state
t7
Setup time, 16th falling edge of SCLK
before rising edge of CS/FS
(1)
(2)
2
ns
5
10
ns
ns
All input signals are specified with tr = tf = 1.5ns (10% to 90% of VBD) and timed from a voltage level of (VIL + VIH)/2.
See timing diagrams.
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TIMING CHARACTERISTICS (1) (2) : 1.8V
All specifications typical at –40°C to 85°C, +VA = 2.7 V, and +VBD = 1.8V, unless otherwise noted.
ADS7279, ADS7280
PARAMETER
fCCLK
Frequency, conversion clock, CCLK
MIN
TYP
MAX
External, 3V ≤ +VA ≤ 3.6V,
fCCLK = 1/2 fSCLK
0.5
21
External, 2.7V ≤ +VA ≤ 3V,
fCCLK = 1/2 fSCLK
0.5
18.9
Internal,
fCCLK = 1/2 fSCLK
20
22
UNIT
MHz
23.5
t1
Setup time, falling edge of CS to EOC
1
CCLK
t2
Hold time, falling edge of CS to EOC
0
ns
tCL
Pulse duration, CONVST low
40
ns
t3
Hold time, falling edge of CS to EOS
20
ns
t4
Setup time, rising edge of CS to EOS
20
ns
t5
Hold time, rising edge of CS to EOS
20
ns
t6
Setup time, falling edge of CS to first t6
falling SCLK
5
ns
tSCLKL
Pulse duration, SCLK low
8
tSCLK – 8
ns
tSCLKH
Pulse duration, SCLK high
ns
tSCLK
Cycle time, SCLK
8
tSCLK – 8
All modes,
3V ≤ +VA ≤ 3.6V
23.8
2000
All modes,
2.7V ≤ +VA < 3V
26.5
2000
ns
tH2
Hold time, falling edge of SCLK to SDO
invalid
10pF load
tD1
Delay time, falling edge of SCLK to SDO
valid
10pF load
16
10pF load,
2.7V ≤ +VA ≤ 3V
13
tD2
Delay time, falling edge of CS to SDO
valid, SDO MSB output
10pF load,
3V ≤ +VA ≤ 3.6V
11
7.5
ns
ns
ns
tS1
Setup time, SDI to falling edge of SCLK
8
ns
tH1
Hold time, SDI to falling edge of SCLK
4
ns
tD3
Delay time, rising edge of CS/FS to SDO
3-state
t7
Setup time, 16th falling edge of SCLK t7
before rising edge of CS/FS
(1)
(2)
8
8
10
ns
ns
All input signals are specified with tr = tf = 1.5ns (10% to 90% of VBD) and timed from a voltage level of (VIL + VIH)/2.
See timing diagrams.
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ADS7279
ADS7280
www.ti.com........................................................................................................................................................................................................ SBAS436 – MAY 2008
PIN ASSIGNMENTS
AGND
COM
+IN0
15
14
13
2
11
+VA
CONVST
3
10
+VBD
EOC/INT/CDI
4
9
SCLK
8
SCLK
NC
BDGND
9
+IN1
7
4
12
SDO
EOC/INT/CDI
1
6
+VBD
REF+ (REFIN)
SDI
10
REF-
+IN
13
3
BDGND
CONVST
16
-IN
14
+VA
8
11
7
2
SDO
NC
6
RESERVED
SDI
12
5
1
FS/CS
REF+ (REFIN)
5
AGND
15
ADS7280
RSA PACKAGE (QFN)
(TOP VIEW)
FS/CS
REF16
ADS7279
RSA PACKAGE (QFN)
(TOP VIEW)
CAUTION: The thermal pad is internally connected to the substrate. This pad can be connected to the analog
ground or left floating. Keep the thermal pad separate from the digital ground, if possible.
ADS7279
PW PACKAGE (TSSOP)
(TOP VIEW)
+VA
RESERVED
+IN
-IN
AGND
REFREF+ (REFIN)
NC
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
ADS7280
PW PACKAGE (TSSOP)
(TOP VIEW)
+VBD
SCLK
BDGND
SDO
SDI
FS/CS
EOC/INT/CDI
CONVST
+VA
+IN1
+IN0
COM
AGND
REFREF+ (REFIN)
NC
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
+VBD
SCLK
BDGND
SDO
SDI
FS/CS
EOC/INT/CDI
CONVST
NC = No internal connection
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ADS7279 Terminal Functions
NO.
QFN
TSSOP
I/O
AGND
NAME
15
5
—
Analog ground
DESCRIPTION
BDGND
8
14
—
Interface ground
CONVST
3
9
I
Freezes sample-and-hold, starts conversion with next rising edge of internal clock
Status output. If programmed as EOC, this pin is low (default) when a conversion is in
progress. If programmed as an interrupt (INT), this pin is low for a preprogrammed
duration after the end of conversion and valid data are to be output. The polarity of
EOC or INT is programmable. This pin can also be used as a chain data input when
the device is operated in daisy-chain mode.
EOC/ INT/ CDI
4
10
I/O
FS/CS
5
11
I
Frame sync signal for TMS320 DSP serial interface or chip select input for SPI
interface slave select (SS–).
+IN
13
3
I
Noninverting input
–IN
14
4
I
Inverting input; usually connected to ground
NC
2
8
—
REF+ (REFIN)
1
7
I
External reference input
REF–
16
6
I
Connect to AGND through individual via
RESERVED
12
2
I
Connect to AGND or +VA
SCLK
9
15
I
Clock for serial interface
SDI
6
12
I
Serial data in
SDO
7
13
O
Serial data out
+VA
11
1
Analog supply, +2.7V to +5.5VDC
+VBD
10
16
Interface supply
No connection
ADS7280 Terminal Functions
NO.
NAME
QFN
TSSOP
I/O
15
5
—
Analog ground
BDGND
8
14
—
Interface ground
COM
14
4
I
Common inverting input; usually connected to ground
CONVST
3
9
I
Freezes sample-and-hold, starts conversion with next rising edge of internal clock
AGND
DESCRIPTION
Status output. If programmed as EOC, this pin is low (default) when a conversion is in
progress. If programmed as an interrupt (INT), this pin is low for a preprogrammed
duration after the end of conversion and valid data are to be output. The polarity of
EOC or INT is programmable. This pin can also be used as a chain data input when
the device is operated in daisy-chain mode.
EOC/ INT/ CDI
4
10
I/O
FS/CS
5
11
I
Frame sync signal for TMS320 DSP serial interface or chip select input for SPI
interface
+IN1
12
2
I
Second noninverting input
+IN0
13
3
I
First noninverting input
NC
2
8
—
REF+ (REFIN)
1
7
I
External reference input
REF–
16
6
I
Connect to AGND through individual via
SCLK
9
15
I
Clock for serial interface
SDI
6
12
I
Serial data in (conversion start and reset possible)
SDO
7
13
O
Serial data out
+VA
11
1
Analog supply, +2.7V to +5.5VDC
+VBD
10
16
Interface supply
10
No connection.
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MANUAL TRIGGER/READ While Sampling
(use internal CCLK, EOC, and INT polarity programmed as active low)
Nth
CONVST
EOC
EOS
EOC
EOC
(active low)
tCL
Nth
Nth - 1
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs Min
INT
(active low)
t4
t2
FS/CS
1……………………16
1
SCLK
Nth - 1
SDO
Nth
1101b
READ Result
SDI
1101b
READ Result
Figure 1. Timing for Conversion and Acquisition Cycles for Manual Trigger (Read While Sampling)
MANUAL TRIGGER/READ While Converting
(use internal CCLK, EOC, and INT polarity programmed as active low)
N + 1th
tCL
EOC
(active low)
EOS
EOS
EOC
Nth
CONVST
Nth + 1
Nth
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs Min
INT
(active low)
t4
t3
FS/CS
1……………………16
1
SCLK
SDO
SDI
Nth - 1
1101b
READ Result
Nth
1101b
READ Result
Figure 2. Timing for Conversion and Acquisition Cycles for Manual Trigger (Read While Converting)
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AUTO TRIGGER/READ While Converting
(use internal CCLK, EOC, and INT polarity programmed as active low)
EOC
(active low)
EOS
EOC
EOS
EOC
EOS
CONVST = 1
Nth
N - 1th
tSAMPLE2 =
3 CCLKs
tCONV = 18 CCLKs
INT
(active low)
Nth + 1
tCONV = 18 CCLKs
tSAMPLE2 =
3 CCLKs
t4
t3
FS/CS
1……………………16
1……………………16
SCLK
N - 2th
SDO
N - 1th
1101b
READ Result
1101b
READ Result
SDI
Figure 3. Timing for Conversion and Acquisition Cycles for Autotrigger (Read While Converting)
1
2
3
4
11
12
14
13
15
16
SCLK
tSCLKH
tSCLKL
tSCLK
t6
t7
FS/CS
tH2
tD2
SDO
MSB
MSB-1
MSB-2
tD3
MSB-3
LSB+3
LSB+2
LSB+1
LSB
tD1
tH1
SDI or CDI
MSB
MSB-1
MSB-2
MSB-3
LSB+5
LSB+4
LSB+3
LSB+2
LSB+1
LSB
tS1
Figure 4. Detailed SPI Transfer Timing
12
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MANUAL TRIGGER/READ While Converting
(use internal CCLK, EOC, and INT polarity programmed as active low, TAG enabled, auto channel select)
Nth CH0
EOC
(active low)
Nth CH1
Nth CH0
tSAMPLE1 =
3 CCLKs Min
EOC
tCL
EOS
tCL
Nth CH1
EOC
EOS
EOC
CONVST
tCONV = 18 CCLKs
tSAMPLE1 =
3 CCLKs Min
tCONV = 18 CCLKs
INT
(active low)
t4
t3
FS/CS
1……………………16 17
1……………………16 17
SCLK
SDO
High-Z
High-Z
N - 1th CH1
TAG = 1
1101b
READ Result
SDI
High-Z
Nth CH0
TAG = 0
1101b
READ Result
Figure 5. Simplified Dual Channel Timing
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TYPICAL CHARACTERISTICS
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
DIFFERENTIAL NONLINEARITY
vs FREE-AIR TEMPERATURE
110
0.6
105
0.5
100
0.4
DNL (LSB)
Crosstalk (dB)
CROSSTALK
vs FREQUENCY
95
5V
90
3V
5V
0.3
0.2
85
0.1
3V
80
0
20
40
60
80
0
-40
100 120 140 160 180 200
35
60
Temperature (°C)
Figure 6.
Figure 7.
INTEGRAL NONLINEARITY
vs FREE-AIR TEMPERATURE
DIFFERENTIAL NONLINEARITY
vs EXTERNAL CLOCK FREQUENCY
0.6
85
1.0
0.8
3V
0.5
+VA = 5V
0.6
0.4
DNL (LSB)
0.4
INL (LSB)
10
-15
Frequency (kHz)
5V
0.3
DNL+
0.2
0
DNL-
-0.2
0.2
-0.4
-0.6
0.1
-0.8
0
-40
1.0
-1.0
10
-15
35
60
85
0.1
10
fSCLK (MHz)
Figure 8.
Figure 9.
INTEGRAL NONLINEARITY
vs EXTERNAL CLOCK FREQUENCY
DIFFERENTIAL NONLINEARITY
vs EXTERNAL CLOCK FREQUENCY
1.0
+VA = 5V
0.8
100
+VA = 3V
0.8
0.6
0.6
INL+
0.4
0.4
DNL (LSB)
INL (LSB)
1
Temperature (°C)
0.2
0
-0.2
DNL+
0.2
0
DNL-
-0.2
INL-0.4
-0.4
-0.6
-0.6
-0.8
-0.8
-1.0
-1.0
0.1
14
1
10
100
0.1
1
10
fSCLK (MHz)
fSCLK (MHz)
Figure 10.
Figure 11.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
INTEGRAL NONLINEARITY
vs EXTERNAL CLOCK FREQUENCY
1.0
OFFSET VOLTAGE
vs FREE-AIR TEMPERATURE
0.50
+VA = 3V
0.8
5V
0.6
INL+
0.2
0
0.25
Offset Voltage (mV)
INL (LSB)
0.4
INL-
-0.2
-0.4
3V
0
-0.25
-0.6
-0.8
-0.50
-40
-1.0
0.1
1
10
100
-15
10
35
60
85
Temperature (°C)
fSCLK (MHz)
Figure 12.
Figure 13.
OFFSET VOLTAGE
vs SUPPLY VOLTAGE
GAIN ERROR
vs FREE-AIR TEMPERATURE
0.050
0.5
0.025
Gain Error (%FSR)
Offset Voltage (mV)
0.4
0.3
0.2
0.1
0
5V
-0.025
0
3V
-0.1
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-0.050
-40
-15
10
35
60
85
Temperature (°C)
+VA Supply Voltage (V)
Figure 14.
Figure 15.
GAIN ERROR
vs SUPPLY VOLTAGE
POWER-SUPPLY REJECTION RATIO
vs SUPPLY RIPPLE FREQUENCY
0.10
-70
-72
0.05
PSRR (dB)
Gain Error (%FSR)
5V
0
3V
-74
-76
-0.05
-78
-0.10
-80
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
20
+VA Supply Voltage (V)
Figure 16.
40
60
80
100
Frequency (kHz)
Figure 17.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
SIGNAL-TO-NOISE RATIO
vs INPUT FREQUENCY
SIGNAL-TO-NOISE AND DISTORTION
vs INPUT FREQUENCY
90
90
88
88
5V
SINAD (dB)
SNR (dB)
5V
86
84
86
84
82
82
3V
3V
80
80
0
20
40
60
100
80
0
20
40
Input Frequency (kHz)
Figure 19.
TOTAL HARMONIC DISTORTION
vs INPUT FREQUENCY
SPURIOUS-FREE DYNAMIC RANGE
vs INPUT FREQUENCY
105
100
3V
SFDR (dB)
SINAD (dB)
100
5V
3V
-90
5V
-95
95
90
-100
85
-105
0
86
20
40
60
80
100
0
20
40
60
80
Input Frequency (kHz)
Input Frequency (kHz)
Figure 20.
Figure 21.
SIGNAL-TO-NOISE RATIO
vs FULL-SCALE RANGE
SIGNAL-TO-NOISE AND DISTORTION
vs FULL-SCALE RANGE
100
86
fIN = 10kHz
fIN = 10kHz
5V
5V
82
82
SINAD (dB)
3V
SNR (dB)
80
Figure 18.
-85
78
74
70
3V
78
74
70
66
66
0
16
60
Input Frequency (kHz)
1
2
3
4
5
0
1
2
3
Full-Scale Range (V)
Full-Scale Range (V)
Figure 22.
Figure 23.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
TOTAL HARMONIC DISTORTION
vs FULL-SCALE RANGE
-80
SPURIOUS-FREE DYNAMIC RANGE
vs FULL-SCALE RANGE
110
fIN = 10kHz
fIN = 10kHz
5V
105
-90
SFDR (dB)
THD (dB)
-85
3V
-95
100
3V
5V
95
-100
90
-105
0
1
2
3
4
5
0
1
Full-Scale Range (V)
2
3
4
5
Full-Scale Range (V)
Figure 24.
Figure 25.
TOTAL HARMONIC DISTORTION
vs FREE-AIR TEMPERATURE
SPURIOUS-FREE DYNAMIC RANGE
vs FREE-AIR TEMPERATURE
105
-85
3V
5V
100
SFDR (dB)
THD (dB)
-90
-95
95
5V
3V
90
-100
-105
-40
-15
10
35
60
85
-40
85
-15
10
35
60
Temperature (°C)
Temperature (°C)
Figure 26.
Figure 27.
SIGNAL-TO-NOISE RATIO
vs FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE AND DISTORTION
vs FREE-AIR TEMPERATURE
85
85
85
5V
SINAD (dB)
SNR (dB)
84
3V
83
84
5V
83
3V
82
-40
-15
10
35
60
85
82
-40
-15
10
35
Temperature (°C)
Temperature (°C)
Figure 28.
Figure 29.
60
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
EFFECTIVE NUMBER OF BITS
vs FREE-AIR TEMPERATURE
INTERNAL CLOCK FREQUENCY
vs SUPPLY VOLTAGE
14.0
Internal Clock Frequency (MHz)
24.0
ENOB (Bits)
13.8
13.6
5V
13.4
3V
13.2
13.0
-40
23.5
23.0
22.5
22.0
21.5
21.0
10
-15
35
60
2.5
85
3.0
INTERNAL CLOCK FREQUENCY
vs FREE-AIR TEMPERATURE
ANALOG SUPPLY CURRENT
vs SUPPLY VOLTAGE
7.0
23.5
6.5
5.0
5.5
fS = 1MSPS
Analog Supply Current (mA)
Internal Clock Frequency (MHz)
4.5
Figure 31.
23.0
22.5
22.0
21.5
6.0
5.5
5.0
4.5
4.0
10
-15
35
60
85
2.5
3.0
3.5
4.0
4.5
Temperature (°C)
+VA Supply Voltage (V)
Figure 32.
Figure 33.
ANALOG SUPPLY CURRENT
vs SUPPLY VOLTAGE
ANALOG SUPPLY CURRENT
vs SUPPLY VOLTAGE
400
5.0
5.5
5.0
5.5
10
PD Mode
Analog Supply Current (nA)
NAP Mode
Analog Supply Current (mA)
4.0
Figure 30.
24.0
21.0
-40
360
320
280
240
200
8
6
4
2
0
2.5
18
3.5
+VA Supply Voltage (V)
Temperature (°C)
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
3.5
4.0
4.5
+VA Supply Voltage (V)
+VA Supply Voltage (V)
Figure 34.
Figure 35.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
ANALOG SUPPLY CURRENT
vs SAMPLE RATE
ANALOG SUPPLY CURRENT
vs SAMPLE RATE
1.4
7
PD Mode
6
Analog Supply Current (mA)
Analog Supply Current (mA)
Auto NAP
5
4
3
5V
2
3V
1
1.2
1.0
5V
0.8
0.6
3V
0.4
0.2
0
0
1
10
0
1000
100
20
10
50
60
70
Figure 37.
ANALOG SUPPLY CURRENT
vs FREE-AIR TEMPERATURE
ANALOG SUPPLY CURRENT
vs FREE-AIR TEMPERATURE
0.35
5V
6.0
5.5
5.0
4.5
3V
4.0
80
90
NAP Mode
fS = 1MSPS
Analog Supply Current (mA)
Analog Supply Current (mA)
40
Figure 36.
7.0
6.5
30
Sample Rate (kSPS)
Sample Rate (kSPS)
5V
0.30
0.25
3V
0.20
3.5
3.0
-40
-15
10
35
60
0.15
-40
85
Figure 38.
Figure 39.
60
85
DIFFERENTIAL NONLINEARITY
0.5
+VA = 5V
0.4
0.4
0.3
0.3
0.2
0.2
DNL (Bits)
INL (Bits)
35
Temperature (°C)
INTEGRAL NONLINEARITY
0.5
10
-15
Temperature (°C)
0.1
0
-0.1
0.1
0
-0.1
-0.2
-0.2
-0.3
-0.3
-0.4
-0.4
-0.5
+VA = 5V
-0.5
0
5000
10000
15000
0
5000
10000
Code
Code
Figure 40.
Figure 41.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
INTEGRAL NONLINEARITY
DIFFERENTIAL NONLINEARITY
0.5
+VA = 5V
0.4
0.4
0.3
0.3
0.2
0.2
DNL (Bits)
INL (Bits)
0.5
0.1
0
-0.1
0.1
0
-0.1
-0.2
-0.2
-0.3
-0.3
-0.4
-0.4
-0.5
+VA = 5V
-0.5
0
5000
10000
15000
0
5000
10000
Code
Code
Figure 42.
Figure 43.
FFT
FFT
0
-60
-80
-100
-40
-60
-80
-100
-120
-120
-140
-140
0
100
200
300
400
10kHz Input
+VA = 3V
fS = 1MSPS
VREF = 2.5V
-20
Amplitude (dB)
-40
Amplitude (dB)
0
5kHz Input
+VA = 3V
fS = 1MSPS
VREF = 2.5V
-20
-160
-160
500
0
100
200
Frequency (kHz)
Figure 44.
Figure 45.
FFT
500
FFT
100kHz Input
+VA = 3V
fS = 1MSPS
VREF = 2.5V
-40
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
0
100
200
300
400
5kHz Input
+VA = 5V
fS = 1MSPS
VREF = 5V
-20
Amplitude (dB)
-40
Amplitude (dB)
400
0
-20
20
300
Frequency (kHz)
0
-160
15000
500
-160
0
100
200
300
Frequency (kHz)
Frequency (kHz)
Figure 46.
Figure 47.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, VREF [(REF+) – (REF–)] = 5V when +VA = +VBD = 5V or VREF [(REF+) – (REF–)] = 2.5V when +VA =
+VBD = 3V, fSCLK = 42MHz, or VREF = 2.5 when +VA = +VBD = 2.7V, fSCLK = 37.8MHz; fi = dc for dc curves, fi = 100kHz for ac
curves with 5V supply and fi = 10kHz for ac curves with 3V supply, unless otherwise noted.
FFT
FFT
0
10kHz Input
+VA = 5V
fS = 1MSPS
VREF = 5V
-40
-40
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
0
100
200
300
400
100kHz Input
+VA = 5V
fS = 1MSPS
VREF = 5V
-20
Amplitude (dB)
-20
Amplitude (dB)
0
-160
500
0
200
100
300
Frequency (kHz)
Frequency (kHz)
Figure 48.
Figure 49.
I/O SUPPLY CURRENT
vs I/O SUPPLY VOLTAGE
400
500
CODE HISTOGRAM
9000
3.0
REF = 2.5V
8000
2.5
7000
Hits per Code
IBVDD (mA)
2.0
1.5
1.0
6000
5000
4000
3000
2000
0.5
1000
0
0
517
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
4.7
4.9
5.1
5.3
5.5
516
518
519
520
Output Code
BVDD (V)
Figure 50.
Figure 51.
CODE HISTOGRAM
9000
REF = 5V
8000
Hits per Code
7000
6000
5000
4000
3000
2000
1000
0
578
579
580
581
582
Output Code
Figure 52.
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THEORY OF OPERATION
The ADS7279 and ADS7280 are two high-speed, low-power, successive approximation register (SAR)
analog-to-digital converters (ADCs) that use an external reference. The architecture of each device is based on a
charge redistribution model that inherently includes a sample-and-hold function.
These devices have an internal clock that runs the conversion; however, these ADCs can also be programmed to
convert data based on an external serial clock, SCLK.
The ADS7279 has one analog input. The analog input is provided to two input pins: +IN and –IN. When a
conversion is initiated, the differential input on these pins is sampled on the internal capacitor array. While a
conversion is in progress, both +IN and –IN inputs are disconnected from any internal function.
The ADS7280 has two inputs. Both inputs share the same common pin, COM. The negative input is the same as
the –IN pin for the ADS7279. The ADS7280 can be programmed to select a channel manually, or it can be
programmed into the auto channel select mode to sweep between channel 0 and channel 1 automatically.
Throughout this document, the term ADS7279/80 refers to both devices, unless specifically noted otherwise.
ANALOG INPUT
When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs is captured on
the internal capacitor array. The voltage on the –IN input is limited between AGND – 0.2V and AGND + 0.2V,
allowing the input to reject small signals that are common to both the +IN and –IN inputs. The +IN input has a
range of –0.2V to (VREF + 0.2V). The input span [(+IN) – (–IN)] is limited to 0V to VREF.
The (peak) input current through the analog inputs depends upon a number of factors: sample rate, input
voltage, and source impedance. The current into the ADS7279/80 charges the internal capacitor array during the
sample period. After this capacitance has been fully charged, there is no further input current. The source of the
analog input voltage must be able to charge the input capacitance (45pF) to a 14-bit settling level within the
minimum acquisition time (120ns). When the converter goes into hold mode, the input impedance is greater than
1GΩ.
Care must be taken regarding the absolute analog input voltage. To maintain converter linearity, the +IN and –IN
inputs and the span [(+IN) – (–IN)] should be within the limits specified. Beyond these ranges, converter linearity
may not meet specifications. To minimize noise, low bandwidth input signals with low-pass filters should be used.
Care should be taken to ensure that the output impedance of the sources driving the +IN and –IN inputs are
matched. If this input matching is not observed, the two inputs could have different settling times. This difference
may result in an offset error, gain error, and linearity errors that change with temperature and input voltage.
Device in Hold Mode
150W
40pF
+IN
4pF
4pF
+VA
AGND
150W
40pF
AGND
-IN
Figure 53. Input Equivalent Circuit
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Driver Amplifier Choice
The analog input to the converter must be driven with a low-noise operational amplifier such as the THS4031 or
OPA365. An RC filter is recommended at the input pins to low-pass filter the noise from the source. Two 20Ω
resistors and a 470pF capacitor are recommended. The input to the converter is a unipolar input voltage in the
range of 0V to VREF. The minimum –3dB bandwidth of the driving operational amplifier can be calculated as:
f3db = (ln(2) × (n+1))/(2π × tACQ)
where n is equal to 14, the resolution of the ADC (in the case of the ADS7279/80). When tACQ = 120ns (minimum
acquisition time), the minimum bandwidth of the driving amplifier is 13.8MHz. The bandwidth can be relaxed if
the acquisition time is increased by the application. Figure 54 shows the THS4031 used in the source follower
configuration to drive the converter in a typical input drive configuration.
Bipolar to Unipolar Driver
In systems where the input is bipolar, the THS4031 can be used in an inverting configuration with an additional
dc bias applied to its positive input to keep the input to the ADS7279/80 within the rated operating voltage range.
This configuration is also recommended when the ADS7279/80 is used in signal processing applications where
good SNR and THD performance are required. The dc bias can be derived from the REF5025 or the REF5040
reference voltage ICs. The input configuration shown in Figure 55 is capable of delivering better than 85dB SNR
and –100dB THD at an input frequency of 10kHz. If bandpass filters are used to filter the input, care should be
taken to ensure that the signal swing at the input of the bandpass filter is small, in order to keep the distortion
introduced by the filter minimal. In this case, the gain of the circuit shown in Figure 55 can be increased to keep
the input to the ADS7279/80 large in order to maintain a high SNR of the system. Note that the gain of the
system from the positive input to the output of the THS4031 in such a configuration is a function of the ac signal
gain. A resistor divider can be used to scale the output of the REF5025 or REF5040 to reduce the voltage at the
dc input to the THS4031 to maintain the voltage at the converter input within its rated operating range.
Input
Signal
(0V to 4V)
5V
ADS7279/80
+VA
THS4031
20W
+IN/(+IN1 or +IN0)
470pF
50W
-IN/COM
20W
Figure 54. Unipolar Input Drive Configuration
ADS7279/80
1V DC
5V
+VA
THS4031
20W
+IN/(+IN1 or +IN0)
470pF
Input
Signal
(-2V to 2V)
-IN/COM
20W
Figure 55. Bipolar Input Drive Configuration
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REFERENCE
The ADS7279/80 must operate with an external reference with a range from 0.3V to 5V. A clean, low-noise,
well-decoupled reference voltage on the REF+ pin is required to ensure good converter performance. A
low-noise bandgap reference such as the REF5040 can be used to drive this pin. A 22µF ceramic decoupling
capacitor is required between the REF+ and REF– pins of the converter. These capacitors should be placed as
close as possible to the device pins. REF– should be connected with an own via to the analog ground plane with
the shortest possible distance. A series resistor between the reference and the REF50xx is neither required
(because the REF50xx is capable of driving a 22µF capacitor while maintaining stability) nor recommended (as a
result of additional nonlinearity); see also Figure 67.
CONVERTER OPERATION
The ADS7279/80 has an oscillator that is used as an internal clock, which controls the conversion rate. The
frequency of this clock is 21MHz (minimum). The oscillator is always on, unless the device is in the deep
power-down state or the device is programmed for using SCLK as the conversion clock (CCLK). The minimum
acquisition (sampling) time takes 3 CCLKs (equivalent to 143ns at 21MHz) and the conversion time takes 18
conversion clocks (CCLK) or approximately 857ns at 21MHz to complete one conversion.
The conversion can also be programmed to run based on an external serial clock, SCLK. This option allows the
designer to fully synchronize the converter with the system. The serial clock SCLK is first reduced to 1/2 of its
frequency before it is used as the conversion clock (CCLK). For example, with a 42MHz SCLK, this reduction
provides a 21MHz clock for conversions. If it is desired to start a conversion at a specific rising edge of SCLK
when the external SCLK is programmed as the source of the conversion clock (and manual conversion start is
selected), the setup time between CONVST and that rising SCLK edge should be observed. This configuration
ensures that the conversion is complete in 18 CCLKs (or 36 SCLKs). The minimum setup time is 20ns to ensure
synchronization between CONVST and SCLK. In many cases, the conversion can start one SCLK period (or
CCLK) later, which results in a conversion length of 19 CCLKs (or 37 SCLKs). The 20ns setup time is not
required if the synchronization is not critical to the application.
The duty cycle of SCLK is not critical as long as it meets the minimum high and low time requirements of 8ns.
The ADS7279/80 is designed for high-speed applications; therefore, a higher serial clock (SCLK) must be
supplied to be able to sustain the high throughput with the serial interface. As a result, the clock period of SCLK
must be at most 1µs (when used as the conversion clock, CCLK). The minimum clock frequency is also
governed by the parasitic leakage of the capacitive digital-to-analog (CDAC) capacitors internal to the
ADS7279/80.
CFR_D10
Conversion Clock
(CCLK)
=1
OSC
=0
Divider
1/2
SPI Serial
Clock (SCLK)
Figure 56. Converter Clock
Manual Channel Select Mode
The conversion cycle starts with selecting an acquisition channel by writing a channel number to the command
register, CMR. The command length can be as short as four SCLKs.
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Auto Channel Select Mode
Channel selection can also be done automatically if auto channel select mode is enabled. This mode is the
default channel select mode. The dual channel converter, ADS7280, has a built-in 2-to-1 MUX. If the device is
programmed for auto channel select mode, then signals from channel 0 and channel 1 are acquired with a fixed
order. Channel 0 is accessed first in the next cycle after the command cycle that configured CFR_D11 to '1' for
auto channel select mode. This automatic access stops the first cycle after the command cycle that sets
CFR_D11 to '0'.
Start of a Conversion
The end of sampling instance (EOS) or acquisition is the same as the start of a conversion. This event is initiated
by bringing the CONVST pin low for a minimum of 40ns. After the minimum requirement has been met, the
CONVST pin can be brought high. CONVST acts independently of FS/CS so it is possible to use one common
CONVST for applications that require a simultaneous sample/hold with multiple converters. The ADS7279/80
switches from sample to hold mode on the falling edge of the CONVST signal. The ADS7279/80 requires 18
conversion clock (CCLK) edges to complete a conversion. The conversion time is equivalent to 857ns with a
21MHz internal clock. The minimum time between two consecutive CONVST signals is 21 CCLKs.
A conversion can also be initiated without using CONVST if auto-trigger mode is used (CFR_D9 = 0). When the
converter is configured as an auto trigger, the next conversion automatically starts three conversion clocks
(CCLK) after the end of a conversion. These three conversion clocks are used as the acquisition time. In this
case, the time to complete one acquisition and conversion cycle is 21 CCLKs. Table 1 summarizes the different
conversion modes.
Table 1. Different Types of Conversion
MODE
SELECT CHANNEL
(1)
Auto Channel Select
Automatic No need to write channel number to the command register (CMR). Use internal
sequencer for the ADS7280.
Manual
(1)
Manual Channel Select
Write the channel number to the CMR.
START CONVERSION
Auto Trigger
Start a conversion based on the conversion
clock CCLK.
Manual Trigger
Start a conversion with CONVST.
Auto channel select should be used with the TAG bit enabled.
Status Output EOC/INT
When the status pin is programmed as EOC and the polarity is set as active low, the pin works in the following
manner: The EOC output goes low immediately after CONVST goes low when the manual trigger is
programmed. EOC stays low throughout the conversion process and returns high when the conversion ends.
The EOC output goes low for three conversion clocks after the previous rising edge of EOC, if auto trigger is
programmed.
This status pin is programmable. It can be used as an EOC output (CFR_D[7:6] = 1, 1) where the low time is
equal to the conversion time. This status pin can also be used as INT (CFR_D[7:6] = 1, 0), which is set low as
the end of a conversion is brought high (cleared) by the next read cycle. The polarity of this pin, used as either
function (that is, EOC or INT), is programmable through CFR_D7.
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Power-Down Modes
The ADS7279/80 has a comprehensive, built-in power-down feature. There are three power-down modes: Deep
power-down mode, Nap power-down mode, and Auto nap power-down mode. All three power-down modes are
enabled by setting the related CFR bits. The first two power-down modes are activated when enabled. A wakeup
command, 1011b, resumes device operation from a power-down mode. Auto nap power-down mode works
slightly differently. When the converter is enabled in Auto nap power-down mode, an end of conversion instance
(EOC) puts the device into auto nap power-down. The beginning of sampling resumes converter operation. The
contents of the configuration register are not affected by any of the power-down modes. Any ongoing conversion
when nap or deep power-down is activated is aborted.
+VA Supply Current (mA)
100
10
1
0.1
0
10000
20000
30000
40000
Settling Time (ns)
Figure 57. Typical Analog Supply Current Drop vs Time After Power-Down
Deep Power-Down Mode
Deep power-down mode can be activated by writing to configuration register bit CFR_D2. When the device is in
Deep power-down mode, all blocks except the interface are in power-down. The external SCLK is internally
blocked. Also, all bias currents and the internal oscillator are turned off. In this mode, power dissipation falls from
5.7mA to 4nA within 100ns. The wake-up time after a deep power-down is 1µs. When bit D2 in the configuration
register is set to '0', the device is in Deep power-down. Setting this bit to '1' or sending a wake-up command
resumes the converter operation from the Deep power-down state.
Nap Mode
In Nap mode, the ADS7279/80 turns off biasing of the comparator and the mid-voltage buffer. In this mode,
supply current falls from 5.7mA in normal mode to about 0.3mA within 200ns after the configuration cycle. The
wake-up (resume) time from Nap power-down mode is 3 CCLKs (143ns with a 21MHz conversion clock). As
soon as the CFR_D3 bit in the control register is set to '0', the device goes into Nap power-down mode,
regardless of the conversion state. Setting this bit to '1' or sending a wake-up command resumes converter
operation from the Nap power-down state.
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Auto Nap Mode
Auto nap mode is almost identical to nap mode. The only difference is the time when the device is actually
powered down and the method used to wake up the device. Configuration register bit D4 is only used to
enable/disable Auto nap mode. If Auto nap mode is enabled, the device turns off the biasing after the conversion
has finished; that is, the end of conversion activates Auto nap power-down mode. Supply current falls from
5.7mA in normal mode to about 0.3mA within 200ns. A CONVST command resumes the device and turns on the
biasing on again in 3 CCLKs (143ns with a 21MHz conversion clock). The device can also be woken up by
disabling auto nap mode when bit D4 of the configuration register is set to '1'. Any channel select command
0XXXb, a wake-up command, or the set default mode command 1111b can also wake up the device from Auto
nap power-down. Table 2 compares the various power-down modes.
NOTE:
1. This wake-up command is the word 1011b in the command word. This command sets bits
D2 and D3 to '1' in the configuration register, but not D4. A wake-up command removes
the device from any of these power-down states, Deep/Nap/Auto nap power-down.
2. Wake-up time is defined as the time between when the host processor tries to wake up the
converter and when a conversion start can occur.
Table 2. Power-Down Mode Comparisons
TYPE OF
POWER-DOWN
SUPPLY
CURRENT
AT 5V/3V
POWER-DOWN BY
TIME TO
POWER-DOWN
(ns)
WAKE-UP BY
WAKE-UP
TIME
Normal operation
5.7mA/4.5mA
—
—
—
—
—
Deep power-down
4nA/1nA
Setting CFR
100
Woken up by command 1011b
1µs
Set CFR
Nap power-down
0.3mA/0.25mA
Setting CFR
200
Woken up by command 1011b
3 CCLKs
Set CFR
200
Woken up by CONVST, any channel
select command, default command
1111b, or wake up command 1011b.
3 CCLKs
Set CFR
Auto nap
power-down
EOC (end of
conversion)
ENABLE
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EOS
EOC
EOS
Converter
State
N+1
Converter State
EOC
N
CONVST
N+1 −th Sampling
N −th Conversion
N+1 −th Conversion
Read While Converting
20ns MIN
CS
(For Read Result)
1 CCLK MIN = t1
Read N−1 −th Result
Read While Sampling
0ns MIN
20ns MIN
CS
(For Read Result)
Read N −th Result
Figure 58. Read While Converting versus Read While Sampling (Manual Trigger)
Manual Trigger
Converter
State
Wake-Up
N −th Sampling
>=3CCLK
N −th Conversion
Activation
Wake-Up
=18 CCLK
N+1 −th Sampling
>=3CCLK
EOC
EOC
EOS
N+1
EOS
N
CONVST
N+1 −th Conversion
Activation
=18 CCLK
20ns MIN
20ns MIN
1 CCLK MIN
Read While Converting
Read N−1 −th
CS
Read N −th
Result
Result
20ns MIN
20ns MIN
Read While Sampling
Read N−1 −th
CS
20ns MIN
0ns MIN
20ns MIN
Read N −th
Result
Result
20ns MIN
20ns MIN
Figure 59. Read While Converting versus Read While Sampling with Deep or Nap Power-Down
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N
N+1
Wake-Up
N −th Sampling
>=3CCLK
N −th Conversion
=18 CCLK
POWERDOWN
Wake-Up
EOC
EOS
EOC
(programmed
Active Low)
Converter
State
40ns MIN
(wake up by CONVST)
EOS
CONVST
EOC
Manual Trigger
N+1 −th Sampling
N+1 −th Conversion
>=3CCLK
=18 CCLK
6 CCLKs
POWERDOWN
6 CCLKs
Read While Converting
20ns MIN
Read N−1 −th
Result
CS
20ns MIN
Read N −th
Result
Figure 60. Read While Converting with Auto Nap Power-Down
Total Acquisition + Conversion Cycle Time:
Auto trigger: = 21 CCLKs
Manual: ≥ 21 CCLKs
Manual + deep ≥ 4 SCLK + 100µs + 3 CCLK + 18 CCLK +16 SCLK + 1µs
power-down:
Manual + nap power-down: ≥ 4 SCLK + 3 CCLK + 3 CCLK + 18 CCLK +16 SCLK
Manual + auto nap ≥ 1 CCLK + 3 CCLK + 3 CCLK + 18 CCLK +16 SCLK (use CONVST to resume)
power-down:
Manual + auto nap ≥ 4 SCLK + 3 CCLK + 3 CCLK + 18 CCLK +16 SCLK (use wake up to resume)
power-down:
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DIGITAL INTERFACE
The serial clock is designed to accommodate the latest high-speed processors with an SCLK frequency up to
50MHz. Each cycle starts with the falling edge of FS/CS. The internal data register content that is made available
to the output register at the EOC (presented on the SDO output pin at the falling edge of FS/CS) is the MSB.
Output data are valid at the falling edge of SCLK with a tD1 delay so that the host processor can read it at the
falling edge. Serial data input is also read at the falling edge of SCLK.
The complete serial I/O cycle starts with the first falling edge of SCLK after the falling edge of FS/CS and ends
16 falling edges of SCLK later (see NOTE). The serial interface is very flexible. It works with CPOL = 0 , CPHA =
1 or CPOL = 1, CPHA = 0. This flexibility means the falling edge of FS/CS may fall while SCLK is high. The
same relaxation applies to the rising edge of FS/CS where SCLK may be high or low as long as the last SCLK
falling edge occurs before the rising edge of FS/CS.
NOTE:
There are cases where a cycle is 4 SCLKs or up to 24 SCLKs depending on the read
mode combination. See Table 3 and Table 6 for details.
Internal Register
The internal register consists of two parts: 4 bits for the command register (CMR) and 12 bits for configuration
data register (CFR). Table 3 summarizes the command set defined by the CMR.
Table 3. Command Set Defined by Command Register (CMR)(1)
D[15:12]
HEX
COMMAND
D[11:0]
(2)
WAKE-UP FROM
AUTO NAP
MINIMUM SCLKs
REQUIRED
R/W
0000b
0h
Select analog input channel 0
Don't care
Y
4
W
0001b
1h
Select analog input channel 1(2)
Don't care
Y
4
W
0010b
2h
Don't care
Don't care
–
–
–
0011b
3h
Don't care
Don't care
–
–
–
0100b
4h
Don't care
Don't care
–
–
–
0101b
5h
Don't care
Don't care
–
–
–
0110b
6h
Don't care
Don't care
–
–
–
0111b
7h
Don't care
Don't care
–
–
–
1000b
8h
Reserved for factory test, don't use
Reserved
–
–
–
1001b
9h
Reserved for factory test, don't use
Reserved
–
–
–
1010b
Ah
Reserved for factory test, don't use
Reserved
–
–
–
1011b
Bh
Wake up
Don't care
Y
4
W
1100b
Ch
Read CFR
Don't care
–
16
R
1101b
Dh
Read data
Don't care
–
14
R
1110
Eh
Write CFR
CFR value
–
16
W
1111b
Fh
Default mode (load CFR with default value)
Don't care
Y
4
W
(1) When SDO is not in 3-state mode (FS/CS low), the bits from SDO are always part of a conversion result (depending on how many
SCLKs are supplied).
(2) These two commands apply to the ADS7280 only.
WRITING TO THE CONVERTER
There are two different types of writes to the register: a 4-bit write to the CMR and a full 16-bit write to the CMR
plus CFR. The command set is listed in Table 3. A simple command requires only 4 SCLKs and the write takes
effect at the fourth falling edge of SCLK. A 16-bit write or read takes at least 16 SCLKs (see Table 6 for
exceptions that require more than 16 SCLKs).
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Configuring the Converter and Default Mode
The converter can be configured with command 1110b (write to the CFR) or command 1111b (default mode). A
write to the CFR requires a 4-bit command followed by 12 bits of data. A 4-bit command takes effect at the fourth
falling edge of SCLK. A CFR write takes effect at the 16th falling edge of SCLK.
A default mode command can be achieved by simply tying SDI to +VBD. As soon as the chip is selected, at least
four '1's are clocked in by SCLK. The default value of the CFR is loaded into the CFR at the fouth falling edge of
SCLK.
CFR default values are all 1s (except for CFR_D1 on the ADS7279; this bit is ignored by the device and is
always read as a '0'). The same default values apply for the CFR after a power-on reset (POR) and software
reset.
READING THE CONFIGURATION REGISTER
The host processor can read back the value programmed in the CFR by issuing command 1100b. The timing is
similar to reading a conversion result, except that CONVST is not used and there is no activity on the EOC/INT
pin. The CFR value read back contains the first four MSBs of conversion data plus valid 12-bit CFR contents.
Table 4 shows the Configuration Register Map.
Table 4. Configuration Register (CFR) Map
SDI BIT
CFR - D[11 - 0]
DEFINITION
Channel select mode
D11 default = 1
D10 default = 1
D9 default = 1
D8 default = 1
D7 default = 1
D6 default = 1
D5 default = 1
D4 default = 1
D3 default = 1
D2 default = 1
D1 default =
0: ADS7279
1: ADS7280
D0 default = 1
0: Manual channel select enabled. Use channel select commands to
access a different channel.
1: Auto channel select enabled. All channels are sampled and
converted sequentially until the cycle after this bit is set to 0.
Conversion clock (CCLK) source select
0: Conversion clock (CCLK) = SCLK/2
1: Conversion clock (CCLK) = Internal OSC
Trigger (conversion start) select: start conversion at the end of sampling (EOS). If D9 = 0, the D4 setting is ignored.
0: Auto trigger automatically starts (4 internal clocks after EOC inactive)
1: Manual trigger manually started by falling edge of CONVST
Don't care
Don't care
Pin 10 polarity select when used as an output (EOC/INT)
0: EOC Active high / INT active high
1: EOC active low / INT active low
Pin 10 function select when used as an output (EOC/INT)
0: Pin used as INT
1: Pin used as EOC
Pin 10 I/O select for chain mode operation
0: Pin 10 is used as CDI input (chain mode enabled)
1: Pin 10 is used as EOC/INT output
Auto nap power-down enable/disable (mid voltage and comparator shut down between cycles). This bit setting is ignored if D9 = 0.
0: Auto nap power-down enabled (not activated)
1: Auto nap power-down disabled
Nap power-down (mid voltage and comparator shut down between cycles). This bit is set to 1 automatically by wake-up command.
0: Enable/activate device in nap power-down
1: Remove device from nap power-down (resume)
Deep power-down. This bit is set to 1 automatically by wake-up command.
0: Enable/activate device in deep power-down
1: Remove device from deep power-down (resume)
TAG bit enable. This bit is ignored by the ADS7279 and is alway read 0.
0: TAG bit disabled.
1: TAG bit output enabled. TAG bit appears at the 17th SCLK.
Reset
0: System reset
1: Normal operation
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READING CONVERSION RESULT
The conversion result is available to the input of the output data register (ODR) at EOC and presented to the
output of the output register at the next falling edge of CS or FS. The host processor can then shift the data out
via the SDO pin any time except during the quiet zone. This quiet zone is 20ns before and 20ns after the end of
sampling (EOS) period. In the quiet zone the FS/CS should be high, to avoid performance loss when switching
from sampling-mode to hold-mode. End of sampling (EOS) is defined as the falling edge of CONVST when
manual trigger is used or the end of the third conversion clock (CCLK) after EOC if auto trigger is used.
The falling edge of FS/CS should not be placed at the precise moment of the end of a conversion; otherwise, the
data may be corrupt. There must be a minimum of at least one conversion clock (CCLK) delay at the end of a
conversion. If FS/CS is placed before the end of a conversion, the previous conversion result is read. If FS/CS is
placed after the end of a conversion, the current conversion result is read.
The conversion result is 14-bit data in straight binary format as shown in Table 5. Generally, 14 SCLKs are
necessary, but there are exceptions where more than 14 SCLKS are required (see Table 6). Data output from
the serial output (SDO) is left-adjusted, MSB first. The 14-bit conversion result is followed by '00', the TAG bit (if
enabled), and additional zeros. SDO remains low until FS/CS is brought high again.
Table 5. Ideal Input Voltages and Output Codes
DESCRIPTION
ANALOG VALUE
DIGITAL OUTPUT
Full-scale range
VREF
STRAIGHT BINARY
Least significant bit (LSB)
VREF/16384
Full-scale
+VREF – 1LSB
11 1111 1111 1111
3FFF
Midscale
VREF/2
10 0000 0000 0000
2000
Midscale – 1LSB
VREF/2– 1LSB
01 1111 1111 1111
1FFF
Zero
0V
00 0000 0000 0000
0000
BINARY CODE
HEX CODE
SDO is active when FS/CS is low. The rising edge of FS/CS 3-states the SDO output.
NOTE:
Whenever SDO is not in 3-state mode (that is, when FS/CS is low), a portion of the
conversion result is output at the SDO pin. The number of bits depends on how many
SCLKs are supplied. For example, a manual select channel command cycle requires
4 SCLKs; therefore, 4MSBs of the conversion result are output at SDO. The exception
is that SDO outputs all 1s during the cycle immediately after any reset (POR or
software reset).
If SCLK is used as the conversion clock (CCLK) and a continuous SCLK is used, it is not possible to clock out all
14 SDO bits during the sampling time (6 SCLKs) because of the quiet zone requirement. In this case, it is better
to read the conversion result during the conversion time (36 SCLKs or 48 SCLKs in Auto nap mode).
TAG Mode
The ADS7280 includes a feature, TAG, that can be used as a tag to indicate which channel sourced the
converted result. An address bit is added after the LSB read out from SDO that indicates which channel the
result came from if TAG mode is enabled. This address bit is '0' for channel 0 and '1' for channel 1. The
converter requires more than the 16 SCLKs that are required for a 4-bit command plus 12-bit CFR or 14 data bits
followed by '00' because of the additional TAG bit.
Chain Mode
The ADS7279/80 can operate as a single converter or in a system with multiple converters. System designers
can take advantage of the simple, high-speed, SPI-compatible serial interface by cascading the devices in a
daisy-chain when multiple converters are used. A bit in the CFR is used to reconfigure the EOC/INT status pin as
a secondary serial data input, chain data input (CDI), for the conversion result from an upstream converter. This
configuration is chain mode operation. A typical connection of three converters is shown in Figure 61.
32
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Micro Controller
INT
GPIO1
GPIO2
SDI SCLK CONVST
CS
ADS7279/80
#1
SDO
EOC/INT
SDOSCLK
GPIO3
SDI SCLK CONVST
CS
ADS7279/80
#2
CDI
SDO
Program device #1 CFR_D[7:5] = XX0b
SDI
SDI SCLK CONVST
CS
ADS7279/80
#3
CDI
SDO
Program device #2 and #3 CFR_D[7:5] = XX1b
Figure 61. Multiple Converters Connected Using Chain Mode
When multiple converters are used in daisy-chain mode, the first converter is configured in regular mode while
the other converters are configured in chain mode. When a converter is configured in chain mode, the CDI input
data go straight to the output register; therefore, the serial input data passes through the converter with a 16
SCLK (if the TAG feature is disabled) or a 24 SCLK delay, as long as CS is active. Figure 62 shows a detailed
timing diagram. In this timing, the conversions in each converter are performed simultaneously.
Cascaded Manual Trigger/Read While Sampling
(Use internal CCLK, EOC, and INT programmed as active low)
CS held low during the N times 16 bits transfer cycle
EOS
EOS
EOC #1
(active low)
EOC
Common CONVST
Nth
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs Min
INT
(active low)
t4
FS/CS #1
1……………………16
1……………………16
1……………………16
Common SCLK
SDO #1
Nth from #1
t4
FS/CS #2
FS/CS #3
SDO #2
Nth from #2
Nth from #1
SDO #3
Nth from #3
Nth from #2
SDI
1101b
READ Result
1101b
READ Result
Nth from #1
1101b
READ Result
Figure 62. Simplified Cascade Mode Timing with Shared CONVST and Continuous CS
Care must be given to handle the multiple CS signals when the converters operate in daisy-chain mode. The
different chip select signals must be low for the entire data transfer (in this example, 48 bits for three converters).
The first 16-bit word after the falling chip select is always the data from the chip that received the chip select
signal.
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Case 1: If chip select is not toggled (CS stays low), the next 16 bits are data from the upstream converter, and so
on. This configuration is shown in Figure 62. If there is no upstream converter in the chain, as with converter #1
in the example, the same data from the converter are going to be shown repeatedly.
Case 2: If the chip select is toggled during a chain mode data transfer cycle, as illustrated in Figure 63, the same
data from the converter are read out again and again in all three discrete 16-bit cycles. This result is not a
desired outcome.
Cascaded Manual Trigger/Read While Sampling
(Use internal CCLK, EOC, and INT programmed as active low)
EOS
EOS
EOC #1
(active low)
EOC
Common CONVST
Nth
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs Min
INT
(active low)
t4
FS/CS #1
1……………………16
1……………………16
1……………………16
Common SCLK
SDO #1
Nth from #1
Nth from #1
Nth from #1
t4
FS/CS #2
SDO #2
Nth from #2
Nth from #1
Nth from #1
Nth from #3
Nth from #3
Nth from #3
t4
FS/CS #3
SDO #3
SDI
1101b
READ Result
1101b
READ Result
1101b
READ Result
Figure 63. Simplified Cascade Mode Timing with Shared CONVST and Discrete CS
34
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Figure 64 shows a slightly different scenario where CONVST is not shared by the second converter. Converters
#1 and #3 have the same CONVST signal. In this case, converter #2 simply passes the previous conversion data
downstream.
Cascaded Manual Trigger/Read While Sampling
(Use internal CCLK, EOC, and INT programmed as active low)
CS held low during the N times 16 bits transfer cycle
CONVST #1
CONVST #3
EOS
EOS
EOC #1
(active low)
EOC
CONVST #2 = 1
Nth
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs Min
INT
(active low)
t4
FS/CS #1
1……………………16
1……………………16
1……………………16
Common SCLK
SDO #1
Nth from #1
t4
FS/CS #2
FS/CS #3
SDO #2
N - 1th #2
Nth from #1
SDO #3
Nth from #3
N - 1th #2
SDI
1101b
READ Result
Nth from #1
1101b
READ Result
1101b
READ Result
Figure 64. Simplified Cascade Timing (Separate CONVST)
The number of SCLKs required for a serial read cycle depends on the combination of different read modes, TAG
bit, chain mode, and the way a channel is selected (that is, auto channel select). These possible configurations
are listed in Table 6.
Table 6. Required SCLKs For Different Read-Out Mode Combinations
CHAIN MODE
AUTO CHANNEL
ENABLED CFR.D5 SELECT CFR.D11
TAG ENABLED CFR.D1
NUMBER OF SCLK
PER SPI READ
TRAILING BITS
0
0
0
14
None
0
0
1
≥ 17
0
1
0
14
0
1
1
≥ 17
1
0
0
16
None
1
0
1
24
TAG bit plus seven zeros
1
1
0
16
None
1
1
1
24
TAG bit plus seven zeros
MSB is TAG bit plus zero(s)
None
TAG bit plus seven zeros
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SCLK skew between converters and data path delay through the converters configured in chain mode can affect
the maximum frequency of SCLK. The delay can also be affected by supply voltage and loading. It may be
necessary to slow down the SCLK when the devices are configured in chain mode. Figure 65 shows a typical
delay process through multiple converters linked in daisy-chain mode.
ADS7279 # 3
CDI
SDO
Logic
Delay
Plus PAD
2.7ns
D
Logic
Delay
< = 8 .3 ns
Serial data
output
Logic
Delay
Plus PAD
8.3ns
Q
CLK
ADS7279 # 2
SDO
CDI
Logic
D
Delay
< = 8 .3 ns
Logic
Delay
Plus PAD
2.7ns
Logic
Delay
Plus PAD
8.3ns
Q
CLK
ADS7279 # 1
CDI
Serial data
input
SDO
Logic
D
Delay
< = 8 .3 ns
Logic
Delay
Plus PAD
2.7ns
Logic
Delay
Plus PAD
8.3ns
Q
CLK
SCLK input
Figure 65. Typical Delay Through Converters Configured in Chain Mode
RESET
The converter has two reset mechanisms: a power-on reset (POR) and a software reset using CFR_D0. These
two mechanisms are NOR-ed internally. When a reset (software or POR) is issued, all register data are set to the
default values (all 1s) and the SDO output (during the cycle immediately after reset) is set to all 1s. The state
machine is reset to the power-on state. Figure 66 illustrates the digital output under a reset condition.
SW RESET
CDI
POR
SET
SAR Shift
Register
Intermediate
Latch
Output
Register
Conversion Clock
Latched by End Of
Conversion
SDO
SCLK
Latched by Falling Edge of CS
CS
EOC
EOC
Figure 66. Digital Output Under Reset Condition
36
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APPLICATION INFORMATION
TYPICAL CONNECTION
Figure 67 shows a typical circuit configuration for the device.
Analog Supply
4.7mF
AGND
Ext Ref Input
100nF
22mF
Analog Input
AGND
+VA REF+ REF- AGND IN+ INFS/CS
SDO
SDI
SCLK
Host
Processor
Interface
Supply
ADS7279/80
BDGND
CONVST
EOC/INT/CDI
4.7mF
+VBD
100nF
Figure 67. Typical Circuit Configuration
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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
ADS7279IPW
ACTIVE
TSSOP
PW
16
90
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IPWG4
ACTIVE
TSSOP
PW
16
90
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IPWR
ACTIVE
TSSOP
PW
16
2000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IPWRG4
ACTIVE
TSSOP
PW
16
2000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IRSAR
ACTIVE
QFN
RSA
16
3000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IRSARG4
ACTIVE
QFN
RSA
16
3000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IRSAT
ACTIVE
QFN
RSA
16
250
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7279IRSATG4
ACTIVE
QFN
RSA
16
250
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IPW
ACTIVE
TSSOP
PW
16
90
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IPWG4
ACTIVE
TSSOP
PW
16
90
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IPWR
ACTIVE
TSSOP
PW
16
2000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IPWRG4
ACTIVE
TSSOP
PW
16
2000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IRSAR
ACTIVE
QFN
RSA
16
3000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IRSARG4
ACTIVE
QFN
RSA
16
3000 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IRSAT
ACTIVE
QFN
RSA
16
250
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
ADS7280IRSATG4
ACTIVE
QFN
RSA
16
250
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
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)
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
11-Jul-2008
(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 2
PACKAGE MATERIALS INFORMATION
www.ti.com
13-Jun-2008
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
Diameter Width
(mm) W1 (mm)
A0 (mm)
B0 (mm)
K0 (mm)
P1
(mm)
W
Pin1
(mm) Quadrant
ADS7279IPWR
TSSOP
PW
16
2000
330.0
12.4
6.67
5.4
1.6
8.0
12.0
Q1
ADS7279IRSAR
QFN
RSA
16
3000
330.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS7279IRSAT
QFN
RSA
16
250
330.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS7280IPWR
TSSOP
PW
16
2000
330.0
12.4
6.67
5.4
1.6
8.0
12.0
Q1
ADS7280IRSAR
QFN
RSA
16
3000
330.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS7280IRSAT
QFN
RSA
16
250
330.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
13-Jun-2008
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS7279IPWR
ADS7279IRSAR
TSSOP
PW
16
2000
346.0
346.0
29.0
QFN
RSA
16
3000
340.5
333.0
20.6
ADS7279IRSAT
QFN
RSA
16
250
340.5
333.0
20.6
ADS7280IPWR
TSSOP
PW
16
2000
346.0
346.0
29.0
ADS7280IRSAR
QFN
RSA
16
3000
340.5
333.0
20.6
ADS7280IRSAT
QFN
RSA
16
250
340.5
333.0
20.6
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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Following are URLs where you can obtain information on other Texas Instruments products and application solutions:
Products
Amplifiers
Data Converters
DSP
Clocks and Timers
Interface
Logic
Power Mgmt
Microcontrollers
RFID
RF/IF and ZigBee® Solutions
amplifier.ti.com
dataconverter.ti.com
dsp.ti.com
www.ti.com/clocks
interface.ti.com
logic.ti.com
power.ti.com
microcontroller.ti.com
www.ti-rfid.com
www.ti.com/lprf
Applications
Audio
Automotive
Broadband
Digital Control
Medical
Military
Optical Networking
Security
Telephony
Video & Imaging
Wireless
www.ti.com/audio
www.ti.com/automotive
www.ti.com/broadband
www.ti.com/digitalcontrol
www.ti.com/medical
www.ti.com/military
www.ti.com/opticalnetwork
www.ti.com/security
www.ti.com/telephony
www.ti.com/video
www.ti.com/wireless
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