TI1 ADS1278 Octal, simultaneous sampling, 24-bit analog-to-digital converter Datasheet

ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
Quad/Octal, Simultaneous Sampling, 24-Bit Analog-to-Digital Converters
Check for Samples: ADS1274, ADS1278
FEATURES
DESCRIPTION
• Simultaneously Measure Four/Eight Channels
• Up to 144kSPS Data Rate
• AC Performance:
70kHz Bandwidth
111dB SNR (High-Resolution Mode)
–108dB THD
• DC Accuracy:
0.8μV/°C Offset Drift
1.3ppm/°C Gain Drift
• Selectable Operating Modes:
High-Speed: 144kSPS, 106dB SNR
High-Resolution: 52kSPS, 111dB SNR
Low-Power: 52kSPS, 31mW/ch
Low-Speed: 10kSPS, 7mW/ch
• Linear Phase Digital Filter
• SPI™ or Frame-Sync Serial Interface
• Low Sampling Aperture Error
• Modulator Output Option (digital filter bypass)
• Analog Supply: 5V
• Digital Core: 1.8V
• I/O Supply: 1.8V to 3.3V
Based on the single-channel ADS1271, the ADS1274
(quad) and ADS1278 (octal) are 24-bit, delta-sigma
(ΔΣ) analog-to-digital converters (ADCs) with data
rates up to 144k samples per second (SPS), allowing
simultaneous sampling of four or eight channels. The
devices are offered in identical packages, permitting
drop-in expandability.
APPLICATIONS
Four operating modes allow for optimization of speed,
resolution, and power. All operations are controlled
directly by pins; there are no registers to program.
The devices are fully specified over the extended
industrial range (–40°C to +105°C) and are available
in an HTQFP-64 PowerPAD™ package.
1
234
•
•
•
•
Vibration/Modal Analysis
Multi-Channel Data Acquisition
Acoustics/Dynamic Strain Gauges
Pressure Sensors
VREFP VREFN
Input1
DS
Input2
DS
Input3
DS
Input4
DS
AVDD
DVDD
Control
Logic
AGND
The
high-order,
chopper-stabilized
modulator
achieves very low drift with low in-band noise. The
onboard decimation filter suppresses modulator and
signal out-of-band noise. These ADCs provide a
usable signal bandwidth up to 90% of the Nyquist
rate with less than 0.005dB of ripple.
IOVDD
SPI
and
FrameSync
Interface
Four
Digital
Filters
Traditionally, industrial delta-sigma ADCs offering
good drift performance use digital filters with large
passband droop. As a result, they have limited signal
bandwidth and are mostly suited for dc
measurements. High-resolution ADCs in audio
applications offer larger usable bandwidths, but the
offset and drift specifications are significantly weaker
than respective industrial counterparts. The ADS1274
and ADS1278 combine these types of converters,
allowing high-precision industrial measurement with
excellent dc and ac specifications.
DGND
ADS1274
VREFP VREFN AVDD
DRDY/FSYNC
SCLK
DOUT[4:1]
DIN
TEST[1:0]
FORMAT[2:0]
CLK
SYNC
PWDN[4:1]
CLKDIV
MODE[1:0]
Input1
DS
Input2
DS
Input3
DS
Input4
DS
Input5
DS
Input6
DS
Input7
DS
Input8
DS
AGND
DVDD
IOVDD
SPI
and
FrameSync
Interface
DRDY/FSYNC
SCLK
DOUT[8:1]
DIN
Control
Logic
TEST[1:0]
FORMAT[2:0]
CLK
SYNC
PWDN[8:1]
CLKDIV
MODE[1:0]
Eight
Digital
Filters
DGND
ADS1278
1
2
3
4
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.
PowerPAD is a trademark of Texas Instruments, Inc.
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.
© 2007–2011, Texas Instruments Incorporated
ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
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 visit the device product folder at www.ti.com.
ABSOLUTE MAXIMUM RATINGS
Over operating free-air temperature range unless otherwise noted (1)
ADS1274, ADS1278
UNIT
AVDD to AGND
–0.3 to +6.0
V
DVDD, IOVDD to DGND
–0.3 to +3.6
V
–0.3 to +0.3
V
Momentary
100
mA
Continuous
10
mA
Analog input to AGND
–0.3 to AVDD + 0.3
V
Digital input or output to DGND
–0.3 to IOVDD + 0.3
V
Maximum junction temperature
+150
°C
ADS1274
–40 to +125
°C
ADS1278
–40 to +105
°C
–60 to +150
°C
AGND to DGND
Input current
Operating temperature range
Storage temperature range
(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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ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
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ELECTRICAL CHARACTERISTICS
All specifications at TA = –40°C to +105°C, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V,
VREFN = 0V, and all channels active, unless otherwise noted.
ADS1274, ADS1278
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUTS
Full-scale input voltage (FSR (1))
VIN = (AINP – AINN)
Absolute input voltage
AINP or AINN to AGND
Common-mode input voltage (VCM)
VCM = (AINP + AINN)/2
Differential input impedance
±VREF
AGND – 0.1
V
AVDD + 0.1
V
2.5
V
High-Speed mode
14
kΩ
High-Resolution mode
14
kΩ
Low-Power mode
28
kΩ
Low-Speed mode
140
kΩ
DC PERFORMANCE
Resolution
No missing codes
Bits
144,531
SPS (3)
fCLK = 32.768MHz
128,000
SPS
fCLK = 27MHz
105,469
SPS
High-Resolution mode
52,734
SPS
Low-Power mode
52,734
SPS
Low-Speed mode
10,547
High-Speed mode (2)
Data rate (fDATA)
24
fCLK = 37MHz
Integral nonlinearity (INL) (4)
SPS
±0.0003
±0.0012
Offset error
0.25
2
Offset drift
0.8
Gain error
0.1
Gain drift
1.3
Noise
Differential input, VCM = 2.5V
0.5
% FSR
ppm/°C
Shorted input
8.5
16
μV, rms
High-Resolution mode
Shorted input
5.5
12
μV, rms
Low-Power mode
Shorted input
8.5
16
μV, rms
Low-Speed mode
Shorted input
8.0
16
μV, rms
fCM = 60Hz
AVDD
DVDD
fPS = 60Hz
IOVDD
VCOM output voltage
(1)
(2)
(3)
(4)
mV
μV/°C
High-Speed mode
Common-mode rejection
Power-supply rejection
% FSR (1)
No load
90
108
dB
80
dB
85
dB
105
dB
AVDD/2
V
FSR = full-scale range = 2VREF.
fCLK = 37MHz max for High-Speed mode, and 27MHz max for all other modes. See Table 7 for fCLK restrictions in High-Speed mode.
SPS = samples per second.
Best fit method.
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ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
All specifications at TA = –40°C to +105°C, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V,
VREFN = 0V, and all channels active, unless otherwise noted.
ADS1274, ADS1278
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
AC PERFORMANCE
f = 1kHz, –0.5dBFS (5)
Crosstalk
High-Speed mode
Signal-to-noise ratio (SNR) (6)
(unweighted)
High-Resolution mode
VREF = 2.5V
–107
dB
101
106
dB
103
110
dB
111
dB
dB
VREF = 3V
Low-Power mode
101
106
Low-Speed mode
101
107
Total harmonic distortion (THD) (7)
VIN = 1kHz, –0.5dBFS
–108
Spurious-free dynamic range
109
Passband
–3dB Bandwidth
Stop band
Group delay
Settling time (latency)
High-Resolution mode
dB
0.453 fDATA
Hz
0.49 fDATA
Hz
95
All other modes
dB
dB
±0.005
Passband ripple
Stop band attenuation
dB
–96
dB
100
High-Resolution mode
0.547 fDATA
127.453 fDATA
Hz
All other modes
0.547 fDATA
63.453 fDATA
Hz
High-Resolution mode
39/fDATA
s
All other modes
38/fDATA
s
High-Resolution mode
Complete settling
78/fDATA
s
All other modes
Complete settling
76/fDATA
s
VOLTAGE REFERENCE INPUTS
AGND – 0.1
Negative reference input (VREFN)
Reference input voltage (VREF) (8)
(VREF = VREFP – VREFN)
ADS1274
Reference Input impedance
ADS1278
Reference Input impedance
AGND + 0.1
V
0.1 ≤ fCLK ≤ 27MHz
0.5
2.5
3.1
V
27 < fCLK ≤ 32.768MHz
0.5
2.5
2.6
V
32.768MHz < fCLK ≤ 37MHz
0.5
2.048
2.1
V
High-Speed mode
1.3
kΩ
High-Resolution mode
1.3
kΩ
Low-Power mode
2.6
kΩ
Low-Speed mode
13
kΩ
High-Speed mode
0.65
kΩ
High-Resolution mode
0.65
kΩ
Low-Power mode
1.3
kΩ
Low-Speed mode
6.5
kΩ
DIGITAL INPUT/OUTPUT (IOVDD = 1.8V to 3.6V)
VIH
0.7 IOVDD
IOVDD
V
VIL
DGND
0.3 IOVDD
V
V
VOH
IOH = 4mA
0.8 IOVDD
IOVDD
VOL
IOL = 4mA
DGND
0.2 IOVDD
V
±10
μA
Input leakage
Master clock rate (fCLK)
(5)
(6)
(7)
(8)
4
0 < VIN DIGITAL < IOVDD
High-Speed mode (8)
0.1
37
MHz
Other modes
0.1
27
MHz
Worst-case channel crosstalk between one or more channels.
Minimum SNR is ensured by the limit of the DC noise specification.
THD includes the first nine harmonics of the input signal; Low-Speed mode includes the first five harmonics.
fCLK = 37MHz max for High-Speed mode, and 27MHz max for all other modes. See Table 7 for VREF restrictions in High-Speed mode.
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ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
All specifications at TA = –40°C to +105°C, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V,
VREFN = 0V, and all channels active, unless otherwise noted.
ADS1274, ADS1278
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
POWER SUPPLY
AVDD
DVDD (9)
4.75
5
5.25
V
0.1 ≤ fCLK ≤ 32.768MHz
1.65
1.8
1.95
V
32.768MHz < fCLK ≤ 37MHz
2.0
2.1
2.2
V
IOVDD
Power-down current
1.65
3.6
V
AVDD
1
10
μA
DVDD
1
15
μA
IOVDD
1
10
μA
High-Speed mode
50
75
mA
High-Resolution mode
50
75
mA
Low-Power mode
23
35
mA
Low-Speed mode
5
9
mA
High-Speed mode
18
24
mA
High-Resolution mode
12
17
mA
Low-Power mode
10
15
mA
Low-Speed mode
2.5
4.5
mA
High-Speed mode
0.15
0.5
mA
High-Resolution mode
0.075
0.3
mA
Low-Power mode
0.075
0.3
mA
Low-Speed mode
0.02
0.15
mA
High-Speed mode
285
420
mW
High-Resolution mode
275
410
mW
Low-Power mode
135
210
mW
Low-Speed mode
30
55
mW
High-Speed mode
97
145
mA
High-Resolution mode
97
145
mA
Low-Power mode
44
64
mA
Low-Speed mode
9
14
mA
High-Speed mode
23
30
mA
High-Resolution mode
16
20
mA
Low-Power mode
12
17
mA
Low-Speed mode
2.5
4.5
mA
ADS1274
ADS1274
AVDD current
ADS1274
DVDD current
ADS1274
IOVDD current
ADS1274
Power dissipation
ADS1278
ADS1278
AVDD current
ADS1278
DVDD current
High-Speed mode
ADS1278
IOVDD current
ADS1278
Power dissipation
(9)
0.25
1
mA
High-Resolution mode
0.125
0.5
mA
Low-Power mode
0.125
0.5
mA
Low-Speed mode
0.035
0.2
mA
High-Speed mode
530
785
mW
High-Resolution mode
515
765
mW
Low-Power mode
245
355
mW
Low-Speed mode
50
80
mW
fCLK = 37MHz max for High-Speed mode, and 27MHz max for all other modes. See Table 7 for DVDD restrictions in High-Speed mode.
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ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
ADS1274/ADS1278 PIN ASSIGNMENTS
VREFP
AGND
AVDD
AINN5(1)
AINP5(1)
AINN6(1)
AINP6(1)
54
53
52
51
50
49
VREFN
57
VCOM
AGND
58
55
AGND
59
56
AINP4
AVDD
AINN4
62
60
AINP3
63
61
AINN3
64
PAP PACKAGE
HTQFP-64
(TOP VIEW)
AINP2
1
48
AINN7(1)
AINN2
2
47
AINP7(1)
AINP1
3
46
AINN8(1)
AINN1
4
45
AINP8(1)
AVDD
5
44
AVDD
AGND
6
43
AGND
DGND
7
42
PWDN1
TEST0
8
41
PWDN2
TEST1
9
40
PWDN3
CLKDIV
10
39
PWDN4
SYNC
11
38
PWDN5(1)
DIN
12
37
PWDN6(1)
DOUT8(1)
13
36
PWDN7(1)
DOUT7(1)
14
35
PWDN8(1)
34
MODE0
33
MODE1
27
28
29
30
31
CLK
SCLK
DRDY/FSYNC
FORMAT2
FORMAT1
32
26
DVDD
FORMAT0
24
25
DGND
23
IOVDD
DGND
22
21
DGND
IOVDD
19
20
DOUT1
DOUT4
18
16
DOUT3
DOUT5
DOUT2
15
(1)
(PowerPAD Outline)
17
DOUT6
(1)
ADS1274/ADS1278
(1) Boldface pin names indicate additional pins for the ADS1278; see Table 1.
Table 1. ADS1274/ADS1278 PIN DESCRIPTIONS
PIN
6
NAME
NO.
FUNCTION
AGND
6, 43, 54,
58, 59
Analog ground
AINP1
3
Analog input
AINP2
1
Analog input
AINP3
63
Analog input
AINP4
61
Analog input
AINP5
51
Analog input
AINP6
49
Analog input
AINP7
47
Analog input
AINP8
45
Analog input
DESCRIPTION
Analog ground; connect to DGND using a single plane.
ADS1278:
AINP[8:1] Positive analog input, channels 8 through 1.
ADS1274:
AINP[8:5] Connected to internal ESD rails. The inputs may float.
AINP[4:1] Positive analog input, channels 4 through 1.
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Table 1. ADS1274/ADS1278 PIN DESCRIPTIONS (continued)
PIN
NAME
NO.
FUNCTION
DESCRIPTION
AINN1
4
Analog input
AINN2
2
Analog input
AINN3
64
Analog input
AINN4
62
Analog input
AINN5
52
Analog input
AINN6
50
Analog input
AINN7
48
Analog input
AINN8
46
Analog input
AVDD
5, 44, 53, 60
Analog power supply
VCOM
55
Analog output
VREFN
57
Analog input
Negative reference input.
VREFP
56
Analog input
Positive reference input.
CLK
27
Digital input
Master clock input (fCLK).
CLKDIV
10
Digital input
DGND
7, 21, 24, 25
Digital ground
ADS1278:
AINN[8:1] Negative analog input, channels 8 through 1.
ADS1274:
AINN[8:5] Connected to internal ESD rails. The inputs may float.
AINN[4:1] Negative analog input, channels 4 through 1.
Analog power supply (4.75V to 5.25V).
AVDD/2 Unbuffered voltage output.
CLK input divider control:
1 = 37MHz (High-Speed mode)/otherwise 27MHz
0 = 13.5MHz (low-power)/5.4MHz (low-speed)
Digital ground power supply.
DIN
12
Digital input
Daisy-chain data input.
DOUT1
20
Digital output
DOUT1 is TDM data output (TDM mode).
DOUT2
19
Digital output
DOUT3
18
Digital output
DOUT4
17
Digital output
DOUT5
16
Digital output
DOUT6
15
Digital output
DOUT7
14
Digital output
DOUT8
13
Digital output
DRDY/
FSYNC
29
Digital input/output
DVDD
26
Digital power supply
FORMAT0
32
Digital input
FORMAT1
31
Digital input
FORMAT2
30
Digital input
IOVDD
22, 23
Digital power supply
MODE0
34
Digital input
MODE1
33
Digital input
PWDN1
42
Digital input
PWDN2
41
Digital input
PWDN3
40
Digital input
PWDN4
39
Digital input
PWDN5
38
Digital input
PWDN6
37
Digital input
PWDN7
36
Digital input
PWDN8
35
Digital input
SCLK
28
Digital input/output
ADS1278:
DOUT[8:1] Data output for channels 8 through 1.
ADS1274:
DOUT[8:5] Internally connected to active circuitry; outputs are
driven.
DOUT[4:1] Data output for channels 4 through 1.
Frame-Sync protocol: frame clock input; SPI protocol: data ready output.
Digital core power supply.
FORMAT[2:0] Selects Frame-Sync/SPI protocol, TDM/discrete data outputs,
fixed/dynamic position TDM data, and modulator mode/normal operating mode.
I/O power supply (+1.65V to +3.6V).
MODE[1:0] Selects High-Speed, High-Resolution, Low-Power, or Low-Speed
mode operation.
ADS1278:
PWDN[8:1] Power-down control for channels 8 through 1.
ADS1274:
PWDN[8:5] must = 0V.
PWDN[4:1] Power-down control for channels 4 through 1.
Serial clock input, Modulator clock output.
SYNC
11
Digital input
Synchronize input (all channels).
TEST0
8
Digital input
TEST[1:0] Test mode select:
TEST1
9
Digital input
00 = Normal operation
11 = Test mode
01 = Do not use
10 = Do not use
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SPI FORMAT TIMING
tCLK
tCPW
CLK
· · ·
tCPW
tCD
tCONV
DRDY
tSD
tDS
tSCLK
tSPW
SCLK
tSPW
tMSBPD
DOUT
Bit 23 (MSB)
tDOPD
tDOHD
Bit 22
tDIST
Bit 21
tDIHD
DIN
SPI FORMAT TIMING SPECIFICATION
For TA = –40°C to +105°C, IOVDD = 1.65V to 3.6V, and DVDD = 1.65V to 1.95V, unless otherwise noted.
SYMBOL
PARAMETER
tCLK
CLK period (1/fCLK) (1)
MIN
37
tCPW
CLK positive or negative pulse width
15
(2)
tCONV
Conversion period (1/fDATA)
tCD (3)
Falling edge of CLK to falling edge of DRDY
tDS (3)
Falling edge of DRDY to rising edge of first SCLK to retrieve data
tMSBPD
DRDY falling edge to DOUT MSB valid (propagation delay)
tSD (3)
Falling edge of SCLK to rising edge of DRDY
tSCLK (4)
SCLK period
tSPW
tDOHD (3) (5)
TYP
MAX
10,000
UNIT
ns
ns
256
2560
22
tCLK
ns
1
tCLK
16
18
ns
ns
1
tCLK
SCLK positive or negative pulse width
0.4
tCLK
SCLK falling edge to new DOUT invalid (hold time)
10
ns
32
ns
26
ns (6)
tDOPD (3)
SCLK falling edge to new DOUT valid (propagation delay)
tDIST
New DIN valid to falling edge of SCLK (setup time)
6
ns
tDIHD (5)
Old DIN valid to falling edge of SCLK (hold time)
6
ns
(1)
(2)
(3)
(4)
(5)
(6)
8
fCLK = 27MHz maximum.
Depends on MODE[1:0] and CLKDIV selection. See Table 8 (fCLK/fDATA).
Load on DRDY and DOUT = 20pF.
For best performance, limit fSCLK/fCLK to ratios of 1, 1/2, 1/4, 1/8, etc.
tDOHD (DOUT hold time) and tDIHD (DIN hold time) are specified under opposite worst-case conditions (digital supply voltage and
ambient temperature). Under equal conditions, with DOUT connected directly to DIN, the timing margin is > 4ns.
DOUT1, TDM mode, IOVDD = 3.15V to 3.45V, and DVDD = 1.7V to 1.9V.
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FRAME-SYNC FORMAT TIMING
tCPW
tCLK
CLK
tCPW
tCS
tFRAME
tFPW
tFPW
FSYNC
tFS
tSCLK
tSPW
tSF
SCLK
tSPW
tMSBPD
DOUT
tDOHD
Bit 23 (MSB)
Bit 22
tDIST
tDOPD
Bit 21
tDIHD
DIN
FRAME-SYNC FORMAT TIMING SPECIFICATION
For TA = –40°C to +105°C, IOVDD = 1.65V to 3.6V, and DVDD = 1.65V to 2.2V, unless otherwise noted.
SYMBOL
PARAMETER
MIN
TYP
MAX
UNIT
High-Speed mode
27
10,000
ns
Other modes
37
10,000
ns
tCLK
CLK period (1/fCLK) (see Table 7)
tCPW
CLK positive or negative pulse width
tCS
Falling edge of CLK to falling edge of SCLK
tFRAME
Frame period (1/fDATA) (1)
tFPW
FSYNC positive or negative pulse width
1
tSCLK
tFS
Rising edge of FSYNC to rising edge of SCLK
5
ns
tSF
Rising edge of SCLK to rising edge of FSYNC
5
ns
(2)
11
ns
–0.25
0.25
tCLK
256
2560
tCLK
tSCLK
SCLK period
1
tCLK
tSPW
SCLK positive or negative pulse width
0.4
tCLK
tDOHD (3) (4)
SCLK falling edge to old DOUT invalid (hold time)
10
tDOPD
(4)
tMSBPD
tDIST
tDIHD
(1)
(2)
(3)
(4)
(5)
(6)
(3)
SCLK falling edge to new DOUT valid (propagation delay)
FSYNC rising edge to DOUT MSB valid (propagation delay)
ns
31
ns
21
ns (5)
25
ns (6)
31
ns
21
ns (5)
25
ns (6)
New DIN valid to falling edge of SCLK (setup time)
6
ns
Old DIN valid to falling edge of SCLK (hold time)
6
ns
Depends on MODE[1:0] and CLKDIV selection. See Table 8 (fCLK/fDATA).
SCLK must be continuously running and limited to ratios of 1, 1/2, 1/4, and 1/8 of fCLK.
tDOHD (DOUT hold time) and tDIHD (DIN hold time) are specified under opposite worst-case conditions (digital supply voltage and
ambient temperature). Under equal conditions, with DOUT connected directly to DIN, the timing margin is > 4ns.
Load on DOUT = 20pF.
DOUT1, TDM mode, IOVDD = 3.15V to 3.45V, and DVDD = 2V to 2.2V.
DOUT1, TDM mode, IOVDD = 3.15V to 3.45V, and DVDD = 1.7V to 1.9V.
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TYPICAL CHARACTERISTICS
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
OUTPUT SPECTRUM
0
OUTPUT SPECTRUM
0
High-Speed Mode
fIN = 1kHz, -0.5dBFS
32,768 Points
-20
-40
-40
Amplitude (dB)
Amplitude (dB)
High-Speed Mode
fIN = 1kHz, -20dBFS
32,768 Points
-20
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
10
100
1k
Frequency (Hz)
10k
100k
10
100
1k
Frequency (Hz)
Figure 1.
Number of Occurrences
-40
Amplitude (dB)
NOISE HISTOGRAM
25k
High-Speed Mode
Shorted Input
262,144 Points
-20
100k
Figure 2.
OUTPUT SPECTRUM
0
10k
-60
-80
-100
-120
-140
High-Speed Mode
Shorted Input
262,144 Points
20k
15k
10k
5k
-160
High-Resolution Mode
fIN = 1kHz, -0.5dBFS
32,768 Points
-20
35
28
High-Resolution Mode
fIN = 1kHz, -20dBFS
32,768 Points
-40
Amplitude (dB)
Amplitude (dB)
21
OUTPUT SPECTRUM
0
-40
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
10
100
1k
Frequency (Hz)
10k
100k
10
Figure 5.
10
14
Figure 4.
OUTPUT SPECTRUM
-20
7
Output (mV)
Figure 3.
0
0
100k
-7
10k
-14
100
1k
Frequency (Hz)
-21
10
-35
1
-28
0
-180
100
1k
Frequency (Hz)
10k
100k
Figure 6.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
OUTPUT SPECTRUM
0
-40
Number of Occurrences
High-Resolution Mode
Shorted Input
262,144 Points
-20
Amplitude (dB)
NOISE HISTOGRAM
25k
-60
-80
-100
-120
-140
High-Resolution Mode
Shorted Input
262,144 Points
20k
15k
10k
5k
Low-Power Mode
fIN = 1kHz, -0.5dBFS
32,768 Points
21.0
24.5
17.5
10.5
14.0
Low-Power Mode
fIN = 1kHz, -20dBFS
32,768 Points
-20
-40
Amplitude (dB)
Amplitude (dB)
3.5
OUTPUT SPECTRUM
0
-40
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
10
100
1k
Frequency (Hz)
10k
100k
10
100
1k
Frequency (Hz)
Figure 9.
Number of Occurrences
-40
100k
NOISE HISTOGRAM
25k
Low-Power Mode
Shorted Input
262,144 Points
-20
10k
Figure 10.
OUTPUT SPECTRUM
0
Amplitude (dB)
7.0
Figure 8.
OUTPUT SPECTRUM
-20
0
Output (mV)
Figure 7.
0
-3.5
100k
-7.0
10k
-10.5
100
1k
Frequency (Hz)
-17.5
10
-14.0
1
-21.0
0
-180
-24.5
-160
-60
-80
-100
-120
-140
20k
Low-Power Mode
Shorted Input
262,144 Points
15k
10k
5k
32
37
26
21
16
5
11
0
-5
100k
-11
10k
-26
100
1k
Frequency (Hz)
-32
10
-37
0
1
-16
-180
-21
-160
Output (mV)
Figure 11.
Figure 12.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
OUTPUT SPECTRUM
0
OUTPUT SPECTRUM
0
Low-Speed Mode
fIN = 100Hz, -0.5dBFS
32,768 Points
-20
-40
Amplitude (dB)
-40
Amplitude (dB)
Low-Speed Mode
fIN = 100Hz, -20dBFS
32,768 Points
-20
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
1
10
100
Frequency (Hz)
1k
10k
1
10
100
Frequency (Hz)
Figure 13.
Number of Occurrences
-40
Amplitude (dB)
NOISE HISTOGRAM
25k
Low-Speed Mode
Shorted Input
262,144 Points
-20
10k
Figure 14.
OUTPUT SPECTRUM
0
1k
-60
-80
-100
-120
-140
20k
Low-Speed Mode
Shorted Input
262,144 Points
15k
10k
5k
-160
THD, THD+N (dB)
-20
TOTAL HARMONIC DISTORTION
vs FREQUENCY
TOTAL HARMONIC DISTORTION
vs INPUT AMPLITUDE
0
-20
-40
-60
-80
THD+N
-100
THD
1k
Frequency (Hz)
High-Speed Mode
fIN = 1kHz
-40
-60
-80
THD+N
-100
-120
-140
100
35
28
21
14
7
Figure 16.
-120
10k
100k
-140
-120
THD
-100
Figure 17.
12
0
Output (mV)
Figure 15.
High-Speed Mode
VIN = -0.5dBFS
10
-7
10k
-14
1k
-21
10
100
Frequency (Hz)
THD, THD+N (dB)
0
1
-35
0.1
-28
0
-180
-80
-60
-40
Input Amplitude (dBFS)
-20
0
Figure 18.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
TOTAL HARMONIC DISTORTION
vs FREQUENCY
THD, THD+N (dB)
-20
0
High-Resolution Mode
VIN = -0.5dBFS
-20
THD, THD+N (dB)
0
TOTAL HARMONIC DISTORTION
vs INPUT AMPLITUDE
-40
-60
-80
THD+N
-100
THD
-120
-140
10
THD, THD+N (dB)
-20
1k
Frequency (Hz)
10k
-120
THD
0
-20
THD+N
-100
THD
-120
-100
-80
-60
-40
Input Amplitude (dBFS)
-20
100
1k
Frequency (Hz)
10k
-40
-60
-80
THD+N
-100
THD
-140
-120
100k
-100
-80
-60
-40
Input Amplitude (dBFS)
-20
Figure 21.
Figure 22.
TOTAL HARMONIC DISTORTION
vs FREQUENCY
TOTAL HARMONIC DISTORTION
vs INPUT AMPLITUDE
0
Low-Speed Mode
VIN = -0.5dBFS
THD, THD+N (dB)
-60
-80
THD+N
THD
-120
0
Low-Speed Mode
-20
-40
-100
0
Low-Power Mode
fIN = 1kHz
-120
-140
THD, THD+N (dB)
THD+N
TOTAL HARMONIC DISTORTION
vs INPUT AMPLITUDE
-80
100
-40
-60
-80
THD+N
-100
THD
-120
-140
10
-100
TOTAL HARMONIC DISTORTION
vs FREQUENCY
-60
-20
-80
Figure 20.
-40
0
-60
Figure 19.
Low-Power Mode
VIN = -0.5dBFS
10
-40
-140
-120
100k
THD, THD+N (dB)
0
100
High-Resolution Mode
fIN = 1kHz
1k
10k
-140
-120
-100
Frequency (Hz)
Figure 23.
-80
-60
-40
Input Amplitude (dBFS)
-20
0
Figure 24.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
OFFSET DRIFT HISTOGRAM
Multi-lot data based on
20°C intervals over the
range -40°C to +105°C.
300
25 units based on
20°C intervals over the
range -40°C to +105°C.
800
700
Number of Occurrences
350
Number of Occurrences
GAIN DRIFT HISTOGRAM
900
250
200
150
100
600
500
400
300
200
100
0
0
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
50
Outliers: T < -20°C
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
400
Offset Drift (mV/°C)
Gain Drift (ppm/°C)
Figure 25.
Figure 26.
OFFSET WARMUP DRIFT RESPONSE BAND
GAIN WARMUP DRIFT RESPONSE BAND
40
40
ADS1278 High-Speed and High-Resolution Modes
ADS1274/78 High-Speed and High-Resolution Modes
Normalized Gain Error (ppm)
Normalized Offset (mV)
30
ADS1278 Low-Power Mode
20
10
0
-10
-20
ADS1278 Low-Speed Mode
-30
30
ADS1278 Low-Power Mode
20
10
0
-10
-20
ADS1278 Low-Speed Mode
-30
ADS1274 High-Speed and High-Resolution Modes
-40
-40
0
50
100
150
200
250
Time (s)
300
350
400
0
50
100
Figure 27.
Number of Occurrences
80
400
30
25
20
15
10
High-Speed Mode
25 Units
70
60
50
40
30
20
5
10
0
0
Gain Error (ppm)
Figure 29.
14
350
-4000
-3600
-3200
-2800
-2400
-2000
-1600
-1200
-800
-400
0
400
800
1200
1600
2000
2400
2800
3200
3600
4000
High-Speed Mode
25 Units
Offset (mV)
300
GAIN ERROR HISTOGRAM
90
-1000
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
Number of Occurrences
35
200
250
Time (s)
Figure 28.
OFFSET ERROR HISTOGRAM
40
150
Figure 30.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
CHANNEL GAIN MATCH HISTOGRAM
High-Speed Mode
10 Units
60
80
Number of Occurrences
70
60
50
40
30
20
50
40
30
20
10
10
0
-1500
-1400
-1300
-1200
-1100
-1000
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
0
High-Speed Mode
10 Units
Channel Gain Match (ppm)
Channel Offset Match (mV)
Figure 31.
Figure 32.
OFFSET AND GAIN
vs TEMPERATURE
20
50
250
18
0
200
-50
150
Gain
100
-150
50
-200
0
-250
-50
0
-20
20
40
60
Temperature (°C)
100
10
8
6
4
0
-100
120 125
VCOM Voltage Output (V)
ADS1274/ADS1278
SAMPLING MATCH ERROR HISTOGRAM
ADS1274 REFERENCE INPUT DIFFERENTIAL
IMPEDANCE vs TEMPERATURE
30 units over 3 production lots,
inter-channel combinations.
30
ADS1278
25
ADS1274
20
15
10
ADS1278
700
600
650
500
550
400
450
300
350
200
250
100
150
5
50
12
Figure 34.
35
0
14
Figure 33.
40
Number of Occurrences
80
16
2
Reference Input Impedance (kW)
-300
-40
AVDD = 5V
25 Units, No Load
2.40
2.41
2.42
2.43
2.44
2.45
2.46
2.47
2.48
2.49
2.50
2.51
2.52
2.53
2.54
2.55
2.56
2.57
2.58
2.59
2.60
-100
Number of Occurrences
Offset
Normalized Gain Error (ppm)
Normalized Offset (mV)
VCOM VOLTAGE OUTPUT HISTOGRAM
300
100
1.36
13.6
1.34
13.4
1.32
13.2
1.30
13.0
1.28
1.26
12.8
High-Speed and
High-Resolution Modes
Low-Speed Mode
1.24
1.22
-40
12.6
12.4
-20
Sampling Match Error (ps)
Figure 35.
0
20
40
60
Temperature (°C)
80
100
Reference Input Impedance (kW)
Number of Occurrences
90
CHANNEL OFFSET MATCH HISTOGRAM
70
- 1500
- 1400
- 1300
- 1200
- 1100
- 1000
- 900
- 800
- 700
- 600
- 500
- 400
- 300
- 200
- 100
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
100
12.2
120 125
Figure 36.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
0.67
6.7
0.66
6.6
0.65
6.5
High-Speed and
High-Resolution Modes
0.64
6.4
Low-Speed Mode
0.63
6.3
0.62
-40
0
20
40
60
Temperature (°C)
80
100
28.8
14.3
28.6
14.2
28.4
14.1
28.2
14.0
28.0
13.9
27.6
13.7
27.4
13.6
27.2
Low-Power Mode
13.5
13.4
-40
6.2
120 125
0
-20
20
40
60
Temperature (°C)
80
100
Figure 37.
Figure 38.
ANALOG INPUT DIFFERENTIAL IMPEDANCE
vs TEMPERATURE
INTEGRAL NONLINEARITY
vs TEMPERATURE
27.0
26.8
120 125
10
Low-Speed Mode
150
8
145
140
135
130
125
6
4
2
120
-20
0
20
40
60
Temperature (°C)
80
100
0
-40
120 125
100
120 125
LINEARITY AND TOTAL HARMONIC DISTORTION
vs REFERENCE VOLTAGE
14
T = +105°C
Linearity (ppm)
Linearity Error (ppm)
80
LINEARITY ERROR
vs INPUT LEVEL
6
T = +25°C
0
-2
-4
-6
20
40
60
Temperature (°C)
Figure 40.
8
2
0
Figure 39.
10
4
-20
12
-104
10
-108
THD
8
T = +125°C
-8
-10
-2.5 -2.0 -1.5 -1.0 -0.5
-116
1.0
-120
Linearity
2
-124
See Electrical Characteristics for VREF Operating Range.
0
0
0.5
VIN (V)
-112
6
4
T = -40°C
-100
THD: fIN = 1kHz, VIN = -0.5dBFS
1.5
2.0
2.5
THD (dB)
115
-40
0
0.5
Figure 41.
16
27.8
High-Speed and
High-Resolution Modes
13.8
INL (ppm of FSR)
Analog Input Impedance (kW)
155
-20
14.4
Analog Input Impedance (kW)
6.8
Analog Input Impedance (kW)
0.68
ANALOG INPUT DIFFERENTIAL IMPEDANCE
vs TEMPERATURE
Reference Input Impedance (kW)
Reference Input Impedance (kW)
ADS1278 REFERENCE INPUT DIFFERENTIAL
IMPEDANCE vs TEMPERATURE
1.0
1.5
2.0
VREF (V)
2.5
3.0
-128
3.5
Figure 42.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
NOISE vs TEMPERATURE
14
14
12
12
12
10
10
Noise
8
8
6
6
Linearity
4
4
2
0
-0.5 0
RMS Noise (mV)
10
Low-Power Mode
INL (ppm of FSR)
RMS Noise (mV)
NOISE AND LINEARITY
vs INPUT COMMON-MODE VOLTAGE
8
Low-Speed Mode
6
4
High-Resolution Mode
2
2
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Common-Mode Voltage (V)
-40
0
-20
20
40
60
Temperature (°C)
80
100
120 125
Figure 43.
Figure 44.
NOISE vs REFERENCE VOLTAGE
TOTAL HARMONIC DISTORTION AND NOISE
vs CLK
12
0
-20
THD (dB)
Low-Speed
6
12
10
8
-60
Noise
6
-80
THD
4
High-Resolution
2
-100
4
-120
2
Noise RMS (mV)
-40
8
14
High-Speed Mode
fCLK > 32.768MHz: VREF = 2.048V, DVDD = 2.1V
THD: AIN = fCLK/5120, -0.5dBFS
Noise: Shorted Input
High-Speed
Low-Power
10
Noise (mV)
High-Speed Mode
See Electrical Characteristics for VREF Operating Range.
0
-140
0
0.5
1.0
1.5
2.0
VREF (V)
2.5
3.0
3.5
10k
1M
CLK (Hz)
10M
Figure 45.
Figure 46.
COMMON-MODE REJECTION
vs INPUT FREQUENCY
POWER-SUPPLY REJECTION
vs POWER-SUPPLY FREQUENCY
0
100M
0
Power-Supply Rejection (dB)
0
Common-Mode Rejection (dB)
100k
-20
-40
-60
-80
-100
-20
-40
-60
AVDD
-80
DVDD
-100
IOVDD
-120
-120
10
100
1k
10k
Input Frequency (Hz)
100k
1M
10
100
1k
10k
100k
Power-Supply Modulation Frequency (Hz)
Figure 47.
1M
Figure 48.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
ADS1274 AVDD CURRENT
vs TEMPERATURE
ADS1274 DVDD CURRENT
vs TEMPERATURE
70
High-Speed and
High-Resolution Modes
High-Speed Mode
20
DVDD Current (mA)
AVDD Current (mA)
60
25
50
40
30
Low-Power Mode
20
15
High-Resolution Mode
10
Low-Power Mode
5
10
Low-Speed Mode
Low-Speed Mode
0
-40
-20
0
20
40
60
Temperature (°C)
80
100
0
-40
120 125
0
-20
ADS1274 IOVDD CURRENT
vs TEMPERATURE
ADS1274 POWER DISSIPATION
vs TEMPERATURE
Power Dissipation (mW)
IOVDD Current (mA)
0.15
High-Speed Mode
High-Resolution Mode
Low-Power Mode
-20
Low-Speed Mode
0
20
40
60
Temperature (°C)
80
100
Low-Power Mode
150
100
Low-Speed Mode
-20
20
40
60
Temperature (°C)
80
ADS1278 AVDD CURRENT
vs TEMPERATURE
ADS1278 DVDD CURRENT
vs TEMPERATURE
100
120 125
100
120 125
30
25
High-Speed and
High-Resolution Modes
Low-Power Mode
40
20
High-Resolution Mode
15
5
0
20
40
60
Temperature (°C)
80
100
120 125
Low-Power Mode
10
Low-Speed Mode
-20
High-Speed Mode
0
-40
Low-Speed Mode
-20
Figure 53.
18
0
Figure 52.
60
0
-40
High-Resolution Mode
200
Figure 51.
80
20
250
0
-40
120 125
DVDD Current (mA)
AVDD Current (mA)
100
High-Speed Mode
300
50
140
120
120 125
400
350
0
-40
100
Figure 50.
0.20
0.05
80
Figure 49.
0.25
0.10
20
40
60
Temperature (°C)
0
20
40
60
Temperature (°C)
80
Figure 54.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, High-Speed mode, AVDD = +5V, DVDD = +1.8V, IOVDD = +3.3V, fCLK = 27MHz, VREFP = 2.5V, and
VREFN = 0V, unless otherwise noted.
ADS1278 IOVDD CURRENT
vs TEMPERATURE
ADS1278 POWER DISSIPATION
vs TEMPERATURE
800
0.5
IOVDD Current (mA)
0.3
High-Speed Mode
0.2
Low-Power Mode
0.1
High-Resolution Mode
0
-40
-20
0
Low-Speed Mode
20
40
60
Temperature (°C)
80
100
Power Dissipation (mW)
700
0.4
600
500
400
300
High-Resolution Mode
Low-Power Mode
200
100
120 125
High-Speed Mode
0
-40
Low-Speed Mode
-20
Figure 55.
0
20
40
60
Temperature (°C)
80
100
120 125
Figure 56.
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OVERVIEW
High-Speed, High-Resolution, Low-Power, and
Low-Speed. Table 2 summarizes the performance of
each mode.
The ADS1274 (quad) and ADS1278 (octal) are 24-bit,
delta-sigma ADCs based on the single-channel
ADS1271. They offer the combination of outstanding
dc accuracy and superior ac performance. Figure 57
shows the block diagram. Note that both devices are
functionally the same, except that the ADS1274 has
four ADCs and the ADS1278 has eight ADCs. The
packages are identical, and the ADS1274 pinout is
compatible with the ADS1278, permitting true drop-in
expandability. The converters are comprised of four
(ADS1274) or eight (ADS1278) advanced, 6th-order,
chopper-stabilized, delta-sigma modulators followed
by low-ripple, linear phase FIR filters. The modulators
measure the differential input signal, VIN = (AINP –
AINN), against the differential reference, VREF =
(VREFP – VREFN). The digital filters receive the
modulator signal and provide a low-noise digital
output. To allow tradeoffs among speed, resolution,
and power, four operating modes are supported:
VREFP
AVDD
R
VREFN
In High-Speed mode, the maximum data rate is
144kSPS. In High-Resolution mode, the SNR =
111dB (VREF = 3.0V); in Low-Power mode, the power
dissipation is 31mW/channel; and in Low-Speed
mode, the power dissipation is only 7mW/channel at
10.5kSPS. The digital filters can be bypassed,
enabling direct access to the modulator output.
The ADS1274/78 is configured by simply setting the
appropriate I/O pins—there are no registers to
program. Data are retrieved over a serial interface
that supports both SPI and Frame-Sync formats. The
ADS1274/78 has a daisy-chainable output and the
ability to synchronize externally, so it can be used
conveniently in systems requiring more than eight
channels.
DVDD
IOVDD
Mod 1
Mod 2
S
Modulator
Output
VCOM
VREF
R
AINP1
AINN1
AINP2
AINN2
VIN1
Mod 8
DS
Modulator1
S
VIN2
Digital
Filter1
DS
Modulator2
S
DRDY/FSYNC
SPI
and
Frame-Sync
Interface
SCLK
DOUT[4:1]/[8:1](1)
DIN
Digital
Filter2
TEST[1:0]
FORMAT[2:0]
CLK
Control
Logic
AINP4/8(1)
AINN4/8
(1)
VIN4/8
S
DS
Modulator4/8(1)
SYNC
PWDN[4:1]/[8:1](1)
Digital
Filter4/8(1)
CLKDIV
MODE[1:0]
AGND
DGND
(1) The ADS1274 has four channels; the ADS1278 has eight channels.
Figure 57. ADS1274/ADS1278 Block Diagram
Table 2. Operating Mode Performance Summary
(1)
20
MODE
MAX DATA RATE (SPS)
PASSBAND (kHz)
SNR (dB)
NOISE (μVRMS)
POWER/CHANNEL (mW)
High-Speed
144,531
65,472
106
8.5
70 (1)
High-Resolution
52,734
23,889
110
5.5
64
Low-Power
52,734
23,889
106
8.5
31
Low-Speed
10,547
4,798
107
8.0
7
Specified at 105kSPS.
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FUNCTIONAL DESCRIPTION
The ADS1274/78 is a delta-sigma ADC consisting of
four/eight independent converters that digitize
four/eight input signals in parallel.
The converter is composed of two main functional
blocks to perform the ADC conversions: the
modulator and the digital filter. The modulator
samples the input signal together with sampling the
reference voltage to produce a 1s density output
stream. The density of the output stream is
proportional to the analog input level relative to the
reference voltage. The pulse stream is filtered by the
internal digital filter where the output conversion
result is produced.
In operation, the input signal is sampled by the
modulator at a high rate (typically 64x higher than the
final output data rate). The quantization noise of the
modulator is moved to a higher frequency range
where the internal digital filter removes it.
Oversampling results in very low levels of noise
within the signal passband.
Since the input signal is sampled at a very high rate,
input signal aliasing does not occur until the input
signal frequency is at the modulator sampling rate.
This architecture greatly relaxes the requirement of
external antialiasing filters because of the high
modulator sampling rate.
SAMPLING APERTURE MATCHING
The ADS1274/78 converters operate from the same
CLK input. The CLK input controls the timing of the
modulator sampling instant. The converter is
designed such that the sampling skew, or modulator
sampling aperture match between channels, is
controlled. Furthermore, the digital filters are
synchronized to start the convolution phase at the
same modulator clock cycle. This design results in
excellent phase match among the ADS1274/78
channels.
Figure 35 shows the inter-device channel sample
matching for the ADS1274 and ADS1278.
The phase match of one 4-channel ADS1274 to that
of another ADS1274 (eight or more channels total)
may not have the same degree of sampling match.
As a result of manufacturing variations, differences in
internal propagation delay of the internal CLK signal
coupled with differences of the arrival of the external
CLK signal to each device may cause larger sampling
match errors. Equal length CLK traces or external
clock distribution devices can be used to reduce the
sampling match error between devices.
FREQUENCY RESPONSE
The digital filter sets the overall frequency response.
The filter uses a multi-stage FIR topology to provide
linear phase with minimal passband ripple and high
stop band attenuation. The filter coefficients are
identical to the coefficients used in the ADS1271. The
oversampling ratio of the digital filter (that is, the ratio
of the modulator sampling to the output data rate, or
fMOD/fDATA) is a function of the selected mode, as
shown in Table 3.
Table 3. Oversampling Ratio versus Mode
MODE SELECTION
OVERSAMPLING RATIO (fMOD/fDATA)
High-Speed
64
High-Resolution
128
Low-Power
64
Low-Speed
64
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High-Speed, Low-Power, and Low-Speed Modes
0
-1
-2
Amplitude (dB)
The digital filter configuration is the same in
High-Speed, Low-Power, and Low-Speed modes with
the oversampling ratio set to 64. Figure 58 shows the
frequency response in High-Speed, Low-Power, and
Low-Speed modes normalized to fDATA. Figure 59
shows the passband ripple. The transition from
passband to stop band is shown in Figure 60. The
overall frequency response repeats at 64x multiples
of the modulator frequency fMOD, as shown in
Figure 61.
-3
-4
-5
-6
-7
-8
-9
-10
0.45
0
0.47
-20
0.51
0.53
0.55
Figure 60. Transition Band Response for
High-Speed, Low-Power, and Low-Speed Modes
-40
-60
-80
20
-100
0
-120
-20
-40
-140
0
0.2
0.6
0.4
0.8
1.0
Normalized Input Frequency (fIN/fDATA)
Figure 58. Frequency Response for High-Speed,
Low-Power, and Low-Speed Modes
Gain (dB)
Amplitude (dB)
0.49
Normalized Input Frequency (fIN/fDATA)
-60
-80
-100
-120
-140
-160
0.02
0
16
32
48
64
Input Frequency (fIN/fDATA)
Amplitude (dB)
0
Figure 61. Frequency Response Out to fMOD for
High-Speed, Low-Power, and Low-Speed Modes
-0.02
-0.04
-0.06
-0.08
-0.10
0
0.1
0.2
0.3
0.4
0.5
0.6
Normalized Input Frequency (fIN/fDATA)
Figure 59. Passband Response for High-Speed,
Low-Power, and Low-Speed Modes
These image frequencies, if present in the signal and
not externally filtered, will fold back (or alias) into the
passband, causing errors. The stop band of the
ADS1274/78 provides 100dB attenuation of
frequencies that begin just beyond the passband and
continue out to fMOD. Placing an antialiasing, low-pass
filter in front of the ADS1274/78 inputs is
recommended to limit possible high-amplitude,
out-of-band signals and noise. Often, a simple RC
filter is sufficient. Table 4 lists the image rejection
versus external filter order.
Table 4. Antialiasing Filter Order Image Rejection
22
IMAGE REJECTION (dB)
(f–3dB at fDATA)
ANTIALIASING
FILTER ORDER
HS, LP, LS
HR
1
39
45
2
75
87
3
111
129
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High-Resolution Mode
0
-1
-2
Amplitude (dB)
The oversampling ratio is 128 in High-Resolution
mode. Figure 62 shows the frequency response in
High-Resolution mode normalized to fDATA. Figure 63
shows the passband ripple, and the transition from
passband to stop band is shown in Figure 64. The
overall frequency response repeats at multiples of the
modulator frequency fMOD (128 × fDATA), as shown in
Figure 65. The stop band of the ADS1274/78
provides 100dB attenuation of frequencies that begin
just beyond the passband and continue out to fMOD.
Placing an antialiasing, low-pass filter in front of the
ADS1274/78 inputs is recommended to limit possible
high-amplitude out-of-band signals and noise. Often,
a simple RC filter is sufficient. Table 4 lists the image
rejection versus external filter order.
-3
-4
-5
-6
-7
-8
-9
-10
0.45
0.47
0.49
0.51
0.53
0.55
Normalized Input Frequency (fIN/fDATA)
Figure 64. Transition Band Response for
High-Resolution mode
0
20
-40
0
-60
-20
-40
-80
Gain (dB)
Amplitude (dB)
-20
-100
-120
-60
-80
-100
-120
-140
0
0.50
0.25
0.75
1
Normalized Input Frequency (fIN/fDATA)
-140
-160
0
Figure 62. Frequency Response for
High-Resolution Mode
32
64
96
128
Normalized Input Frequency (fIN/fDATA)
Figure 65. Frequency Response Out to fMOD for
High-Resolution Mode
0.02
Amplitude (dB)
0
-0.02
-0.04
-0.06
-0.08
-0.10
0
0.1
0.2
0.3
0.4
0.5
0.6
Normalized Input Frequency (fIN/fDATA)
Figure 63. Passband Response for
High-Resolution Mode
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Table 5. Ideal Output Code versus Input Signal
PHASE RESPONSE
The ADS1274/78 incorporates a multiple stage, linear
phase digital filter. Linear phase filters exhibit
constant delay time versus input frequency (constant
group delay). This characteristic means the time
delay from any instant of the input signal to the same
instant of the output data is constant and is
independent of input signal frequency. This behavior
results in essentially zero phase errors when
analyzing multi-tone signals.
INPUT SIGNAL VIN
(AINP – AINN)
IDEAL OUTPUT CODE(1)
≥ +VREF
7FFFFFh
) VREF
2 23 * 1
000001h
0
000000h
* VREF
2 23 * 1
FFFFFFh
23
ǒ2 2* 1Ǔ
v −VREF
SETTLING TIME
As with frequency and phase response, the digital
filter also determines settling time. Figure 66 shows
the output settling behavior after a step change on
the analog inputs normalized to conversion periods.
The X-axis is given in units of conversion. Note that
after the step change on the input occurs, the output
data change very little prior to 30 conversion periods.
The output data are fully settled after 76 conversion
periods for High-Speed and Low-Power modes, and
78 conversion periods for High-Resolution mode.
Final Value
Settling (%)
100
23
800000h
(1) Excludes effects of noise, INL, offset, and gain errors.
ANALOG INPUTS (AINP, AINN)
The ADS1274/78 measures each differential input
signal VIN = (AINP – AINN) against the common
differential reference VREF = (VREFP – VREFN). The
most positive measurable differential input is +VREF,
which produces the most positive digital output code
of 7FFFFFh. Likewise, the most negative measurable
differential input is –VREF, which produces the most
negative digital output code of 800000h.
For optimum performance, the inputs of the
ADS1274/78 are intended to be driven differentially.
For single-ended applications, one of the inputs
(AINP or AINN) can be driven while the other input is
fixed (typically to AGND or +2.5V). Fixing the input to
2.5V permits bipolar operation, thereby allowing full
use of the entire converter range.
Fully Settled Data
at 76 Conversions
(78 Conversions for
High-Resolution mode)
Initial Value
0
0
10
20
30
40
50
60
70
80
Conversions (1/fDATA)
Figure 66. Step Response
DATA FORMAT
The ADS1274/78 outputs 24 bits of data in twos
complement format.
A positive full-scale input produces an ideal output
code of 7FFFFFh, and the negative full-scale input
produces an ideal output code of 800000h. The
output clips at these codes for signals exceeding
full-scale. Table 5 summarizes the ideal output codes
for different input signals.
24
While the ADS1274/78 measures the differential input
signal, the absolute input voltage is also important.
This value is the voltage on either input (AINP or
AINN) with respect to AGND. The range for this
voltage is:
–0.1V < (AINN or AINP) < AVDD + 0.1V
If either input is taken below –0.4V or above
(AVDD + 0.4V), ESD protection diodes on the inputs
may turn on. If these conditions are possible, external
Schottky clamp diodes or series resistors may be
required to limit the input current to safe values (see
the Absolute Maximum Ratings table).
The ADS1274/78 is a very high-performance ADC.
For optimum performance, it is critical that the
appropriate circuitry be used to drive the ADS1274/78
inputs. See the Application Information section for
several recommended circuits.
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The ADS1274/78 uses switched-capacitor circuitry to
measure the input voltage. Internal capacitors are
charged by the inputs and then discharged. Figure 67
shows a conceptual diagram of these circuits. Switch
S2 represents the net effect of the modulator circuitry
in discharging the sampling capacitor; the actual
implementation is different. The timing for switches S1
and S2 is shown in Figure 68. The sampling time
(tSAMPLE) is the inverse of modulator sampling
frequency (fMOD) and is a function of the mode, the
CLKDIV input, and CLK frequency, as shown in
Table 6.
S1
9pF
AINN
Zeff = 14kW ´ (6.75MHz/fMOD)
AINN
Figure 69. Effective Input Impedances
VOLTAGE REFERENCE INPUTS
(VREFP, VREFN)
AVDD AGND
AINP
AINP
S2
S1
AGND AVDD
ESD Protection
Figure 67. Equivalent Analog Input Circuitry
The voltage reference for the ADS1274/78 ADC is
the differential voltage between VREFP and VREFN:
VREF = (VREFP – VREFN). The voltage reference is
common to all channels. The reference inputs use a
structure similar to that of the analog inputs with the
equivalent circuitry on the reference inputs shown in
Figure 70. As with the analog inputs, the load
presented by the switched capacitor can be modeled
with an effective impedance, as shown in Figure 71.
However, the reference input impedance depends on
the number of active (enabled) channels in addition to
fMOD. As a result of the change of reference input
impedance caused by enabling and disabling
channels, the regulation and setting time of the
external reference should be noted, so as not to
affect the readings.
tSAMPLE = 1/fMOD
S1
VREFP
ON
VREFN
OFF
S2
ON
AGND
AGND
AVDD
AVDD
OFF
Figure 68. S1 and S2 Switch Timing for Figure 67
ESD
Protection
Table 6. Modulator Frequency (fMOD) Mode
Selection
MODE SELECTION
CLKDIV
fMOD
High-Speed
1
fCLK/4
High-Resolution
1
fCLK/4
1
fCLK/8
Low-Power
Low-Speed
0
fCLK/4
1
fCLK/40
0
fCLK/8
Figure 70. Equivalent Reference Input Circuitry
VREFP
The average load presented by the switched
capacitor input can be modeled with an effective
differential impedance, as shown in Figure 69. Note
that the effective impedance is a function of fMOD.
Zeff =
VREFN
5.2kW
´ (6.75MHz/fMOD)
N
N = number of active channels.
Figure 71. Effective Reference Impedance
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ESD diodes protect the reference inputs. To keep
these diodes from turning on, make sure the voltages
on the reference pins do not go below AGND by
more than 0.4V, and likewise do not exceed AVDD by
0.4V. If these conditions are possible, external
Schottky clamp diodes or series resistors may be
required to limit the input current to safe values (see
the Absolute Maximum Ratings table).
A high-quality reference voltage with the appropriate
drive strength is essential for achieving the best
performance from the ADS1274. Noise and drift on
the reference degrade overall system performance.
See the Application Information section for example
reference circuits.
CLOCK INPUT (CLK)
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; keeping the clock trace as short as
possible, and using a 50Ω series resistor placed
close to the source end, often helps.
Table 8. Clock Input Options
MODE
SELECTION
MAX fCLK
(MHz)
CLKDIV
fCLK/fDATA
DATA RATE
(SPS)
High-Speed
37
1
256
144,531
High-Resolution
27
1
512
52,734
27
1
512
13.5
0
256
27
1
2,560
5.4
0
512
Low-Power
Low-Speed
The ADS1274/78 requires a clock input for operation.
The individual converters of the ADS1274/78 operate
from the same clock input. At the maximum data rate,
the clock input can be either 27MHz or 13.5MHz for
Low-Power mode, or 27MHz or 5.4MHz for
Low-Speed mode, determined by the setting of the
CLKDIV input. For High-Speed mode, the maximum
CLK input frequency is 37MHz. For High-Resolution
mode, the maximum CLK input frequency is 27MHz.
In High-Speed mode, operating conditions are
restricted depending on the clock input frequency.
The limitations are summarized in Table 7.
fCLK (MHz)
The ADS1274/78 supports four modes of operation:
High-Speed, High-Resolution, Low-Power, and
Low-Speed. The modes offer optimization of speed,
resolution, and power. Mode selection is determined
by the status of the digital input MODE[1:0] pins, as
shown in Table 9. The ADS1274/78 continually
monitors the status of the MODE pin during
operation.
Table 9. Mode Selection
INTERFACE
0.1 ≤ fCLK ≤ 27
0.5 to
3.1
27 < fCLK ≤ 32.768
0.5 to
2.6
1.65 to 1.95
Frame-Sync
32.768 < fCLK ≤ 37
0.5 to
2.1
2.0 to 2.2
Frame-Sync
1.65 to 1.95
Frame-Sync or SPI
MAX fDATA (1)
00
High-Speed
144,531
01
High-Resolution
52,734
10
Low-Power
52,734
11
Low-Speed
10,547
(1) fCLK = 27MHz max (37MHz max in High-Speed mode).
The selection of the external clock frequency (fCLK)
does not affect the resolution of the ADS1274/78.
Use of a slower fCLK can reduce the power
consumption of an external clock buffer. The output
data rate scales with clock frequency, down to a
minimum clock frequency of fCLK = 100kHz. Table 8
summarizes the ratio of the clock input frequency
(fCLK) to data rate (fDATA), maximum data rate and
corresponding maximum clock input for the four
operating modes.
26
MODE SELECTION
MODE[1:0]
DVDD (V)
10,547
MODE SELECTION (MODE)
Table 7. High-Speed Mode fCLK Conditions
VREF
(V)
52,734
When using the SPI protocol, DRDY is held high after
a mode change occurs until settled (or valid) data are
ready; see Figure 72 and Table 10.
In Frame-Sync protocol, the DOUT pins are held low
after a mode change occurs until settled data are
ready; see Figure 72 and Table 10. Data can be read
from the device to detect when DOUT changes to
logic 1, indicating that the data are valid.
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MODE[1:0]
Pins
ADS1274/78
Mode
Previous
Mode
New Mode
tNDR-SPI
SPI
Protocol
DRDY
New Mode
Valid Data Ready
tNDR-FS
Frame-Sync DOUT
Protocol
New Mode
Valid Data on DOUT
Figure 72. Mode Change Timing
Table 10. New Data After Mode Change
SYMBOL
(1)
DESCRIPTION
MIN
tNDR-SPI
Time for new data to be ready (SPI)
tNDR-FS
Time for new data to be ready (Frame-Sync) (1)
127
TYP
MAX
UNITS
129
Conversions (1/fDATA)
128
Conversions (1/fDATA)
If mode change is asynchronous to the FSYNC clock, tNDR-FS varies from 127 to 128 conversions. If the mode change is made
synchronous to FSYNC, tNDR-FS is stable.
SYNCHRONIZATION (SYNC)
The ADS1274/78 can be synchronized by pulsing the
SYNC pin low and then returning the pin high. When
the pin goes low, the conversion process stops, and
the internal counters used by the digital filter are
reset. When the SYNC pin returns high, the
conversion process restarts. Synchronization allows
the conversion to be aligned with an external event,
such as the changing of an external multiplexer on
the analog inputs, or by a reference timing pulse.
Because the ADS1274/78 converters operate in
parallel from the same master clock and use the
same SYNC input control, they are always in
synchronization with each other. The aperture match
among internal channels is typically less than 500ps.
However, the synchronization of multiple devices is
somewhat different. At device power-on, variations in
internal reset thresholds from device to device may
result in uncertainty in conversion timing.
The SYNC pin can be used to synchronize multiple
devices to within the same CLK cycle. Figure 73
illustrates the timing requirement of SYNC and CLK
in SPI format.
See Figure 74 for the Frame-Sync format timing
requirement.
After synchronization, indication of valid data
depends on whether SPI or Frame-Sync format was
used.
In the SPI format, DRDY goes high as soon as SYNC
is taken low; see Figure 73. After SYNC is returned
high, DRDY stays high while the digital filter is
settling. Once valid data are ready for retrieval,
DRDY goes low.
In the Frame-Sync format, DOUT goes low as soon
as SYNC is taken low; see Figure 74. After SYNC is
returned high, DOUT stays low while the digital filter
is settling. Once valid data are ready for retrieval,
DOUT begins to output valid data. For proper
synchronization, FSYNC, SCLK, and CLK must be
established before taking SYNC high, and must then
remain running. If the clock inputs (CLK, FSYNC or
SCLK) are subsequently interrupted or reset,
re-assert the SYNC pin.
For consistent performance, re-assert SYNC after
device power-on when data first appear.
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tCSHD
CLK
tSCSU
tSYN
SYNC
tNDR
DRDY
Figure 73. Synchronization Timing (SPI Protocol)
Table 11. SPI Protocol
SYMBOL
DESCRIPTION
MIN
TYP
MAX
UNITS
tCSHD
CLK to SYNC hold time
10
ns
tSCSU
SYNC to CLK setup time
5
ns
tSYN
Synchronize pulse width
1
tNDR
Time for new data to be ready
CLK periods
129
Conversions (1/fDATA)
tCSHD
CLK
tSCSU
tSYN
SYNC
FSYNC
tNDR
Valid Data
DOUT
Figure 74. Synchronization Timing (Frame-Sync Protocol)
Table 12. Frame-Sync Protocol
SYMBOL
(1)
28
DESCRIPTION
MIN
TYP
MAX
UNITS
tCSHD
CLK to SYNC hold time
10
tSCSU
SYNC to CLK setup time
5
ns
tSYN
Synchronize pulse width
1
CLK periods
tNDR
Time for new data to be ready (1)
127
ns
128
Conversions (1/fDATA)
If SYNC is asynchronous to the FSYNC clock, then tNDR varies from 127 to 128 conversions, starting from the rising edge of SYNC. If
SYNC is made synchronous to the FSYNC clock, then tNDR is stable.
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POWER-DOWN (PWDN)
The channels of the ADS1274/78 can be
independently powered down by use of the PWDN
inputs. To enter the power-down mode, hold the
respective PWDN pin low for at least two CLK cycles.
To exit power-down, return the corresponding PWDN
pin high. Note that when all channels are powered
down, the ADS1274/78 enters a microwatt (μW)
power state where all internal biasing is disabled. In
this state, the TEST[1:0] input pins must be driven; all
other input pins can float. The ADS1274/78 outputs
remain driven.
As shown in Figure 75 and Table 13, a maximum of
130 conversion cycles must elapse for SPI interface,
and 129 conversion cycles must elapse for
Frame-Sync, before reading data after exiting
power-down. Data from channels already running are
not affected. The user software can perform the
required delay time in any of the following ways:
1. Count the number of data conversions after
taking the PWDN pin high.
3. Detect for non-zero data in the powered-up
channel.
After powering up one or more channels, the
channels are synchronized to each other. It is not
necessary to use the SYNC pin to synchronize them.
When a channel is powered down in TDM data
format, the data for that channel are either forced to
zero (fixed-position TDM data mode) or replaced by
shifting the data from the next channel into the
vacated data position (dynamic-position TDM data
mode).
In Discrete data format, the data are always forced to
zero.
When
powering-up
a
channel
in
dynamic-position TDM data format mode, the channel
data remain packed until the data are ready, at which
time the data frame is expanded to include the
just-powered channel data. See the Data Format
section for details.
2. Delay 129/fDATA or 130/fDATA after taking the
PWDN pins high, then read data.
···
CLK
tPWDN
PWDN
DRDY/FSYNC
···
tNDR
(1)
DOUT
(Discrete Data Output Mode)
Post Power-Up Data
DOUT1
(TDM Mode, Dynamic Position)
Normal Position
Data Shifts Position
Normal Position
DOUT1
(TDM Mode, Fixed Position)
Normal Position
Data Remains in Position
Normal Position
(1) In SPI protocol, the timing occurs on the falling edge of DRDY/FSYNC. Powering down all channels forces DRDY/FSYNC high.
Figure 75. Power-Down Timing
Table 13. Power-Down Timing
SYMBOL
tPWDN
tNDR
tNDR
(1)
DESCRIPTION
MIN
PWDN pulse width to enter Power-Down mode
Time for new data ready (SPI)
Time for new data ready (Frame-Sync)
(1)
TYP
MAX
2
UNITS
CLK periods
129
130
Conversions (1/fDATA)
128
129
Conversions (1/fDATA)
FSYNC clock running prior to the rising edge of PWDN. If PWDN is asynchronous to the FSYNC clock, tNDR-FS varies from 127 to 128
conversions. If PWDN is made synchronous to FSYNC, then tNDR-FS is stable.
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FORMAT[2:0]
Data can be read from the ADS1274/78 with two
interface protocols (SPI or Frame-Sync) and several
options of data formats (TDM/Discrete and
Fixed/Dynamic data positions). The FORMAT[2:0]
inputs are used to select among the options. Table 14
lists the available options. See the DOUT Modes
section for details of the DOUT Mode and Data
Position.
Table 14. Data Output Format
FORMAT[2:0]
INTERFACE
PROTOCOL
DOUT
MODE
DATA
POSITION
000
SPI
TDM
Dynamic
001
SPI
TDM
Fixed
010
SPI
Discrete
—
011
Frame-Sync
TDM
Dynamic
100
Frame-Sync
TDM
Fixed
101
Frame-Sync
Discrete
—
110
Modulator Mode
—
—
SERIAL INTERFACE PROTOCOLS
Data are retrieved from the ADS1274/78 using the
serial interface. Two protocols are available: SPI and
Frame-Sync. The same pins are used for both
interfaces:
SCLK,
DRDY/FSYNC,
DOUT[4:1]
(DOUT[8:1] for ADS1278), and DIN. The
FORMAT[2:0] pins select the desired interface
protocol.
Even though the SCLK input has hysteresis, it is
recommended to keep SCLK as clean as possible to
prevent glitches from accidentally shifting the data.
SCLK may be run as fast as the CLK frequency.
SCLK may be either in free-running or stop-clock
operation between conversions. Note that one fCLK is
required after the falling edge of DRDY until the first
rising edge of SCLK. For best performance, limit
fSCLK/fCLK to ratios of 1, 1/2, 1/4, 1/8, etc. When the
device is configured for modulator output, SCLK
becomes the modulator clock output (see the
Modulator Output section).
DRDY/FSYNC (SPI Format)
In the SPI format, this pin functions as the DRDY
output. It goes low when data are ready for retrieval
and then returns high on the falling edge of the first
subsequent SCLK. If data are not retrieved (that is,
SCLK is held low), DRDY pulses high just before the
next conversion data are ready, as shown in
Figure 76. The new data are loaded within one CLK
cycle before DRDY goes low. All data must be shifted
out before this time to avoid being overwritten.
1/fDATA
1/fCLK
DRDY
SCLK
Figure 76. DRDY Timing with No Readback
SPI SERIAL INTERFACE
DOUT
The SPI-compatible format is a read-only interface.
Data ready for retrieval are indicated by the falling
DRDY output and are shifted out on the falling edge
of SCLK, MSB first. The interface can be
daisy-chained using the DIN input when using
multiple devices. See the Daisy-Chaining section for
more information.
The conversion data are output on DOUT[4:1]/[8:1].
The MSB data are valid on DOUT[4:1]/[8:1] after
DRDY goes low. Subsequent bits are shifted out with
each falling edge of SCLK. If daisy-chaining, the data
shifted in using DIN appear on DOUT after all
channel data have been shifted out. When the device
is configured for modulator output, DOUT[4:1]/[8:1]
becomes the modulator data output for each channel
(see the Modulator Output section).
NOTE: The SPI format is limited to a CLK input
frequency of 27MHz, maximum. For CLK input
operation above 27MHz (High-Speed mode only),
use Frame-Sync format.
SCLK
The serial clock (SCLK) features a Schmitt-triggered
input and shifts out data on DOUT on the falling
edge. It also shifts in data on the falling edge on DIN
when this pin is being used for daisy-chaining. The
device shifts data out on the falling edge and the user
normally shifts this data in on the rising edge.
30
DIN
This input is used when multiple ADS1274/78s are to
be daisy-chained together. The DOUT1 pin of the first
device connects to the DIN pin of the next, etc. It can
be used with either the SPI or Frame-Sync formats.
Data are shifted in on the falling edge of SCLK. When
using only one ADS1274/78, tie DIN low. See the
Daisy-Chaining section for more information.
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FRAME-SYNC SERIAL INTERFACE
DOUT
Frame-Sync format is similar to the interface often
used on audio ADCs. It operates in slave
fashion—the user must supply framing signal FSYNC
(similar to the left/right clock on stereo audio ADCs)
and the serial clock SCLK (similar to the bit clock on
audio ADCs). The data are output MSB first or
left-justified on the rising edge of FSYNC. When
using Frame-Sync format, the FSYNC and SCLK
inputs must be continuously running with the
relationships shown in the Frame-Sync Timing
Requirements.
The conversion data are shifted out on
DOUT[4:1]/[8:1]. The MSB data become valid on
DOUT[4:1]/[8:1] after FSYNC goes high. The
subsequent bits are shifted out with each falling edge
of SCLK. If daisy-chaining, the data shifted in using
DIN appear on DOUT[4:1]/[8:1] after all channel data
have been shifted out. When the device is configured
for modulator output, DOUT becomes the modulator
data output (see the Modulator Output section).
DIN
This input is used when multiple ADS1274/78s are to
be daisy-chained together. It can be used with either
SPI or Frame-Sync formats. Data are shifted in on
the falling edge of SCLK. When using only one
ADS1274/78, tie DIN low. See the Daisy-Chaining
section for more information.
SCLK
The serial clock (SCLK) features a Schmitt-triggered
input and shifts out data on DOUT on the falling
edge. It also shifts in data on the falling edge on DIN
when this pin is being used for daisy-chaining. Even
though SCLK has hysteresis, it is recommended to
keep SCLK as clean as possible to prevent glitches
from accidentally shifting the data. When using
Frame-Sync format, SCLK must run continuously. If it
is shut down, the data readback will be corrupted.
The number of SCLKs within a frame period (FSYNC
clock) can be any power-of-2 ratio of CLK cycles (1,
1/2, 1/4, etc), as long as the number of cycles is
sufficient to shift the data output from all channels
within one frame. When the device is configured for
modulator output, SCLK becomes the modulator
clock output (see the Modulator Output section).
DOUT MODES
For both SPI and Frame-Sync interface protocols, the
data are shifted out either through individual channel
DOUT pins, in a parallel data format (Discrete mode),
or the data for all channels are shifted out, in a serial
format, through a common pin, DOUT1 (TDM mode).
TDM Mode
In TDM (time-division multiplexed) data output mode,
the data for all channels are shifted out, in sequence,
on a single pin (DOUT1). As shown in Figure 77, the
data from channel 1 are shifted out first, followed by
channel 2 data, etc. After the data from the last
channel are shifted out, the data from the DIN input
follow. The DIN is used to daisy-chain the data output
from an additional ADS1274/78 or other compatible
device. Note that when all channels of the
ADS1274/78 are disabled, the interface is disabled,
rendering the DIN input disabled as well. When one
or more channels of the device are powered down,
the data format of the TDM mode can be fixed or
dynamic.
DRDY/FSYNC (Frame-Sync Format)
In Frame-Sync format, this pin is used as the FSYNC
input. The frame-sync input (FSYNC) sets the frame
period, which must be the same as the data rate. The
required number of fCLK cycles to each FSYNC period
depends on the mode selection and the CLKDIV
input. Table 8 indicates the number of CLK cycles to
each frame (fCLK/fDATA). If the FSYNC period is not
the proper value, data readback will be corrupted.
SCLK
1
2
23
24
25
47
48
49
71
72
73
95
96
97
DOUT1
(ADS1274)
CH1
CH2
CH3
CH4
DIN
DOUT1
(ADS1278)
CH1
CH2
CH3
CH4
CH5
167
168
CH7
169
191
CH8
192
193
194
195
DIN
DRDY
(SPI)
FSYNC
(Frame-Sync)
Figure 77. TDM Mode (All Channels Enabled)
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TDM Mode, Fixed-Position Data
TDM Mode, Dynamic Position Data
In this TDM data output mode, the data position of
the channels remain fixed, regardless of whether the
channels are powered down. If a channel is powered
down, the data are forced to zero but occupy the
same position within the data stream. Figure 78
shows the data stream with channel 1 and channel 3
powered down.
In this TDM data output mode, when a channel is
powered down, the data from higher channels shift
one position in the data stream to fill the vacated data
slot. Figure 79 shows the data stream with channel 1
and channel 3 powered down.
Discrete Data Output Mode
In Discrete data output mode, the channel data are
shifted out in parallel using individual channel data
output pins DOUT[4:1]/[8:1]. After the 24th SCLK, the
channel data are forced to zero. The data are also
forced to zero for powered down channels. Figure 80
shows the discrete data output format.
SCLK
1
2
23
25
24
47
48
49
71
72
73
95
96
97
167
DOUT1
(ADS1274)
CH1
CH2
CH3
CH4
DIN
DOUT1
(ADS1278)
CH1
CH2
CH3
CH4
CH5
168
169
CH7
191
192
193
CH8
194
195
DIN
DRDY
(SPI)
FSYNC
(Frame-Sync)
Figure 78. TDM Mode, Fixed-Position Data (Channels 1 and 3 Shown Powered Down)
SCLK
1
2
23
24
25
47
48
49
50
DOUT1
(ADS1274)
CH2
CH4
DIN
DOUT1
(ADS1278)
CH2
CH4
CH5
119
120
CH7
121
143
CH8
144
145
145
146
DIN
DRDY
(SPI)
FSYNC
(Frame- Sync)
Figure 79. TDM Mode, Dynamic Position Data (Channels 1 and 3 Shown Powered Down)
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SCLK
1
2
22
DOUT1
CH1
DOUT2
CH2
DOUT3
CH3
DOUT4
CH4
DOUT5
CH5
DOUT6
CH6
DOUT7
CH7
DOUT8
CH8
23
24
25
26
ADS1278 Only
DRDY
(SPI)
FSYNC
(Frame-Sync)
Figure 80. Discrete Data Output Mode
DAISY-CHAINING
Multiple ADS1274/78s can be daisy-chained together
to output data on a single pin. The DOUT1 data
output pin of one device is connected to the DIN of
the next device. As shown in Figure 81, the DOUT1
pin of device 1 provides the output data to a
controller, and the DIN of device 2 is grounded.
Figure 82 shows the data format when reading back
data.
The maximum number of channels that may be
daisy-chained in this way is limited by the frequency
of fSCLK, the mode selection, and the CLKDIV input.
The frequency of fSCLK must be high enough to
completely shift the data out from all channels within
one fDATA period. Table 15 lists the maximum number
of daisy-chained channels when fSCLK = fCLK.
To increase the number of data channels possible in
a chain, a segmented DOUT scheme may be used,
producing two data streams. Figure 83 illustrates four
ADS1274/78s,
with
pairs
of
ADS1274/78s
daisy-chained together. The channel data of each
daisy-chained pair are shifted out in parallel and
received by the processor through independent data
channels.
Table 15. Maximum Channels in a Daisy-Chain
(fSCLK = fCLK)
MODE SELECTION
CLKDIV
MAXIMUM NUMBER
OF CHANNELS
High-Speed
1
10
High-Resolution
1
21
1
21
0
10
1
106
0
21
Low-Power
Low-Speed
Whether the interface protocol is SPI or Frame-Sync,
it is recommended to synchronize all devices by tying
the SYNC inputs together. When synchronized in SPI
protocol, it is only necessary to monitor the DRDY
output of one ADS1274/78.
In Frame-Sync interface protocol, the data from all
devices are ready after the rising edge of FSYNC.
Since DOUT1 and DIN are both shifted on the falling
edge of SCLK, the propagation delay on DOUT1
creates a setup time on DIN. Minimize the skew in
SCLK to avoid timing violations.
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CLK
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ADS1274/78
U2
SYNC
ADS1274/78
U1
SYNC
CLK
CLK
DIN
SCLK
DOUT1
DRDY
DRDY Output from Device 1
DOUT1
DOUT from Devices 1 and 2
DIN
SCLK
SCLK
NOTE: The number of chained devices is limited by the SCLK rate and device mode.
Figure 81. Daisy-Chaining of Two Devices, SPI Protocol (FORMAT[2:0] = 000 or 001)
SCLK
1
DOUT1
2
25
CH1, U1
26
49
CH2, U1
50
CH3, U1
73
74
97
CH4, U1
98
CH5, U1
193
194
217
CH1, U2
218
CH2, U2
385
386
DIN2
DRDY
(SPI)
FSYNC
(Frame-Sync)
Figure 82. Daisy-Chain Data Format of Figure 81 (ADS1278 shown)
SYNC
CLK
Serial Data
Devices 3 and 4
ADS1274/78
U4
ADS1274/78
U3
ADS1274/78
U2
ADS1274/78
U1
SYNC
SYNC
SYNC
SYNC
CLK
CLK
CLK
CLK
DIN
DOUT1
DIN
DOUT1
DIN
DOUT1
DIN
FSYNC
FSYNC
FSYNC
FSYNC
SCLK
SCLK
SCLK
SCLK
DOUT1
Serial Data
Devices 1 and 2
SCLK
FSYNC
NOTE: The number of chained devices is limited by the SCLK rate and device mode.
Figure 83. Segmented DOUT Daisy-Chain, Frame-Sync Protocol (FORMAT[2:0] = 011 or 100)
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POWER SUPPLIES
MODULATOR OUTPUT
The ADS1274/78 has three power supplies: AVDD,
DVDD, and IOVDD. AVDD is the analog supply that
powers the modulator, DVDD is the digital supply that
powers the digital core, and IOVDD is the digital I/O
power supply. The IOVDD and DVDD power supplies
can be tied together if desired (+1.8V). To achieve
rated performance, it is critical that the power
supplies are bypassed with 0.1μF and 10μF
capacitors placed as close as possible to the supply
pins. A single 10μF ceramic capacitor may be
substituted in place of the two capacitors.
The ADS1274/78 incorporates a 6th-order, single-bit,
chopper-stabilized
modulator
followed
by
a
multi-stage digital filter that yields the conversion
results. The data stream output of the modulator is
available directly, bypassing the internal digital filter.
The digital filter is disabled, reducing the DVDD
current, as shown in Table 16. In this mode, an
external digital filter implemented in an ASIC, FPGA,
or similar device is required. To invoke the modulator
output, tie FORMAT[2:0], as shown in Figure 85.
DOUT[4:1]/[8:1] then becomes the modulator data
stream outputs for each channel and SCLK becomes
the modulator clock output. The DRDY/FSYNC pin
becomes an unused output and can be ignored. The
normal operation of the Frame-Sync and SPI
interfaces is disabled, and the functionality of SCLK
changes from an input to an output, as shown in
Figure 85.
Figure 84 shows the start-up sequence of the
ADS1274/78. At power-on, bring up the DVDD supply
first, followed by IOVDD and then AVDD. Check the
power-supply sequence for proper order, including
the ramp rate of each supply. DVDD and IOVDD may
be sequenced at the same time (for example, if the
supplies are tied together). Each supply has an
internal reset circuit whose outputs are summed
together to generate a global power-on reset. After
the supplies have exceeded the reset thresholds, 218
fCLK cycles are counted before the converter initiates
the conversion process. Following the CLK cycles,
the data for 129 conversions are suppressed by the
ADS1274/78 to allow output of fully-settled data. In
SPI protocol, DRDY is held high during this interval.
In frame-sync protocol, DOUT is forced to zero. The
power supplies should be applied before any analog
or digital pin is driven. For consistent performance,
assert SYNC after device power-on when data first
appear.
DVDD
IOVDD
AVDD
1V nom
Table 16. Modulator Output Clock Frequencies
MODE
[1:0]
CLKDIV
MODULATOR
CLOCK
OUTPUT
(SCLK)
00
1
fCLK/4
4.5
8
01
1
fCLK/4
4.0
7
1
fCLK/8
2.5
4
0
fCLK/4
2.5
4
1
fCLK/40
1.0
1
0
fCLK/8
0.5
1
10
11
(1)
1V nom
DOUT1
DOUT2
ADS1274
DVDD
(mA)
ADS1278
DVDD
(mA)
Modulator Data Channel 1
Modulator Data Channel 2
IOVDD
(1)
3V nom
(1)
DIN
Internal Reset
FORMAT0
CLK
18
2
fCLK
129 (max)
tDATA
FORMAT1 DOUT4/8(1)
Modulator Data Channel 4/8(1)
FORMAT2
Modulator Clock Output
SCLK
(1) The ADS1274 has four channels; the ADS1278 has eight
channels.
DRDY
(SPI Protocol)
DOUT
(Frame-Sync Protocol)
Figure 85. Modulator Output
Valid Data
(1) The power-supply reset thresholds are approximate.
Figure 84. Start-Up Sequence
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In modulator output mode, the frequency of the
modulator clock output (SCLK) depends on the mode
selection of the ADS1274/78. Table 16 lists the
modulator clock output frequency and DVDD current
versus device mode.
Figure 86 shows the timing relationship of the
modulator clock and data outputs.
The data output is a modulated 1s density data
stream. When VIN = +VREF, the 1s density is
approximately 80% and when VIN = –VREF, the 1s
density is approximately 20%.
Modulator
Clock Output
SCLK
Modulator
Data Output
DOUT
(13ns max)
Figure 86. Modulator Output Timing
PIN TEST USING TEST[1:0] INPUTS
The test mode feature of the ADS1274 and ADS1278
allows continuity testing of the digital I/O pins. In this
mode, the normal functions of the digital pins are
disabled and routed to each other as pairs through
internal logic, as shown in Table 17. The pins in the
left column drive the output pins in the right column.
Note: some of the digital input pins become outputs;
these outputs must be accommodated in the design.
The analog input, power supply, and ground pins all
remain connected as normal. The test mode is
engaged by setting the pins TEST [1:0] = 11. For
normal converter operation, set TEST[1:0] = 00. Do
not use '01' or '10'.
Table 17. Test Mode Pin Map (TEST[1:0] = 11)
TEST MODE PIN MAP
INPUT PINS
OUTPUT PINS
PWDN1
DOUT1
PWDN2
DOUT2
PWDN3
DOUT3
PWDN4
DOUT4
PWDN5
DOUT5
PWDN6
DOUT6
PWDN7
DOUT7
PWDN8
DOUT8
MODE0
DIN
MODE1
SYNC
FORMAT0
CLKDIV
FORMAT1
FSYNC/DRDY
FORMAT2
SCLK
VCOM OUTPUT
The VCOM pin provides a voltage output equal to
AVDD/2. The intended use of this output is to set the
output common-mode level of the analog input
drivers. The drive capability of the output is limited;
therefore, the output should only be used to drive
high-impedance nodes (> 1MΩ). In some cases, an
external buffer may be necessary. A 0.1μF bypass
capacitor is recommended to reduce noise pickup.
ADS1274/78
OPA350
VCOM » (AVDD/2)
0.1mF
Figure 87. VCOM Output
36
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ADS1274
ADS1278
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www.ti.com
APPLICATION INFORMATION
To obtain the specified performance from the
ADS1274/78, the following layout and component
guidelines should be considered.
1. Power Supplies: The device requires three
power supplies for operation: DVDD, IOVDD, and
AVDD. The allowed range for DVDD is 1.65V to
1.95V; (for 32.768MHz < fCLK ≤ 37MHz: 2.0V to
2.2V) the range of IOVDD is 1.65V to 3.6V;
AVDD is restricted to 4.75V to 5.25V. For all
supplies, use a 10μF tantalum capacitor,
bypassed with a 0.1μF ceramic capacitor, placed
close to the device pins. Alternatively, a single
10μF ceramic capacitor can be used. The
supplies should be relatively free of noise and
should not be shared with devices that produce
voltage spikes (such as relays, LED display
drivers, etc.). If a switching power-supply source
is used, the voltage ripple should be low (less
than 2mV) and the switching frequency outside
the passband of the converter.
2. Ground Plane: A single ground plane connecting
both AGND and DGND pins can be used. If
separate digital and analog grounds are used,
connect the grounds together at the converter.
3. Digital Inputs: It is recommended to
source-terminate the digital inputs to the device
with 50Ω series resistors. The resistors should be
placed close to the driving end of digital source
(oscillator, logic gates, DSP, etc.) This placement
helps to reduce ringing on the digital lines (ringing
may lead to degraded ADC performance).
4. Analog/Digital Circuits: Place analog circuitry
(input buffer, reference) and associated tracks
together, keeping them away from digital circuitry
(DSP, microcontroller, logic). Avoid crossing
digital tracks across analog tracks to reduce
noise coupling and crosstalk.
5. Reference Inputs: It is recommended to use a
minimum 10μF tantalum with a 0.1μF ceramic
capacitor directly across the reference inputs,
VREFP and VREFN. The reference input should
be driven by a low-impedance source. For best
performance, the reference should have less than
3μVRMS in-band noise. For references with noise
higher than this level, external reference filtering
may be necessary.
6. Analog Inputs: The analog input pins must be
driven differentially to achieve specified
performance. A true differential driver or
transformer (ac applications) can be used for this
purpose. Route the analog inputs tracks (AINP,
AINN) as a pair from the buffer to the converter
using short, direct tracks and away from digital
tracks. A 1nF to 10nF capacitor should be used
directly across the analog input pins, AINP and
AINN. A low-k dielectric (such as COG or film
type) should be used to maintain low THD.
Capacitors from each analog input to ground can
be used. They should be no larger than 1/10 the
size of the difference capacitor (typically 100pF)
to preserve the ac common-mode performance.
7. Component Placement: Place the power supply,
analog input, and reference input bypass
capacitors as close as possible to the device
pins. This layout is particularly important for
small-value ceramic capacitors. Larger (bulk)
decoupling capacitors can be located farther from
the device than the smaller ceramic capacitors.
Figure 88 to Figure 90 illustrate basic connections
and interfaces that can be used with the ADS1274.
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37
ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
THS4521
(1)
ADS1274/ADS1278
IN1(+)
AINP1
IN1(-)
2.2nF
(3)
+3.3V
TMS320VC5509
IOVDD
10mF
AINN1
CLK
50W
DRDY/FSYNC
¼
¼
DOUT1
DOUT2
DOUT3
AINP4/8
IN4/8(-)
+5V
2.2nF
+
(3)
AVDD
(2)
10mF
AINN4/8
+1.8V
(6)
DVDD
(2)
10mF
U1
0 Q
CVDD
(CORE)
50W
+1.6V
CLKR
See
Note (5)
200MHz
DOUT4
SYNC
PWDN1
I/O
PWDN2
PWDN4
REF5025
+
VREFP
(2)
10mF
0.1mF
VREFN
CLKDIV
+3.3V
(High-Speed, Frame-Sync, TDM,
and Fixed-Position data selected.)
MODE0
VCOM
+5V
(2)
0.1mF
Buffered
VCOM
Output
DR
> Q
PWDN3
See
Note (6)
1mF
FSR
U2
SCLK
IN4/8(+)
DVDD (I/O)
(2)
(4)
100W
OPA350
TEST0
TEST1
DIN
AGND
DGND
MODE1
FORMAT2
FORMAT1
+3.3V
FORMAT0
(1) External Schottky clamp diodes or series resistors may be needed to prevent overvoltage on the inputs. Place the THS4521 drivers close
to the ADS1278 inputs.
(2) Indicates ceramic capacitors.
(3) Indicates COG ceramic capacitors.
(4) Optional. For pin test mode.
(5) U1: SN74LVC1G04; U2: SN74LVC2G74. These components re-clock the ADS1274/78 data output to interface to the TMS320VC5509.
(6) If CLK > 32.768MHz, use the REF5020 and DVDD = 2.1V.
Figure 88. ADS1274 Basic Connection Drawing
38
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ADS1278
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www.ti.com
1kW
1kW
1.5nF
Buffered
VCOM
Output
+5V
(2)
Buffered
VCOM
Output
(1)
AINP
THS4521
49.9W
0.1mF
AINN
(3)
1.5nF
1kW
249W
5.6nF
49.9W
VOCM
VIN
1kW
VIN
+5V
(1)
49.9W
VOCM
AINP
THS4521
49.9W
0.1mF
AINN
(3)
(2)
5.6nF
1kW
1kW
(2)
VO DIFF = 0.25 ´ VIN
VO COMM = VREF
(2)
249W
(1) Bypass with 10μF and 0.1μF capacitors.
(2) 2.7nF for Low-Power mode; 15nF for Low-Speed mode.
(3) Alternate driver OPA1632 (using ±12V supplies).
Figure 89. Basic Differential Input Signal
Interface
(1) Bypass with 10μF and 0.1μF capacitors.
(2) 10nF for Low-Power mode; 56nF for Low-Speed mode.
(3) Alternate driver OPA1632 (using ±12V supplies).
Figure 90. Basic Single-Ended Input Signal
Interface
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39
ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
PowerPAD THERMALLY-ENHANCED
PACKAGING
The PowerPAD concept is implemented in standard
epoxy resin package material. The integrated circuit
is attached to the leadframe die pad using thermally
conductive epoxy. The package is molded so that the
leadframe die pad is exposed at a surface of the
package. This design provides an extremely low
thermal resistance to the path between the IC
junction and the exterior case. The external surface
of the leadframe die pad is located on the printed
circuit board (PCB) side of the package, allowing the
IC Die
die pad to be attached to the PCB using standard
flow soldering techniques. This configuration allows
efficient attachment to the PCB and permits the board
structure to be used as a heatsink for the package.
Using a thermal pad identical in size to the die pad
and vias connected to the PCB ground plane, the
board designer can now implement power packaging
without additional thermal hardware (for example,
external heatsinks) or the need for specialized
assembly instructions.
Figure 91 illustrates a cross-section view of a
PowerPAD package.
Mold Compound
(Epoxy)
Wire Bond
Wire Bond
Leadframe Die Pad
Exposed at Base of Package
Die Attach Epoxy
(thermally conductive)
Leadframe
Figure 91. Cross-Section View of a PowerPAD Thermally-Enhanced Package
40
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ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
PowerPAD PCB Layout Considerations
Figure 92 shows the recommended layer structure for
thermal management when using a PowerPad
package on a 4-layer PCB design. Note that the
thermal pad is placed on both the top and bottom
sides of the board. The ground plane is used as the
heatsink, while the power plane is thermally isolated
from the thermal vias.
Figure 93 shows the required thermal pad etch
pattern for the HTQFP-64 package used for the
ADS1274. Nine 13mil (0.33mm) thermal vias plated
with 1 ounce of copper are placed within the thermal
pad area for the purpose of connecting the pad to the
ground plane layer. The ground plane is used as a
heatsink in this application. It is very important that
the thermal via diameter be no larger than 13mils in
order to avoid solder wicking during the reflow
process. Solder wicking results in thermal voids that
reduce heat dissipation efficiency and hampers heat
flow away from the IC die.
The via connections to the thermal pad and internal
ground plane should be plated completely around the
hole, as opposed to the typical web or spoke thermal
relief connection. Plating entirely around the thermal
via provides the most efficient thermal connection to
the ground plane.
Additional PowerPAD Package Information
Texas Instruments publishes the PowerPAD
Thermally Enhanced Package Application Report (TI
literature number SLMA002), available for download
at www.ti.com, that provides a more detailed
discussion of PowerPAD design and layout
considerations. Before attempting a board layout with
the ADS1274, it is recommended that the hardware
engineer and/or layout designer be familiar with the
information contained in this document.
Package
Thermal Pad
Component
Traces
13mils (0.33mm)
Component (top) Side
Thermal Via
Ground Plane
Power Plane
Thermal Isolation
(power plane only)
Solder (bottom) Side
Package
Thermal Pad
(bottom trace)
Figure 92. Recommended PCB Structure for a 4-Layer Board
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Product Folder Link(s): ADS1274 ADS1278
41
ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
118mils (3mm)
40mils (1mm)
40mils (1mm)
www.ti.com
Package Outline
Thermal Pad
40mils (1mm)
40mils (1mm)
118mils (3mm)
316mils (8mm)
Thermal Via
13mils (0.33mm)
316mils (8mm)
Figure 93. Thermal Pad Etch and Via Pattern for the HTQFP-64 Package
42
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Product Folder Link(s): ADS1274 ADS1278
ADS1274
ADS1278
SBAS367F – JUNE 2007 – REVISED FEBRUARY 2011
www.ti.com
REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision E (September 2010) to Revision F
•
Page
Deleted selective disclosure statement from document ....................................................................................................... 1
Changes from Revision D (July 2009) to Revision E
Page
•
Added supplemental timing requirements (tDOPD) to SPI Format Timing Specification table ............................................... 8
•
Added supplemental timing requirements (tDOPD and tMSBPD) to Frame-Sync Format Timing Specification table ................ 9
Submit Documentation Feedback
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43
PACKAGE OPTION ADDENDUM
www.ti.com
16-Jan-2012
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
ADS1274IPAPR
ACTIVE
HTQFP
PAP
64
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1274IPAPRG4
ACTIVE
HTQFP
PAP
64
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1274IPAPT
ACTIVE
HTQFP
PAP
64
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1274IPAPTG4
ACTIVE
HTQFP
PAP
64
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1278IPAPR
ACTIVE
HTQFP
PAP
64
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1278IPAPRG4
ACTIVE
HTQFP
PAP
64
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1278IPAPT
ACTIVE
HTQFP
PAP
64
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS1278IPAPTG4
ACTIVE
HTQFP
PAP
64
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
Samples
(Requires Login)
(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.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
16-Jan-2012
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.
OTHER QUALIFIED VERSIONS OF ADS1278 :
NOTE: Qualified Version Definitions:
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Jul-2012
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
ADS1274IPAPR
HTQFP
PAP
64
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
1000
330.0
24.4
13.0
13.0
1.5
16.0
24.0
Q2
ADS1274IPAPT
HTQFP
PAP
64
250
330.0
24.4
13.0
13.0
1.5
16.0
24.0
Q2
ADS1278IPAPR
HTQFP
PAP
64
1000
330.0
24.4
13.0
13.0
1.5
16.0
24.0
Q2
ADS1278IPAPT
HTQFP
PAP
64
250
330.0
24.4
13.0
13.0
1.5
16.0
24.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Jul-2012
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1274IPAPR
HTQFP
PAP
64
1000
367.0
367.0
45.0
ADS1274IPAPT
HTQFP
PAP
64
250
367.0
367.0
45.0
ADS1278IPAPR
HTQFP
PAP
64
1000
367.0
367.0
45.0
ADS1278IPAPT
HTQFP
PAP
64
250
367.0
367.0
45.0
Pack Materials-Page 2
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