ADS5271
AD
S
52
71
www.ti.com...................................................................................................................................................... SBAS313C – JUNE 2004 – REVISED JANUARY 2009
8-Channel, 12-Bit, 50MSPS Analog-to-Digital Converter
with Serial LVDS Interface
FEATURES
1
•
•
•
•
23
•
•
•
•
•
•
•
•
•
•
Maximum Sample Rate: 50MSPS
12-Bit Resolution
No Missing Codes
Total Power Dissipation:
Internal Reference: 927mW
External Reference: 861mW
CMOS Technology
Simultaneous Sample-and-Hold
70.5dB SNR at 10MHz IF
3.3V Digital/Analog Supply
Serialized LVDS Outputs
Integrated Frame and Bit Patterns
Option to Double LVDS Clock Output Currents
Four Current Modes for LVDS
Pin- and Format-Compatible Family
TQFP-80 PowerPAD™ Package
An integrated phase lock loop (PLL) multiplies the
incoming ADC sampling clock by a factor of 12. This
high-frequency LVDS clock is used in the data
serialization and transmission process. The word
output of each internal ADC is serialized and
transmitted either MSB or LSB first. In addition to the
eight data outputs, a bit clock and a word clock are
also transmitted. The bit clock is at 6x the speed of
the sampling clock, whereas the word clock is at the
same speed of the sampling clock.
The ADS5271 provides internal references, or can
optionally be driven with external references. Best
performance is achieved through the internal
reference mode.
The device is available in a TQFP-80 PowerPAD
package and is specified over a –40°C to +85°C
operating range.
LCLKP
6x A DC L K
LCLKN
12 x A D C L K
PLL
A DC L K P
1x A DC L K
AD C LK
A DC L K N
APPLICATIONS
DESCRIPTION
S /H
IN 4 P
S /H
The ADS5271 is a high-performance, 50MSPS,
8-channel analog-to-digital converter (ADC). Internal
references are provided, simplifying system design
requirements. Low power consumption allows for the
highest of system integration densities. Serial LVDS
(low-voltage differential signaling) outputs reduce the
number of interface lines and package size.
MODEL
IN 5 P
S /H
IN 5 N
IN 6 P
S /H
IN 6 N
IN 7 P
IN 7 N
S /H
IN 8 P
RELATED PRODUCTS
RESOLUTION
SAMPLE
(BITS)
RATE (MSPS)
IN 4 N
IN 8 N
CHANNELS
ADS5270
12
40
8
ADS5272
12
65
8
ADS5273
12
70
8
ADS5277
10
65
8
S /H
S e rialize r
1 2− B it
A DC
S e rialize r
1 2− B it
A DC
S e rialize r
1 2− B it
A DC
S e rialize r
1 2− B it
A DC
S e rialize r
1 2− B it
A DC
S e rialize r
1 2− B it
A DC
S e rialize r
IN T /E X T
OUT2N
OUT3P
OUT3N
OUT4P
OUT4N
OUT5P
OUT5N
OUT6P
OUT6N
OUT7P
OUT7N
OUT8P
OUT8N
R eg is te rs
R e fe re n ce
OUT2P
C o n tro l
PD
IN 3 P
IN 3 N
1 2− B it
A DC
OUT1P
OUT1N
R E SE T
S /H
S e rialize r
SDATA
IN 2 P
IN 2 N
1 2− B it
A DC
CS
S /H
R EF T
IN 1 N
SCLK
IN 1 P
Portable Ultrasound Systems
Tape Drives
Test Equipment
Optical Networking
V CM
REFB
•
•
•
•
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.
PowerPAD is a trademark of Texas Instruments.
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 © 2004–2009, Texas Instruments Incorporated
ADS5271
SBAS313C – JUNE 2004 – REVISED JANUARY 2009...................................................................................................................................................... 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)
PRODUCT
ADS5271
(1)
(2)
PACKAGE-LEAD
(2)
PACKAGE
DESIGNATOR
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
PFP
–40°C to +85°C
ADS5271IPFP
HTQFP-80
ORDERING
NUMBER
TRANSPORT
MEDIA, QUANTITY
ADS5271IPFP
Tray, 96
ADS5271IPFPT
Tape and Reel, 250
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.
Thermal pad size: 4.69mm × 4.69mm (min), 6.20mm × 6.20mm (max).
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage Range, AVDD
–0.3V to +3.8V
Supply Voltage Range, LVDD
–0.3V to +3.8V
Voltage Between AVSS and LVSS
–0.3V to +0.3V
Voltage Between AVDD and LVDD
–0.3V to +0.3V
Voltage Applied to External REF Pins
–0.3V to +2.4V
All LVDS Data and Clock Outputs
–0.3V to +2.4V
Analog Input Pins (2)
–0.3V to min. [3.3V, (AVDD + 0.3V)]
Digital Input Pins, Set 1 (pin 69, 76-78)
–0.3V to min. [3.9V, (AVDD + 0.3V)] (3)
Digital Input Pins, Set 2 (pins 16, 45)
–0.3V to min. [3.9V, (LVDD + 0.3V)] (3)
Operating Free-Air Temperature Range, TA
–40°C to +85°C
Lead Temperature, 1.6mm (1/16" from case for 10s)
+260°C
Junction Temperature
+105°C
Storage Temperature Range
(1)
(2)
(3)
2
–65°C to +150°C
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not supported.
The dc voltage applied on the input pins should not go below –0.3V. Also, the dc voltage should be limited to the lower of either 3.3V or
(AVDD + 0.3V). If the input can go higher than +3.3V, then a resistor greater than or equal to 25Ω should be added in series with each
of the input pins. Also, the duty cycle of the overshoot beyond +3.3V should be limited. The overshoot duty cycle can be defined either
as a percentage of the time of overshoot over a clock period, or over the entire device lifetime. For a peak voltage between +3.3V and
+3.5V, a duty cycle up to 10% is acceptable. For a peak voltage between +3.5V and +3.7V, the overshoot duty cycle should not exceed
1%. Any overshoot beyond +3.7V should be restricted to less than 0.1% duty cycle, and never exceed +3.9V.
It is recommended to use a series resistor of 1kΩ or greater if the digital input pins are tied to AVDD or LVDD.
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ADS5271
www.ti.com...................................................................................................................................................... SBAS313C – JUNE 2004 – REVISED JANUARY 2009
RECOMMENDED OPERATING CONDITIONS
ADS5271
MIN
TYP
MAX
UNITS
3.0
3.3
3.6
V
SUPPLIES AND REFERENCES
Analog Supply Voltage, AVDD
Output Driver Supply Voltage, LVDD
3.0
3.3
3.6
V
REFT — External Reference Mode
1.825
1.95
2.0
V
REFB — External Reference Mode
0.9
0.95
1.075
V
REFCM = (REFT + REFB )/ 2 — External Reference Mode
Reference = (REFT – REFB ) — External Reference Mode
(1)
VCM ± 50mV
0.75
Analog Input Common-Mode Range (1)
1.0
V
1.1
V
VCM ± 50mV
V
CLOCK INPUT AND OUTPUTS
ADCLK Input Sample Rate (low-voltage TTL)
20
50
MSPS
ADCLK Duty Cycle
45
55
%
0.6
V
Low-Level Voltage Clock Input
High-Level Voltage Clock Input
2.2
ADCLKP and ADCLKN Outputs (LVDS)
20
50
MHz
V
LCLKP and LCLKN Outputs (LVDS) (2)
120
300
MHz
Operating Free-Air Temperature, TA
–40
+85
°C
Thermal Characteristics:
(1)
(2)
θJA
19.4
°C/W
θJC
4.2
°C/W
These voltages need to be set to 1.45V ±50mV if they are derived independent of VCM.
6 × ADCLK.
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ADS5271
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ELECTRICAL CHARACTERISTICS
TMIN = –40°C and TMAX = +85°C. Typical values are at TA = +25°C, clock frequency = maximum specified, 50% clock duty
cycle, AVDD = 3.3V, LVDD = 3.3V, –1dBFS, ISET = 56.2kΩ, internal voltage reference, and LVDS buffer current at 3.5mA per
channel, unless otherwise noted.
ADS5271
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
LSB
DC ACCURACY
No Missing Codes
Tested
DNL Differential Nonlinearity
INL Integral Nonlinearity
fIN = 5MHz
–0.9
±0.5
+0.9
fIN = 5MHz
–2.0
±0.6
+2.0
LSB
+0.75
%FS
Offset Error (1)
–0.75
Offset Temperature Coefficient
Fixed Attenuation in Channel
±6
(2)
1.5
Fixed Attenuation Matching Across Channels
Gain Error/Reference Error (3)
ppm/°C
VREFT – VREFB
–2.5
Gain Error Temperature Coefficient
%FS
0.01
0.2
dB
±1.0
+2.5
%FS
±20
ppm/°C
POWER REQUIREMENTS (4)
Internal Reference
Power Dissipation
Analog Only (AVDD)
743
792
mW
Output Driver (LVDD)
184
208
mW
927
1000
mW
Total Power Dissipation
External Reference
Power Dissipation
Analog Only (AVDD)
677
mW
Output Driver (LVDD)
184
mW
861
mW
Total Power Dissipation
Power-Down
Clock Running
92
149
mW
REFERENCE VOLTAGES
VREFT Reference Top (internal)
1.9
1.95
2.0
V
VREFB Reference Bottom (internal)
0.9
0.95
1.0
V
VCM Common-Mode Voltage
1.4
1.45
1.5
VCM Output Current (5)
±50mV Change in Voltage
VREFT Reference Top (external)
1.825
VREFB Reference Bottom (external)
(1)
(2)
(3)
(4)
(5)
(6)
4
±2.0
0.9
V
mA
1.95
2.0
0.95
1.075
V
V
External Reference Common-Mode
VCM ± 50mV
mV
External Reference Input Current (6)
1.0
mA
Offset error is the deviation of the average code from mid-code with –1dBFS sinusoid from ideal mid-code (2048). Offset error is
expressed in terms of % of full-scale.
Fixed attenuation in the channel arises due to a fixed attenuation in the sample-and-hold amplifier. When the differential voltage at the
analog input pins are changed from –VREF to +VREF, the swing of the output code is expected to deviate from the full-scale code
(4096LSB) by the extent of this fixed attenuation. NOTE: VREF is defined as (REFT – REFB).
The reference voltages are trimmed at production so that (VREFT – VREFB) is within ± 25mV of the ideal value of 1V. This specification
does not include fixed attenuation.
Supply current can be calculated from dividing the power dissipation by the supply voltage of 3.3V.
VCM provides the common-mode current for the inputs of all eight channels when the inputs are ac-coupled. The VCM output current
specified is the additional drive of the VCM buffer if loaded externally.
Average current drawn from the reference pins in the external reference mode.
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www.ti.com...................................................................................................................................................... SBAS313C – JUNE 2004 – REVISED JANUARY 2009
ELECTRICAL CHARACTERISTICS (continued)
TMIN = –40°C and TMAX = +85°C. Typical values are at TA = +25°C, clock frequency = maximum specified, 50% clock duty
cycle, AVDD = 3.3V, LVDD = 3.3V, –1dBFS, ISET = 56.2kΩ, internal voltage reference, and LVDS buffer current at 3.5mA per
channel, unless otherwise noted.
ADS5271
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
ANALOG INPUT
Differential Input Capacitance
4.0
Analog Input Common-Mode Range
Differential Full-Scale Input Voltage Range
VCM ± 50mV
mV
Internal Reference
2.03
VPP
External Reference
2.03 × (VREFT – VREFB)
VPP
3.0
CLK Cycles
300
MHz
Voltage Overhead Recovery Time (7)
Input Bandwidth
pF
–3dBFS, 25Ω Series
Resistances
DIGITAL DATA INPUTS
VIH High-Level Input Voltage
2.2
V
VIL Low-Level Input Voltage
0.6
CIN Input Capacitance
V
3.0
pF
DIGITAL DATA OUTPUTS
Data Format
Straight Offset Binary
Data Bit Rate
240
600
Mbps
20
MHz
SERIAL INTERFACE
SCLK Serial Clock Input Frequency
(7)
A differential ON/OFF pulse is applied to the ADC input. The differential amplitude of the pulse in its ON (high) state is twice the
full-scale range of the ADC, while the differential amplitude of the pulse in its OFF (low) state is zero. The overload recovery time of the
ADC is measured as the time required by the ADC output code to settle within 1% of full-scale, as measured from its mid-code value
when the pulse is switched from ON (high) to OFF (low).
REFERENCE SELECTION
MODE
INT/EXT
DESCRIPTION
Internal Reference; FSR = 2.03VPP
1
Default with internal pull-up.
External Reference; FSR = 2.03 x (REFT – REFB)
0
Internal reference is powered down. The common-mode voltage
of the external reference should be within 50mV of VCM. VCM is
derived from the internal bandgap voltage.
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ADS5271
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AC CHARACTERISTICS
TMIN = –40°C and TMAX = +85°C. Typical values are at TA = +25°C, clock frequency = maximum specified, 50% clock duty
cycle, AVDD = 3.3V, LVDD = 3.3V, –1dBFS, ISET = 56.2kΩ, internal voltage reference, and LVDS buffer current at 3.5mA per
channel, unless otherwise noted.
ADS5271
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DYNAMIC CHARACTERISTICS
fIN = 1MHz
SFDR Spurious-Free Dynamic Range
HD2 2nd-Order Harmonic Distortion
HD3 3rd-Order Harmonic Distortion
SNR Signal-to-Noise Ratio
SINAD Signal-to-Noise and Distortion
ENOB Effective Number of Bits
Crosstalk
IMD3
6
Two-Tone, Third-Order
Intermodulation Distortion
87
dBc
85
dBc
fIN = 10MHz
84
dBc
fIN = 20MHz
82
dBc
fIN = 1MHz
90
dBc
90
dBc
fIN = 10MHz
87
dBc
fIN = 20MHz
85
dBc
fIN = 1MHz
87
dBc
85
dBc
fIN = 10MHz
84
dBc
fIN = 20MHz
82
dBc
fIN = 1MHz
70.5
dBFS
fIN = 5MHz
78
fIN = 5MHz
85
fIN = 5MHz
78
70.5
dBFS
fIN = 10MHz
fIN = 5MHz
69.5
70.5
dBFS
fIN = 20MHz
70.5
dBFS
fIN = 1MHz
70
dBFS
70
dBFS
fIN = 10MHz
70
dBFS
fIN = 20MHz
70
dBFS
fIN = 5MHz
11.3
Bits
5MHz Full-Scale Signal Applied to 7 Channels;
Measurement Taken on the Channel with No Input Signal
–90
dBc
f1 = 9.5MHz at –7dBFS
f2 = 10.2MHz at –7dBFS
–85
dBFS
fIN = 5MHz
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ADS5271
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LVDS DIGITAL DATA AND CLOCK OUTPUTS
Test conditions at IO = 3.5mA, RLOAD = 100Ω, CLOAD = 6pF, and 50% duty cycle. IO refers to the current setting for the LVDS buffer. RLOAD is
the differential load resistance between the differential LVDS pair. CLOAD is the effective single-ended load capacitance between each of the
LVDS pins and ground. CLOAD includes the receiver input parasitics as well as the routing parasitics. Measurements are done with a 1-inch
transmission line of 100Ω characteristic impedance between the device and the load. All LVDS specifications are characterized, but not
parametrically tested at production. LCLKOUT refers to (LCLKP – LCLKN); ADCLKOUT refers to (ADCLKP – ADCLKN); DATA OUT refers to
(OUTP – OUTN); and ADCLK refers to the input sampling clock.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VOH Output Voltage High, OUTP or OUTN
RLOAD = 100Ω ± 1%; See LVDS Timing Diagram, Page 8
1265
1365
1465
mV
VOL Output Voltage Low, OUTP or OUTN
RLOAD = 100Ω ± 1%
940
1040
1140
mV
|VOD| Output Differential Voltage
RLOAD = 100Ω ± 1%
275
325
375
mV
VOS Output Offset Voltage (2)
RLOAD = 100Ω ± 1%; See LVDS Timing Diagram, Page 8
1.1
1.2
1.3
DC SPECIFICATIONS (1)
V
RO Output Impedance, Differential
Normal Operation
13
kΩ
RO Output Impedance, Differential
Power-Down
20
kΩ
CO Output Capacitance (3)
|ΔVOD| Change in |VOD| Between 0 and 1
4
pF
RLOAD = 100Ω ± 1%
10
mV
ΔVOS Change Between 0 and 1
RLOAD = 100Ω ± 1%
25
mV
ISOUT Output Short-Circuit Current
Drivers Shorted to Ground
40
mA
Drivers Shorted Together
12
mA
%
ISOUTNP Output Current
DRIVER AC SPECIFICATIONS
ADCLKOUT Clock Duty Cycle (4)
45
50
55
LCLKOUT Duty Cycle (4)
45
50
55
Data Setup Time (5) (6)
0.6
Data Hold Time (6) (7)
0.42
LVDS Outputs Rise/Fall Time (8)
ns
IO = 2.5mA
400
IO = 3.5mA
%
ns
180
300
IO = 4.5mA
230
IO = 6.0mA
180
ps
500
ps
ps
ps
LCLKOUT Rising Edge to ADCLKOUT Rising Edge (9)
0.60
0.83
1.05
ns
ADCLKOUT Rising Edge to LCLKOUT Falling Edge (9)
0.60
0.83
1.05
ns
ADCLKOUT Rising Edge to DATA OUT Transition (9)
–0.35
0
+0.35
ns
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
The dc specifications refer to the condition where the LVDS outputs are not switching, but are permanently at a valid logic level 0 or 1.
VOS refers to the common-mode of OUTP and OUTN.
Output capacitance inside the device, from either OUTP or OUTN to ground.
Measured between zero crossings.
DATA OUT (OUTP – OUTN) crossing zero to LCLKOUT (LCLKP – LCLKN) crossing zero.
Data setup and hold time accounts for data-dependent skews, channel-to-channel mismatches, as well as effects of clock jitter within
the device.
LCLKOUT crossing zero to DATA OUT crossing zero.
Measured from –100mV to +100mV on the differential output for rise time, and +100mV to –100mV for fall time.
Measured between zero crossings.
SWITCHING CHARACTERISTICS
TMIN = –40°C and TMAX = +85°C. Typical values are at TA = +25°C, clock frequency = maximum specified, 50% clock duty
cycle, AVDD = 3.3V, LVDD = 3.3V, –1dBFS, internal voltage reference, and LVDS buffer current at 3.5mA per channel,
unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
50
ns
4
6.5
SWITCHING SPECIFICATIONS
tSAMPLE
20
tD(A) Aperture Delay
2
Aperture Jitter (uncertainty)
tD(pipeline) Latency
tPROP Propagation Delay
3
ps rms
6.5
Cycles
4.8
6.5
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ns
1
ns
7
ADS5271
SBAS313C – JUNE 2004 – REVISED JANUARY 2009...................................................................................................................................................... www.ti.com
LVDS TIMING DIAGRAM (PER ADC CHANNEL)
Sample n
Sample n + 6
Input
1
tSAMPLE
ADCLK
tS
2
LCLKP
6X ADCLK
LCLKN
OUTP
SERIAL DATA
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D0 D1
OUTN
Sample n data
ADCLKP
1X ADCLK
ADCLKN
tD(A)
tPROP
6.5 Clock Cycles
NOTE: Serial data bit format shown in LSB first mode.
RECOMMENDED POWER-UP SEQUENCING AND RESET TIMING
AVDD (3V to 3.6V)
t1
AVDD
LVDD (3V to 3.6V)
t2
LVDD
t3
t4
t7
t5
Device Ready
For ADC Operation
t6
RESET
Device Ready
For Serial Register Write
CS
Device Ready
For ADC Operation
Start of Clock
ADCLK
t8
NOTE: 10µs < t1 < 50ms; 10µs < t2 < 50ms; −10ms < t 3 < 10ms; t4 > 10ms; t5 > 100ns; t6 > 100ns; t7 > 10ms; and t8 > 100µs.
8
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ADS5271
www.ti.com...................................................................................................................................................... SBAS313C – JUNE 2004 – REVISED JANUARY 2009
POWER-DOWN TIMING
1µs
500µs
PD
Device Fully
Powers Down
Device Fully
Powers Up
NOTE: The shown power−up time is based on 1µF bypass capacitors on the reference pins.
See the Theory of Operation section for details.
SERIAL INTERFACE TIMING
Outputs change on
next rising clock edge
after CS goes high.
ADCLK
CS
Start Sequence
t6
t1
t7
Data latched on
each rising edge of SCLK.
t2
SCLK
t3
D7
(MSB)
SDATA
D6
D5
D4
D3
D2
D1
D0
t4
t5
NOTE: Data is shifted in MSB first.
PARAMETER
DESCRIPTION
MIN
TYP
MAX
UNIT
t1
Serial CLK Period
50
ns
t2
Serial SLK High Time
20
ns
t3
Serial CLK Low Time
20
ns
t4
Data Setup Time
5
ns
t5
Data Hold Time
5
ns
t6
CS Fall to SCLK Rise
8
ns
t7
SCLK Rise to CS Rise
8
ns
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SERIAL INTERFACE REGISTERS
ADDRESS
DATA
D7
D6
D5
D4
0
0
0
0
0
0
0
0
0
0
0
0
D1
D2
D0
LVDS BUFFERS (Register 0)
All Data Outputs
0
0
Normal ADC Output
(default after reset)
0
1
Deskew Pattern
1
0
Sync Pattern
1
1
Custom Pattern
0
Output Current in LVDS = 3.5mA
0
1
Output Current in LVDS = 2.5mA
1
0
Output Current in LVDS = 4.5mA
1
1
Output Current in LVDS = 6.0mA
CLOCK CURRENT (Register 1)
X
X
0
Default LVDS Clock Output Current
IOUT = 3.5mA (default)
0
X
X
1
2x LVDS Clock Output Current (1)
IOUT = 7.0mA
LSB/MSB MODE (Register 1)
0
0
X
X
LSB First Mode
0
1
X
X
MSB First Mode
0
1
(default after reset)
0
1
1
See Test Patterns
0
1
0
REMARKS
D3
(default after reset)
POWER-DOWN ADC CHANNELS
(Register 2)
X
0
DESCRIPTION
X
X
X
Power-Down Channels 1 to 4; D3 is
for Channel 4 and D0 for Channel 1
1
Example: 1010 Powers Down
Channels 4 and 2 and
Keeps Channels 1 and 3 Active
POWER-DOWN ADC CHANNELS
(Register 3)
X
X
X
X
Power-Down Channels 5 to 8; D3 is
for Channel 8 and D0 for Channel 5
D3
D2
D1
D0
CUSTOM PATTERN (Registers 4–6)
(1)
0
1
0
0
X
X
X
X
0
1
0
1
X
X
X
X
0
1
1
0
X
X
X
X
Bits for Custom Pattern
See Test Patterns
Output current drive for the two clock LVDS buffers (LCLKP and LCLKN and ADCLKP and ADCLKN) is double the output current setting
programmed in register 0. The current drive of the data buffers remains the same as the setting in register 0.
TEST PATTERNS
Serial Output (1)
ADC Output (2)
LSB
MSB
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
Deskew Pattern
1
0
1
0
1
0
1
0
1
0
1
0
Sync Pattern
0
0
0
0
0
0
1
1
1
1
1
1
D0(4)
D1(4)
D2(4)
D3(4)
D0(5)
D1(5)
D2(5)
D3(5)
D0(6)
D1(6)
D2(6)
D3(6)
Custom Pattern (3)
(1)
(2)
(3)
10
The serial output stream comes out LSB first by default.
D11...D0 represent the 12 output bits from the ADC.
D0(4) represents the content of bit D0 of register 4, D3(6) represents the content of bit D3 of register 6, etc.
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PIN CONFIGURATION
AVSS
SCLK
SDATA
CS
AVDD
AVSS
AVSS
AVSS
ADCLK
AVDD
INT/EXT
AVSS
REFT
REFB
VCM
ISET
AVDD
AVSS
AVSS
HTQFP
AVSS
Top View
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
AVDD
1
60 AVDD
IN1P
2
59 IN8N
IN1N
3
58 IN8P
AVSS
4
57 AVSS
IN2P
5
56 IN7N
IN2N
6
55 IN7P
AVDD
7
54 AVDD
AVSS
8
53 AVSS
IN3P
9
52 IN6N
51 IN6P
IN3N 10
ADS5271
AVSS 11
50 AVSS
IN4P 12
49 IN5N
IN4N 13
48 IN5P
AVDD 14
47 AVDD
LVSS 15
46 LVSS
45 RESET
PD 16
LVSS 17
44 LVSS
LVSS 18
43 LVSS
33
34
35
36
37
38
39
40
OUT8N
OUT3N
32
OUT8P
OUT3P
31
OUT7N
LVSS
30
OUT7P
LVDD
29
LVSS
28
LVDD
27
OUT6N
26
OUT6P
25
OUT5N
24
OUT5P
23
OUT4N
22
OUT4P
21
OUT2N
41 ADCLKP
OUT2P
LCLKN 20
OUT1N
42 ADCLKN
OUT1P
LCLKP 19
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PIN DESCRIPTIONS
12
NAME
PIN #
I/O
ADCLK
71
I
DESCRIPTION
Data Converter Clock Input
ADCLKN
42
O
Negative LVDS ADC Clock Output
ADCLKP
41
O
Positive LVDS ADC Clock Output
AVDD
1, 7, 14, 47, 54, 60, 63, 70, 75
I
Analog Power Supply
AVSS
4, 8, 11, 50, 53, 57, 61, 62, 68, 72–74, 79, 80
I
Analog Ground
CS
76
I
Chip Select; 0 = Select, 1 = No Select
IN1N
3
I
Channel 1 Differential Analog Input Low
IN1P
2
I
Channel 1 Differential Analog Input High
IN2N
6
I
Channel 2 Differential Analog Input Low
IN2P
5
I
Channel 2 Differential Analog Input High
IN3N
10
I
Channel 3 Differential Analog Input Low
IN3P
9
I
Channel 3 Differential Analog Input High
IN4N
13
I
Channel 4 Differential Analog Input Low
IN4P
12
I
Channel 4 Differential Analog Input High
IN5N
49
I
Channel 5 Differential Analog Input Low
IN5P
48
I
Channel 5 Differential Analog Input High
IN6N
52
I
Channel 6 Differential Analog Input Low
IN6P
51
I
Channel 6 Differential Analog Input High
IN7N
56
I
Channel 7 Differential Analog Input Low
IN7P
55
I
Channel 7 Differential Analog Input High
IN8N
59
I
Channel 8 Differential Analog Input Low
IN8P
58
I
Channel 8 Differential Analog Input High
INT/EXT
69
I
Internal/External Reference Select; 0 = External, 1 = Internal. Weak pull-up to supply.
ISET
64
I/O
Bias Current Setting Resistor of 56.2kΩ to Ground
LCLKN
20
O
Negative LVDS Clock
LCLKP
19
O
Positive LVDS Clock
LVDD
25, 35
I
LVDS Power Supply
LVSS
15, 17, 18, 26, 36, 43, 44, 46
I
LVDS Ground
OUT1N
22
O
Channel 1 Negative LVDS Data Output
OUT1P
21
O
Channel 1 Positive LVDS Data Output
OUT2N
24
O
Channel 2 Negative LVDS Data Output
OUT2P
23
O
Channel 2 Positive LVDS Data Output
OUT3N
28
O
Channel 3 Negative LVDS Data Output
OUT3P
27
O
Channel 3 Positive LVDS Data Output
OUT4N
30
O
Channel 4 Negative LVDS Data Output
OUT4P
29
O
Channel 4 Positive LVDS Data Output
OUT5N
32
O
Channel 5 Negative LVDS Data Output
OUT5P
31
O
Channel 5 Positive LVDS Data Output
OUT6N
34
O
Channel 6 Negative LVDS Data Output
OUT6P
33
O
Channel 6 Positive LVDS Data Output
OUT7N
38
O
Channel 7 Negative LVDS Data Output
OUT7P
37
O
Channel 7 Positive LVDS Data Output
OUT8N
40
O
Channel 8 Negative LVDS Data Output
OUT8P
39
O
Channel 8 Positive LVDS Data Output
PD
16
I
Power-Down; 0 = Normal, 1 = Power-Down
REFB
66
I/O
Reference Bottom Voltage (2Ω resistor in series with a 0.1F capacitor to ground)
REFT
67
I/O
Reference Top Voltage (2Ω resistor in series with a 0.1F capacitor to ground)
RESET
45
I
Reset to Default; 0 = Reset, 1 = Normal. Weak pull-down to ground.
SCLK
78
I
Serial Data Clock
SDATA
77
I
Serial Data Input
VCM
65
O
Common-Mode Output Voltage
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DEFINITION OF SPECIFICATIONS
Analog Bandwidth
Minimum Conversion Rate
The analog input frequency at which the spectral
power of the fundamental frequency (as determined
by FFT analysis) is reduced by 3dB.
This is the minimum sampling rate where the ADC
still works.
Signal-to-Noise and Distortion (SINAD)
Aperture Delay
The delay in time between the rising edge of the input
sampling clock and the actual time at which the
sampling occurs.
Aperture Uncertainty (Jitter)
The sample-to-sample variation in aperture delay.
Clock Duty Cycle
Pulse width high is the minimum amount of time that
the ADCLK pulse should be left in logic ‘1’ state to
achieve rated performance. Pulse width low is the
minimum time that the ADCLK pulse should be left in
a low state (logic ‘0’). At a given clock rate, these
specifications define an acceptable clock duty cycle.
Differential Nonlinearity (DNL)
An ideal ADC exhibits code transitions that are
exactly 1 LSB apart. DNL is the deviation of any
single LSB transition at the digital output from an
ideal 1 LSB step at the analog input. If a device
claims to have no missing codes, it means that all
possible codes (for a 12-bit converter, 4096 codes)
are present over the full operating range.
SINAD is the ratio of the power of the fundamental
(PS) to the power of all the other spectral components
including noise (PN) and distortion (PD), but not
including dc.
PS
SINAD + 10Log 10
PN ) PD
SINAD is either given in units of dBc (dB to carrier)
when the absolute power of the fundamental is used
as the reference, or dBFS (dB to full-scale) when the
power of the fundamental is extrapolated to the
full-scale range of the converter.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the power of the fundamental (PS)
to the noise floor power (PN), excluding the power at
dc and the first eight harmonics.
P
SNR + 10Log 10 S
PN
SNR is either given in units of dBc (dB to carrier)
when the absolute power of the fundamental is used
as the reference, or dBFS (dB to full-scale) when the
power of the fundamental is extrapolated to the
full-scale range of the converter.
Effective Number of Bits (ENOB)
Spurious-Free Dynamic Range
The ENOB is a measure of converter performance as
compared to the theoretical limit based on
quantization noise.
ENOB + SINAD * 1.76
6.02
The ratio of the power of the fundamental to the
highest other spectral component (either spur or
harmonic). SFDR is typically given in units of dBc (dB
to carrier).
Two-Tone, Third-Order Intermodulation
Distortion
Integral Nonlinearity (INL)
INL is the deviation of the transfer function from a
reference line measured in fractions of 1 LSB using a
best straight line or best fit determined by a least
square curve fit. INL is independent from effects of
offset, gain or quantization errors.
Maximum Conversion Rate
The encode rate at which parametric testing is
performed. This is the maximum sampling rate where
certified operation is given.
Two-tone IMD3 is the ratio of power of the
fundamental (at frequencies f1 and f2) to the power of
the worst spectral component of third-order
intermodulation distortion at either frequency 2f1 – f2
or 2f2 – f1. IMD3 is either given in units of dBc (dB to
carrier) when the absolute power of the fundamental
is used as the reference, or dBFS (dB to full-scale)
when the power of the fundamental is extrapolated to
the full-scale range of the converter.
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TYPICAL CHARACTERISTICS
Typical values are at TA = +25C, clock frequency = maximum specified, 50% clock duty cycle, AVDD = 3.3V, LVDD = 3.3V,
–1dBFS, ISET = 56.2kΩ, internal voltage reference, and LVDS buffer current at 3.5mA per channel, unless otherwise noted.
SPECTRAL PERFORMANCE
0
−20
f IN = 5MHz (−1dBFS)
SNR = 70.9dBFS
SINAD = 70.8dBFS
SFDR = 89dBc
−20
−40
Amplitude (dB)
Amplitude (dB)
SPECTRAL PERFORMANCE
0
fIN = 1MHz (−1dBFS)
SNR = 71.1dBFS
SINAD = 70.9dBFS
SFDR = 87.7dBc
−60
−80
−100
−40
−60
−80
−100
−120
−120
0
5
10
15
20
25
0
5
Figure 1.
Figure 2.
SPECTRAL PERFORMANCE
25
−40
−60
−80
20
25
f IN = 20MHz (−1dBFS)
SNR = 70.5dBFS
SINAD = 70.4dBFS
SFDR = 85.6dBc
−20
Amplitude (dB)
Amplitude (dB)
20
SPECTRAL PERFORMANCE
0
f IN = 10MHz (−1dBFS)
SNR = 70.9dBFS
SINAD = 70.7dBFS
SFDR = 85.4dBc
−20
−100
−40
−60
−80
−100
−120
−120
0
5
10
15
20
25
0
5
10
15
Input Frequency (MHz)
Input Frequency (MHz)
Figure 3.
Figure 4.
INTERMODULATION DISTORTION
DIFFERENTIAL NONLINEARITY
0
0.5
f1 = 9.5MHz (−7dBFS)
f 2 = 10.2MHz (−7dBFS)
IMD = −85dBFS
−20
fIN = 5MHz
0.4
0.3
0.2
−40
DNL (LSB)
Amplitude (dB)
15
Input Frequency (MHz)
0
−60
−80
0.1
0
−0.1
−0.2
−0.3
−100
−0.4
−0.5
−120
0
14
10
Input Frequency (MHz)
5
10
15
20
25
0
512
1024
1536
2048
2560
Input Frequency (MHz)
Code
Figure 5.
Figure 6.
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3072
3584
4096
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TYPICAL CHARACTERISTICS (continued)
Typical values are at TA = +25C, clock frequency = maximum specified, 50% clock duty cycle, AVDD = 3.3V, LVDD = 3.3V,
–1dBFS, ISET = 56.2kΩ, internal voltage reference, and LVDS buffer current at 3.5mA per channel, unless otherwise noted.
INTEGRAL NONLINEARITY
1.0
SWEPT INPUT POWER
90
fIN = 5MHz
0.8
80
SFDR, SNR (dBc, dBFS)
0.6
0.4
INL (LSB)
f IN = 5MHz
0.2
0
−0.2
−0.4
−0.6
−0.8
SNR (dBFS)
70
60
SFDR (dBc)
50
40
SNR (dBc)
30
20
10
−1.0
0
512
1024
1536
2048
2560
3072
3584
0
−70
4096
−20
f IN = 10MHz
SNR (dBFS)
60
50
SFDR (dBc)
40
SNR (dBc)
30
−10
0
DYNAMIC PERFORMANCE vs DUTY CYCLE
SFDR, SNR, SINAD (dBFS)
SFDR, SNR (dBc, dBFS)
−30
Figure 8.
80
20
10
fIN = 5MHz
90
SFDR
85
80
75
SNR
70
SINAD
65
60
0
−70
−60
−50
−40
−30
−20
−10
0
20
30
40
Input Amplitude (dBFS)
50
60
70
80
Duty Cycle (%)
Figure 9.
Figure 10.
DYNAMIC PERFORMANCE vs INPUT FREQUENCY
DYNAMIC PERFORMANCE vs SAMPLE RATE
95
95
90
SFDR, SNR, SINAD (dBFS)
90
SFDR
SFDR, SNR (dBFS)
−40
Figure 7.
95
70
−50
Input Amplitude (dBFS)
SWEPT INPUT POWER
90
−60
Code
85
80
75
SNR
70
65
fIN = 5MHz
SFDR
85
80
75
SNR
70
SINAD
65
60
55
60
50
0
5
10
15
20
25
30
35
40
45
50
15
20
25
30
35
40
45
50
55
60
Sample Rate (MSPS)
Input Frequency (MHz)
Figure 11.
Figure 12.
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TYPICAL CHARACTERISTICS (continued)
Typical values are at TA = +25C, clock frequency = maximum specified, 50% clock duty cycle, AVDD = 3.3V, LVDD = 3.3V,
–1dBFS, ISET = 56.2kΩ, internal voltage reference, and LVDS buffer current at 3.5mA per channel, unless otherwise noted.
DYNAMIC PERFORMANCE vs SAMPLE RATE
SUPPLY CURRENT vs SAMPLE RATE
95
SFDR
250
85
IAVDD
80
75
Current (mA)
SFDR, SNR, SINAD (dBFS)
90
300
fIN = 10MHz
SNR
70
SINAD
65
200
150
100
ILVDD
60
50
55
0
50
15
20
25
30
35
40
45
50
55
60
10
Sample Rate (MSPS)
20
25
30
35
40
45
50
Sample Rate (MSPS)
Figure 13.
16
15
Figure 14.
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THEORY OF OPERATION
OVERVIEW
The ADS5271 is an 8-channel, high-speed, CMOS
ADC.
It
consists
of
a
high-performance
sample-and-hold circuit at the input, followed by a
12-bit ADC. The 12 bits given out by each channel
are serialized and sent out on a single pair of pins in
LVDS format. All eight channels of the ADS5271
operate from a single clock referred to as ADCLK.
The sampling clocks for each of the eight channels
are generated from the input clock using a carefully
matched clock buffer tree. The 12x clock required for
the serializer is generated internally from ADCLK
using a phase lock loop (PLL). A 6x and a 1x clock
are also output in LVDS format along with the data to
enable easy data capture. The ADS5271 operates
from internally generated reference voltages that are
trimmed to ensure matching across multiple devices
on a board. This feature eliminates the need for
external routing of reference lines and also improves
matching of the gain across devices. The nominal
values of REFT and REFB are 1.95V and 0.95V,
respectively. These values imply that a differential
input of –1V corresponds to the zero code of the
ADC, and a differential input of +1V corresponds to
the full-scale code (4095 LSB). VCM (common-mode
voltage of REFT and REFB) is also made available
externally through a pin, and is nominally 1.45V.
The ADC employs a pipelined converter architecture
consisting of a combination of multi-bit and single-bit
internal stages. Each stage feeds its data into the
digital error correction logic, ensuring excellent
differential linearity and no missing codes at the
12-bit level. The pipeline architecture results in a data
latency of 6.5 clock cycles.
The output of the ADC goes to a serializer that
operates from a 12x clock generated by the PLL. The
12 data bits from each channel are serialized and
sent LSB first. In addition to serializing the data, the
serializer also generates a 1x clock and a 6x clock.
These clocks are generated in the same way the
serialized data is generated, so these clocks maintain
perfect synchronization with the data. The data and
clock outputs of the serializer are buffered externally
using LVDS buffers. Using LVDS buffers to transmit
data externally has multiple advantages, such as a
reduced number of output pins (saving routing space
on the board), reduced power consumption, and
reduced effects of digital noise coupling to the analog
circuit inside the ADS5271.
The ADS5271 operates from two sets of supplies and
grounds. The analog supply/ground set is denoted as
AVDD/AVSS, while the digital set is denoted by
LVDD/LVSS.
DRIVING THE ANALOG INPUTS
The analog input biasing is shown in Figure 15. The
inputs are biased internally using two 600Ω resistors
to enable ac-coupling. A resistor greater than 20Ω is
recommended in series with each input pin.
A 4pF sampling capacitor is used to sample the
inputs. The choice of the external ac-coupling
capacitor is dictated by the attenuation at the lowest
desired input frequency of operation. The attenuation
resulting from using a 10nF ac-coupling capacitor is
0.04%.
ADS5271
IN+
600Ω
Input
Circuitry
600Ω
IN−
VCM
CM Buffer
Internal
Voltage
Reference
NOTE: Dashed area denotes one of eight channels.
Figure 15. Analog Input Bias Circuitry
If the input is dc-coupled, then the output
common-mode voltage of the circuit driving the
ADS5271 should match the VCM (which is provided as
an output pin) to within ±50mV. It is recommended
that the output common-mode of the driving circuit be
derived from VCM provided by the device.
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Figure 16 shows a detailed RLC model of the
sample-and-hold circuit. The circuit operates in two
phases. In the sample phase, the input is sampled on
two capacitors that are nominally 4pF. The sampling
circuit consists of a low-pass RC filter at the input to
filter out noise components that might be differentially
coupled on the input pins. The next phase is the hold
phase wherein the voltage sampled on the capacitors
is transferred (using the amplifier) to a subsequent
pipeline ADC stage.
INPUT OVER-VOLTAGE RECOVERY
The differential full-scale range supported by the
ADS5271 is nominally 2.03V. The ADS5271 is
specially designed to handle an over-voltage
condition where the differential peak-to-peak voltage
can exceed up to twice the ADC full-scale range. If
the input common-mode is not considerably off from
VCM during overload (less than 300mV around the
nominal value of 1.45V), recovery from an
over-voltage pulse input of twice the amplitude of a
full-scale pulse is expected to be within three clock
cycles when the input switches from overload to zero
signal. All of the amplifiers in the SHA and ADC are
specially designed for excellent recovery from an
overload signal.
In most applications, the ADC inputs are driven with
differential sinusoidal inputs. While the pulse-type
signal remains at peak overload conditions
throughout its HIGH state, the sinusoid signal only
attains peak overload intermittently, at its minima and
maxima. This condition is much less severe for the
ADC input and the recovery of the ADC output (to 1%
of full-scale around the expected code). This typically
happens within the second clock when the input is
driven with a sinusoid of amplitude equal to twice that
of the ADC differential full-scale range.
IN
OUT
5nH
to 9nH
INP
1.5pF to
2.5pF
15Ω
to 25Ω
1Ω
15Ω
to 25Ω
IN
3.2pF
to 4.8pF
60Ω
to 120Ω
OUT
IN
OUT
500Ω
to 720Ω
OUT
OUTP
1.5pF
to 1.9pF
IN
OUTN
500Ω
to 720Ω
15Ωto 35Ω
15Ω
to 25Ω
15Ω
to 25Ω
IN
3.2pF
to 4.8pF
OUT
60Ω
to 120Ω
IN
OUT
5nH
to 9nH
INN
1.5pF to
2.5pF
Switches that are ON
in SAMPLE phase.
1Ω
Switches that are ON
in HOLD phase.
IN
OUT
Figure 16. Overall Structure of the Sample-and-Hold Circuit
18
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REFERENCE CIRCUIT DESIGN
The digital beam-forming algorithm relies heavily on
gain matching across all receiver channels. A typical
system would have about 12 octal ADCs on the
board. In such a case, it is critical to ensure that the
gain is matched, essentially requiring the reference
voltages seen by all the ADCs to be the same.
Matching references within the eight channels of a
chip is done by using a single internal reference
voltage buffer. Trimming the reference voltages on
each chip during production ensures the reference
voltages are well matched across different chips.
All bias currents required for the internal operation of
the device are set using an external resistor to
ground at pin ISET. Using a 56.2kΩ resistor on ISET
generates an internal reference current of 20µA. This
current is mirrored internally to generate the bias
current for the internal blocks. Using a larger external
resistor at ISET reduces the reference bias current and
thereby scales down the device operating power.
However, it is recommended that the external resistor
be within 10% of the specified value of 56.2kΩ so
that the internal bias margins for the various blocks
are proper.
Buffering the internal bandgap voltage also generates
a voltage called VCM, which is set to the midlevel of
REFT and REFB, and is accessible on a pin. It is
meant as a reference voltage to derive the input
common-mode in case the input is directly coupled. It
can also be used to derive the reference
common-mode voltage in the external reference
mode.
When using the internal reference mode, a 2Ω
resistor should be added between the reference pins
(REFT and REFB) and the decoupling capacitor, as
shown in Figure 17. If the device is used in the
external reference mode, this 2Ω resistor is not
required.
ADS5271
ISET
REFT
REFB
2Ω
0.1µF
2.2µF
56.2kΩ
2Ω
2.2µF
0.1µF
Figure 17. Internal Reference Mode
The device also supports the use of external
reference voltages. This mode involves forcing REFT
and REFB externally. In this mode, the internal
reference buffer is tri-stated. Since the switching
current for the eight ADCs come from the externally
forced references, it is possible for the performance
to be slightly less than when the internal references
are used. It should be noted that in this mode, VCM
and ISET continue to be generated from the internal
bandgap voltage, as in the internal reference mode. It
is therefore important to ensure that the
common-mode voltage of the externally forced
reference voltages matches to within 50mV of VCM.
The state of the reference voltages during various
combinations of PD and INT/EXT is shown in
Table 1.
Table 1. State of Reference Voltages for Various
Combinations of PD and INT/EXT
PD
0
0
1
INT/EXT
0
1
0
1
1
REFT
Tri-State
1.95V
Tri-State
Tri-State
REFB
Tri-State
0.95V
Tri-State
Tri-State
VCM
1.45V
1.45V
Tri-State(1)
Tri-State(1)
(1) Weak pull-down (approximately 5kΩ) to ground.
CLOCKING
The eight channels on the chip operate from a single
ADCLK input. To ensure that the aperture delay and
jitter are same for all the channels, a clock tree
network is used to generate individual sampling
clocks to each channel. The clock paths for all the
channels are matched from the source point all the
way to the sample-and-hold amplifier. This ensures
that the performance and timing for all the channels
are identical. The use of the clock tree for matching
introduces an aperture delay, which is defined as the
delay between the rising edge of ADCLK and the
actual instant of sampling. The aperture delays for all
the channels are matched to the best possible extent.
However, a mismatch of ±20ps (±3σ) could exist
between the aperture instants of the eight ADCs
within the same chip. However, the aperture delays of
ADCs across two different chips can be several
hundred picoseconds apart. Another critical
specification is the aperture jitter that is defined as
the uncertainty of the sampling instant. The gates in
the clock path are designed to provide an rms jitter of
approximately 1ps.
Ideally, the input ADCLK should have a 50% duty
cycle. However, while routing ADCLK to different
components onboard, the duty cycle of the ADCLK
reaching the ADS5271 could deviate from 50%. A
smaller (or larger) duty cycle reduces the time
available for sample or hold phases of each circuit,
and is therefore not optimal. For this reason, the
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internal PLL is used to generate an internal clock that
has 50% duty cycle. The input sampling instant,
however, is determined by the rising edge of the
external clock and is not affected by jitter in the PLL.
In addition to generating a 50% duty cycle clock for
the ADC, the PLL also generates a 12x clock that is
used by the serializer to convert the parallel data from
the ADC to a serial stream of bits.
The use of the PLL automatically dictates the
minimum sample rate to be about 20MSPS. The PLL
also requires the input clock to be free-running. If the
input clock is momentarily stopped (for a duration of
less than 300ns) then the PLL would require
approximately 10µs to lock back to the input clock
frequency.
LVDS BUFFERS
The LVDS buffer has two current sources, as shown
in Figure 18. OUTP and OUTN are loaded externally
by a resistive load that is ideally about 100Ω.
Depending on whether the data is 0 or 1, the currents
are directed in one direction or the other through the
resistor. The LVDS buffer has four current settings.
The default current setting is 3.5mA, and provides a
differential drop of about ±350mV across the 100Ω
resistor.
The LVDS buffer receives data from a serializer that
takes the output data from each channel and
serializes it into a single data stream. For a clock
frequency of 50MHz, the data rate output of the
serializer is 600MBPS. The data comes out LSB first,
with a register programmability that allows it to revert
to MSB first. The serializer also transmits a 1x clock
and a 6x clock. The 6x clock (denoted as
LCLKP/LCLKN) is meant to synchronize the capture of
the LVDS data.
Deskew mode can be enabled as well, using a
register setting. This mode gives out a data stream of
alternate 0s and 1s and can be used determine the
relative delay between the 6x clock and the output
data for optimum capture. A 1x clock is also
generated by the serializer and transmitted through
the LVDS buffer. The 1x clock (referred to as
ADCLKP/ADCLKN) is used to determine the start of
the 12-bit data frame. Sync mode (enabled through a
register setting) gives out a data of six 0s followed by
six 1s. Using this mode, the 1x clock can be used to
determine the start of the data frame. In addition to
the deskew mode pattern and the sync mode pattern,
a custom pattern can be defined by the user and
output from the LVDS buffer. The LVDS buffers are
tri-stated in the power-down mode. The LVDS outputs
are weakly forced to 1.2V through 10kΩ resistors
(from each output pin to 1.2V).
NOISE COUPLING ISSUES
High
External
Termination
Resistor
High-speed mixed signals are sensitive to various
types of noise coupling. One of the main sources of
noise is the switching noise from the serializer and
the output buffers. Maximum care is taken to isolate
these noise sources from the sensitive analog blocks.
As a starting point, the analog and digital domains of
the chip are clearly demarcated. AVDD and AVSS
are used to denote the supplies for the analog
sections, while LVDD and LVSS are used to denote
the digital supplies. Care is taken to ensure that there
is minimal interaction between the supply sets within
the device. The extent of noise coupled and
transmitted from the digital to the analog sections
depends on the following:
1. The effective inductances of each of the
supply/ground sets.
2. The isolation between the digital and analog
supply/ground sets.
Low
OUTP
OUTN
Low
High
Figure 18. LVDS Buffer
The single-ended output impedance of the LVDS
drivers is very high because they are current-source
driven. If there are excessive reflections from the
receiver, it might be necessary to place a 100Ω
termination resistor across the outputs of the LVDS
drivers to minimize the effect of reflections. In such a
situation, the output current of the LVDS drivers can
be increased to regain the output swing.
20
Smaller effective inductance of the supply/ground
pins leads to better suppression of the noise. For this
reason, multiple pins are used to drive each
supply/ground. It is also critical to ensure that the
impedances of the supply and ground lines on board
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RESET
are kept to the minimum possible values. Use of
ground planes in the board as well as large
decoupling capacitors between the supply and
ground lines are necessary to get the best possible
SNR from the device.
After the supplies have stabilized, it is necessary to
give the device an active RESET pulse. This results
in all internal registers resetting to their default value
of 0 (inactive). Without a reset, it is possible that
some registers may be in their non-default state on
power-up. This may cause the device to malfunction.
When a reset is active, the device outputs ‘0’ code on
all channels. However, the LVDS output clocks are
unaffected by reset.
It is recommended that the isolation be maintained on
board by using separate supplies to drive AVDD and
LVDD, as well as separate ground planes for AVSS
and LVSS.
The use of LVDS buffers reduces the injected noise
considerably, compared to CMOS buffers. The
current in the LVDS buffer is independent of the
direction of switching. Also, the low output swing as
well as the differential nature of the LVDS buffer
results in low-noise coupling.
LAYOUT OF PCB WITH PowerPAD
THERMALLY-ENHANCED PACKAGES
The ADS5271 is housed in an 80-lead PowerPAD
thermally-enhanced package. To make optimum use
of the thermal efficiencies designed into the
PowerPAD package, the printed circuit board (PCB)
must be designed with this technology in mind.
Please refer to SLMA004 PowerPAD brief PowerPAD
Made Easy (refer to our web site at www.ti.com),
which addresses the specific considerations required
when integrating a PowerPAD package into a PCB
design. For more detailed information, including
thermal modeling and repair procedures, please see
the
technical
brief
SLMA002,
PowerPAD
Thermally-Enhanced Package (www.ti.com).
POWER-DOWN MODE
The ADS5271 has a power-down pin, referred to as
PD. Pulling PD high causes the device to enter the
power-down mode. In this mode, the reference and
clock circuitry, as well as all the channels, are
powered down. Device power consumption drops to
less than 100mW in this mode. In power-down mode,
the internal buffers driving REFT and REFB are
tri-stated and their outputs are forced to a voltage
roughly equal to half of the voltage on AVDD. Speed
of recovery from power-down mode depends on the
value of the external capacitance on the REFT and
REFB pins. For capacitances on REFT and REFB less
than 1µF, the reference voltages settle to within 1%
of their steady-state values in less than 500µs.
Individual channels can also be selectively powered
down by programming registers.
Interfacing High-Speed LVDS Outputs (SBOA104),
an application report discussing the design of a
simple deserializer that can deserialize LVDS outputs
up to 840Mbps, can also be found on the TI web site
(www.ti.com).
CONNECTING HIGH-SPEED,
MULTI-CHANNEL ADCs TO XILINX FPGAs
The ADS5271 also has an internal circuit that
monitors the state of stopped clocks. If ADCLK is
stopped for longer than 300ns (or if it runs at a speed
less than 3MHz), this monitoring circuit generates a
logic signal that puts the device in a partial
power-down state. As a result, the power
consumption of the device is reduced when ADCLK is
stopped. The recovery from such a partial
power-down takes ap- proximately 100µs; this is
described in Table 2.
A separate application note (XAPP774) describing
how to connect TI's high-speed, multi-channel ADCs
with serial LVDS outputs to Xilinx FPGAs can be
downloaded directly from the Xilinx web site
(http://www.xilinx.com).
Table 2. Time Constraints Associated with Device Recovery from Power-Down and Clock Stoppage
DESCRIPTION
TYP
Recovery from power-down mode (PD = 1 to PD = 0).
500µs
Recovery from momentary clock stoppage ( < 300ns).
10µs
Recovery from extended clock stoppage ( > 300ns).
100µs
REMARKS
Capacitors on REFT and REFB less than 1µF.
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ADS5271
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Revision History
Changes from Revision B (September 2005) to Revision C .......................................................................................... Page
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Updated Absolute Maximum Ratings table: added entries for Digital Input Pins, Set 1 and Set 2 and added footnote 3.... 2
Changes from Revision A (August 2005) to Revision B ................................................................................................ Page
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Changed component image to having TI logo....................................................................................................................... 1
Changed X to x (for instance, 12X, 6X, 1X, etc) globally. ..................................................................................................... 1
Changed ISET to ISET globally. .............................................................................................................................................. 1
Changed 56kΩ to 56.2kΩ globally. ........................................................................................................................................ 1
Changed fourth bullet of Features section............................................................................................................................. 1
Deleted eighth and 12th bullets of Features section. ............................................................................................................ 1
Changed Synch to Bit in 11th bullet of Features section....................................................................................................... 1
Added Four Current Modes for LVDS as 14th bullet in Features section. ........................................................................... 1
Changed Description section and block diagram. ................................................................................................................. 1
Changed Ordering Information table and footnotes............................................................................................................... 2
Changed Absolute Maximum Ratings table and footnotes.................................................................................................... 2
Changed Recommended Operating Conditions table and footnotes. ................................................................................... 3
Changed Electrical Characteristics table, conditions, and footnotes..................................................................................... 4
Changed Electrical Characteristics table, conditions, and footnotes..................................................................................... 5
Changed Reference Selection table. ..................................................................................................................................... 5
Changed AC Characteristics table conditions to include ISET = 56.2kΩ. ............................................................................... 6
Changed 68 to 69.5 in second row of SNR section in AC Characteristics table. .................................................................. 6
Changed 67.5 to 69 in second row of SINAD section in AC Characteristics table................................................................ 6
Changed Crosstalk row of AC Characteristics table.............................................................................................................. 6
Added IMD3 row of AC Characteristics table. ....................................................................................................................... 6
Changed entire LVDS table, conditions, and footnotes......................................................................................................... 7
Deleted condition value from CO row in LVDS table.............................................................................................................. 7
Changed minimum unit values for Data Setup Time and Data Hold Time rows in LVDS table............................................ 7
Changed Switching Characteristics table. ............................................................................................................................. 7
Changed LVDS timing diagram. ............................................................................................................................................ 8
Changed Reset timing diagram. ............................................................................................................................................ 8
Changed Power-Down timing diagram. ................................................................................................................................. 9
Changed Serial Interface Timing figure and table. ................................................................................................................ 9
Changed Serial Interface Registers table. ........................................................................................................................... 10
Changed Test Patterns table. .............................................................................................................................................. 10
Changed Pin Configuration figure........................................................................................................................................ 11
Changed Pin Descriptions table. ......................................................................................................................................... 12
Added Definition of Specifications section........................................................................................................................... 13
Changed Typical Characteristics conditions. ....................................................................................................................... 14
Changed Figure 1. ............................................................................................................................................................... 14
Changed Figure 2. ............................................................................................................................................................... 14
Changed Figure 3. ............................................................................................................................................................... 14
Changed Figure 4. ............................................................................................................................................................... 14
Changed Figure 5. ............................................................................................................................................................... 14
Changed Typical Characteristics conditions. ....................................................................................................................... 15
Changed Figure 12. ............................................................................................................................................................. 15
Changed Typical Characteristics conditions. ....................................................................................................................... 16
Changed Figure 13. ............................................................................................................................................................. 16
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Changed Figure 14. .............................................................................................................................................................
Deleted Figure 15 (Power Dissipation vs Temperature)......................................................................................................
Changed figure numbers in Theory of Operation to reflect addition of Typical Characteristics section..............................
Changed operates to operate in first paragraph of Overview section in Theory of Operation. ...........................................
Changed 2V to 1.95V, 1V to 0.95V, and 1.5V to 1.45V in first paragraph of Overview section in Theory of Operation. ...
Added second paragraph of Driving the Analog Inputs section in Theory of Operation. ....................................................
Changed Figure 16. .............................................................................................................................................................
Deleted second paragraph of Driving the Analog Inputs section in Theory of Operation. ..................................................
Added fourth paragraph of Driving the Analog Inputs section in Theory of Operation........................................................
Deleted fourth paragraph of Driving the Analog Inputs section in Theory of Operation and Figure 2 (Input Circuitry).......
Changed Input Over-Voltage Recovery section. .................................................................................................................
Added Figure 17. .................................................................................................................................................................
Changed third paragraph of Reference Circuit Design section in Theory of Operation. .....................................................
Changed fourth paragraph of Reference Circuit Design section in Theory of Operation....................................................
Changed Figure 18. .............................................................................................................................................................
Changed Clocking section in Theory of Operation. .............................................................................................................
Changed 2.0ps to 20ps and added (±3σ) to seventh sentence of first paragraph of Clocking section in Theory of
Operation. ............................................................................................................................................................................
Changed LVDS Buffers section in Theory of operation.......................................................................................................
Changed Power-Down Mode section in Theory of Operation. ............................................................................................
Added Table 2......................................................................................................................................................................
Deleted Supply Sequence section. ......................................................................................................................................
Added Reset section............................................................................................................................................................
Changed Layout of PCB with PowerPAD Thermally-Enhanced Packages section in Theory of Operation. ......................
Added Connecting High-Speed, Multi-Channel ADCs to XILINX FPGAs section in Theory of Operation..........................
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
(3)
Device Marking
(4/5)
(6)
ADS5271IPFP
ACTIVE
HTQFP
PFP
80
96
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 85
ADS5271IPFP
ADS5271IPFPT
ACTIVE
HTQFP
PFP
80
250
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 85
ADS5271IPFP
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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