MAXIM MAX3671

19-4437; Rev 0; 2/09
KIT
ATION
EVALU
E
L
B
A
AVAIL
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
Features
♦ Two Reference Clock Inputs: LVPECL
♦ Nine Phase-Aligned Clock Outputs: LVPECL
♦ Input Frequencies: 62.5MHz,125MHz, 250MHz,
312.5MHz
♦ Output Frequencies: 62.5MHz, 125MHz,
156.25MHz, 250MHz, 312.5MHz
The MAX3671 is a low-jitter frequency synthesizer that
accepts two reference clock inputs and generates nine
phase-aligned outputs. The device features 40kHz jitter
transfer bandwidth, 0.3psRMS (12kHz to 20MHz) integrated phase jitter, and best-in-class power-supply
noise rejection (PSNR), making it ideal for jitter cleanup, frequency translation, and clock distribution in
Gigabit Ethernet applications.
The MAX3671 operates from a single +3.3V supply and
typically consumes 400mW. The IC is available in an
8mm x 8mm, 56-pin TQFN package, and operates from
-40°C to +85°C.
♦ Low-Jitter Generation: 0.3psRMS (12kHz to 20MHz)
♦ Clock Failure Indicator for Both Reference Clocks
♦ External Feedback Provides Zero-Delay Capability
♦ Low Output Skew: 20ps Typical
Applications
Ordering Information
Gigabit Ethernet Routers and Switches
PART
TEMP RANGE
PIN-PACKAGE
Jitter Cleanup
MAX3671ETN+
-40°C to +85°C
56 TQFN-EP*
Clock Distribution
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Frequency Translation
Pin Configuration and Typical Application Circuits appear at
end of data sheet.
Functional Diagram
SEL_CLK
CPLL
0.1μF
DM
CREG
0.22μF
DA
REFCLK0
0
REFCLK0
DIV M
REFCLK1
1
REFCLK1
PFD
CP
VCO
62.5MHz
DIV A
PLL_BYPASS
OUTA_EN
1
OUTA3
0
OUTA3
OUTA2
2.5GHz
OUTA2
OUTA1
IN0FAIL
IN1FAIL
OUTA1
SIGNAL QUALIFIER
AND
LOCK DETECT
OUTA0
OUTA0
LOCK
DIV N
MR
OUTB_EN
POWER-ON
RESET
(POR)
DIV B
1
OUTB4
0
OUTB4
OUTB3
OUTB3
OUTB2
1
OUTB2
0
OUTB1
MAX3671
OUTB1
OUTB0
OUTB0
FB_SEL
FB_IN
FB_IN
DB
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
MAX3671
General Description
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
ABSOLUTE MAXIMUM RATINGS
Supply Voltage Range (VCC, VCC_VCO)..............-0.3V to +4.0V
LVPECL Output Current (OUTA[3:0],
OUTA[3 : 0], OUTB[4:0], OUTB[4 : 0]) .............................-56mA
All Other Pins..............................................-0.3V to (VCC + 0.3V)
Continuous Power Dissipation (TA = +70°C)
56-Pin TQFN (derate 47.6mW/°C above 70°C)..........3808mW
Operating Junction Temperature (TJ)................-55°C to +150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +3.6V, TA = -40°C to +85°C, CPLL = 0.1µF, CREG = 0.22µF. Typical values are at VCC = +3.3V, TA = +25°C, unless
otherwise noted.)
PARAMETER
TYP
MAX
UNITS
LVPECL outputs unterminated
120
175
mA
VCC Rising
(Note 1)
2.55
V
VCC Falling
(Note 1)
2.45
V
Supply Current
SYMBOL
ICC
CONDITIONS
MIN
POWER-ON RESET
LVCMOS/LVTTL INPUTS (MR, SEL_CLK, PLL_BYPASS, FB_SEL)
Input High Voltage
VIH
Input Low Voltage
VIL
2.0
Input High Current
I IH
VIN = VCC
Input Low Current
I IL
VIN = GND
V
0.8
V
75
μA
-75
μA
2.4
V
LVCMOS/LVTTL OUTPUTS (IN0FAIL, IN1FAIL, LOCK)
Output High Voltage
VOH
I OH = -8mA
Output Low Voltage
VOL
I OL = +8mA
0.4
V
VCC 0.7
V
LVPECL INPUTS (REFCLK0, REFCLK0, REFCLK1, REFCLK1, FB_IN, FB_IN) (Note 2)
Input High Voltage
VIH
Input Low Voltage
VIL
VCC 2.0
Input Bias Voltage
VCMI
VCC 1.8
Differential-Input Swing
V
VCC 1.34
0.15
V
1.9
VP-P
Differential-Input Impedance
> 40
k
Common-Mode Input Impedance
> 14
k
1.5
pF
Input Capacitance
Input Current
Input Inrush Current When Power
is Off (Steady State)
Input Inrush Current Overshoot
When Power is Off
2
VIH = VCC - 0.7V, VIL = VCC - 2.0V
-100
+100
μA
(Notes 3, 4)
8
mA
IOVERSHOOT (Notes 3, 4)
6
mA
IDC
_______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
(VCC = +3.0V to +3.6V, TA = -40°C to +85°C, CPLL = 0.1µF, CREG = 0.22µF. Typical values are at VCC = +3.3V, TA = +25°C, unless
otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
REFERENCE CLOCK INPUTS (REFCLK0, REFCLK0, REFCLK1, REFCLK1)
Reference Clock Frequency
fREF
Table 1
MHz
Reference Clock Frequency
Tolerance
-200
+200
ppm
Reference Clock Duty Cycle
40
60
%
Reference Clock Amplitude
Detection Assert Threshold
VDT
Differential swing (Notes 5, 6)
200
mVP-P
LVPECL OUTPUTS (OUTA[3:0], OUTA[3:0], OUTB[4:0], OUTB[4:0]) (Note 7)
Output High Voltage
VOH
VCC 1.13
VCC 0.98
VCC 0.83
V
Output Low Voltage
VOL
VCC 1.85
VCC 1.70
VCC 1.55
V
1.1
1.45
1.8
VP-P
130
μA
Differential-Output Swing
Output Current When Disabled
VO = VCC - 2.0V to VCC - 0.7V
Output Frequency
f OUT
Output Rise/Fall Time
tR, tF
Output Duty Cycle
Output-to-Output Skew
t SKEW
Tables
2, 3
20% to 80% (Note 8)
150
MHz
500
PLL_BYPASS = 0
48
52
PLL_BYPASS = 1 (Note 9)
45
55
Within output bank
20
All outputs
40
ps
%
ps
OTHER AC ELECTRICAL SPECIFICATIONS
PLL Jitter Transfer Bandwidth
40
Jitter Peaking
0.1
dB
PFD Compare Frequency
62.5
MHz
VCO Center Frequency
kHz
2.5
Random Jitter Generation
Integrated 12kHz to 20MHz (Notes 5, 8)
Determinisitic Jitter Caused by
Power-Supply Noise
(Note 10)
0.3
GHz
1.0
psRMS
5
psP-P
Frequency Difference Between
Reference Clock and VCO
Within Which the PLL is
Considered in Lock
500
ppm
Frequency Difference Between
Reference Clock and VCO at
Which the PLL is Considered
Out-of-Lock
800
ppm
600
μs
PLL Lock Time
tLOCK
Figure 2
_______________________________________________________________________________________
3
MAX3671
ELECTRICAL CHARACTERISTICS (continued)
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40°C to +85°C, CPLL = 0.1µF, CREG = 0.22µF. Typical values are at VCC = +3.3V, TA = +25°C, unless
otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
Master Reset (MR) Minimum
Pulse Width
TYP
MAX
100
Propagation Delay from Input to
FB_IN
FB_SEL = 1 (Notes 8, 11)
Propagation Delay from Input to
Any Output
PLL_BYPASS = 1
-120
ns
+120
1.0
UNITS
ps
ns
During the power-on-reset time, the LVPECL outputs are held to logic-low (OUTxx = low, OUTxx = high). See the PowerOn-Reset (POR) section for more information.
Note 2: LVPECL inputs can be AC- or DC-coupled.
Note 3: For hot-pluggable purposes, the device can receive LVPECL inputs when no supply voltage is applied. Measured with
VCC pins connected to GND. See Figure 1.
Note 4: Measured with LVPECL input (VIH, VIL) as specified.
Note 5: Measured using reference clock input with 550ps rise/fall time (20% to 80%).
Note 6: When input differential swing is below the specified threshold, a clock failure is declared. See Figure 4.
Note 7: LVPECL outputs terminated 50Ω to VTT = VCC - 2V.
Note 8: Guaranteed by design and characterization.
Note 9: Measured with 50% duty cycle at reference clock input.
Note 10: Measured with 50mVP-P sinusoidal noise on the power supply, fNOISE = 100kHz.
Note 11: Measured with fREFCLKx = fFB_IN and matched slew rates.
Note 1:
4
_______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
MAX3671
INRUSH CURRENT
(mA)
IOVERSHOOT
IDC
t
Figure 1. LVPECL Input Inrush Current
POWER-ON-RESET (~ 20μs)
VCC
REFCLK0
REFCLK1
OUTxx
IN0FAIL
IN1FAIL
HIGH
HIGH
tLOCK (~ 600μs)
LOCK
SEL_CLK
PLL LOCKED TO REFCLK0
LOW
Figure 2. Power-Up, PLL Locks to REFCLK0
_______________________________________________________________________________________
5
Typical Operating Characteristics
(VCC = 3.3V, TA = +25°C, unless otherwise noted.)
-90
-100
-110
-120
-130
-90
-100
-110
-120
-130
-80
-90
-100
-110
-120
-130
-140
-140
-140
-150
-150
-160
-160
10k
100k
1M
10M
100M
100
1k
OFFSET FREQUENCY (Hz)
1M
10M
100
100M
-90
-100
-110
-120
-130
-90
-110
-120
-130
-140
-150
-150
-160
RANDOM JITTER = 0.28psRMS
INTEGRATED 12kHz TO 20MHz
-100
-140
10k
100k
1M
10M
100M
100M
0
-5
-10
-15
-20
-30
1k
10k
100k
1M
10M
1k
100M
10k
DIFFERENTIAL OUTPUT WAVEFORM
AT 312.5MHz
MAX3671 toc07
1M
100k
JITTER FREQUENCY (Hz)
OFFSET FREQUENCY (Hz)
DIFFERENTIAL OUTPUT WAVEFORM
AT 156.25MHz
10M
-25
100
OFFSET FREQUENCY (Hz)
1M
5
-160
1k
100k
JITTER TRANSFER
-80
PHASE NOISE (dBc/Hz)
-80
-70
10k
OFFSET FREQUENCY (Hz)
JITTER TRANSFER (dB)
RANDOM JITTER = 0.27psRMS
INTEGRATED 12kHz TO 20MHz
100
1k
PHASE NOISE AT 312.5MHz
-60
MAX3671 toc04
-70
100k
OFFSET FREQUENCY (Hz)
PHASE NOISE AT 250MHz
-60
10k
MAX3671 toc06
1k
MAX3671 toc05
100
RANDOM JITTER = 0.28psRMS
INTEGRATED 12kHz TO 20MHz
-70
-150
-160
MAX3671 toc03
RANDOM JITTER = 0.29psRMS
INTEGRATED 12kHz TO 20MHz
-80
PHASE NOISE (dBc/Hz)
PHASE NOISE (dBc/Hz)
-80
-70
PHASE NOISE (dBc/Hz)
RANDOM JITTER = 0.41psRMS
INTEGRATED 12kHz TO 20MHz
-60
REFERENCE CLOCK AMPLITUDE DETECTION
ASSERT THRESHOLD vs. INPUT FREQUENCY
MAX3671 toc08
300
MAX3671 toc09
MAX3671 toc01
-70
PHASE NOISE AT 156.25MHz
PHASE NOISE AT 125MHz
-60
MAX3671 toc02
PHASE NOISE AT 62.5MHz
-60
PHASE NOISE (dBc/Hz)
280
200mV/div
ASSERT THRESHOLD (mVP-P)
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
200mV/div
260
INPUT RISE/FALL TIME = 550ps
240
220
200
180
INPUT RISE/FALL TIME = 270ps
160
140
120
100
800ps/div
400ps/div
50
100
150
200
250
300
350
REFERENCE CLOCK INPUT FREQUENCY (MHz)
6
_______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
JITTER HISTOGRAM WITH SUPPLY NOISE
(SUPPLY NOISE = 50mVP-P, 100kHz)
MAX3671 toc11
400
DJ = 5psP-P
350
300
250
ALL OUTPUTS ENABLED
AND UNTERMINATED
200
fNOISE = 100kHz
35
DETERMINISTIC JITTER (psP-P)
ALL OUTPUTS ENABLED
AND TERMINATED
450
40
MAX3671 toc10
500
SUPPLY CURRENT (mA)
DETERMINISTIC JITTER
vs. POWER-SUPPLY NOISE AMPLITUDE
150
100
30
fNOISE = 200kHz
25
20
fNOISE = 1MHz
15
10
5
50
0
0
-40
-15
10
35
60
85
0
2ps/div
SPUR POWER (dBc)
-20
-30
-40
SUPPLY NOISE = 100mVP-P
-50
-60
-70
-80
100
150
200
250
300
35
SUPPLY NOISE = 50mVP-P
POWER-ON-RESET
MAX3671 toc15
40
MAX3671 toc14
fOUT = 125MHz
DETERMINISTIC JITTER
vs. POWER-SUPPLY NOISE FREQUENCY
DETERMINISTIC JITTER (psP-P)
MAX3671 toc13
SPURS CAUSED BY POWER-SUPPLY NOISE
vs. SUPPLY NOISE FREQUENCY
-10
50
SUPPLY NOISE AMPLITUDE (mVP-P)
TEMPERATURE (°C)
0
MAX3671 toc12
SUPPLY CURRENT
vs. TEMPERATURE
VCC
30
SUPPLY NOISE = 100mVP-P
25
OUTxx
20
15
SUPPLY NOISE = 50mVP-P
10
LOCK
5
-90
-100
0
10k
100k
10M
1M
10k
SUPPLY NOISE FREQUENCY (Hz)
100k
10M
1M
200μs/div
SUPPLY NOISE FREQUENCY (Hz)
REFERENCE CLOCK FAILURE DETECTION
MASTER RESET
MAX3671 toc17
MAX3671 toc16
MR
REFCLK1
OUTxx
IN1FAIL
LOCK
LOCK
40μs/div
2ms/div
_______________________________________________________________________________________
7
MAX3671
Typical Operating Characteristics (continued)
(VCC = 3.3V, TA = +25°C, unless otherwise noted.)
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
MAX3671
Pin Description
PIN
8
NAME
FUNCTION
1
IN0FAIL
REFCLK0 Failure Indicator, LVCMOS/LVTTL Output. Low indicates REFCLK0 fails the clock
qualification. Once a failed clock is detected, the indicator status is latched and updated
every 128 PFD cycles (~ 2μs).
2
RSVD1
Reserved. Leave pin open.
3
4
5
6
RSVD2
REFCLK0
REFCLK0
DM
Reserved. Connect to GND.
7, 22, 30, 41,
49, 52
VCC
Power Supply. Connect to +3.3V.
8, 14, 23, 29,
42, 48, 53
GND
Supply Ground
Reference Clock Input 0, Differential LVPECL
Four-Level Control Input for Reference Clock Input Divider. See Table 1.
Master Reset, LVCMOS/LVTTL Input. Connect this pin high or leave open for normal
operation. Has internal 90k pullup to VCC. Connect low to reset the device. A reset is not
required at power-up. If the output divider settings are changed on the fly, a reset is
required to phase align the outputs. This input has a 100ns minimum pulse width and is
asynchronous to the reference clock. While in reset, all clock outputs are held to logiclow. See Table 6.
9
MR
10
11
REFCLK1
REFCLK1
Reference Clock Input 1, Differential LVPECL
12
SEL_CLK
Reference Clock Select, LVCMOS/LVTTL Input. Connect low or leave open to select REFCLK0
as the reference clock. Has internal 90k pulldown to GND. Connect high to select REFCLK1
as the reference clock.
13
VCC_VCO
Power Supply for VCO. Connect to +3.3V.
15
CPLL
Connection for PLL Filter Capacitor. Connect a 0.1μF capacitor between this pin and GND.
16
CREG
Connection for VCO Regulator Capacitor. Connect a 0.22μF capacitor between this pin and
GND.
17
FB_SEL
External Feedback Select, LVCMOS/LVTTL Input. Connect high to select external feedback
for zero-delay buffer configuration. Connect low or leave open for internal feedback. Has
internal 90k pulldown to GND.
18
19
20
21
24
25
26
27
28
31
32
33
34
35
36
FB_IN
FB_IN
OUTB0
OUTB0
OUTB1
OUTB1
OUTB2
OUTB2
DB
OUTB3
OUTB3
OUTB4
OUTB4
OUTB_EN
OUTA_EN
External Feedback Clock Input, Differential LVPECL. Used for zero-delay buffer
configuration.
Clock Output B0, Differential LVPECL
Clock Output B1, Differential LVPECL
Clock Output B2, Differential LVPECL
Four-Level Control Input for B-Group Output Divider. See Table 3.
Clock Output B3, Differential LVPECL
Clock Output B4, Differential LVPECL
Three-Level Control Input for B-Group Output Enable. See Table 5.
Three-Level Control Input for A-Group Output Enable. See Table 4.
_______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
PIN
NAME
37
38
39
40
43
44
45
46
47
OUTA3
OUTA3
OUTA2
OUTA2
DA
OUTA1
OUTA1
OUTA0
OUTA0
50
PLL_BYPASS
FUNCTION
Clock Output A3, Differential LVPECL
Clock Output A2, Differential LVPECL
Four-Level Control Input for A-Group Output Divider. See Table 2.
Clock Output A1, Differential LVPECL
Clock Output A0, Differential LVPECL
PLL Bypass Control, LVCMOS/LVTTL Input. Connect low or open for normal operation. Has
internal 90k pulldown to GND. Connect high to bypass the PLL, connecting the selected
reference clock directly to the clock outputs. In this mode, the clock qualification function
is not valid. To reduce spurious jitter in bypass mode, the internal VCO should be disabled
by shorting the CREG pin to GND.
51
RSVD3
Reserved. Connect to VCC.
54
RSVD4
Reserved. Leave pin open.
55
LOCK
PLL Lock Indicator, LVCMOS/LVTTL Output. Low indicates PLL is locked.
56
IN1FAIL
—
EP
REFCLK1 Failure Indicator, LVCMOS/LVTTL Output. Low indicates REFCLK1 fails the clock
qualification. Once a failed clock is detected, the indicator status is latched and updated
every 128 PFD cycles (~ 2μs).
Exposed Pad. Connect to supply ground for proper electrical and thermal performance.
Detailed Description
The MAX3671 integrates two differential LVPECL reference inputs with a 2:1 mux, a PLL with configurable
dividers, nine differential LVPECL clock outputs, and a
selectable external feedback input for zero-delay buffer
applications (see the Functional Diagram).
The two reference clock inputs are continuously monitored for clock failure by the internal PLL and associated logic. If the primary clock fails, the user can switch
over to the secondary clock using the 2:1 mux.
The PLL accepts reference input frequencies of 62.5,
125, 250, or 312.5MHz and generates output frequencies of 62.5, 125, 156.25, 250, or 312.5MHz. The nine
clock outputs are organized into two groups (A and B).
Each group has a configurable frequency divider and
output-enable control.
Phase-Locked Loop (PLL)
The PLL contains a phase-frequency detector (PFD),
charge pump (CP) with a lowpass filter, and voltagecontrolled oscillator (VCO). The PFD compares the
divided reference frequency to the divided VCO output
at 62.5MHz, and generates a control signal to keep the
VCO phase and frequency locked to the selected reference clock. Using a high-frequency VCO (2.5GHz) and
low-loop bandwidth (40kHz), the MAX3671 attenuates
reference clock jitter while maintaining lock and generates low-jitter clock outputs at multiple frequencies.
Typical jitter generation is 0.3psRMS (integrated 12kHz
to 20MHz).
To minimize supply noise-induced jitter, the VCO supply (VCC_VCO) is isolated from the core logic and output buffer supplies. Additionally, the MAX3671 uses an
internal low-dropout (LDO) regulator to attenuate noise
from the power supply. This allows the device to
achieve excellent power-supply noise rejection, significantly reducing the impact on jitter generation.
Clock Failure Conditions
The MAX3671 clock failure detection is performed
using the combination of amplitude qualification and
PLL frequency and phase-error qualification. The failure
status is indicated for REFCLK0 and REFCLK1 at
_______________________________________________________________________________________
9
MAX3671
Pin Description (continued)
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
IN0FAIL and IN1FAIL, respectively. Once an indicator
is asserted low, it is latched and updated every 128
PFD cycles (~ 2µs).
It should be noted that when the PLL is locked to a reference clock, the clock failure indicator for the other
reference clock is only valid for amplitude qualification
and frequency qualification.
BOTH INPUTS
OPEN
VCC
130Ω
VCC
130Ω
Amplitude Qualification
A reference clock input fails amplitude qualification if
any of the following conditions occur:
• Either one or both inputs (REFCLKx, REFCLKx) are
shorted to VCC or GND.
• Both inputs (REFCLKx, REFCLKx) are disconnected from the source and have 130Ω to VCC and 82Ω
to GND at each input. See Figure 3.
• Input reference clock differential swing is below the
clock failure assert threshold as specified in the
Electrical Characteristics. See Figure 4.
The response time for these conditions is typically
between 50ns and 300ns.
MAX3671
LVPECL
82Ω
82Ω
Figure 3. Positions for Open-Circuit Detection
DIFFERENTIAL INPUT: (REFCLKx - REFCLKx)
Phase Qualification
A reference clock input fails phase qualification when
the phase error at the PFD output exceeds the error
window (0.75ns typical) for more than five of eight PFD
cycles. A reference clock input is qualified when phase
error at the PFD output is within the phase-error window
for eight consecutive PFD cycles. Note that phase qualification only applies to the reference input currently
being used by the PLL.
Frequency Qualification
A reference clock input becomes frequency qualified if
the input frequency is within ±2.4% of the nominal frequency. The reference input becomes frequency disqualified if the input frequency moves away from the
nominal frequency by more than ±8%.
10
0V
VDT
Figure 4. Input Amplitude Detection Threshold
______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
CONNECTION FROM DM PIN
INPUT FREQUENCY (MHz)
GND
62.5
VCC
125
Open
250
10k to GND
312.5
If the frequency difference between the reference clock
input and the VCO at the PFD input becomes within
500ppm, the PLL is considered to be in lock (LOCK =
0). When the frequency difference between the reference clock input and the VCO at the PFD input
becomes greater than 800ppm, the PLL is considered
out-of-lock. It should be noted that the LOCK indicator
is not part of the frequency qualification used for the
INxFAIL indicators.
Table 2. Divider A Configuration for
A-Group Output Frequencies
Input and Output Frequencies
CONNECTION FROM DA PIN
OUTPUT FREQUENCY AT
OUTA[3:0] (MHz)
GND
62.5
VCC
125
Open
156.25
10k to GND
312.5
The MAX3671 input and output dividers are configured
using four-level control inputs DM, DA, and DB. Each
divider is independent and can have a unique setting.
The input connection and associated frequencies are
listed in Tables 1, 2, and 3.
Output-Enable Controls
Each output group (A and B) has a three-level control
input OUTA_EN and OUTB_EN. See Tables 4 and 5 for
configuration settings. When clock outputs are disabled, they are high impedance. Unused enabled outputs should be left open.
Table 3. Divider B Configuration for
B-Group Output Frequencies
CONNECTION FROM DB PIN
OUTPUT FREQUENCY AT
OUTB[4:0] (MHz)
GND
62.5
VCC
125
Open
250
10k to GND
312.5
Power-On-Reset (POR)
At power-on, an internal signal is generated to hold the
MAX3671 in a reset state. This internal reset time is
about 20µs after VCC reaches 3.0V (Figure 2). During
the POR time, the outputs are held to logic-low (OUTxx
= low and OUTxx = high). See Table 6 for output signal
status during POR. After this internal reset time, the PLL
starts to lock to the reference clock selected by
SEL_CLK.
Table 4. OUTA[3:0] Enable Control
CONNECTION FROM OUTA_EN PIN
A-GROUP OUTPUT ENABLED
A-GROUP OUTPUT DISABLED TO HIGH
IMPEDANCE
GND
OUTA0, OUTA1, OUTA2, OUTA3
—
VCC*
—
OUTA0, OUTA1, OUTA2, OUTA3
Open
OUTA0, OUTA1
OUTA2, OUTA3
*Connecting both OUTA_EN and OUTB_EN to VCC enables a factory test mode and forces all indicators to GND. This is not a valid
mode of operation.
Table 5. OUTB[4:0] Enable Control
B-GROUP OUTPUT DISABLED TO HIGH
IMPEDANCE
CONNECTION FROM OUTB_EN PIN
B-GROUP OUTPUT ENABLED
GND
OUTB0, OUTB1, OUTB2, OUTB3, OUTB4
—
VCC*
OUTB0
OUTB1, OUTB2, OUTB3, OUTB4
Open
OUTB0, OUTB1, OUTB2
OUTB3, OUTB4
*Connecting both OUTA_EN and OUTB_EN to VCC enables a factory test mode and forces all indicators to GND. This is not a valid
mode of operation.
______________________________________________________________________________________
11
MAX3671
PLL Out-of-Lock Condition
Table 1. Divider M Configuration for Input
Frequencies
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
Master Reset
After power-up, an external master reset (MR) can be
provided to reset the internal dividers. This input
requires a minimum reset pulse width of 100ns (active
low) and is asynchronous to the reference clock. While
MR is low, all clock outputs are held to logic-low (OUTxx
= low, OUTxx = high). See Table 6 for the output signal
status during master reset. When the master reset input
is deasserted (MR = 1), the PLL starts to lock to the reference clock selected by SEL_CLK.
Master reset is only needed for applications where
divider configurations are changed on the fly and the
clock outputs need to maintain phase alignment. A
master reset is not required at power-up.
External Feedback for Zero-Delay Buffer
The MAX3671 can be operated with either internal or
external PLL feedback path, controlled by the FB_SEL
input. Connecting FB_SEL to GND selects internal feedback. For applications where a known phase relationship between the reference clock input and the external
feedback input (FB_IN, FB_IN) are needed for phase
synchronization, connect FB_SEL to VCC for zero-delay
buffer configuration and provide external feedback to
the FB_IN input.
PLL Bypass Mode
PLL bypass mode is provided for test purposes. In PLL
bypass mode (PLL_BYPASS = 1), the selected reference clock is connected to the LVPECL clock outputs
directly. The output clock frequency is the same as the
input clock frequency and the clock qualification function is not valid. To reduce spurious jitter in bypass
mode, the internal VCO should be disabled by shorting
the CREG pin to GND.
Applications Information
Interfacing with LVPECL Inputs
Figure 5 shows the equivalent LVPECL input circuit for
REFCLK0, REFCLK1, and FB_IN. These inputs are
internally biased to allow AC- or DC-coupling and have
> 40kΩ differential input impedance. When AC-coupled, these inputs can accept LVDS, CML, and
LVPECL signals. Unused reference clock inputs should
be left open.
Interfacing with LVPECL Outputs
Figure 6 shows the equivalent LVPECL output circuit.
These outputs are designed to drive a pair of 50Ω
transmission lines terminated with 50Ω to VTT = VCC 2V. If a separate termination voltage (VTT) is not available, other termination methods can be used such as
those shown in Figures 7 and 8. Unused outputs,
enabled or disabled, can be left open or properly terminated. For more information on LVPECL terminations
and how to interface with other logic families, refer to
Application Note 291: HFAN-01.0: Introduction to LVDS,
PECL, and CML.
Layout Considerations
The clock inputs and outputs are critical paths for the
MAX3671, and care should be taken to minimize discontinuities on the transmission lines. Maintain 100Ω
differential (or 50Ω single-ended) impedance in and out
of the MAX3671. Avoid using vias and sharp corners.
Termination networks should be placed as close as
possible to receiving clock inputs. Provide space
between differential output pairs to reduce crosstalk,
especially if the A and B group outputs are operating at
different frequencies.
Table 6. Output Signal Status During Power-On-Reset or Master Reset
OUTPUT
12
DURING POWER-ON-RESET
(FOR ~ 20μs AFTER VCC > 3.0V)
DURING MASTER RESET
(MR = 0)
NOTES
IN0FAIL
1
Forced high regardless of reference
input qualification.
IN1FAIL
1
Forced high regardless of reference
input qualification.
PLL out-of-lock.
LOCK
1
OUTA[3:0]
Logic-Low
—
OUTB[4:0]
Logic-Low
—
______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
The 56-pin TQFN package features an exposed pad
(EP), which provides a low-resistance thermal path for
heat removal from the IC and must be connected to the
circuit board ground plane for proper operation.
VCC
VCC
VCC - 1.34V
> 20kΩ
> 20kΩ
200Ω
REFCLKx, FB_IN
200Ω
REFCLKx, FB_IN
MAX3671
ESD
STRUCTURES
Figure 5. Equivalent LVPECL Input Circuit
+3.3V
VCC
+3.3V
130Ω
+3.3V
+3.3V
130Ω
Z = 50Ω
LVPECL
OUTxx
LVPECL
Z = 50Ω
82Ω
82Ω
OUTxx
ESD
STRUCTURES
Figure 7. Thevenin Equivalent LVPECL Termination
MAX3671
Figure 6. Equivalent LVPECL Output Circuit
______________________________________________________________________________________
13
MAX3671
Power Supply and Ground Connections
The MAX3671 has seven supply connection pins;
installation of a bypass capacitor at each supply pin is
recommended. All seven supply connections should be
driven from the same source to eliminate the possibility
of independent power-supply sequencing. Excessive
supply noise can result in increased jitter.
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
+3.3V
+3.3V
0.1μF
Z = 50Ω
50Ω
LVPECL
LVPECL
0.1μF
50Ω
0.1μF
Z = 50Ω
150Ω
150Ω
Figure 8. AC-Coupled LVPECL Termination
OUTA1
DA
OUTA1
OUTA0
OUTA0
GND
PLL_BYPASS
VCC
RSVD3
VCC
RSVD4
GND
LOCK
TOP VIEW
IN1FAIL
Pin Configuration
56 55 54 53 52 51 50 49 48 47 46 45 44 43
IN0FAIL 1
42 GND
RSVD1 2
41 VCC
RSVD2 3
40 OUTA2
REFCLK0 4
39 OUTA2
REFCLK0 5
38 OUTA3
DM 6
37 OUTA3
VCC 7
36 OUTA_EN
MAX3671
GND 8
35 OUTB_EN
MR 9
34 OUTB4
REFCLK1 10
33 OUTB4
REFCLK1 11
32 OUTB3
SEL_CLK 12
31 OUTB3
EP*
VCC_VCO 13
30 VCC
GND 14
29 GND
DB
OUTB2
OUTB2
OUTB1
GND
OUTB1
VCC
OUTB0
FB_IN
OUTB0
FB_IN
FB_SEL
CPLL
CREG
15 16 17 18 19 20 21 22 23 24 25 26 27 28
THIN QFN
(8mm × 8mm × 0.8mm)
*THE EXPOSED PAD OF THE TQFN PACKAGE MUST BE SOLDERED TO GROUND FOR PROPER THERMAL AND
ELECTRICAL OPERATION.
14
______________________________________________________________________________________
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
+3.3V
Z = 50Ω
VCC
REFCLK0
VCC_VCO
0.1μF
0.22μF
CREG
CPLL
0.1μF
0.1μF
0.1μF
156.25MHz
Z = 50Ω
OUTA3
50Ω
62.5MHz
BACKPLANE
REFERENCE
CLOCK
50Ω
0.1μF
0.1μF
50Ω
0.1μF
50Ω
0.1μF
Z = 50Ω
REFCLK0
Z = 50Ω
OUTA3
150Ω
MAX3671
REFCLK1
10GE
PHY
150Ω
0.1μF
156.25MHz
Z = 50Ω
OUTA0
50Ω
REFCLK1
0.1μF
10GE
PHY
50Ω
0.1μF
Z = 50Ω
OUTA0
150Ω
150Ω
DM
DA
OUTA_EN
OUTB_EN
DB
OUTB4
+3.3V
0.1μF
125MHz
Z = 50Ω
50Ω
0.1μF
GBE
PHY
50Ω
0.1μF
Z = 50Ω
OUTB4
150Ω
150Ω
SEL_CLK
PLL_BYPASS
0.1μF
FB_IN
FB_IN
FB_SEL
MR
125MHz
Z = 50Ω
OUTB0
50Ω
0.1μF
50Ω
Z = 50Ω
OUTB0
GND
EP
IN1FAIL
IN0FAIL
0.1μF
LOCK
GBE
PHY
150Ω
150Ω
______________________________________________________________________________________
15
MAX3671
Typical Application Circuits
MAX3671
Low-Jitter Frequency Synthesizer
with Selectable Input Reference
Typical Application Circuits (continued)
OUTA[3:0]
62.5MHz
4 x 156.25MHz
MAX3671
8kHz
IN0
CLK0
62.5MHz
REFCLK0
OUTB[4:0]
5 x 125MHz
MAX9450
8kHz
IN1
OUTA[3:0]
4 x 156.25MHz
MAX3671
QA
25MHz
125MHz
REFCLK0
OUTB[4:0]
5 x 312.5MHz
MAX3624
2 x 125MHz
QB[1:0]
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
56 TQFN-EP
T5688+3
21-0135
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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