Maxim MAX3624 Low-jitter, precision clock generator with four output Datasheet

19-0977; Rev 0; 8/07
Low-Jitter, Precision Clock Generator
with Four Outputs
Features
o Crystal Oscillator Interface: 19.375MHz to 27MHz
The MAX3624 is a low-jitter precision clock generator
optimized for network application. The device integrates a crystal oscillator and a phase-locked loop
(PLL) clock multiplier to generate high-frequency clock
outputs for Ethernet, Fibre Channel, SONET/SDH, and
other networking applications.
Maxim’s proprietary PLL design features ultra-low jitter
(0.36psRMS) and excellent power-supply noise rejection, minimizing design risk for network equipment.
o CMOS Input: 19MHz to 40.5MHz
o Output Frequencies
Ethernet: 62.5MHz, 125MHz, 156.25MHz,
312.5MHz
Fibre Channel: 106.25MHz, 159.375MHz,
212.5MHz, 318.5MHz
SONET/SDH: 77.76MHz, 155.52MHz, 311.04MHz
o Low Jitter
0.14psRMS (1.875MHz to 20MHz)
0.36psRMS (12kHz to 20MHz)
The MAX3624 has three LVPECL outputs and one
LVCMOS output. Selectable output dividers and a
selectable feedback divider allow a range of output
frequencies.
o Excellent Power-Supply Noise Rejection
o No External Loop Filter Capacitor Required
Applications
Ethernet Networking Equipment
Ordering Information
Fibre Channel Storage Area Network
PART
SONET/SDH Network
MAX3624UTJ+
Pin Configuration and Typical Application Circuit appear at
end of data sheet.
TEMP RANGE PIN-PACKAGE
0°C to +85°C
32 TQFN-EP*
PKG
CODE
T3255-3
+Denotes a lead-free package.
*EP = Exposed pad.
Block Diagram
MR
IN_SEL
BYPASS
SELA[1:0]
QAC_OE
LVCMOS
BUFFER
SELA[1:0]
SELB[1:0]
FB_SEL[1:0]
BYPASS
RESET LOGIC/POR
RESET
DIVIDER
NA
RESET
0
LVPECL
BUFFER
QA
QA
620MHz TO 648MHz
PFD
27pF
1
X_IN
QA_OE
0
LVCMOS
REF_IN
QA_C
FILTER
VCO
QB1_OE
1
RESET
RESET
DIVIDER
M
DIVIDER
NB
CRYSTAL
OSCILLATOR
X_OUT
LVPECL
BUFFER
QB1
QB1
QB0_OE
33pF
DIVIDERS:
LVPECL
BUFFER
M = 16, 24, 25, 32
NA = 1, 2, 3, 4, 5, 6, 8, 10, 12
NB = 1, 2, 3, 4, 5, 6, 8, 10, 12
MAX3624
FB_SEL[1:0]
QB0
QB0
SELB[1:0]
________________________________________________________________ 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
MAX3624
General Description
MAX3624
Low-Jitter, Precision Clock Generator
with Four Outputs
ABSOLUTE MAXIMUM RATINGS
Supply Voltage Range VCC, VCCA,
VDDO_A, VCCO_A, VCCO_B ................................-0.3V to +4.0V
Voltage Range at REF_IN, IN_SEL,
FB_SEL[1:0], SELA[1:0], SELB[1:0],
QAC_OE, QA_OE, QB0_OE, QB1_OE,
MR, BYPASS ..........................................-0.3V to (VCC + 0.3V)
Voltage Range at X_IN Pin ...................................-0.3V to +1.2V
Voltage Range at GNDO_A...................................-0.3V to +0.3V
Voltage Range at X_OUT Pin ......................-0.3V to (VCC - 0.6V)
Current into QA_C ...........................................................±50mA
Current into QA, QA, QB0, QB0, QB1, QB1 .....................-56mA
Continuous Power Dissipation (TA = +70°C)
32-Pin TQFN (derate 34.5mW/°C above +70°C) .......2759mW
Operating Junction Temperature Range ...........-55°C to +150°C
Storage Temperature Range .............................-65°C to +160°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 = 0°C to +85°C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +25°C, unless otherwise
noted.) (Notes 1, 2, and 3)
PARAMETER
Power-Supply Current
SYMBOL
ICC
CONDITIONS
MIN
(Note 4)
TYP
MAX
UNITS
77
100
mA
CONTROL INPUT CHARACTERISTICS
(SELA[1:0], SELB[1:0], FB_SEL[1:0], IN_SEL, QAC_OE, QA_OE, QB1_OE, QB0_OE, MR, BYPASS Pins)
Input Capacitance
Input Pulldown Resistor
Input Logic Bias Resistor
Input Pullup Resistor
CIN
2
pF
75
kΩ
Pins SELA[1:0], SELB[1:0], QB0_OE
50
kΩ
Pins QAC_OE, QA_OE, QB1_OE, IN_SEL,
BYPASS
75
kΩ
RPULLDOWN Pins MR, FB_SEL[1:0]
RBIAS
RPULLUP
LVPECL OUTPUTS (QA, QA, QB0, QB0, QB1, QB1 PINS)
Output High Voltage
VOH
VCC 1.13
VCC 0.98
VCC 0.83
V
Output Low Voltage
VOL
VCC 1.85
VCC 1.7
VCC 1.55
V
Peak-to-Peak Output-Voltage
Swing (Single-Ended)
(Note 2)
0.6
0.72
0.9
VP-P
Clock Output Rise/Fall Time
20% to 80% (Note 2)
200
350
600
ps
PLL enabled
48
50
52
PLL bypassed (Note 5)
40
50
60
Output Duty-Cycle Distortion
%
LVCMOS/LVTTL INPUTS
(SELA[1:0], SELB[1:0], FB_SEL[1:0], IN_SEL, QAC_OE, QA_OE, QB1_OE, QB0_OE, MR, BYPASS Pins)
Input-Voltage High
VIH
Input-Voltage Low
VIL
Input High Current
IIH
VIN = VCC
Input Low Current
IIL
VIN = 0V
2
2.0
-80
_______________________________________________________________________________________
V
0.8
V
80
µA
µA
Low-Jitter, Precision Clock Generator
with Four Outputs
(VCC = +3.0V to +3.6V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +25°C, unless otherwise
noted.) (Notes 1, 2, and 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
REF_IN SPECIFICATIONS (Input DC- or AC-Coupled)
Reference Clock Frequency
PLL enabled
40.5
PLL bypassed
320
Input-Voltage High
VIH
Input-Voltage Low
VIL
Input High Current
IIH
VIN = VCC
Input Low Current
IIL
VIN = 0V
Reference Clock Duty Cycle
2.0
PLL enabled
V
0.8
V
240
µA
-240
µA
30
Input Capacitance
MHz
70
2.5
%
pF
QA_C SPECIFICATIONS
Output High Voltage
VOH
QA_C sourcing 12mA
Output Low Voltage
VOL
QA_C sinking 12mA
Output Rise/Fall Time
Output Duty Cycle Distortion
2.6
V
0.4
V
ps
(Notes 3 and 6)
250
500
1000
PLL enabled
42
50
58
PLL bypassed (Note 5)
40
Output Impedance
60
%
Ω
14
CLOCK OUTPUT AC SPECIFICATIONS
VCO Frequency Range
Random Jitter (Note 7)
Total Time Interval Error (TIE)
with Supply Noise
(Notes 7, 8, and 9)
Total Time Interval Error (TIE)
Without Supply Noise
(Notes 7, 8)
Spurs Induced by Power-Supply
Noise (Notes 7, 9, 10)
Nonharmonic and Subharmonic
Spurs
620
RJRMS
648
12kHz to 20MHz
0.36
1.875MHz to 20MHz
0.14
LVPECL output
14
LVCMOS output
25
1.0
MHz
psRMS
psP-P
0.9
psRMS
9
psP-P
LVPECL output, LVCMOS output
LVPECL output
-57
LVCMOS output
-47
-70
dBc
dBc
_______________________________________________________________________________________
3
MAX3624
ELECTRICAL CHARACTERISTICS (continued)
MAX3624
Low-Jitter, Precision Clock Generator
with Four Outputs
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +25°C unless otherwise
noted.) (Notes 1, 2, and 3)
PARAMETER
SYMBOL
Output Skew
CONDITIONS
MIN
15
Between QA and QB0 or QB1,
PECL outputs
20
f = 1kHz
Clock Output SSB Phase Noise
at 125MHz (Note 11)
TYP
Between QB0 and QB1
MAX
UNITS
ps
-124
f = 10kHz
-125
f = 100kHz
-130
f = 1MHz
-145
f > 10MHz
-153
dBc/Hz
A series resistor of up to 10.5Ω is allowed between VCC and VCCA for filtering supply noise when system power-supply tolerance is VCC = 3.3V ±5%. See Figure 3.
Note 2: Guaranteed up to 320MHz for LVPECL output.
Note 3: Guaranteed up to 160MHz for LVCMOS output.
Note 4: All outputs enabled and unloaded. IN_SEL set high.
Note 5: Measured with crystal or AC-coupled, 50% duty-cycle signal on REF_IN.
Note 6: Measured using setup shown in Figure 1 with VCC = 3.3V ±5%.
Note 7: Measured with crystal source.
Note 8: Total TIE including random and deterministic jitter. Measured with Agilent DSO81304A 40GS/s real-time oscilloscope
using 2M sample record length.
Note 9: Measured with 40mVP-P, 100kHz sinusoidal signal on the supply.
Note 10: Measured at 156.25MHz output.
Note 11: Measured with 25MHz crystal or 25MHz reference clock at LVCMOS input with a slew rate of 0.5V/ns or greater.
Note 1:
36Ω
MAX3624
499Ω
OSCILLOSCOPE
0.1μF
Z0 = 50Ω
QA_C
4.7pF
50Ω
Figure 1. LVCMOS Output Measurement Setup
4
_______________________________________________________________________________________
Low-Jitter, Precision Clock Generator
with Four Outputs
SUPPLY CURRENT
vs. TEMPERATURE
DIFFERENTIAL OUTPUT WAVEFORM
AT 156.25MHz (LVPECL OUTPUT)
MAX3624 toc02
MAX3624 toc03
MAX3624 toc01
250
ALL OUTPUTS ACTIVE AND TERMINATED
175
150
125
100
ALL OUTPUTS ACTIVE AND UNTERMINATED
75
AMPLITUDE (50mV/div)
200
MEASURED USING 50Ω OSCILLOSCOPE INPUT
THROUGH NETWORK SHOWN IN FIGURE 1
AMPLITUDE (200mv/div)
225
SUPPLY CURRENT (mA)
OUTPUT WAVEFORM AT 125MHz
(LVCMOS OUTPUT)
50
25
0
0
10
20
30
40
50
60
70
80
90
1ns/div
1ns/div
PHASE NOISE AT 125MHz
CLOCK FREQUENCY
PHASE NOISE AT 212.5MHz
CLOCK FREQUENCY
(26.5625MHz CRYSTAL)
AMBIENT TEMPERATURE (°C)
-90
-120
-130
-100
-110
-120
-130
-100
-110
-120
-130
-140
-140
-140
-150
-150
-150
-160
-160
1
10
100
1000 10,000 100,000
-160
0.1
OFFSET FREQUENCY (kHz)
1
10
100
1000 10,000 100,000
0.1
1
OFFSET FREQUENCY (kHz)
JITTER HISTOGRAM (312.5MHz OUTPUT,
40mVP-P SUPPLY NOISE AT 100kHz)
MAX3624 toc07
0
fC = 312.5MHz
NOISE AMPLITUDE = 40mVP-P
-10
DJ = 5.6psP-P
10
100
1000 10,000 100,000
OFFSET FREQUENCY (kHz)
SPURS INDUCED BY POWER-SUPPLY NOISE
vs. NOISE FREQUENCY
SPUR AMPLITUDE (dBc)
0.1
-20
MAX3624 toc08
-110
-90
AMPLITUDE (dBc/Hz)
AMPLITUDE (dBc/Hz)
-100
-80
MAX3624 toc05
-90
AMPLITUDE (dBc/Hz)
-80
MAX3624 toc04
-80
MAX3624 toc06
PHASE NOISE AT 312.5MHz
CLOCK FREQUENCY
-30
-40
-50
-60
-70
DJ + RJ = 14psP-P
5ps/div
-80
-90
10
100
1000
10,000
NOISE FREQUENCY (kHz)
_______________________________________________________________________________________
5
MAX3624
Typical Operating Characteristics
(Typical values are at VCC = +3.3V, TA = +25°C, crystal frequency = 25MHz.)
Low-Jitter, Precision Clock Generator
with Four Outputs
MAX3624
Pin Description
6
PIN
NAME
1
VCCO_B
2, 19, 24
GND
3
QB0_OE
4, 5
SELB1,
SELB0
6
QAC_OE
7
MR
8
GNDO_A
FUNCTION
Power Supply for QB0 and QB1 Clock Outputs. Connect to +3.3V.
Supply Ground
LVCMOS/LVTTL Input. Enables/disables QB0 clock output. Connect pin high or leave open to enable
LVPECL clock output QB0. Connect low to set QB0 to a logic 0. Has internal 50k input impedance.
LVCMOS/LVTTL Input. Controls NB divider setting. Has 50k input impedance. See Table 2 for
more information.
LVCMOS/LVTTL Input. Enables/disables QA_C clock output. Connect pin high or leave open to enable
QA_C. Connect low to set QA_C to a high-impedance state. Has internal 75k pullup to VCC.
LVCMOS/LVTTL Input. Master reset input. Pulse high for > 1μs to reset all dividers. Has internal
75k pulldown to GND. Not required for normal operation.
Ground for QA_C Output. Connect to supply ground.
9
QA_C
10
VDDO_A
Power Supply for QA_C Clock Output. Connect to +3.3V.
LVCMOS Clock Output
11
VCCO_A
Power Supply for QA Clock Output. Connect to +3.3V.
12
QA
Noninverting Clock Output, LVPECL
13
QA
Inverting Clock Output, LVPECL
14
BYPASS
15, 16
FB_SEL1,
FB_SEL0
LVCMOS/LVTTL Input. Controls M divider setting. See Table 3 for more information. Has internal
75k pulldown to GND.
17
VCCA
Analog Power Supply for the VCO. Connect to +3.3V. For additional power-supply noise filtering,
this pin can connect to VCC through 10.5 as shown in Figure 2 (requires VCC = +3.3V ±5%).
18
VCC
Core Power Supply. Connect to +3.3V.
20
QA_OE
LVCMOS/LVTTL Input. Enables/disables the QA clock output. Connect this pin high or leave open to
enable the LVPECL clock output QA. Connect low to set QA to a logic 0. Has internal 75k pullup to VCC.
21, 22
SELA0,
SELA1
LVCMOS/LVTTL Input. Controls NA divider setting. See Table 2 for more information. Has 50k
input impedance.
23
QB1_OE
25
X_OUT
26
X_IN
27
REF_IN
LVCMOS Reference Clock Input. Self-biased to allow AC- or DC-coupling.
28
IN_SEL
LVCMOS/LVTTL Input. Connect high or leave open to use a crystal. Connect low to use REF_IN.
Has internal 75k pullup to VCC.
29
QB1
LVPECL, Inverting Clock Output
30
QB1
LVPECL, Noninverting Clock Output
31
QB0
LVPECL, Inverting Clock Output
32
QB0
—
EP
LVCMOS/LVTTL Input (Active Low). Connect low to bypass the internal PLL. Connect high or leave
open for normal operation. When in bypass mode the output dividers are set to divide by 1. Has
internal 75k pullup to VCC.
LVCMOS/LVTTL Input. Enables/disables QB1 clock output. Connect pin high or leave open to enable
LVPECL clock output QB1. Connect low to set QB1 to a logic 0. Has internal 50k input impedance.
Crystal Oscillator Output
Crystal Oscillator Input
LVPECL, Noninverting Clock Output
Exposed Pad. Connect to supply ground for proper electrical and thermal performance.
_______________________________________________________________________________________
Low-Jitter, Precision Clock Generator
with Four Outputs
The MAX3624 is a low-jitter clock generator designed
to operate at Ethernet, Fibre Channel, and SONET/SDH
frequencies. It consists of an on-chip crystal oscillator,
PLL, programmable dividers, LVCMOS output buffer,
and LVPECL output buffers. Using a low-frequency
clock (crystal or CMOS input) as a reference, the internal PLL generates a high-frequency output clock with
excellent jitter performance.
Crystal Oscillator
An integrated oscillator provides the low-frequency reference clock for the PLL. This oscillator requires an
external crystal connected between X_IN and X_OUT.
Crystal frequency is 19.375MHz to 27MHz.
REF_IN Buffer
An LVCMOS-compatible clock source can be connected to REF_IN to serve as the reference clock.
The LVCMOS REF_IN buffer is internally biased to allow
AC- or DC-coupling. It is designed to operate up to
320MHz.
PLL
The PLL takes the signal from the crystal oscillator or
reference clock input and synthesizes a low-jitter, highfrequency clock. The PLL contains a phase-frequency
detector (PFD), a lowpass filter, and a voltage-controlled oscillator (VCO) with a 620MHz to 648MHz operating range. The VCO output is connected to the PFD
input through a feedback divider. See Table 3 for
divider values. The PFD compares the reference frequency to the divided-down VCO output (fVCO/M) and
generates a control signal that keeps the VCO locked
to the reference clock. The high-frequency VCO output
clock is sent to the output dividers. To minimize noiseinduced jitter, the VCO supply (VCCA) is isolated from
the core logic and output buffer supplies.
LVPECL Drivers
The high-frequency outputs—QA, QB0, and QB1—are
differential PECL buffers designed to drive transmission
lines terminated with 50Ω to VCC - 2.0V. The maximum
operating frequency is specified up to 320MHz. Each
output can be individually disabled, if not used. The
outputs go to a logic 0 when disabled.
LVCMOS Driver
QA_C, the LVCMOS output, is designed to drive a single-ended high-impedance load. The maximum operating frequency is specified up to 160MHz. This output
can be disabled by the QAC_OE pin if not used and
goes to a high impedance when disabled.
Reset Logic/POR
During power-on, the power-on reset (POR) signal is
generated to synchronize all dividers. An external master reset (MR) signal is not required.
Applications Information
Power-Supply Filtering
The MAX3624 is a mixed analog/digital IC. The PLL
contains analog circuitry susceptible to random noise.
In addition to excellent on-chip power-supply noise
rejection, the MAX3624 provides a separate powersupply pin, VCCA, for the VCO circuitry. Figure 2 illustrates the recommended power-supply filter network for
V CCA . The purpose of this design technique is to
ensure clean input power supply to the VCO circuitry
and to improve the overall immunity to power-supply
noise. This network requires that the power supply is
+3.3V ±5%. Decoupling capacitors should be used on
all other supply pins for best performance.
+3.3V ±5%
VCC
0.1μF
Output Dividers
The output divider is programmable to allow a range of
output frequencies. See Table 2 for the divider input
settings. The output dividers are automatically set to
divide by 1 when the MAX3624 is in bypass mode
(BYPASS = 0).
10.5Ω
VCCA
0.1μF
10μF
Figure 2. Analog Supply Filtering
_______________________________________________________________________________________
7
MAX3624
Detailed Description
MAX3624
Low-Jitter, Precision Clock Generator
with Four Outputs
Table 1. Output Frequency Determination Chart
XO OR CMOS
INPUT
FREQUENCY
(MHz)
25
25.78125
26.04166
26.5625
19.44
38.88
(CMOS input)
FEEDBACK
DIVIDER, M
25
25
24
24
32
16
VCO
FREQUENCY
(MHz)
625
644.53125
625
637.5
622.08
622.08
Output Divider Configuration
Table 2 shows the input settings required to set the output dividers. Leakage in the OPEN case must be less
than 1µA. Note that when the MAX3624 is in bypass
mode (BYPASS set low), the output dividers are automatically set to divide by 1.
OUTPUT
FREQUENCY
(MHz)
OUTPUT
DIVIDER,
NA AND NB
2
312.5
4
156.25
5
125
8
78.125
10
62.5
4
161.132812
2
312.5
4
156.25
5
125
8
78.125
10
62.5
2
318.75
3
212.5
4
159.375
6
106.25
12
53.125
2
311.04
4
155.52
8
77.76
2
311.04
4
155.52
8
77.76
APPLICATIONS
Ethernet
10Gbps Ethernet
Ethernet
Fibre Channel
SONET/SDH
SONET/SDH
Table 2. Output Divider Configuration Chart
INPUT
NA/NB DIVIDER
SELA1/SELB1
SELA0/SELB0
0
0
/ 2*
0
1
/ 3*
1
0
/4
1
1
/5
1
OPEN
/6
OPEN
1
/8
0
OPEN
/ 10
OPEN
0
/ 12
OPEN
OPEN
/ 1*
*Maximum guaranteed output frequency is 160MHz for CMOS
and 320MHz for LVPECL output.
8
_______________________________________________________________________________________
Low-Jitter, Precision Clock Generator
with Four Outputs
Crystal Selection
The crystal oscillator is designed to drive a fundamental mode, AT-cut crystal resonator. See Table 4 for recommended crystal specifications. See Figure 4 for
external capacitance connection.
Table 3. PLL Divider Configuration Chart
INPUT
M DIVIDER
FB_SEL1
FB_SEL0
0
0
/ 25
0
1
/ 24
1
0
/ 32
1
1
/ 16
Crystal Input Layout and Frequency
Stability
The crystal, trace, and two external capacitors should
be placed on the board as close as possible to the
MAX3624’s X_IN and X_OUT pins to reduce crosstalk
of active signals into the oscillator.
The layout shown in Figure 3 gives approximately 3pF
of trace plus footprint capacitors per side of the crystal
(Y1). The dielectric material is FR-4 and dielectric thickness of the reference board is 15 mils. Using a 25MHz
crystal and the capacitor values of C22 = 27pF and
C23 = 33pF, the measured output frequency accuracy
is -14ppm at +25°C ambient temperature.
Table 4. Crystal Selection Parameters
PARAMETER
Crystal Oscillation Frequency
SYMBOL
MIN
fOSC
19.375
TYP
MAX
UNITS
27
MHz
7.0
Shunt Capacitance
CO
2.0
Load Capacitance
CL
18
Equivalent Series Resistance
(ESR)
RS
Maximum Crystal Drive Level
pF
pF
50
Ω
300
µW
27pF
X_IN
CRYSTAL
(CL = 18pF)
X_OUT
33pF
Figure 4. Crystal, Capacitors Connection
Figure 3. Crystal Layout
_______________________________________________________________________________________
9
MAX3624
PLL Divider Configuration
Table 3 shows the input settings required to set PLL
feedback divider.
MAX3624
Low-Jitter, Precision Clock Generator
with Four Outputs
Interfacing with LVPECL Outputs
Interface Models
The equivalent LVPECL output circuit is given in Figure
8. 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 terminations methods can be used such as
shown in Figure 5 and Figure 6. Unused outputs should
be disabled and may be left open. For more information
on LVPECL terminations and how to interface with other
logic families, refer to Maxim Application Note HFAN01.0: Introduction to LVDS, PECL, and CML.
Figure 7, Figure 8, and Figure 9 show examples of
interface models.
VCC
VB = 1.4V
VCC
VB
14.5kΩ
VB
REF_IN
+3.3V
130Ω
MAX3624 Qx
Z0 = 50Ω
Qx
Z0 = 50Ω
130Ω
ESD
STRUCTURES
HIGH
IMPEDANCE
Figure 7. Simplified REF_IN Pin Circuit Schematic
82Ω
82Ω
VCC
Figure 5. Thevenin Equivalent of Standard PECL Termination
0.1μF
Z0 = 50Ω
Qx
100Ω
MAX3624
0.1μF
Qx
HIGH
IMPEDANCE
Qx
Z0 = 50Ω
Qx
150Ω
150Ω
NOTE: AC-COUPLING IS OPTIONAL.
ESD
STRUCTURES
Figure 6. AC-Coupled PECL Termination
Figure 8. Simplified LVPECL Output Circuit Schematic
10
______________________________________________________________________________________
Low-Jitter, Precision Clock Generator
with Four Outputs
The exposed pad on the 32-pin TQFN package provides a very low inductance path for return current traveling to the PCB ground plane. The pad is also
electrical ground on the MAX3624 and must be soldered to the circuit board ground for proper electrical
performance.
DISABLE
10Ω
IN
QAC
Pin Configuration
SELB1
4
SELB0
5
QAC_OE
6
• An uninterrupted ground plane should be positioned beneath the clock I/Os.
• Ground pin vias should be placed close to the IC
and the input/output interfaces to allow a return
current path to the MAX3624 and the receive
devices.
• Supply decoupling capacitors should be placed
close to the MAX3624 supply pins.
• Maintain 100Ω differential (or 50Ω single-ended)
transmission line impedance out of the MAX3624.
• Use good high-frequency layout techniques and
multilayer boards with an uninterrupted ground
plane to minimize EMI and crosstalk.
Refer to the MAX3624 Evaluation Kit for more information.
MR
7
GNDO_A
8
QB0
QB1
QB1
IN_SEL
REF_IN
X_IN
X_OUT
26
25
+
MAX3624
*EP
9
10
11
12
13
14
15
16
FB_SEL0
Layout Considerations
The inputs and outputs are critical paths for the
MAX3624, and care should be taken to minimize discontinuities on these transmission line. Here are some
suggestions for maximizing the MAX3624’s performance:
27
BYPASS
3
28
FB_SEL1
QB0_OE
Figure 9. Simplified LVCMOS Output Circuit Schematic
29
QA
2
30
QA
1
GND
31
VCCO_A
VCCO_B
32
VDDO_A
ESD
STRUCTURES
QA_C
TOP VIEW
QB0
10Ω
24
GND
23
QB1_OE
22
SELA1
21
SELA0
20
QA_OE
19
GND
18
VCC
17
VCCA
THIN QFN-EP
(5mm × 5mm)
*EXPOSED PAD CONNECTED TO GROUND.
Chip Information
TRANSISTOR COUNT: 10,780
PROCESS: BiCMOS
______________________________________________________________________________________
11
MAX3624
Exposed-Pad Package
VDDO_A
MAX3624
Low-Jitter, Precision Clock Generator
with Four Outputs
Typical Application Circuit
+3.3V ±5%
0.01μF
10.5Ω
VCC
10μF
VCCO_A
VCCO_B
36Ω
Z0 = 50Ω
QA_C
VCCA
0.1μF
VDDO_A
0.1μF
ASIC
125MHz
MR
REF_IN
IN_SEL
QA
Z0 = 50Ω
QA
Z0 = 50Ω
ASIC
125MHz
QAC_OE
50Ω
50Ω
QA_OE
QB0_OE
VCC
(VCC - 2V)
QB1_OE
MAX3624
BYPASS
QB0
Z0 = 50Ω
QB0
Z0 = 50Ω
ASIC
312.5MHz
SELA1
50Ω
SELA0
50Ω
SELB1
(VCC - 2V)
SELB0
FB_SEL1
QB1
Z0 = 50Ω
FB_SEL0
QB1
Z0 = 50Ω
X_OUT
X_IN
GND
GNDO_A
312.5MHz
50Ω
25MHz
(CL = 18pF)
33pF
ASIC
50Ω
(VCC - 2V)
27pF
Package Information
For the latest package outline information, go to
www.maxim-ic.com/packages.
PACKAGE TYPE
DOCUMENT NO.
32 TQFN-EP
21-0140
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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© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.