ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
10-Bit, Octal-Channel ADC Up to 65MSPS
Check for Samples: ADS5287
LCLKN
12x ADCLK
PLL
ADCLKP
1x ADCLK
ADCLKN
PowerDown
Channels
2 to 7
OUT8P
OUT8N
Drive Current
ADC
Control
PD
SCLK
SDATA
CS
RESET
OUT1N
Test Patterns
Output Format
Digital Gain
(0dB to 12dB)
REFT
REFB
VCM
ISET
Serializer
Registers
Reference
INT/EXT
Digital
OUT1P
¼
10-Bit
ADC
Serializer
¼
¼
IN8P
IN8N
Digital
¼
10-Bit
ADC
¼
IN1P
IN1N
¼
Medical Imaging
Wireless Base-Station Infrastructure
Test and Measurement Instrumentation
LCLKP
6x ADCLK
Clock
Buffer
APPLICATIONS
•
•
•
LVDD
(1.8V)
The ADS5287 is a high-performance, low-power,
octal channel analog-to-digital converter (ADC).
Available in a 9mm × 9mm QFN package, with
serialized low-voltage differential signaling (LVDS)
outputs and a wide variety of programmable features,
the ADS5287 is highly customizable for a wide range
of applications and offers an unprecedented level of
system integration. An application note, XAPP774
(available at www.xilinx.com), describes how to
interface the serial LVDS outputs of TI's ADCs to
Xilinx® field-programmable gate arrays (FPGAs). The
ADS5287 is specified over the industrial temperature
range of –40°C to +85°C.
AVDD
(3.3V)
• Speed and Resolution Grades:
– 10-bit, 65MSPS
• Power Dissipation:
– 46mW/Channel at 30MSPS
– 53mW/Channel at 40MSPS
– 62mW/Channel at 50MSPS
– 74mW/Channel at 65MSPS
• 61.7dBFS SNR at 10MHz IF
• Analog Input Full-Scale Range: 2VPP
• Low-Frequency Noise Suppression Mode
• 6dB Overload Recovery in One Clock
• External and Internal (Trimmed) Reference
• 3.3V Analog Supply, 1.8V Digital Supply
• Single-Ended or Differential Clock:
– Clock Duty Cycle Correction Circuit (DCC)
• Programmable Digital Gain: 0dB to 12dB
• Serialized DDR LVDS Output
• Programmable LVDS Current Drive, Internal
Termination
• Test Patterns for Enabling Output Capture
• Straight Offset Binary or Two's Complement
Output
• Package Options:
– 9mm × 9mm QFN-64
234
(AVSS)
CLKN
DESCRIPTION
(ADCLK)
CLKP
FEATURES
1
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.
Xilinx is a registered trademark of Xilinx, Inc.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
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.
RELATED PRODUCTS
MODEL
RESOLUTION (BITS)
SAMPLE RATE (MSPS)
CHANNELS
ADS5281
12
50
8
ADS5282
12
65
8
ADS5287
10
65
8
ADS5270
12
40
8
ADS5271
12
50
8
ADS5272
12
65
8
ADS5273
12
70
8
ADS5242
12
65
4
Table 1. ORDERING INFORMATION (1)
(1)
(2)
(3)
PRODUCT
PACKAGE-LEAD
PACKAGE
DESIGNATOR
ADS5287
QFN-64
RGC
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
–40°C to +85°C
AZ5287
(2)
ORDERING
NUMBER
TRANSPORT
MEDIA, QUANTITY (3)
ADS5287IRGCT
Tape and Reel
ADS5287IRGCR
Tape and Reel
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.
These devices meet the following planned eco-friendly classification:
Green (RoHS and No Sb/Br): Texas Instruments defines Green to mean Pb-free (RoHS compatible) and free of bromine (Br)- and
antimony (Sb)-based flame retardants. Refer to the Quality and Lead-Free (Pb-Free) Data web site for more information. These devices
have a Cu NiPdAu lead/ball finish.
Refer to the Package Option Addendum at the end of this document for specific transport media and quantity information.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range, unless otherwise noted.
ADS5287
UNIT
Supply voltage range, AVDD
–0.3 to +3.9
V
Supply voltage range, LVDD
–0.3 to +2.2
V
Voltage between AVSS and LVSS
–0.3 to +0.3
V
External voltage applied to REFT pin
–0.3 to +3
V
External voltage applied to REFB pin
–0.3 to +2
V
Voltage applied to analog input pins
–0.3 to minimum [3.6, (AVDD + 0.3)]
V
Voltage applied to digital input pins
–0.3 to minimum [3.9, (AVDD + 0.3)]
V
Peak solder temperature
+260
°C
Junction temperature
+125
°C
–65 to +150
°C
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 supported.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
RECOMMENDED OPERATING CONDITIONS
ADS5287
PARAMETER
MIN
TYP
MAX
UNIT
V
SUPPLIES, ANALOG INPUTS, AND REFERENCE VOLTAGES
AVDD
Analog supply voltage
3.0
3.3
3.6
LVDD
Digital supply voltage
1.7
1.8
1.9
Differential input voltage range
Input common-mode voltage
V
2
VPP
VCM ± 0.05
V
REFT
External reference mode
2.5
V
REFB
External reference mode
0.5
V
CLOCK INPUTS
ADCLK input sample rate 1/ tC
10
50, 65
MSPS
Input clock amplitude differential (VCLKP–VCLKN) peak-to-peak
Sine wave, ac-coupled
3.0
VPP
LVPECL, ac-coupled
1.6
VPP
LVDS, ac-coupled
0.7
VPP
Input clock CMOS, single-ended (VCLKP)
VIL
0.6
VIH
2.2
Input clock duty cycle
V
V
50
%
DIGITAL OUTPUTS
ADCLKP and ADCLKN outputs (LVDS)
10
1x (sample rate)
50, 65
MHz
LCLKP and LCLKN outputs (LVDS)
60
6x (sample rate)
300, 390
MHz
CLOAD
Maximum external capacitance from each pin to LVSS
RLOAD
Differential load resistance between the LVDS output pairs
TA
Operating free-air temperature
5
pF
100
Ω
–40
+85
°C
INITIALIZATION REGISTERS
If the analog input is ac-coupled, the following registers must be written to in the order listed below.
ADDRESS (hex)
DATA (hex)
Initialization Register 1
01
0010
Initialization Register 5
E2
00C0
To disable the PLL configuration switching (especially useful in systems where a system-level timing calibration is done once
after power-up), the following registers must be written to in the order listed below. Also, see section PLL Operation Across
Sampling Frequency.
For 10 ≤ Fs ≤ 25
(1)
For 15 ≤ Fs = ≤ 45
(1)
(1)
ADDRESS (hex)
DATA (hex)
E3
0060
E3
00A0
where Fs = sampling clock frequency
Copyright © 2008–2012, Texas Instruments Incorporated
3
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
DIGITAL CHARACTERISTICS
DC specifications refer to the condition where the digital outputs are not switching, but are permanently at a valid logic level
'0' or '1'. At CLOAD = 5pF (1), IOUT = 3.5mA (2), RLOAD = 100Ω (2), and no internal termination, unless otherwise noted.
ADS5287
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DIGITAL INPUTS
High-level input voltage
1.4
V
Low-level input voltage
0.3
V
High-level input current
33
μA
Low-level input current
–33
μA
3
pF
High-level output voltage
1375
mV
Low-level output voltage
1025
mV
Output differential voltage, |VOD|
350
mV
Common-mode voltage of OUTP and OUTN
1200
mV
Output capacitance inside the device,
from either output to ground
2
pF
Input capacitance
LVDS OUTPUTS
VOS output offset voltage
Output capacitance
(1)
(2)
4
CLOAD is the effective external single-ended load capacitance between each output pin and ground.
IOUT refers to the LVDS buffer current setting; RLOAD is the differential load resistance between the LVDS output pair.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
ELECTRICAL CHARACTERISTICS
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
ADS5287
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
INTERNAL REFERENCE VOLTAGES
VREFB
Reference bottom
0.5
VREFT
Reference top
2.5
VCM
V
V
VREFT – VREFB
1.95
2.0
2.05
Common-mode voltage (internal)
1.425
1.5
1.575
VCM output current
±2
V
V
mA
EXTERNAL REFERENCE VOLTAGES
VREFB
Reference bottom
0.4
0.5
0.6
V
VREFT
Reference top
2.4
2.5
2.6
V
VREFT – VREFB
1.9
2.0
2.1
V
ANALOG INPUT
Differential input voltage range
2.0
Differential input capacitance
Analog input bandwidth
VPP
3
pF
520
MHz
Analog input common-mode range
DC-coupled input
VCM ± 0.05
V
Analog input common-mode current
Per input pin per MSPS of sampling
speed
2.5
μA/MHz
per pin
Recovery from 6dB overload to within 1%
accuracy
1
Clock cycle
Standard deviation seen on a periodic
first data within full-scale range in a 6dB
overloaded sine wave
1
LSB
Voltage overload recovery time
Voltage overload recovery repeatability
DC ACCURACY
Offset error
–1.25
Offset error temperature coefficient (1)
DC PSRR
±0.2
+1.25
%FS
±5
ppm/°C
Channel gain error
Excludes error in internal reference
–0.8
%FS
Channel gain error temperature
coefficient
Excludes temperature coefficient of
internal reference
±10
ppm/°C
Internal reference error temperature
coefficient (2)
±15
ppm/°C
DC power-supply rejection ratio (3)
1.5
mV/V
POWER-DOWN MODES
Power in complete power-down mode
Power in partial power-down mode
45
mW
135
mW
88
mW
5MHz full-scale signal applied to seven
channels, measurement taken on channel
with no input signal
–90
dBc
f1 = 9.5MHz at –7dBFs
f2 = 10.2MHz at –7dBFs
–92
dBFS
Clock at 65MSPS
Power with no clock
DYNAMIC PERFORMANCE
Crosstalk
Two-tone, third-order intermodulation
distortion
DC ACCURACY
No missing codes
DNL
Differential nonlinearity
INL
Integral nonlinearity
Assured
–0.55
±0.1
+0.55
LSB
–1
±0.1
+1
LSB
POWER SUPPLY—INTERNAL REFERENCE MODE
(1)
(2)
(3)
The offset temperature coefficient in ppm/°C is defined as (O1 – O2) × 106/(T1 – T2)/1024, where O1 and O2 are the offset codes in LSB
at the two extreme temperatures, T1 and T2.
The internal reference temperature coefficient is defined as (REF1 – REF2) × 106/(T1 – T2)/2, where REF1 and REF2 are the internal
reference voltages (VREFT – VREFB) at the two extreme temperatures, T1 and T2.
DC PSRR is defined as the ratio of the change in the ADC output (expressed in mV) to the change in supply voltage (in volts).
Copyright © 2008–2012, Texas Instruments Incorporated
5
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
ADS5287
PARAMETER
IAVDD
Analog supply current
ILVDD
Digital current
TEST CONDITIONS
MIN
Zero input to all channels
Total power
Incremental power saving
Obtained on powering down one channel
at a time
TYP
MAX
UNIT
139
165
mA
87
97
mA
615
719.1
mW
61
mW
132
mA
POWER SUPPLY—EXTERNAL REFERENCE MODE
IAVDD
Analog supply current
ILVDD
Digital current
Zero input to all channels
87
mA
592
mW
Obtained on powering down one channel
at a time
59
mW
Current drawn by the eight ADCs from the
external reference voltages; sourcing for
REFT, sinking for REFB.
3.5
mA
85
dBc
80
dBc
85
dBc
82
dBc
85
dBc
80
dBc
80
dBc
78
dBc
61.7
dBc
61.7
dBc
61.6
dBc
61.6
dBc
Total power
Incremental power saving
EXTERNAL REFERENCE LOADING
Switching current
DYNAMIC CHARACTERISTICS
SFDR
HD2
HD3
THD
SNR
SINAD
6
Spurious-free dynamic range
Magnitude of second harmonic
Magnitude of third harmonic
Total harmonic distortion
Signal-to-noise ratio
Signal-to-noise and distortion
fIN = 5MHz, single-ended clock
72
fIN = 30MHz, differential clock
fIN = 5MHz, single-ended clock
72
fIN = 30MHz, differential clock
fIN = 5MHz, single-ended clock
72
fIN = 30MHz, differential clock
fIN = 5MHz, single-ended clock
70
fIN = 30MHz, differential clock
fIN = 5MHz, single-ended clock
60.5
fIN = 30MHz, differential clock
fIN = 5MHz, single-ended clock
fIN = 30MHz, differential clock
60.4
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
PIN CONFIGURATION
CLKP
AVDD
INT/EXT
REFT
59
58
57
56
55
54
AVDD
CLKN
60
AVDD
AVDD
61
ISET
CS
62
TP
SDATA
63
VCM
SCLK
64
REFB
RESET
QFN-64 PowerPAD™
TOP VIEW
53
52
51
50
49
IN1P
1
48
IN8N
IN1N
2
47
IN8P
AVSS
3
46
AVSS
IN2P
4
45
IN7N
IN2N
5
44
IN7P
AVSS
6
43
AVSS
IN3P
7
42
IN6N
IN3N
8
AVSS
9
40
AVSS
IN4P
10
39
IN5N
IN4N
11
38
IN5P
LVSS
12
37
AVSS
PD
13
36
LVSS
LVSS
14
35
LVDD
OUT1P
15
34
OUT8N
OUT1N
16
33
OUT8P
41 IN6P
19
20
21
22
23
24
25
26
27
28
29
30
OUT2N
OUT3P
OUT3N
OUT4P
OUT4N
ADCLKP
ADCLKN
LCLKP
LCLKN
OUT5P
OUT5N
OUT6P
OUT6N
31
32
OUT7N
18
OUT7P
17
OUT2P
ADS5287
Table 2. PIN DESCRIPTIONS: QFN-64
PIN NAME
DESCRIPTION
ADCLKN
LVDS frame clock (1X)—negative output
ADCLKP
LVDS frame clock (1X)—positive output
# OF PINS
24
1
23
1
49, 50, 57, 60
4
3, 6, 9, 37, 40, 43, 46
7
Negative differential clock input
Tie CLKN to 0V for a single-ended clock
59
1
Positive differential clock input
58
1
AVDD
Analog power supply, 3.3V
AVSS
Analog ground
CLKN
CLKP
CS
PIN NUMBER
Serial enable chip select—active low digital input
61
1
IN1N
Negative differential input signal, channel 1
2
1
IN1P
Positive differential input signal, channel 1
1
1
IN2N
Negative differential input signal, channel 2
5
1
IN2P
Positive differential input signal, channel 2
4
1
IN3N
Negative differential input signal, channel 3
8
1
IN3P
Positive differential input signal, channel 3
7
1
IN4N
Negative differential input signal, channel 4
11
1
IN4P
Positive differential input signal, channel 4
10
1
Copyright © 2008–2012, Texas Instruments Incorporated
7
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
Table 2. PIN DESCRIPTIONS: QFN-64 (continued)
PIN NAME
PIN NUMBER
# OF PINS
IN5N
Negative differential input signal, channel 5
39
1
IN5P
Positive differential input signal, channel 5
38
1
IN6N
Negative differential input signal, channel 6
42
1
IN6P
Positive differential input signal, channel 6
41
1
IN7N
Negative differential input signal, channel 7
45
1
IN7P
Positive differential input signal, channel 7
44
1
IN8N
Negative differential input signal, channel 8
48
1
IN8P
Positive differential input signal, channel 8
47
1
Internal/external reference mode select input
56
1
Bias pin—56.2kΩ to ground
51
1
LCLKN
LVDS bit clock (6X)—negative output
26
1
LCLKP
LVDS bit clock (6X)—positive output
25
1
LVDD
Digital and I/O power supply, 1.8V
35
1
LVSS
Digital ground
12, 14, 36
3
INT/EXT
ISET
OUT1N
LVDS channel 1—negative output
16
1
OUT1P
LVDS channel 1—positive output
15
1
OUT2N
LVDS channel 2—negative output
18
1
OUT2P
LVDS channel 2—positive output
17
1
OUT3N
LVDS channel 3—negative output
20
1
OUT3P
LVDS channel 3—positive output
19
1
OUT4N
LVDS channel 4—negative output
22
1
OUT4P
LVDS channel 4—positive output
21
1
OUT5N
LVDS channel 5—negative output
28
1
OUT5P
LVDS channel 5—positive output
27
1
OUT6N
LVDS channel 6—negative output
30
1
OUT6P
LVDS channel 6—positive output
29
1
OUT7N
LVDS channel 7—negative output
32
1
OUT7P
LVDS channel 7—positive output
31
1
OUT8N
LVDS channel 8—negative output
34
1
OUT8P
LVDS channel 8—positive output
33
1
Power-down input
13
1
REFB
Negative reference input/output
54
1
REFT
Positive reference input/output
55
1
Active low RESET input
64
1
SCLK
Serial clock input
63
1
SDATA
Serial data input
62
1
TP
Test pin, do not use
52
1
VCM
Common-mode output pin, 1.5V output
53
1
PD
RESET
8
DESCRIPTION
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
LVDD
(1.8V)
AVDD
(3.3V)
(AVSS)
CLKN
(ADCLK)
CLKP
FUNCTIONAL BLOCK DIAGRAM
LCLKP
6x ADCLK
Clock
Buffer
LCLKN
12x ADCLK
PLL
ADCLKP
1x ADCLK
ADCLKN
IN6P
IN6N
IN7P
IN7N
IN8P
Digital
10-Bit
ADC
Digital
10-Bit
ADC
Digital
10-Bit
ADC
Digital
10-Bit
ADC
Digital
10-Bit
ADC
Digital
Digital Gain
(0dB to 12dB)
IN8N
10-Bit
ADC
REFT
REFB
VCM
ISET
INT/EXT
Copyright © 2008–2012, Texas Instruments Incorporated
OUT2N
OUT3P
Serializer
OUT3N
OUT4P
Serializer
OUT4N
OUT5P
Serializer
OUT5N
OUT6P
Serializer
OUT6N
OUT7P
Serializer
OUT7N
OUT8P
Serializer
OUT8N
Registers
Reference
OUT2P
Serializer
Drive Current
IN5P
IN5N
Digital
OUT1N
PowerDown
ADC
Control
PD
IN4P
IN4N
10-Bit
ADC
OUT1P
Serializer
Test Patterns
IN3P
IN3N
Digital
Output Format
IN2P
IN2N
10-Bit
ADC
SCLK
SDATA
CS
RESET
IN1P
IN1N
9
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
LVDS TIMING DIAGRAM
Sample n
Analog Input
Sample n + 12
tD(A)
Sample n + 13
Clock Input
tSAMPLE
12 clocks latency
LCLKN
6X ADCLK
LCLKP
OUTP
SERIAL DATA
0
0
D0
D1
D2 D3 D4
D5
D6
D7
D8
D9
0
0
D0 D1
D2 D3
D4
D5 D6
D7 D8
D9
0
0
D0 D1
D2
D3 D4 D5
D6 D7 D8
D9
OUTN
ADCLKN
1X ADCLK
ADCLKP
tPROP
DEFINITION OF SETUP AND HOLD TIMES
LCLKN
LCLKP
OUTN
OUTP
tH1
tSU1
tH2
tSU2
tSU = min(tSU1, tSU2)
tH = min(tH1, tH2)
TIMING CHARACTERISTICS (1)
ADS5287
PARAMETER
tA
TEST CONDITIONS
Aperture delay
Aperture delay variation
tJ
Wake-up time
Channel-to-channel within the same device (3σ)
10
MAX
UNIT
4.5
ns
±20
ps
400
fs
Time to valid data after coming out of
COMPLETE POWER-DOWN mode
50
μs
Time to valid data after coming out of PARTIAL
POWER-DOWN mode (with clock continuing to
run during power-down)
2
μs
Time to valid data after stopping and restarting
the input clock
40
μs
12
Clock
cycles
Data latency
(1)
TYP
1.5
Aperture jitter
tWAKE
MIN
Timing parameters are ensured by design and characterization; not production tested.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
LVDS OUTPUT TIMING CHARACTERISTICS (1)
Typical values are at +25°C, minimum and maximum values are measured across the specified temperature range of TMIN = –40°C to TMAX =
+85°C, sampling frequency = as specified, CLOAD = 5pF (2), IOUT = 3.5mA, RLOAD = 100Ω (3), and no internal termination, unless otherwise
noted.
ADS5287
40MSPS
PARAMETER
tSU
Data setup time
(5)
50MSPS
65MSPS
TEST CONDITIONS (4)
MIN
Data valid (6) to zero-crossing of
LCLKP
0.67
0.47
0.27
ns
Zero-crossing of LCLKP to data
becoming invalid (6)
0.85
0.65
0.4
ns
TYP
MAX
MIN
TYP
MAX
MIN
TYP
MAX
tH
Data hold time (5)
tPROP
Clock propagation delay
Input clock (ADCLK) rising edge
cross-over to output clock (ADCLKP)
rising edge cross-over
10
14
16.6
10
12.5
14.1
9.7
11.5
14
LVDS bit clock duty cycle
Duty cycle of differential clock,
(LCLKP – LCLKN)
45.5
50
53
45
50
53.5
41
50
57
UNIT
ns
Bit clock cycle-to-cycle
jitter
250
250
250
ps, pp
Frame clock cycle-to-cycle
jitter
150
150
150
ps, pp
tRISE,
tFALL
Data rise time, data fall
time
Rise time is from –100mV to +100mV
Fall time is from +100mV to –100mV
0.09
0.2
0.4
0.09
0.2
0.4
0.09
0.2
0.4
ns
tCLKRISE,
tCLKFALL
Output clock rise time,
output clock fall time
Rise time is from –100mV to +100mV
Fall time is from +100mV to –100mV
0.09
0.2
0.4
0.09
0.2
0.4
0.09
0.2
0.4
ns
(1)
(2)
(3)
(4)
(5)
(6)
Timing parameters are ensured by design and characterization; not production tested.
CLOAD is the effective external single-ended load capacitance between each output pin and ground.
IOUT refers to the LVDS buffer current setting; RLOAD is the differential load resistance between the LVDS output pair.
Measurements are done with a transmission line of 100Ω characteristic impedance between the device and the load.
Setup and hold time specifications take into account the effect of jitter on the output data and clock. These specifications also assume
that data and clock paths are perfectly matched within the receiver. Any mismatch in these paths within the receiver would appear as
reduced timing margin.
Data valid refers to a logic high of +100mV and a logic low of –100mV.
LVDS OUTPUT TIMING CHARACTERISTICS (1)
Typical values are at +25°C, minimum and maximum values are measured across the specified temperature range of TMIN = –40°C to TMAX =
+85°C, sampling frequency = as specified, CLOAD = 5pF (2), IOUT = 3.5mA, RLOAD = 100Ω (3), and no internal termination, unless otherwise
noted.
ADS5287
30MSPS
PARAMETER
TEST CONDITIONS (4)
MIN
TYP
20MSPS
MAX
MIN
TYP
10MSPS
MAX
MIN
TYP
MAX
UNIT
tSU
Data setup time (5)
Data valid (6) to zero-crossing of
LCLKP
0.8
1.5
3.7
ns
tH
Data hold time (5)
Zero-crossing of LCLKP to data
becoming invalid (6)
1.2
1.9
3.9
ns
tPROP
Clock propagation delay
Input clock (ADCLK) rising edge
cross-over to output clock (ADCLKP)
rising edge cross-over
9.5
13.5
17.3
9.5
14.5
17.3
10
14.7
17.1
LVDS bit clock duty cycle
Duty cycle of differential clock,
(LCLKP – LCLKN)
46.5
50
52
48
50
51
49
50
51
ns
Bit clock cycle-to-cycle
jitter
250
250
750
ps, pp
Frame clock cycle-to-cycle
jitter
150
150
500
ps, pp
tRISE,
tFALL
Data rise time, data fall
time
Rise time is from –100mV to +100mV
Fall time is from +100mV to –100mV
0.09
0.2
0.4
0.09
0.2
0.4
0.09
0.2
0.4
ns
tCLKRISE,
tCLKFALL
Output clock rise time,
output clock fall time
Rise time is from –100mV to +100mV
Fall time is from +100mV to –100mV
0.09
0.2
0.4
0.09
0.2
0.4
0.09
0.2
0.4
ns
(1)
(2)
(3)
(4)
(5)
(6)
Timing parameters are ensured by design and characterization; not production tested.
CLOAD is the effective external single-ended load capacitance between each output pin and ground.
IOUT refers to the LVDS buffer current setting; RLOAD is the differential load resistance between the LVDS output pair.
Measurements are done with a transmission line of 100Ω characteristic impedance between the device and the load.
Setup and hold time specifications take into account the effect of jitter on the output data and clock. These specifications also assume
that data and clock paths are perfectly matched within the receiver. Any mismatch in these paths within the receiver would appear as
reduced timing margin.
Data valid refers to a logic high of +100mV and a logic low of –100mV.
Copyright © 2008–2012, Texas Instruments Incorporated
11
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
LVDS OUTPUT TIMING CHARACTERISTICS
PARAMETER (1)
TIMINGS WHEN USING REGISTER 0xE3 (2)
At 40 MSPS
TEST CONDITIONS
MIN
Data setup time
Data valid (3) to zero-crossing of LCLKp
0.60
Data hold time
Zero-crossing of LCLKP to data becoming invalid (3)
0.92
Clock propagation delay
Input clock (ADCLK) rising edge cross-over to output clock (ADCLK) rising edge
crossover
(1)
(2)
(3)
TYP
MAX
12
14.6
8
Only the setup time, hold time and clock propagation delay parameters are affected. Rest of the parameters are same as given in
previous two tables.
Only timing specifications for 40MSPS are affected when using register 0xE3 (as specified in the recommended operating table section).
The timing specifications for other clock frequencies are same as given in previous two tables.
Data valid refers to logic high of +100mV and logic low of –100mV.
RECOMMENDED POWER-UP SEQUENCING AND RESET TIMING
t1
AVDD (3V to 3.6V)
AVDD
t2
LVDD
LVDD (1.7V to 1.9V)
t3
t4
t7
High-Level RESET
(1.4V to 3.6V)
t5
RESET
t6
CS
Device Ready for
High-Level CS
(1.4V to 3.6V)
Serial Register Write
Start of Clock
(2)
Device Ready for
Data Conversion
ADCLK
t8
10μs < t1 < 50ms, 10μs < t2 < 50ms, –10ms < t3 < 10ms, t4 > 10ms, t5 > 100ns, t6 > 100ns, t7 > 10ms, and t8 > 100μs.
(1) The AVDD and LVDD power-on sequence does not matter as long as –10ms < t3 < 10ms. Similar considerations apply while shutting
down the device.
(2) Write initialization registers listed in the Initialization Registers table.
12
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
POWER-DOWN TIMING
1ms
tWAKE
PD
Device Fully
Powers Down
Device Fully
Powers Up
Power-up time shown is based on 1μF bypass capacitors on the reference pins. tWAKE is the time it takes for the device to wake up
completely from power-down mode. The ADS5287 has two power-down modes: complete power-down mode and partial power-down mode.
The device can be configured in partial power-down mode through a register setting.
tWAKE < 50μs for complete power-down mode.
tWAKE < 2μs for partial power-down mode (provided the clock is not shut off during power-down).
Copyright © 2008–2012, Texas Instruments Incorporated
13
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
SERIAL INTERFACE
The ADS5287 has a set of internal registers that can be accessed through the serial interface formed by pins CS
(chip select, active low), SCLK (serial interface clock), and SDATA (serial interface data). When CS is low, the
following actions occur:
• Serial shift of bits into the device is enabled
• SDATA (serial data) is latched at every rising edge of SCLK
• SDATA is loaded into the register at every 24th SCLK rising edge
If the word length exceeds a multiple of 24 bits, the excess bits are ignored. Data can be loaded in multiples of
24-bit words within a single active CS pulse. The first eight bits form the register address and the remaining 16
bits form the register data. The interface can work with SCLK frequencies from 20MHz down to very low speeds
(a few hertz) and also with a non-50% SCLK duty cycle.
Register Initialization
After power-up, the internal registers must be initialized to the respective default values. Initialization can be
done in one of two ways:
1. Through a hardware reset, by applying a low-going pulse on the RESET pin; or
2. Through a software reset; using the serial interface, set the RST bit high. Setting this bit initializes the
internal registers to the respective default values and then self-resets the RST bit low. In this case, the
RESET pin stays high (inactive).
SERIAL INTERFACE TIMING
Start Sequence
End Sequence
CS
t6
t1
t7
t2
Data latched on rising edge of SCLK
SCLK
t3
A7 A6 A5 A4 A3 A2 A1 A0 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
SDATA
t4
t5
ADS5287
14
PARAMETER
DESCRIPTION
MIN
t1
SCLK period
50
TYP
MAX
UNIT
ns
t2
SCLK high time
20
ns
t3
SCLK 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
Time between last SCLK rising edge to CS rising edge
8
ns
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
SERIAL REGISTER MAP
Table 3. SUMMARY OF FUNCTIONS SUPPORTED BY SERIAL INTERFACE (1)
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
00
X
X
X
X
X
X
X
(2) (3) (4)
D0
NAME
X
RST
Self-clearing software RESET.
Inactive
X
PDN_CH
Channel-specific ADC powerdown mode.
Inactive
PDN_PARTIAL
Partial power-down mode (fast
recovery from power-down).
Inactive
PDN_COMPLETE
Register mode for complete
power-down (slower recovery).
Inactive
X
DESCRIPTION
DEFAULT
0F
X
X
X
11
X
X
X
X
X
X
PDN_PIN_CFG
Configures the PD pin for partial
power-down mode.
Complete
power-down
ILVDS_LCLK
LVDS current drive
programmability for LCLKN and
LCLKP pins.
3.5mA drive
LVDS current drive
programmability for ADCLKN and
ADCLKP pins.
3.5mA drive
ILVDS_DAT
LVDS current drive
programmability for OUTN and
OUTP pins.
3.5mA drive
EN_LVDS_TERM
Enables internal termination for
LVDS buffers.
Termination
disabled
TERM_LCLK
Programmable termination for
LCLKN and LCLKP buffers.
Termination
disabled
TERM_FRAME
Programmable termination for
ADCLKN and ADCLKP buffers.
Termination
disabled
TERM_DAT
Programmable termination for
OUTN and OUTP buffers.
Termination
disabled
ILVDS_FRAME
X
X
X
1
X
X
X
12
1
X
1
X
X
X
X
X
14
X
X
X
X
X
X
X
X
LFNS_CH
Channel-specific, low-frequency
noise suppression mode enable.
Inactive
24
X
X
X
X
X
X
X
X
INVERT_CH
Swaps the polarity of the analog
input pins electrically.
INP is
positive
input
X
0
0
EN_RAMP
Enables a repeating full-scale
ramp pattern on the outputs.
Inactive
0
X
0
DUALCUSTOM_
PAT
Enables the mode wherein the
output toggles between two
defined codes.
Inactive
0
0
X
SINGLE_CUSTOM
_PAT
Enables the mode wherein the
output is a constant specified
code.
Inactive
BITS_CUSTOM1
2MSBs for a single custom
pattern (and for the first code of
the dual custom pattern). is
the MSB.
Inactive
BITS_CUSTOM2
2MSBs for the second code of
the dual custom pattern.
Inactive
Inactive
25
X
X
X
X
26
X
X
X
X
X
X
X
X
BITS_CUSTOM1
8 lower bits for the single custom
pattern (and for the first code of
the dual custom pattern). is
the LSB.
27
X
X
X
X
X
X
X
X
BITS_CUSTOM2
8 lower bits for the second code
of the dual custom pattern.
Inactive
GAIN_CH1
Programmable gain channel 1.
0dB gain
GAIN_CH2
Programmable gain channel 2.
0dB gain
GAIN_CH3
Programmable gain channel 3.
0dB gain
X
X
X
X
X
X
X
X
2A
X
X
X
X
X
X
X
X
GAIN_CH4
Programmable gain channel 4.
0dB gain
X
X
X
X
GAIN_CH5
Programmable gain channel 5.
0dB gain
GAIN_CH6
Programmable gain channel 6.
0dB gain
GAIN_CH7
Programmable gain channel 7.
0dB gain
GAIN_CH8
Programmable gain channel 8.
0dB gain
X
X
X
X
2B
X
X
X
X
X
(1)
(2)
(3)
(4)
X
X
X
The unused bits in each register (identified as blank table cells) must be programmed as '0'.
X = Register bit referenced by the corresponding name and description (default is 0).
Bits marked as '0' should be forced to 0, and bits marked as '1' should be forced to 1 when the particular register is programmed.
Multiple functions in a register should be programmed in a single write operation.
Copyright © 2008–2012, Texas Instruments Incorporated
15
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
Table 3. SUMMARY OF FUNCTIONS SUPPORTED BY SERIAL INTERFACE(1) (2)
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
1
1
D0
NAME
X
DIFF_CLK
X
EN_DCC
(3) (4)
(continued)
DESCRIPTION
Differential clock mode.
Enables the duty-cycle correction
circuit.
X
1
X
X
Singleended clock
Disabled
EXT_REF_VCM
Drives the external reference
mode through the VCM pin.
External
reference
drives REFT
and REFB
PHASE_DDR
Controls the phase of LCLK
output relative to data.
90 degrees
42
1
DEFAULT
0
X
PAT_DESKEW
Enables deskew pattern mode.
Inactive
X
0
PAT_SYNC
Enables sync pattern mode.
Inactive
BTC_MODE
Binary two's complement format
for ADC output.
MSB_FIRST
Serialized ADC output comes
out MSB-first.
45
46
1
1
1
1
1
1
X
EN_SDR
1
1
FALL_SDR
1
X
X
X
Straight
offset binary
LSB-first
output
Enables SDR output mode
(LCLK becomes a 12x input
clock).
DDR output
mode
Controls whether the LCLK rising
or falling edge comes in the
middle of the data window when
operating in SDR output mode.
Rising edge
of LCLK in
middle of
data window
SUMMARY OF FEATURES
FEATURES
POWER IMPACT (relative to default)
AT fS = 65MSPS
DEFAULT
SELECTION
Internal or external reference
(driven on the REFT and REFB pins)
N/A
Pin
External reference driven on the VCM pin
Off
Register 42
Approximately 9mW less power on AVDD
Duty cycle correction circuit
Off
Register 42
Approximately 7mW more power on AVDD
Low-frequency noise suppression
Off
Register 14
With zero input to the ADC, low-frequency noise suppression causes
digital switching at fS/2, thereby increasing LVDD power by
approximately 7mW/channel
Single-ended or differential clock
Single-ended
Register 42
Differential clock mode takes approximately 7mW more power on
AVDD
Off
Pin and register 0F
ANALOG FEATURES
Power-down mode
Internal reference mode takes approximately 23mW more power on
AVDD
Refer to the Power-Down Modes section in the Electrical
Characteristics table
DIGITAL FEATURES
Programmable digital gain (0dB to 12dB)
Straight offset or BTC output
Swap polarity of analog input pins
0dB
Registers 2A and 2B
No difference
Straight offset
Register 46
No difference
Off
Register 24
No difference
LVDS OUTPUT PHYSICAL LAYER
LVDS internal termination
LVDS current programmability
Off
Register 12
Approximately 7mW more power on AVDD
3.5mA
Register 11
As per LVDS clock and data buffer current setting
LSB-first
Register 46
No difference
DDR
Register 46
SDR mode takes approximately 2mW more power on LVDD
(at fS = 30MSPS)
Refer to Figure 1
Register 42
No difference
LVDS OUTPUT TIMING
LSB- or MSB-first output
DDR or SDR output
LCLK phase relative to data output
16
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
DESCRIPTION OF SERIAL REGISTERS
SOFTWARE RESET
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
00
D0
NAME
X
RST
Software reset is applied when the RST bit is set to '1'; setting this bit resets all internal registers and self-clears
to '0'.
POWER-DOWN MODES
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
NAME
X
X
X
X
X
X
X
X
PDN_CH
X
PDN_PARTIAL
0F
0
X
PDN_COMPLETE
X
0
PDN_PIN_CFG
Each of the eight channels can be individually powered down. PDN_CH controls the power-down mode for
the ADC channel .
In addition to channel-specific power-down, the ADS5287 also has two global power-down modes—partial
power-down mode and complete power-down mode. Partial power-down mode partially powers down the chip;
recovery from this mode is much quicker, provided that the clock has been running for at least 50μs before
exiting this mode. Complete power-down mode, on the other hand, completely powers down the chip, and
involves a much longer recovery time.
In addition to programming the device for either of these two power-down modes (through either the
PDN_PARTIAL or PDN_COMPLETE bits, respectively), the PD pin itself can be configured as either a partial
power-down pin or a complete power-down pin control. For example, if PDN_PIN_CFG = 0 (default), when the
PD pin is high, the device enters complete power-down mode. However, if PDN_PIN_CFG = 1, when the PD pin
is high, the device enters partial power-down mode.
LVDS DRIVE PROGRAMMABILITY
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
11
D7
D6
X
X
X
X
D5
X
D4
X
D3
D2
D1
D0
NAME
X
X
X
ILVDS_LCLK
ILVDS_FRAME
ILVDS_DAT
The LVDS drive strength of the bit clock (LCLKP or LCLKN) and the frame clock (ADCLKP or ADCLKN) can be
individually programmed. The LVDS drive strengths of all the data outputs OUTP and OUTN can also be
programmed to the same value.
Copyright © 2008–2012, Texas Instruments Incorporated
17
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
All three drive strengths (bit clock, frame clock, and data) are programmed using sets of three bits. Table 4
shows an example of how the drive strength of the bit clock is programmed (the method is similar for the frame
clock and data drive strengths).
Table 4. Bit Clock Drive Strength (1)
(1)
ILVDS_LCLK
ILVDS_LCLK
ILVDS_LCLK
LVDS DRIVE STRENGTH FOR LCLKP AND LCLKN
0
0
0
3.5mA (default)
0
0
1
2.5mA
0
1
0
1.5mA
0
1
1
0.5mA
1
0
0
7.5mA
1
0
1
6.5mA
1
1
0
5.5mA
1
1
1
4.5mA
Current settings lower than 1.5mA are not recommended.
LVDS INTERNAL TERMINATION PROGRAMMABILITY
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
NAME
X
EN_LVDS_TERM
1
X
X
X
TERM_LCLK
12
1
X
1
X
X
X
X
TERM_FRAME
X
TERM_DAT
The LVDS buffers have high-impedance current sources driving the outputs. When driving traces whose
characteristic impedance is not perfectly matched with the termination impedance on the receiver side, there may
be reflections back to the LVDS output pins of the ADS5287 that cause degraded signal integrity. By enabling an
internal termination (between the positive and negative outputs) for the LVDS buffers, the signal integrity can be
significantly improved in such scenarios. To set the internal termination mode, the EN_LVDS_TERM bit should
be set to '1'. Once this bit is set, the internal termination values for the bit clock, frame clock, and data buffers
can be independently programmed using sets of three bits. Table 5 shows an example of how the internal
termination of the LVDS buffer driving the bit clock is programmed (the method is similar for the frame clock and
data buffers). These termination values are only typical values and can vary by up to ±20% across temperature
and from device to device.
Table 5. Bit Clock Drive Strengths
18
TERM_LCLK
TERM_LCLK
TERM_LCLK
INTERNAL TERMINATION BETWEEN
LCLKP AND LCLKN IN Ω
0
0
0
None
0
0
1
260
0
1
0
150
0
1
1
94
1
0
0
125
1
0
1
80
1
1
0
66
1
1
1
55
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
LOW-FREQUENCY NOISE SUPPRESSION MODE
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
14
D7
D6
D5
D4
D3
D2
D1
D0
NAME
X
X
X
X
X
X
X
X
LFNS_CH
The low-frequency noise suppression mode is specifically useful in applications where good noise performance is
desired in the frequency band of 0MHz to 1MHz (around dc). Setting this mode shifts the low-frequency noise of
the ADS5287 to approximately fS/2, thereby moving the noise floor around dc to a much lower value.
LFNS_CH enables this mode individually for each channel.
ANALOG INPUT INVERT
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
24
D7
D6
D5
D4
D3
D2
D1
D0
NAME
X
X
X
X
X
X
X
X
INVERT_CH
Normally, the INP pin represents the positive analog input pin, and INN represents the complementary negative
input. Setting the bits marked INVERT_CH (individual control for each channel) causes the inputs to be
swapped. INN now represents the positive input, and INP the negative input.
LVDS TEST PATTERNS
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
25
D7
D6
D5
D4
X
0
0
D3
D2
D1
0
X
0
DUALCUSTOM_PAT
0
0
X
SINGLE_CUSTOM_PAT
X
X
X
X
X
X
X
X
X
27
X
X
X
X
X
X
X
X
NAME
EN_RAMP
X
26
D0
X
X
BITS_CUSTOM1
BITS_CUSTOM2
BITS_CUSTOM1
BITS_CUSTOM2
0
X
PAT_DESKEW
X
0
PAT_SYNC
45
The ADS5287 can output a variety of test patterns on the LVDS outputs. These test patterns replace the normal
ADC data output. Setting EN_RAMP to '1' causes all the channels to output a repeating full-scale ramp pattern.
The ramp increments from zero code to full-scale code in steps of 1LSB every clock cycle. After hitting the fullscale code, it returns back to zero code and ramps again.
The device can also be programmed to output a constant code by setting SINGLE_CUSTOM_PAT to '1', and
programming the desired code in BITS_CUSTOM1. In this mode, BITS_CUSTOM1 take the place of
the 10-bit ADC data at the output, and are controlled by LSB-first and MSB-first modes in the same way as
normal ADC data are.
The device may also be made to toggle between two consecutive codes by programming DUAL_CUSTOM_PAT
to '1'. The two codes are represented by the contents of BITS_CUSTOM1 and BITS_CUSTOM2.
In addition to custom patterns, the device may also be made to output two preset patterns:
1. Deskew patten: Set using PAT_DESKEW, this mode causes the 12 serial bits to come out as
010101010101 (the rightmost bit representing the first bit in the LSB-first mode)
2. Sync pattern: Set using PAT_SYNC, this mode causes the 12 serial bits to come out as 111111000000 (the
rightmost bit representing the first bit in the LSB-first mode)
Note that only one of the above patterns should be active at any given instant.
Copyright © 2008–2012, Texas Instruments Incorporated
19
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
PROGRAMMABLE GAIN
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
X
D6
X
D5
D4
X
D3
D2
D1
D0
NAME
X
X
X
X
GAIN_CH1
X
GAIN_CH2
2A
X
X
X
X
X
X
X
X
X
X
X
X
GAIN_CH3
GAIN_CH4
GAIN_CH5
X
X
X
X
GAIN_CH6
2B
X
X
X
X
GAIN_CH7
X
X
X
X
GAIN_CH8
In applications where the full-scale swing of the analog input signal is much less than the 2VPP range supported
by the ADS5287, a programmable gain can be set to achieve the full-scale output code even with a lower analog
input swing. The programmable gain not only fills the output code range of the ADC, but also enhances the SNR
of the device by utilizing quantization information from some extra internal bits. The programmable gain for each
channel can be individually set using a set of four bits, indicated as GAIN_CHN for Channel N. The gain
setting is coded in binary from 0dB to 12dB, as shown in Table 6.
Table 6. Gain Setting for Channel 1
20
GAIN_CH1
GAIN_CH1
GAIN_CH1
GAIN_CH1
CHANNEL 1 GAIN SETTING
0
0
0
0
0dB
0
0
0
1
1dB
0
0
1
0
2dB
0
0
1
1
3dB
0
1
0
0
4dB
0
1
0
1
5dB
0
1
1
0
6dB
0
1
1
1
7dB
1
0
0
0
8dB
1
0
0
1
9dB
1
0
1
0
10dB
1
0
1
1
11dB
1
1
0
0
12dB
1
1
0
1
Do not use
1
1
1
0
Do not use
1
1
1
1
Do not use
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
CLOCK, REFERENCE, AND DATA OUTPUT MODES
ADDRESS
IN HEX
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
1
1
X
D1
D0
NAME
X
DIFF_CLK
EN_DCC
42
1
X
1
X
1
1
1
1
EXT_REF_VCM
X
PHASE_DDR
X
X
BTC_MODE
MSB_FIRST
46
1
1
X
1
X
EN_SDR
1
1
FALL_SDR
INPUT CLOCK
The ADS5287 is configured by default to operate with a single-ended input clock—CLKP is driven by a CMOS
clock and CLKN is tied to '0'. However, by programming DIFF_CLK to '1', the device can be made to work with a
differential input clock on CLKP and CLKN. Operating with a low-jitter differential clock usually gives better SNR
performance, especially at input frequencies greater than 30MHz.
In cases where the duty cycle of the input clock falls outside the 45% to 55% range, it is recommended to enable
an internal duty cycle correction circuit. This enabling is done by setting the EN_DCC bit to '1'.
EXTERNAL REFERENCE
The ADS5287 can be made to operate in external reference mode by pulling the INT/EXT pin to '0'. In this mode,
the REFT and REFB pins should be driven with voltage levels of 2.5V and 0.5V, respectively, and must have
enough drive strength to drive the switched capacitance loading of the reference voltages by each ADC. The
advantage of using the external reference mode is that multiple ADS5287 units can be made to operate with the
same external reference, thereby improving parameters such as gain matching across devices. However, in
applications that do not have an available high drive, differential external reference, the ADS5287 can still be
driven with a single external reference voltage on the VCM pin. When EXT_REF_VCM is set as '1' (and the
INT/EXT pin is set to '0'), the VCM pin is configured as an input pin, and the voltages on REFT and REFB are
generated as shown in Equation 1 and Equation 2.
VCM
VREFT = 1.5V +
1.5V
(1)
VCM
VREFB = 1.5V 1.5V
(2)
Copyright © 2008–2012, Texas Instruments Incorporated
21
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
BIT CLOCK PROGRAMMABILITY
The output interface of the ADS5287 is normally a DDR interface, with the LCLK rising edge and falling edge
transitions in the middle of alternate data windows. Figure 1 shows this default phase.
ADCLKP
LCLKP
OUTP
Figure 1. Default Phase of LCLK
The phase of LCLK can be programmed relative to the output frame clock and data using bits
PHASE_DDR. The LCLK phase modes are shown in Figure 2.
PHASE_DDR = '00'
PHASE_DDR = '10'
ADCLKP
ADCLKP
LCLKP
LCLKP
OUTP
OUTP
PHASE_DDR = '01'
PHASE_DDR = '11'
ADCLKP
ADCLKP
LCLKP
LCLKP
OUTP
OUTP
Figure 2. Phase Programmability Modes for LCLK
22
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
In addition to programming the phase of LCLK in the DDR mode, the device can also be made to operate in SDR
mode by setting the EN_SDR bit to '1'. In this mode, the bit clock (LCLK) is output at 12x times the input clock, or
twice the rate as in DDR mode. Depending on the state of FALL_SDR, LCLK may be output in either of the two
manners shown in Figure 3. As shown in Figure 3, only the LCLK rising (or falling) edge is used to capture the
output data in SDR mode.
EN_SDR = '1', FALL_SDR = '0'
ADCLKP
LCLKP
OUTP
EN_SDR = '1', FALL_SDR = '1'
ADCLKP
LCLKP
OUTP
Figure 3. SDR Interface Modes
The SDR mode does not work well beyond 40MSPS because the LCLK frequency becomes very high.
DATA OUTPUT FORMAT MODES
The ADC output, by default, is in straight offset binary mode. Programming the BTC_MODE bit to '1' inverts the
MSB, and the output becomes binary two's complement mode.
Also by default, the first two bits of the frame (following the rising edge of ADCLKP) are zeroes, followed by the
LSB of the ADC output. Programming the MSB_FIRST mode inverts the bit order in the word. Thus, in the
MSB_FIRST mode, the MSB is output as the first bit following the ADCLKP rising edge. The two zeroes come
after the LSB at the end of the word.
Copyright © 2008–2012, Texas Instruments Incorporated
23
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
TYPICAL CHARACTERISTICS
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
SPECTRAL PERFORMANCE
(fS = 40MHz, fIN = 10MHz)
SPECTRAL PERFORMANCE
(fS = 40MHz, fIN = 25MHz)
0
0
SFDR = 84.8dBc
SNR = 61.8dBFS
SINAD = 61.79dBFS
THD = 87.6dBc
-20
-40
Amplitude (dB)
Amplitude (dB)
-40
SFDR = 82.5dBc
SNR = 61.76dBFS
SINAD = 61.72dBFS
THD = 80.9dBc
-20
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
0
2
4
6
8
10
12
14
16
18
20
0
2
4
Input Frequency (MHz)
10
12
14
Figure 4.
Figure 5.
SPECTRAL PERFORMANCE
(fS = 50MHz, fIN = 10MHz)
SPECTRAL PERFORMANCE
(fS = 50MHz, fIN = 25MHz)
16
18
20
0
SFDR = 84.7dBc
SNR = 61.78dBFS
SINAD = 61.77dBFS
THD = 86.5dBc
-20
SFDR = 85.5dBc
SNR = 61.75dBFS
SINAD = 61.72dBFS
THD = 83.1dBc
-20
-40
Amplitude (dB)
-40
Amplitude (dB)
8
Input Frequency (MHz)
0
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
-180
0
5
10
15
Input Frequency (MHz)
Figure 6.
24
6
20
25
0
5
10
15
20
25
Input Frequency (MHz)
Figure 7.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
TYPICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
SPECTRAL PERFORMANCE
(fS = 65MHz, fIN = 10MHz)
SPECTRAL PERFORMANCE
(fS = 65MHz, fIN = 25MHz)
0
0
SFDR = 86.9dBc
SNR = 61.73dBFS
SINAD = 61.72dBFS
THD = 86.5dBc
-20
-40
Amplitude (dB)
Amplitude (dB)
-40
-60
-80
-100
SFDR = 85.9dBc
SNR = 62.02dBFS
SNR (0MHz to 1MHz) = 76.5dBFS
SINAD = 62dBFS
THD = 84.1dBc
-20
-60
-80
-100
-120
-120
-140
-140
-160
-160
-180
0
5
10
15
20
25
30 33
0
5
10
Input Frequency (MHz)
20
25
Figure 8.
Figure 9.
SPECTRAL PERFORMANCE, LOW-FREQUENCY NOISE
SUPPRESSION MODE ENABLED
(fS = 65MHz, fIN = 25MHz)
DYNAMIC PERFORMANCE
vs
INPUT FREQUENCY
0
Dynamic Performance (SNR, SFDR)
-40
30 33
90
SFDR = 85.8dBc
SNR = 62.1dBFS
SNR (0MHz to 1MHz) = 77dBFS
SINAD = 62dBFS
THD = 84.6dBc
-20
Amplitude (dB)
15
Input Frequency (MHz)
-60
-80
-100
-120
-140
85
SFDR (dBc)
80
75
fS = 40MHz
70
65
SNR (dBFS)
60
-160
0
5
10
15
20
Input Frequency (MHz)
Figure 10.
Copyright © 2008–2012, Texas Instruments Incorporated
25
30 33
5
10
15
20
25
30
Input Frequency (MHz)
Figure 11.
25
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
DYNAMIC PERFORMANCE
vs
INPUT FREQUENCY
DYNAMIC PERFORMANCE
vs
INPUT FREQUENCY
95
Dynamic Performance (SNR, SFDR)
Dynamic Performance (SNR, SFDR)
90
85
SFDR (dBc)
80
75
fS = 50MHz
70
65
SNR (dBFS)
60
90
SFDR (dBc)
85
80
fS = 65MHz
75
70
65
SNR (dBFS)
60
10
5
15
20
25
5
30
10
25
Figure 13.
DYNAMIC PERFORMANCE
vs
DIGITAL GAIN
DYNAMIC PERFORMANCE
vs
AVDD
30
90
Output amplitude adjusted to -1dBFS for each gain setting.
88
SFDR (dBc)
83
fS = 65MHz
fIN = 10MHz
78
73
68
63
SNR (dBFS)
58
Dynamic Performance (SNR, SFDR)
Dynamic Performance (SNR, SFDR)
20
Figure 12.
93
SFDR (dBc)
85
80
fS = 65MHz
fIN = 10MHz
75
70
65
SNR (dBFS)
60
0
2
4
6
Digital Gain (dB)
Figure 14.
26
15
Input Frequency (MHz)
Input Frequency (MHz)
8
10
12
3.0
3.1
3.2
3.3
3.4
3.5
3.6
AVDD (V)
Figure 15.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
TYPICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
DYNAMIC PERFORMANCE
vs
INPUT AMPLITUDE
DYNAMIC PERFORMANCE
vs
CLOCK AMPLITUDE
90
Dynamic Performance (SNR, SFDR)
Dynamic Performance (SNR, SFDR)
90
80
70
60
SNR (dBFS)
50
40
30
SFDR (dBc)
fS = 65MHz
fIN = 10MHz
20
-45 -40 -35 -30 -25 -20 -15 -10
-5
80
fS = 65MHz
fIN = 10MHz
75
70
65
SNR (dBFS)
60
10
-50
SFDR (dBc)
85
0.1
0
0.6
2.1
2.3
Figure 17.
DYNAMIC PERFORMANCE
vs
ANALOG INPUT COMMON-MODE VOLTAGE
DYNAMIC PERFORMANCE
vs
EXTERNAL REFERENCE DIFFERENTIAL VOLTAGE
90
Dynamic Performance (SNR, SFDR)
Dynamic Performance (SNR, SFDR)
1.6
Figure 16.
90
SFDR (dBc)
85
80
75
1.1
Clock Amplitude (VPP Differential)
Input Amplitude (dBFS)
fS = 65MHz
fIN = 10MHz
70
65
SNR (dBFS)
60
1.30
SFDR (dBc)
85
80
75
fS = 65MHz
fIN = 10MHz
External reference common-mode voltage
maintained at 1.5V.
70
65
SNR (dBFS)
60
1.35
1.40
1.45
1.50
1.55
1.60
1.65
Analog Input Common-Mode Voltage (V)
Figure 18.
Copyright © 2008–2012, Texas Instruments Incorporated
1.70
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
External Reference Differential Voltage, REFT - REFB (V)
Figure 19.
27
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
DYNAMIC PERFORMANCE
vs
EXTERNAL REFERENCE COMMON-MODE VOLTAGE
DYNAMIC PERFORMANCE
vs
EXTERNAL REFERENCE FORCED THROUGH VCM
90
Dynamic Performance (SNR, SFDR)
Dynamic Performance (SNR, SFDR)
90
SFDR (dBc)
85
80
fS = 65MHz
fIN = 10MHz
75
External reference differential voltage maintained at 2V.
70
65
SNR (dBFS)
60
1.35
1.40
1.45
1.50
1.55
1.60
75
fS = 65MHz
fIN = 10MHz
70
65
SNR (dBFS)
1.40
1.45
1.50
1.55
External Reference Common-Mode Voltage, (REFT + REFB)/2 (V)
Voltage on VCM (V)
Figure 20.
Figure 21.
DYNAMIC PERFORMANCE
vs
CLOCK DUTY CYCLE
(DCC DISABLED)
DYNAMIC PERFORMANCE
vs
CLOCK DUTY CYCLE
(DCC ENABLED)
1.60
1.65
70
80
95
Dynamic Performance (SNR, SFDR)
Dynamic Performance (SNR, SFDR)
80
60
1.35
1.65
90
85
SFDR (dBc)
80
75
fS = 65MHz
fIN = 10MHz
70
65
SNR (dBFS)
60
55
90
SFDR (dBc)
85
fS = 65MHz
fIN = 10MHz
80
75
70
65
SNR (dBFS)
60
35
40
45
50
55
Clock Duty Cycle (%)
Figure 22.
28
SFDR (dBc)
85
60
65
20
30
40
50
60
Clock Duty Cycle (%)
Figure 23.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
TYPICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
HISTOGRAM OF OUTPUT CODE FOR ZERO INPUT
INTERMODULATION DISTORTION
10
70
fS = 65MHz
f1 = 10MHz (-7dBFS)
f2 = 16.1MHz (-7dBFS)
IMD = -96dBFS
fS = 65MSPS
-10
50
-30
Amplitude (dB)
Occurrence (%)
61.1%
60
38.9%
40
30
-50
-70
-90
20
-110
10
-130
0%
0%
0
-150
512
511
513
0
514
6
8
10
12
14
16
Figure 25.
INTEGRAL NONLINEARITY
DIFFERENTIAL NONLINEARITY
(fS = 65MSPS, fIN = 5MHz)
0.10
0.15
0.08
18
20
0.06
0.10
0.04
0.05
DNL (LSB)
INL (LSB)
4
Figure 24.
0.20
0
-0.05
0.02
0
-0.20
-0.40
-0.10
-0.15
2
Input Frequency (MHz)
Code Bin (LSB)
-0.60
fS = 65MSPS
fIN = 5MHz
-0.80
-0.20
64
192
320
448
576
704
Code (LSB)
Figure 26.
Copyright © 2008–2012, Texas Instruments Incorporated
832
960
-0.10
64
320
576
832
960
Code (LSB)
Figure 27.
29
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Typical values at +25°C. Minimum and maximum values are measured across the specified temperature range of TMIN =
–40°C to TMAX = +85°C, AVDD = 3.3V, LVDD = 1.8V, clock frequency = 10MSPS to 65MSPS, 50% clock duty cycle, –1dBFS
differential analog input, internal reference mode, ISET resistor = 56.2kΩ, and LVDS buffer current setting = 3.5mA, unless
otherwise noted.Typical values at +25°C.
AVDD AND LVDD POWER-SUPPLY CURRENTS
vs
CLOCK FREQUENCY
OVERLOAD RECOVERY AT 65MSPS
0.6
170
IAVDD, ILVDD (mA)
Standard Deviation (LSB)
Zero Input on All Channels
Internal Reference Mode
150
130
IAVDD
110
90
70
ILVDD
50
0.5
0.4
Standard Deviation of
1st Point After Overload
0.3
0.2
0.1
fS = 65MSPS
fIN = 5MHz
0
30
5
15
25
35
45
55
65
75
Standard Deviation of
2nd Point After Overload
0
1
Clock Frequency (MSPS)
3
2
4
5
6
Overload Signal Amplitude (dBFS)
Figure 28.
Figure 29.
16384 tS (Group 1)
First point after overload (Set 1)
Second point after overload (Set 1)
+FS
Set 1, Point 1 (of 16)
Set 1, Point 2 (of 16)
tS
Overload
Amplitude
-FS
Second point after overload (Set 2)
First point after overload (Set 2)
NOTES:
Input sine wave phase is repetitive over 16384 clock cycles.
16 such repetitive groups (of 16384 clock cycles) are captured–a total of 262,144 points.
Standard deviation of every set of first and second points after overload are analyzed over the 16 groups.
Worst case of all such standard deviations are plotted in the graphs.
Figure 30. Overload Recovery
30
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
APPLICATION INFORMATION
THEORY OF OPERATION
The ADS5287 is an 8-channel, high-speed, CMOS
ADC. Two zeroes are appended on the LSB side to
the 10 bits given out by each channel. The resulting
12 bits are serialized and sent out on a single pair of
pins in LVDS format. All eight channels of the
ADS5287 operate from a single clock (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-locked loop (PLL). A 6x and a 1x clock
are also output in LVDS format, along with the data,
to enable easy data capture. The ADS5287 operates
from internally-generated reference voltages that are
trimmed to achieve a high level of accuracy. Trimmed
references improve the gain matching across
devices, and provide the option to operate the
devices without having to externally drive and route
reference lines. The nominal values of REFT and
REFB are 2.5V and 0.5V, respectively. The
references are internally scaled down differentially by
a factor of 2. This scaling results in a differential input
of –1V to correspond to the zero code of the ADC,
and a differential input of +1V to correspond to the
full-scale code (1023 LSB). VCM (the common-mode
voltage of REFT and REFB) is also made available
externally through a pin, and is nominally 1.5V.
The ADC employs a pipelined converter architecture
that consists of a combination of multi-bit and singlebit internal stages. Each stage feeds its data into the
digital error correction logic, ensuring excellent
differential linearity and no missing codes at the 10bit level.
Copyright © 2008–2012, Texas Instruments Incorporated
The ADC output 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 are 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 ADS5287.
The ADS5287 operates from two sets of supplies and
grounds. The analog supply and ground set is
identified as AVDD and AVSS, while the digital set is
identified by LVDD and LVSS.
ANALOG INPUT
The analog input consists of a switched-capacitor
based, differential sample-and-hold architecture. This
differential topology results in very good ac
performance, even for high input frequencies at high
sampling rates. The INN and INP pins must be
externally biased around a common-mode voltage of
1.5V, available on VCM. For a full-scale differential
input, each input pin (INN and INP) must swing
symmetrically between VCM + 0.5V and VCM – 0.5V,
resulting in a 2VPP differential input swing. The
maximum input peak-to-peak differential swing is
determined to be the difference between the internal
reference voltages REFT (2.5V nominal) and REFB
(0.5V nominal). Figure 31 illustrates the model of the
input driving circuit.
31
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
5nH to 9nH (TQFP-80)
2nH to 3nH (QFN-64)
IN
OUT
INP
1.5pF to
2.5pF
5W
to 10W
1W
15W
to 25W
IN
1.5pF
to 2.4pF
15W
to 30W
OUT
IN
1000W
to 1440W
OUT
OUT
OUTP
0.2pF
to 0.3pF
IN
OUTN
1000W
to 1440W
16W to 32W
5W
to 10W
5nH to 9nH (TQFP-80)
2nH to 3nH (QFN-64)
15W
to 25W
IN
OUT
1.5pF
to 2.4pF
15W
to 30W
IN
OUT
INN
1.5pF to
2.5pF
Switches that are ON
in SAMPLE phase.
1W
Switches that are ON
in HOLD phase.
IN
OUT
Figure 31. Analog Input Circuit Model
Input Common-Mode Current
The input stage of all eight ADCs together sinks a
common-mode current on the order of 2mA at
50MSPS. Equation 3 describes the dependency of
the common-mode current and the sampling
frequency.
(2mA) ´ fS
50MSPS
ADS5287
INP
1.2kW
(3)
If the driving stage is dc-coupled to the inputs, then
Equation 3 can be used to determine its commonmode drive capability and impedance. The inputs can
also be ac-coupled to the INN and INP pins. In that
case, the input common-mode is set by two internal
1.2kΩ resistors connecting the input pins to VCM. This
architecture is shown in Figure 32.
When the inputs are ac-coupled, there is a drop in
the voltages at INP and INN relative to VCM. This can
be computed from Equation 3. At 50MSPS, for
example, the drop at each of the 16 input pins is
150mV, which is not optimal for ADC operation.
Initialization Registers 1 and 5, described in the
Initialization Register table, can be used to partially
reduce the effect of this input common-mode drop
32
during ac-coupling by increasing VCM by roughly
75mV. When operating above 50MSPS, it is
recommended that additional parallel resistors be
added externally to restore the input common-mode
to at least 1.4V, if the inputs are to be ac-coupled.
Input
Circuitry
1.2kW
INN
Internal
Voltage
Reference
VCM
CM Buffer
Dashed area denotes one of eight channels.
Figure 32. Common-Mode Biasing of Input Pins
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
Driving Circuit
At high input frequencies, the mismatch in the
transformer parasitic capacitance (between the
windings) results in degraded even-order harmonic
performance.
Connecting
two
identical
RF
transformers back-to-back helps to minimize this
mismatch, and good performance is obtained for
high-frequency
input
signals.
An
additional
termination resistor pair is required between the two
transformers, as shown in Figure 34. The center point
of this termination is connected to ground to improve
the balance between the positive and negative sides.
The values of the terminations between the
transformers and on the secondary side must be
chosen to achieve an overall 50Ω (in the case of 50Ω
source impedance).
For optimum performance, the analog inputs must be
driven differentially. This approach improves the
common-mode noise immunity and even-order
harmonic rejection. Input configurations using RF
transformers suitable for low and high input
frequencies are shown in Figure 33 and Figure 34,
respectively. The single-ended signal is fed to the
primary winding of the RF transformer. The
transformer is terminated by 50Ω resistor on the
secondary side. Placing the termination on the
secondary side helps to shield the kicks caused by
the input sampling capacitors from the RF
transformer leakage inductances. The termination is
accomplished by two 25Ω resistors, connected in
series, with the center point connected to the 1.5V
common-mode. The 4.7Ω resistor in series with each
input pin is required to damp the ringing caused by
the device package parasitics.
4.7W
0.1mF
INP
1:1
25W
0.1mF
25W
4.7W
INN
VCM
Figure 33. Drive Circuit at Low Input Frequencies
1:2
2:1
INP
0.1mF
200W
200W
0.1mF
50W
50W
INN
VCM
Figure 34. Drive Circuit at High Input Frequencies
Copyright © 2008–2012, Texas Instruments Incorporated
33
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
CLOCK INPUT
The eight channels on the device operate from a
single ADCLK input. To ensure that the aperture
delay and jitter are the same for all 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 to the
sampling circuit. This architecture ensures that the
performance and timing for all channels are identical.
The use of the clock tree for matching introduces an
aperture delay that 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. 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.
The ADS5287 can be made to operate either in
CMOS single-ended clock mode (default is
DIFF_CLK = 0) or differential clock mode (SINE,
LVPECL, or LVDS). When operating in the singleended clock mode, CLKN must be forced to 0VDC,
and the single-ended CMOS applied on the CLKP pin.
This operation is shown in Figure 35.
CMOS Single-Ended
Clock
CLKP
VCM
VCM
5kW
5kW
CLKP
CLKN
Figure 36. Internal Clock Buffer
0.1mF
CLKP
Differential Sine-Wave,
PECL, or LVDS Clock Input
0.1mF
CLKN
Figure 37. Differential Clock Driving Circuit
(DIFF_CLK = 1)
0.1mF
0V
CLKN
CMOS Clock Input
CLKP
0.1mF
Figure 35. Single-Ended Clock Driving Circuit
(DIFF_CLK = 0)
When configured to operate in the differential clock
mode (register bit DIFF_CLK = 1) the ADS5287 clock
inputs can be driven differentially (SINE, LVPECL, or
LVDS) with little or no difference in performance
between them, or with a single-ended (LVCMOS).
The common-mode voltage of the clock inputs is set
to VCM using internal 5kΩ resistors, as shown in
Figure 36. This method allows using transformercoupled drive circuits for a sine wave clock or accoupling for LVPECL and LVDS clock sources, as
shown in Figure 37. When operating in the differential
clock mode, the single-ended CMOS clock can be accoupled to the CLKP input, with CLKN (pin 11)
connected to ground with a 0.1μF capacitor, as
shown in Figure 38.
34
CLKN
Figure 38. Single-Ended Clock Driving Circuit
When DIFF_CLK = 1
For best performance, the clock inputs must be
driven differentially in order to reduce susceptibility to
common-mode noise. For high input frequency
sampling, it is recommended to use a clock source
with very low jitter. Bandpass filtering of the clock
source can help reduce the effect of jitter. If the duty
cycle deviates from 50% by more than 2% or 3%, it is
recommended to enable the DCC through register bit
EN_DCC.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
PLL OPERATION ACROSS SAMPLING
FREQUENCY
The ADS528X uses a PLL for generating the high
speed bit clock (LCLK), the frame clock (ADCLK) &
internal clocks for the serializer operation.
To enable operation across the entire frequency
range, the PLL is automatically configured to one of
four states, depending on the sampling clock
frequency range. The frequency range detection is
automatic and each time the sampling frequency
crosses a threshold, the PLL changes its
configuration to a new state. To prevent unwanted
toggling of PLL state around a threshold, the circuit
has an inbuilt hysteresis. The ADS528x has three
thresholds – taking into account the hysteresis range
of each threshold, variation across devices and
temperature, the thresholds can span the sampling
clock frequency range from 10MHz to 45MHz.
Threshold 1
Threshold 2
Threshold 3
Step 2: Disable the PLL automatic switch and set
the PLL configuration depending on the clock
frequency
SAMPLE CLOCK FREQUENCY
RANGE (MSPS)
REGISTER SETTING (Hex)
Min
Max
Address
Data
10
25
E3
0060
15
45
E3
00A0
With the above settings applied for the respective
frequency ranges, the part will continue to
operate as per the stated datasheet specifications
for all timing parameters at all specified
frequencies, EXCEPT for the timing specifications
at 40MSPS. At 40MSPS, the affected parameters
are – Data setup time, Data hold time and Clock
propagation delay (refer to LVDS Timing ).
2. For sampling clock frequency ≥ 45MSPS
As there are no PLL thresholds beyond 45MHz,
no change in PLL configuration can occur as the
temperature in the system stabilizes. The
ADS528x can be used in the system without
using the above software fix.
INPUT OVER-VOLTAGE RECOVERY
45 MHz
10 MHz
65 MHz
Sampling Frequency
Figure 39. Variation of Thresholds Across
Sampling Frequency
Based on actual system clock frequency, there are
two scenarios:
1. For sampling clock frequency < 45MSPS
After system power up, depending on the
frequency of operation and the frequency
threshold for the given device, the frequency
range detection circuit may change state once. In
some applications where a timing calibration
might be done at the system level once after
power up, this subsequent change of the PLL
state might be undesirable as it can cause a loss
of alignment in the received data. A software fix
for eliminating this one-time change of PLL state
exists using the serial register interface:
– Disable the automatic switch of the PLL
configuration based on frequency detected.
– In addition to disabling the switching, it is also
required to set the PLL to the correct
configuration, depending on the sample clock
frequency used in the system.
The following sequence of register writes must be
followed:
Step 1: Write Address = 0x01, Data = 0x0010
Copyright © 2008–2012, Texas Instruments Incorporated
The differential peak-to-peak full-scale range
supported by the ADS5287 is nominally 2.0V. The
ADS5287 is specially designed to handle an overvoltage condition where the differential peak-to-peak
voltage can be 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 1.5V), recovery from an overvoltage pulse input of twice the amplitude of a fullscale pulse is expected to be within one clock cycle
when the input switches from overload to zero signal.
REFERENCE CIRCUIT
The digital beam-forming algorithm in an ultrasound
system relies 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 that 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 the ISET pin. 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
35
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
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.
The device also supports the use of external
reference voltages. There are two methods to force
the references externally. The first method involves
pulling INT/EXT low and forcing externally REFT and
REFB to 2.5V and 0.5V nominally, respectively. In this
mode, the internal reference buffer goes to a 3-state
output. The external reference driving circuit should
be designed to provide the required switching current
for the eight ADCs inside the chip. 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.
Buffering the internal bandgap voltage also generates
the common-mode voltage VCM, which is set to the
midlevel of REFT and REFB, and is accessible on pin
53. It is meant as a reference voltage to derive the
input common-mode if the input is directly coupled. It
can also be used to derive the reference commonmode voltage in the external reference mode. The
suggested decoupling for the reference pins is shown
in Figure 40.
The second method of forcing the reference voltages
externally can be accessed by pulling INT/EXT low,
and programming the serial interface to drive the
external reference mode through the VCM pin (register
bit called EXT_REF_VCM). In this mode, VCM
becomes configured as an input pin that can be
driven from external circuitry. The internal reference
buffers driving REFT and REFB are active in this
mode. Forcing 1.5V on the VCM pin in the mode
results in REFT and REFB coming to 2.5V and 0.5V,
respectively. In general, the voltages on REFT and
REFB in this mode are given by Equation 4 and
Equation 5, respectively:
VCM
VREFT = 1.5V +
1.5V
(4)
VCM
VREFB = 1.5V 1.5V
(5)
ADS5287
ISET
REFT
REFB
0W to
2W
0.1mF
56.2kW
0W to
2W
2.2mF
2.2mF
0.1mF
Figure 40. Suggested Decoupling on the
Reference Pins
Table 7 describes the state of the reference voltage
internal buffers during various combinations of the
PD, INT/EXT, and EXT_REF_VCM register bits.
Table 7. State of Reference Voltages for Various Combinations of PD, INT/EXT, and EXT_REF_VCM
REGISTER BIT
(1)
INTERNAL BUFFER STATE
PD
0
0
1
1
0
0
1
1
INT/EXT
0
1
0
1
0
1
0
1
EXT_REF_VCM
0
0
0
0
1
1
1
1
REFT buffer
3-state
2.5V
3-state
2.5V (1)
1.5V + VCM/1.5V
Do not use
2.5V (1)
Do not use
REFB buffer
3-state
0.5V
3-state
0.5V (1)
1.5V – VCM/1.5V
Do not use
0.5V (1)
Do not use
VCM pin
1.5V
1.5V
1.5V
1.5V
Force
Do not use
Force
Do not use
Weakly forced with reduced strength.
NOISE COUPLING ISSUES
High-speed mixed signals are sensitive to various
types of noise coupling. One primary source 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 device are clearly demarcated. AVDD and AVSS
are used to denote the supplies for the analog
36
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:
1. The effective inductances of each of the supply
and ground sets.
2. The isolation between the digital and analog
supply and ground sets.
Copyright © 2008–2012, Texas Instruments Incorporated
ADS5287
www.ti.com
Smaller effective inductance of the supply and ground
pins leads to better noise suppression. For this
reason, multiple pins are used to drive each supply
and ground. It is also critical to ensure that the
impedances of the supply and ground lines on the
board are kept to the minimum possible values. Use
of ground planes in the printed circuit board (PCB) as
well as large decoupling capacitors between the
supply and ground lines are necessary to obtain the
best possible SNR performance from the device.
Copyright © 2008–2012, Texas Instruments Incorporated
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
It is recommended that the isolation be maintained on
the 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.
37
ADS5287
SBAS428D – JANUARY 2008 – REVISED JUNE 2012
www.ti.com
REVISION HISTORY
Changes from Revision B (March 2008) to Revision C
Page
•
Changed Initialization Registers section to include Initialization Register 1 ......................................................................... 3
•
In the Input Common-Mode Current section, changed Initialization Register 5 to Initialization Registers 1 and 5 to
reflect change in Initialization Registers table .................................................................................................................... 32
Changes from Revision C (March 2008) to Revision D
Page
•
Added table in the INITIALIZATION REGISTERS section ................................................................................................... 3
•
Added table in the LVDS OUTPUT TIMING CHARACTERISTICS section ....................................................................... 12
•
Added PLL OPERATION ACROSS SAMPLING FREQUENCY section ............................................................................ 35
38
Copyright © 2008–2012, Texas Instruments Incorporated
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)
Device Marking
(3)
(4/5)
(6)
ADS5287IRGCR
ACTIVE
VQFN
RGC
64
2000
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 85
AZ5287
ADS5287IRGCT
ACTIVE
VQFN
RGC
64
250
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 85
AZ5287
(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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