TI1 LMK00306 3-ghz 6-output differential clock buffer/level translator Datasheet

LMK00306
3-GHz 6-Output Differential Clock Buffer/Level Translator
1.0 General Description
■ Servers, Workstations, and Computing
The LMK00306 is a 3-GHz, 6-output differential fanout buffer
intended for high-frequency, low-jitter clock/data distribution
and level translation. The input clock can be selected from
two universal inputs or one crystal input. The selected input
clock is distributed to two banks of 3 differential outputs and
one LVCMOS output. Both differential output banks can be
independently configured as LVPECL, LVDS, or HCSL
drivers, or disabled. The LVCMOS output has a synchronous
enable input for runt-pulse-free operation when enabled or
disabled. The LMK00306 operates from a 3.3 V core supply
and 3 independent 3.3 V/2.5 V output supplies.
The LMK00306 provides high performance, versatility, and
power efficiency, making it ideal for replacing fixed-output
buffer devices while increasing timing margin in the system.
3.0 Features
2.0 Target Applications
■ Clock Distribution and Level Translation for high-speed
ADCs, DACs, Serial Interfaces (Multi-Gigabit Ethernet,
XAUI, Fibre Channel, PCIe, SATA/SAS, SONET/SDH,
CPRI), and high-frequency backplanes
■ Remote Radio Units (RRU) and Baseband Units (BBU)
■ Switches and Routers
■ 3:1 Input Multiplexer
■
■
■
■
■
■
■
■
— Two universal inputs operate up to 3.1 GHz and accept
LVPECL, LVDS, CML, SSTL, HSTL, HCSL (ACcoupled), or single-ended clocks
— One crystal input accepts a 10 to 40 MHz crystal or
single-ended clock
Two Banks with 3 Differential Outputs each
— LVPECL, LVDS, HCSL, or Hi-Z (selectable per bank)
— LVPECL Additive Jitter with LMK03806 clock source:
■ 20 fs RMS at 156.25 MHz (10 kHz – 1 MHz)
■ 51 fs RMS at 156.25 MHz (12 kHz – 20 MHz)
High PSRR: -65 / -76 dBc (LVPECL/LVDS) at 156.25 MHz
LVCMOS output with synchronous enable input
Pin-controlled configuration
VCC Core Supply: 3.3 V ± 5%
3 Independent VCCO Output Supplies: 3.3 V/2.5 V ± 5%
Industrial temperature range: -40°C to +85°C
Package: 36-pin LLP (6.0 x 6.0 x 0.8 mm)
4.0 Functional Block Diagram
30177401
© 2012 Texas Instruments Incorporated
301774 SNAS578A
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LMK00306 3-GHz 6-Output Differential Clock Buffer/Level Translator
March 14, 2012
LMK00306
5.0 Connection Diagram
36-Pin LLP Package
30177402
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2
Pin #
Pin Name(s)
Type
DAP
DAP
GND
Die Attach Pad. Connect to the PCB ground plane for heat dissipation.
Description
1, 19, 28
GND
GND
Ground
2, 5
VCCOA
PWR
Power supply for Bank A Output buffers. VCCOA can operate from 3.3 V or
2.5 V. The VCCOA pins are internally tied together. Bypass with a 0.1 uF
low-ESR capacitor placed very close to each Vcco pin. (Note 1)
3, 4
CLKoutA0, CLKoutA0*
O
Differential clock output A0. Output type set by CLKoutA_TYPE pins.
6, 7
CLKoutA1, CLKoutA1*
O
Differential clock output A1. Output type set by CLKoutA_TYPE pins.
8, 9
CLKoutA2, CLKoutA2*
O
Differential clock output A2. Output type set by CLKoutA_TYPE pins.
10, 36
CLKoutA_TYPE0,
CLKoutA_TYPE1
I
Bank A output buffer type selection pins (Note 2)
11, 32
Vcc
PWR
12
OSCin
I
Input for crystal. Can also be driven by a XO, TCXO, or other external
single-ended clock.
13
OSCout
O
Output for crystal. Leave OSCout floating if OSCin is driven by a singleended clock.
14, 17
CLKin_SEL0, CLKin_SEL1
I
Clock input selection pins (Note 2)
15, 16
CLKin0, CLKin0*
I
Universal clock input 0 (differential/single-ended)
18, 29
CLKoutB_TYPE0,
CLKoutB_TYPE1
I
Bank B output buffer type selection pins (Note 2)
20, 21
CLKoutB2*, CLKoutB2
O
Differential clock output B2. Output type set by CLKoutB_TYPE pins.
22, 23
CLKoutB1*, CLKoutB1
O
Differential clock output B1. Output type set by CLKoutB_TYPE pins.
24, 27
VCCOB
PWR
25, 26
CLKoutB0*, CLKoutB0
O
Differential clock output B0. Output type set by CLKoutB_TYPE pins.
30, 31
CLKin1*, CLKin1
I
Universal clock input 1 (differential/single-ended)
33
REFout
O
LVCMOS reference output. Enable output by pulling REFout_EN pin high.
34
VCCOC
PWR
Power supply for REFout Output buffer. VCCOC can operate from 3.3 V or
2.5 V. Bypass with a 0.1 uF low-ESR capacitor placed very close to each
Vcco pin. (Note 1)
35
REFout_EN
I
REFout enable input. Enable signal is internally synchronized to selected
clock input. (Note 2)
Power supply for Core and Input buffer blocks. The Vcc supply operates
from 3.3 V. Bypass with a 0.1 uF low-ESR capacitor placed very close to
each Vcc pin.
Power supply for Bank B Output buffers. VCCOB can operate from 3.3 V or
2.5 V. The VCCOB pins are internally tied together. Bypass with a 0.1 uF
low-ESR capacitor placed very close to each Vcco pin. (Note 1)
Note 1: The output supply voltages or pins (VCCOA, VCCOB, and VCCOC) will be called VCCO in general when no distinction is needed, or when the output supply
can be inferred from the output bank/type.
Note 2: CMOS control input with internal pull-down resistor.
Note 3: Any unused output pins should be left floating with minimum copper length (Note 5), or properly terminated if connected to a transmission line, or disabled/
Hi-Z if possible. See Section 7.3 Clock Outputs for output configuration or Section 14.3 Termination and Use of Clock Drivers for output interface and termination
techniques.
3
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LMK00306
6.0 Pin Descriptions
LMK00306
7.3 Clock Outputs
The differential output buffer type for Bank A and Bank B outputs can be separately configured using the CLKoutA_TYPE
[1:0] and CLKoutB_TYPE[1:0] inputs, respectively, as shown
in Table 3. For applications where all differential outputs are
not needed, any unused output pin should be left floating with
a minimum copper length (Note 5) to minimize capacitance
and potential coupling and reduce power consumption. If an
entire output bank will not be used, it is recommended to disable/Hi-Z the bank to reduce power. Refer to Section 14.3
Termination and Use of Clock Drivers for more information on
output interface and termination techniques.
7.0 Functional Description
The LMK00306 is a 6-output differential clock fanout buffer
with low additive jitter that can operate up to 3.1 GHz. It features a 3:1 input multiplexer with an optional crystal oscillator
input, two banks of 3 differential outputs with multi-mode
buffers (LVPECL, LVDS, HCSL, or Hi-Z), one LVCMOS output, and 3 independent output buffer supplies. The input
selection and output buffer modes are controlled via pin strapping. The device is offered in a 36-pin LLP package and
leverages much of the high-speed, low-noise circuit design
employed in the LMK04800 family of clock conditioners.
Note 5: For best soldering practices, the minimum trace length for any
unused output pin should extend to include the pin solder mask. This way
during reflow, the solder has the same copper area as connected pins. This
allows for good, uniform fillet solder joints helping to keep the IC level during
reflow.
7.1 VCC and VCCO Power Supplies
The LMK00306 has separate 3.3 V core supply (VCC) and 3
independent 3.3 V/2.5 V output power supplies (VCCOA,
VCCOB, VCCOC). Output supply operation at 2.5 V enables lower power consumption and output-level compatibility with 2.5
V receiver devices. The output levels for LVPECL (VOH, VOL)
and LVCMOS (VOH) are referenced to the respective Vcco
supply, while the output levels for LVDS and HCSL are relatively constant over the specified Vcco range. Refer to Section 14.4 Power Supply and Thermal Considerations for
additional supply related considerations, such as power dissipation, power supply bypassing, and power supply ripple
rejection (PSRR).
TABLE 3. Differential Output Buffer Type Selection
Note 4: Care should be taken to ensure the Vcco voltages do not exceed
the Vcc voltage to prevent turning-on the internal ESD protection circuitry.
CLKin_SEL0
Selected Input
0
CLKin0, CLKin0*
0
1
CLKin1, CLKin1*
1
X
OSCin
TABLE 2. CLKin Input vs. Output States
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State of
Enabled Outputs
CLKinX and CLKinX*
inputs floating
Logic low
CLKinX and CLKinX*
inputs shorted together
Logic low
CLKin logic low
Logic low
CLKin logic high
Logic high
0
0
LVPECL
0
1
LVDS
1
0
HCSL
1
1
Disabled (Hi-Z)
REFout_EN
REFout State
0
Disabled (Hi-Z)
1
Enabled
The REFout_EN input is internally synchronized with the selected input clock by the SYNC block. This synchronizing
function prevents glitches and runt pulses from occurring on
the REFout clock when enabled or disabled. REFout will be
enabled within 3 cycles (tEN) of the input clock after
REFout_EN is toggled high. REFout will be disabled within 3
cycles (tDIS) of the input clock after REFout_EN is toggled low.
When REFout is disabled, the use of a resistive loading can
be used to set the output to a predetermined level. For example, if REFout is configured with a 1 kΩ load to ground,
then the output will be pulled to low when disabled.
Table 2 shows the output logic state vs. input state when either CLKin0/CLKin0* or CLKin1/CLKin1* is selected. When
OSCin is selected, the output state will be an inverted copy of
the OSCin input state.
State of
Selected CLKin
CLKoutX Buffer Type
(Bank A or B)
TABLE 4. Reference Output Enable
TABLE 1. Input Selection
0
CLKoutX_
TYPE0
7.3.1 Reference Output
The reference output (REFout) provides a LVCMOS copy of
the selected input clock. The LVCMOS output high level is
referenced to the Vcco voltage. REFout can be enabled or
disabled using the enable input pin, REFout_EN, as shown in
Table 4.
7.2 Clock Inputs
The input clock can be selected from CLKin0/CLKin0*,
CLKin1/CLKin1*, or OSCin. Clock input selection is controlled
using the CLKin_SEL[1:0] inputs as shown in Table 1. Refer
to Section 14.1 Driving the Clock Inputs for clock input requirements. When CLKin0 or CLKin1 is selected, the crystal
circuit is powered down. When OSCin is selected, the crystal
oscillator circuit will start-up and its clock will be distributed to
all outputs. Refer to Section 14.2 Crystal Interface for more
information. Alternatively, OSCin may be be driven by a single-ended clock (up to 250 MHz) instead of a crystal.
CLKin_SEL1
CLKoutX_
TYPE1
4
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for
availability and specifications.
Parameter
Supply Voltages
Symbol
VCC, VCCO
Ratings
Units
-0.3 to 3.6
V
VIN
-0.3 to (VCC + 0.3)
V
Input Voltage
TSTG
-65 to +150
°C
Lead Temperature (solder 4 s)
TL
+260
°C
Junction Temperature
TJ
+150
°C
Storage Temperature Range
9.0 Recommended Operating Conditions
Parameter
Symbol
TA
Ambient Temperature Range
Min
Typ
Max
Units
-40
25
85
°C
125
°C
VCC
3.15
3.3
3.45
V
VCCO
3.3 – 5%
2.5 – 5%
3.3
2.5
3.3 + 5%
2.5 + 5%
V
TJ
Junction Temperature
Core Supply Voltage Range
Output Supply Voltage Range (Note 8,
Note 9)
Note 6: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Section 11.0 Electrical
Characteristics. The guaranteed specifications apply only to the test conditions listed.
Note 7: This device is a high-performance integrated circuit with an ESD rating up to 2 kV Human Body Model, up to 150 V Machine Model, and up to 750 V
Charged Device Model and is ESD sensitive. Handling and assembly of this device should only be done at ESD-free workstations.
Note 8: The output supply voltages or pins (VCCOA, VCCOB, and VCCOC) will be called VCCO in general when no distinction is needed, or when the output supply
can be inferred from the output bank/type.
Note 9: Vcco should be less than or equal to Vcc (Vcco ≤ Vcc).
10.0 Package Thermal Resistance
Package
θJA
θJC (DAP)
36-Lead LLP (Note 10)
31.8 °C/W
7.2 °C/W
Note 10: Specification assumes 9 thermal vias connect the die attach pad (DAP) to the embedded copper plane on the 4-layer JEDEC board. These vias play a
key role in improving the thermal performance of the LLP. It is recommended that the maximum number of vias be used in the board layout.
11.0 Electrical Characteristics
Unless otherwise specified: Vcc = 3.3 V ± 5%, Vcco = 3.3 V ± 5%, 2.5 V ±
5%, -40 °C ≤ TA ≤ 85 °C, CLKin driven differentially, input slew rate ≥ 3 V/ns. Typical values represent most likely parametric
norms at Vcc = 3.3 V, Vcco = 3.3 V, TA = 25 °C, and at the Recommended Operation Conditions at the time of product
characterization and are not guaranteed. (Note 8, Note 11)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
CLKinX selected
8.5
10.5
mA
OSCin selected
Current Consumption
ICC_CORE
Core Supply Current, All Outputs
Disabled
10
13.5
mA
ICC_PECL
Additive Core Supply Current,
Per LVPECL Bank Enabled
20
26.5
mA
ICC_LVDS
Additive Core Supply Current,
Per LVDS Bank Enabled
24
29.5
mA
ICC_HCSL
Additive Core Supply Current,
Per HCSL Bank Enabled
29
35
mA
ICC_CMOS
Additive Core Supply Current,
LVCMOS Output Enabled
3.5
5.5
mA
ICCO_PECL
Additive Output Supply Current,
Per LVPECL Bank Enabled
100
123
mA
Includes Output Bank Bias and Load
Currents, RT = 50 Ω to Vcco - 2V on all
outputs in bank
5
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LMK00306
8.0 Absolute Maximum Ratings (Note 6, Note 7)
LMK00306
Symbol
Parameter
ICCO_LVDS
Additive Output Supply Current,
Per LVDS Bank Enabled
ICCO_HCSL
Additive Output Supply Current,
Per HCSL Bank Enabled
ICCO_CMOS
Conditions
Additive Output Supply Current,
LVCMOS Output Enabled
Min
Typ
Max
Units
20
27.5
mA
50
65
mA
Vcco =
3.3 V ± 5%
9
10
mA
Vcco =
2.5 V ± 5%
7
8
mA
Includes Output Bank Bias and Load
Currents, RT = 50 Ω on all outputs in bank
200 MHz,
CL = 5 pF
Power Supply Ripple Rejection (PSRR)
PSRRPECL
Ripple-Induced
Phase Spur Level (Note 13)
Differential LVPECL Output
PSRRLVDS
Ripple-Induced
Phase Spur Level (Note 13)
Differential LVDS Output
PSRRHCSL
Ripple-Induced
Phase Spur Level (Note 13)
Differential HCSL Output
100 kHz, 100 mVpp
Ripple Injected on
Vcco, Vcco = 2.5 V
156.25 MHz
-65
312.5 MHz
-63
156.25 MHz
-76
312.5 MHz
-74
156.25 MHz
-72
312.5 MHz
-63
dBc
dBc
dBc
CMOS Control Inputs (CLKin_SELn, CLKoutX_TYPEn, REFout_EN)
VIH
High-Level Input Voltage
1.6
Vcc
V
VIL
Low-Level Input Voltage
GND
0.4
V
50
µA
IIH
High-Level Input Current
VIH = Vcc, Internal pull-down resistor
IIL
Low-Level Input Current
VIL = 0 V, Internal pull-down resistor
-5
0.1
µA
Clock Inputs (CLKin0/CLKin0*, CLKin1/CLKin1*)
fCLKin
Input Frequency Range
(Note 20)
VIHD
Differential Input High Voltage
VILD
Differential Input Low Voltage
VID
Differential Input Voltage Swing
(Note 14)
VCMD
Differential Input
Common Mode Voltage
VIH
Single-Ended Input
High Voltage
VIL
Single-Ended Input
Low Voltage
VCM
Single-Ended Input
Common Mode Voltage
ISOMUX
Mux Isolation,
CLKin0 to CLKin1
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Functional up to 3.1 GHz
Output frequency range and timing specified
per output type (refer to LVPECL, LVDS,
HCSL, LVCMOS output specifications)
CLKin driven differentially
DC
3.1
GHz
Vcc
V
GND
V
0.15
1.3
VID = 150 mV
0.5
Vcc 1.2
VID = 350 mV
0.5
Vcc 1.1
VID = 800 mV
0.5
Vcc -0.9
VCM +
0.15
Vcc
V
GND
VCM
-0.15
V
0.5
Vcc 1.2
V
CLKinX driven single-ended,
CLKinX* AC coupled to GND
fOFFSET > 50 kHz,
PCLKinX = 0 dBm
6
fCLKin0 = 100 MHz
-84
fCLKin0 = 200 MHz
-82
fCLKin0 = 500 MHz
-71
fCLKin0 = 1000 MHz
-65
V
V
dBc
Parameter
FCLK
External Clock
Frequency Range
(Note 20)
Conditions
Min
Typ
Max
Units
250
MHz
40
MHz
Crystal Interface (OSCin, OSCout)
OSCin driven single-ended,
OSCout floating
Fundamental mode crystal
FXTAL
Crystal Frequency Range
CIN
OSCin Input Capacitance
ESR ≤ 200 Ω (10 to 30 MHz)
ESR ≤ 125 Ω (30 to 40 MHz)
(Note 15)
10
1
pF
LVPECL Outputs (CLKoutAn/CLKoutAn*, CLKoutBn/CLKoutBn*)
fCLKout_FS
fCLKout_RS
Maximum Output Frequency
Full VOD Swing
(Note 20, Note 21)
VOD ≥ 600 mV,
Maximum Output Frequency
Reduced VOD Swing
(Note 20, Note 21)
VOD ≥ 400 mV,
Additive RMS Jitter
Integration Bandwidth
1 MHz to 20 MHz
(Note 16)
Vcco = 3.3 V,
RT = 160 Ω to GND,
RL = 100 Ω
differential
RL = 100 Ω
differential
Vcco = 3.3 V ± 5%,
RT = 160 Ω to GND
1.0
Vcco = 2.5 V ± 5%,
RT = 91 Ω to GND
0.75
1.0
Vcco = 3.3 V ± 5%,
RT = 160 Ω to GND
1.5
3.1
Vcco = 2.5 V ± 5%,
RT = 91 Ω to GND
1.5
2.3
GHz
GHz
CLKin: 100 MHz, Slew
JitterADD
RL = 100 Ω
differential
59
rate ≥ 3 V/ns
CLKin: 156.25 MHz,
64
Slew rate ≥ 2.7 V/ns
CLKin: 625 MHz, Slew
JitterADD
CLKin: 156.25 MHz,
Vcco = 3.3 V,
JSOURCE = 190 fs RMS
(10 kHz to 1 MHz)
RT = 160 Ω to GND,
RL = 100 Ω
differential
20
fs
CLKin: 156.25 MHz,
JSOURCE = 195 fs RMS
(12 kHz to 20 MHz)
51
CLKin: 100 MHz, Slew
Noise Floor
Noise Floor
fOFFSET ≥ 10 MHz
Vcco = 3.3 V,
RT = 160 Ω to GND,
RL = 100 Ω
differential
-162.5
rate ≥ 3 V/ns
CLKin: 156.25 MHz,
-158.1
Slew rate ≥ 2.7 V/ns
CLKin: 625 MHz, Slew
Duty Cycle (Note 20)
VOH
Output High Voltage
VOL
Output Low Voltage
VOD
Output Voltage Swing
(Note 14)
tR
Output Rise Time
20% to 80%
tF
Output Fall Time
80% to 20%
50% input clock duty cycle
TA = 25 °C, DC Measurement,
RT = 50 Ω to Vcco - 2 V
RT = 160 Ω to GND,
RL = 100 Ω differential
7
dBc/Hz
-154.4
rate ≥ 3 V/ns
DUTY
fs
30
rate ≥ 3 V/ns
Additive RMS Jitter with
LVPECL clock source from
LMK03806
(Note 16, Note 17)
1.2
55
%
Vcco 1.2
45
Vcco 0.9
Vcco 0.7
V
Vcco 2.0
Vcco 1.75
Vcco 1.5
V
600
830
1000
mV
175
ps
175
ps
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LMK00306
Symbol
LMK00306
Symbol
Parameter
Conditions
fCLKout_FS
Maximum Output Frequency
Full VOD Swing
(Note 20, Note 21)
RL = 100 Ω differential
fCLKout_RS
Maximum Output Frequency
Reduced VOD Swing
(Note 20, Note 21)
RL = 100 Ω differential
Min
Typ
Max
Units
LVDS Outputs (CLKoutAn/CLKoutAn*, CLKoutBn/CLKoutBn*)
VOD ≥ 250 mV,
VOD ≥ 200 mV,
1.0
1.6
GHz
1.5
2.1
GHz
CLKin: 100 MHz, Slew
JitterADD
Additive RMS Jitter
Integration Bandwidth
1 MHz to 20 MHz
(Note 16)
89
rate ≥ 3 V/ns
Vcco = 3.3 V,
RL = 100 Ω
differential
CLKin: 156.25 MHz,
CLKin: 625 MHz, Slew
37
rate ≥ 3 V/ns
CLKin: 100 MHz, Slew
Noise Floor
Noise Floor
fOFFSET ≥ 10 MHz
-159.5
rate ≥ 3 V/ns
Vcco = 3.3 V,
RL = 100 Ω
differential
CLKin: 156.25 MHz,
-157.0
Slew rate ≥ 2.7 V/ns
CLKin: 625 MHz, Slew
Duty Cycle (Note 20)
VOD
Output Voltage Swing
(Note 14)
ΔVOD
Change in Magnitude of VOD for
Complementary Output States
50% input clock duty cycle
45
55
%
450
mV
50
mV
1.375
V
-35
35
mV
250
TA = 25 °C,
DC Measurement,
RL = 100 Ω differential
dBc/Hz
-152.7
rate ≥ 3 V/ns
DUTY
fs
77
Slew rate ≥ 2.7 V/ns
400
-50
VOS
Output Offset Voltage
ΔVOS
Change in Magnitude of VOS for
Complementary Output States
ISA
ISB
Output Short Circuit Current
Single Ended
TA = 25 °C,
Single ended outputs shorted to GND
-24
24
mA
ISAB
Output Short Circuit Current
Differential
Complementary outputs tied together
-12
12
mA
tR
Output Rise Time
20% to 80%
tF
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Output Fall Time
80% to 20%
1.125
1.25
175
ps
175
ps
RL = 100 Ω differential
8
Parameter
fCLKout
Output Frequency Range
(Note 20)
JitterADD
Additive RMS Jitter
Integration Bandwidth
1 MHz to 20 MHz
(Note 16)
Conditions
Min
Typ
Max
Units
400
MHz
HCSL Outputs (CLKoutAn/CLKoutAn*, CLKoutBn/CLKoutBn*)
RL = 50 Ω to GND, CL ≤ 5 pF
DC
CLKin: 100 MHz, Slew
Vcco = 3.3 V,
RT = 50 Ω to GND
77
rate ≥ 3 V/ns
fs
CLKin: 156.25 MHz,
86
Slew rate ≥ 2.7 V/ns
CLKin: 100 MHz, Slew
Noise Floor
Noise Floor
fOFFSET ≥ 10 MHz
Vcco = 3.3 V,
RT = 50 Ω to GND
-161.3
rate ≥ 3 V/ns
dBc/Hz
CLKin: 156.25 MHz,
-156.3
Slew rate ≥ 2.7 V/ns
DUTY
Duty Cycle (Note 20)
50% input clock duty cycle
45
VOH
Output High Voltage
TA = 25 °C, DC Measurement,
520
VOL
Output Low Voltage
RT = 50 Ω to GND
-150
VCROSS
Absolute Crossing Voltage
(Note 20, Note 22)
RL = 50 Ω to GND,
160
ΔVCROSS
Total Variation of VCROSS
(Note 20, Note 22)
tR
Output Rise Time
20% to 80% (Note 22)
tF
Output Fall Time
80% to 20% (Note 22)
fCLKout
Output Frequency Range
(Note 20)
JitterADD
Additive RMS Jitter
Integration Bandwidth
1 MHz to 20 MHz
(Note 16)
55
%
810
920
mV
0.5
150
mV
350
460
mV
140
mV
CL ≤ 5 pF
250 MHz, RL = 50 Ω to GND,
CL ≤ 5 pF
300
ps
300
ps
LVCMOS Output (REFout)
CL ≤ 5 pF
Vcco = 3.3 V,
100 MHz, Input Slew
CL ≤ 5 pF
rate ≥ 3 V/ns
Noise Floor
Noise Floor
Vcco = 3.3 V,
100 MHz, Input Slew
fOFFSET ≥ 10 MHz
CL ≤ 5 pF
rate ≥ 3 V/ns
DUTY
Duty Cycle (Note 20)
DC
50% input clock duty cycle
45
1 mA load
Vcco 0.1
VOH
Output High Voltage
VOL
Output Low Voltage
IOH
Output High Current (Source)
IOL
Output Low Current (Sink)
tR
Output Rise Time
20% to 80% (Note 22)
tF
Output Fall Time
80% to 20% (Note 22)
CL ≤ 5 pF
tEN
Output Enable Time (Note 23)
tDIS
Output Disable Time (Note 23)
CL ≤ 5 pF
250
95
fs
-159.3
dBc/Hz
55
Vcco = 3.3 V
28
Vcco = 2.5 V
20
Vcco = 3.3 V
28
Vcco = 2.5 V
20
250 MHz, RL = 50 Ω to GND,
9
%
V
0.1
Vo = Vcco / 2
MHz
V
mA
mA
225
ps
225
ps
3
cycles
3
cycles
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LMK00306
Symbol
LMK00306
Symbol
Parameter
Conditions
tPD_PECL
Propagation Delay
CLKin-to-LVPECL
RL = 100 Ω differential
tPD_LVDS
Propagation Delay
CLKin-to-LVDS
RL = 100 Ω differential
tPD_HCSL
Propagation Delay
CLKin-to-HCSL (Note 22)
RT = 50 Ω to GND,
tPD_CMOS
Propagation Delay
CLKin-to-LVCMOS (Note 22)
tSK(O)
Output Skew
LVPECL/LVDS/HCSL
(Note 20, Note 22, Note 24)
tSK(PP)
Part-to-Part Output Skew
LVPECL/LVDS/HCSL
(Note 22, Note 24)
Min
Typ
Max
Units
Propagation Delay and Output Skew
RT = 160 Ω to GND,
CL ≤ 5 pF
CL ≤ 5 pF
360
ps
400
ps
590
ps
Vcco = 3.3 V
1475
Vcco = 2.5 V
1550
Skew specified between any two CLKouts
with the same buffer type. Load conditions
per output type are the same as propagation
delay specifications.
30
ps
50
80
ps
ps
Note 11: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified
or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed.
Note 12: See Section 14.4 Power Supply and Thermal Considerations for more information on current consumption and power dissipation calculations.
Note 13: Power supply ripple rejection, or PSRR, is defined as the single-sideband phase spur level (in dBc) modulated onto the clock output when a single-tone
sinusoidal signal (ripple) is injected onto the Vcco supply. Assuming no amplitude modulation effects and small index modulation, the peak-to-peak deterministic
jitter (DJ) can be calculated using the measured single-sideband phase spur level (PSRR) as follows: DJ (ps pk-pk) = [ (2 * 10(PSRR / 20)) / (π * fCLK) ] * 1E12
Note 14: See Section 12.1 Differential Voltage Measurement Terminology for definition of VID and VOD voltages.
Note 15: The ESR requirements stated must be met to ensure that the oscillator circuitry has no startup issues. However, lower ESR values for the crystal may
be necessary to stay below the maximum power dissipation (drive level) specification of the crystal. Refer to Section 14.2 Crystal Interface for crystal drive level
considerations.
Note 16: For the 100 MHz and 156.25 MHz clock input conditions, Additive RMS Jitter (JADD) is calculated using Method #1: JADD = SQRT(JOUT2 - JSOURCE2),
where JOUT is the total RMS jitter measured at the output driver and JSOURCE is the RMS jitter of the clock source applied to CLKin. For the 625 MHz clock input
condition, Additive RMS Jitter is approximated using Method #2: JADD = SQRT(2*10dBc/10) / (2*π*fCLK), where dBc is the phase noise power of the Output Noise
Floor integrated from 1 to 20 MHz bandwidth. The phase noise power can be calculated as: dBc = Noise Floor + 10*log10(20 MHz - 1 MHz). The additive RMS
jitter was approximated for 625 MHz using Method #2 because the RMS jitter of the clock source was not sufficiently low enough to allow practical use of Method
#1. Refer to the “Noise Floor vs. CLKin Slew Rate” and “RMS Jitter vs. CLKin Slew Rate” plots in Section 13.0 Typical Performance Characteristics.
Note 17: (Note 16)156.25 MHz LVPECL clock source from LMK03806 with 20 MHz crystal reference (crystal part number: ECS-200-20-30BU-DU). JSOURCE =
190 fs RMS (10 kHz to 1 MHz) and 195 fs RMS (12 kHz to 20 MHz). Refer to the LMK03806 datasheet for more information.
Note 18: The noise floor of the output buffer is measured as the far-out phase noise of the buffer. Typically this offset is ≥ 10 MHz, but for lower frequencies this
measurement offset can be as low as 5 MHz due to measurement equipment limitations.
Note 19: Phase noise floor will degrade as the clock input slew rate is reduced. Compared to a single-ended clock, a differential clock input (LVPECL, LVDS)
will be less susceptible to degradation in noise floor at lower slew rates due to its common mode noise rejection. However, it is recommended to use the highest
possible input slew rate for differential clocks to achieve optimal noise floor performance at the device outputs.
Note 20: Specification is guaranteed by characterization and is not tested in production.
Note 21: See Section 13.0 Typical Performance Characteristics for output operation over frequency.
Note 22: AC timing parameters for HCSL or CMOS are dependent on output capacitive loading.
Note 23: Output Enable Time is the number of input clock cycles it takes for the output to be enabled after REFout_EN is pulled high. Similarly, Output Disable
Time is the number of input clock cycles it takes for the output to be disabled after REFout_EN is pulled low. The REFout_EN signal should have an edge transition
much faster than that of the input clock period for accurate measurement.
Note 24: Output skew is the propagation delay difference between any two outputs with identical output buffer type and equal loading while operating at the same
supply voltage and temperature conditions.
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10
12.1 Differential Voltage Measurement Terminology
The differential voltage of a differential signal can be described by two different definitions causing confusion when reading
datasheets or communicating with other engineers. This section will address the measurement and description of a differential
signal so that the reader will be able to understand and discern between the two different definitions when used.
The first definition used to describe a differential signal is the absolute value of the voltage potential between the inverting and
non-inverting signal. The symbol for this first measurement is typically VID or VOD depending on if an input or output voltage is being
described.
The second definition used to describe a differential signal is to measure the potential of the non-inverting signal with respect to
the inverting signal. The symbol for this second measurement is VSS and is a calculated parameter. Nowhere in the IC does this
signal exist with respect to ground, it only exists in reference to its differential pair. VSS can be measured directly by oscilloscopes
with floating references, otherwise this value can be calculated as twice the value of VOD as described in the first description.
Figure 1 illustrates the two different definitions side-by-side for inputs and Figure 2 illustrates the two different definitions side-byside for outputs. The VID (or VOD) definition show the DC levels, VIH and VOL (or VOH and VOL), that the non-inverting and inverting
signals toggle between with respect to ground. VSS input and output definitions show that if the inverting signal is considered the
voltage potential reference, the non-inverting signal voltage potential is now increasing and decreasing above and below the noninverting reference. Thus the peak-to-peak voltage of the differential signal can be measured.
VID and VOD are often defined as volts (V) and VSS is often defined as volts peak-to-peak (VPP).
30177407
FIGURE 1. Two Different Definitions for Differential Input Signals
30177408
FIGURE 2. Two Different Definitions for Differential Output Signals
Note 25: Refer to Application Note AN-912 Common Data Transmission Parameters and their Definitions for more information.
11
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LMK00306
12.0 Measurement Definitions
TA = 25 °C, CLKin driven differentially, input slew rate ≥ 3 V/ns.
LVPECL Output Swing (VOD) vs. Frequency
1.0
Unless otherwise specified: Vcc = 3.3 V, Vcco = 3.3 V,
LVDS Output Swing (VOD) vs. Frequency
0.45
Vcco=2.5 V, Rterm=91 Ω
Vcco=3.3 V, Rterm=160 Ω
0.40
0.8
OUTPUT SWING (V)
OUTPUT SWING (V)
0.9
0.7
0.6
0.5
0.4
0.3
0.2
0.0
100
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.1
0.00
1000
FREQUENCY (MHz)
10000
100
1000
FREQUENCY (MHz)
10000
30177476
30177475
LVDS Output Swing @ 156.25 MHz
0.8
0.4
0.6
0.3
0.4
0.2
OUTPUT SWING (V)
OUTPUT SWING (V)
LVPECL Output Swing @ 156.25 MHz
0.2
0.0
-0.2
-0.4
0.1
0.0
-0.1
-0.2
-0.6
-0.3
-0.8
-0.4
0.0
2.5
5.0
TIME (ns)
7.5
10.0
0.0
2.5
5.0
TIME (ns)
7.5
30177491
LVDS Output Swing @ 1.5 GHz
0.4
0.3
0.3
0.2
0.2
OUTPUT SWING (V)
0.4
0.1
0.0
-0.1
-0.2
-0.3
0
-0.1
-0.2
-0.4
0.25
0.50
TIME (ns)
0.75
1.00
0.00
30177493
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0.1
-0.3
-0.4
0.00
10.0
30177492
LVPECL Output Swing @ 1.5 GHz
OUTPUT SWING (V)
LMK00306
13.0 Typical Performance Characteristics
0.25
0.50
TIME (ns)
0.75
1.00
30177494
12
LVCMOS Output Swing @ 250 MHz
1.0
1.00
Vcco=3.3 V, AC coupled, 50Ω load
Vcco=2.5 V, AC coupled, 50Ω load
0.75
OUTPUT SWING (V)
0.8
OUTPUT SWING (V)
LMK00306
HCSL Output Swing @ 250 MHz
0.6
0.4
0.2
0.0
0.50
0.25
0.00
-0.25
-0.50
-0.75
-0.2
-1.00
0
1
2
3
TIME (ns)
4
5
0
1
2
3
4
TIME (ns)
5
6
30177498
30177499
Noise Floor vs. CLKin Slew Rate @ 100 MHz
-145
LVPECL
LVDS
HCSL
LVCMOS
CLKin Source
-135
Fclk=100 MHz
Foffset=20 MHz
NOISE FLOOR (dBc/Hz)
NOISE FLOOR (dBc/Hz)
-140
Noise Floor vs. CLKin Slew Rate @ 156.25 MHz
-150
-155
-160
-165
-170
-140
LVPECL
LVDS
HCSL
CLKin Source
Fclk=156.25 MHz
Foffset=20 MHz
-145
-150
-155
-160
-165
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL INPUT SLEW RATE (V/ns)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL INPUT SLEW RATE (V/ns)
30177477
30177478
Noise Floor vs. CLKin Slew Rate @ 625 MHz
-140
LVPECL
LVDS
CLKin Source
RMS Jitter vs. CLKin Slew Rate @ 100 MHz (Note 26)
400
Fclk=625 MHz
Foffset=20 MHz
350
RMS JITTER (fs)
NOISE FLOOR (dBc/Hz)
-135
-145
-150
-155
-160
300
LVPECL
LVDS
HCSL
LVCMOS
CLKin Source
Fclk=100 MHz
Int. BW=1-20 MHz
250
200
150
100
50
-165
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL INPUT SLEW RATE (V/ns)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL INPUT SLEW RATE (V/ns)
30177479
30177480
13
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500
LVPECL
LVDS
HCSL
CLKin Source
450
200
Fclk=156.25 MHz
Int. BW=1-20 MHz
LVPECL
LVDS
CLKin Source
175
350
RMS JITTER (fs)
RMS JITTER (fs)
400
300
250
200
150
100
Fclk=625 MHz
Int. BW=1-20 MHz
150
125
100
75
50
25
50
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL INPUT SLEW RATE (V/ns)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL INPUT SLEW RATE (V/ns)
30177482
30177481
-50
LVPECL
LVDS
HCSL
-55
PSRR vs. Ripple Frequency @ 312.5 MHz
RIPPLE INDUCED SPUR LEVEL (dBc)
RIPPLE INDUCED SPUR LEVEL (dBc)
PSRR vs. Ripple Frequency @ 156.25 MHz
Fclk=156.25 MHz
Vcco Ripple=100 mVpp
-60
-65
-70
-75
-80
-85
-90
.1
1
RIPPLE FREQUENCY (MHz)
10
650
Right Y-axis plot
1850
1750
1650
450
1550
350
1450
250
1350
-25
0
25
50
75
TEMPERATURE (°C)
-60
-65
-70
-75
-80
-85
-90
1
RIPPLE FREQUENCY (MHz)
10
LVPECL Phase Noise @ 100 MHz (Note 26)
1950
550
-50
Fclk=312.5 MHz
Vcco Ripple=100 mVpp
REFout PROPAGATION DELAY (ps)
750
LVPECL (0.35 ps/°C)
LVDS (0.35 ps/°C)
HCSL (0.35 ps/°C)
LVCMOS (2.2 ps/°C)
LVPECL
LVDS
HCSL
-55
30177484
Propagation Delay vs. Temperature
850
-50
.1
30177483
CLKout PROPAGATION DELAY (ps)
LMK00306
RMS Jitter vs. CLKin Slew Rate @ 625 MHz
RMS Jitter vs. CLKin Slew Rate @ 156.25 MHz (Note 26)
100
30177485
30177495
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14
HCSL Phase Noise @ 100 MHz (Note 26)
30177497
Crystal Power Dissipation vs. RLIM
(Note 27, Note 28)
LVDS Phase Noise in Crystal Mode
(Note 27, Note 28)
200
-60
20 MHz Crystal
40 MHz Crystal
PHASE NOISE (dBc/Hz)
CRYSTAL POWER DISSIPATION (μW)
30177496
175
LMK00306
LVDS Phase Noise @ 100 MHz (Note 26)
150
125
100
75
50
25
20 MHz Crystal, Rlim = 1.5 kΩ
40 MHz Crystal, Rlim = 1.0 kΩ
-80
-100
-120
-140
-160
-180
0
0
10
500 1k 1.5k 2k 2.5k 3k 3.5k 4k
RLIM (Ω)
100
1k
10k 100k 1M
OFFSET FREQUENCY (Hz)
10M
30177432
30177431
Note 26: The typical RMS jitter values in the plots show the total output RMS jitter (JOUT) for each output buffer type and the source clock RMS jitter (JSOURCE).
From these values, the Additive RMS Jitter can be calculated as: JADD = SQRT(JOUT2 - JSOURCE2).
Note 27: 20 MHz crystal characteristics: Abracon ABL series, AT cut, CL = 18 pF , C0 = 4.4 pF measured (7 pF max), ESR = 8.5 Ω measured (40 Ω max), and
Drive Level = 1 mW max (100 µW typical).
Note 28: 40 MHz crystal characteristics: Abracon ABLS2 series, AT cut, CL = 18 pF , C0 = 5 pF measured (7 pF max), ESR = 5 Ω measured (40 Ω max), and
Drive Level = 1 mW max (100 µW typical).
15
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LMK00306
14.0 Application Information
14.1 Driving the Clock Inputs
The LMK00306 has two universal inputs (CLKin0/CLKin0*
and CLKin1/CLKin1*) that can accept AC- or DC-coupled
3.3V/2.5V LVPECL, LVDS, CML, SSTL, and other differential
and single-ended signals that meet the input requirements
specified in Section 11.0 Electrical Characteristics. The device can accept a wide range of signals due to its wide input
common mode voltage range (VCM ) and input voltage swing
(VID) / dynamic range. For 50% duty cycle and DC-balanced
signals, AC coupling may also be employed to shift the input
signal to within the VCM range. Refer to Section 14.3 Termination and Use of Clock Drivers for signal interfacing and
termination techniques.
To achieve the best possible phase noise and jitter performance, it is mandatory for the input to have high slew rate of
3 V/ns (differential) or higher. Driving the input with a lower
slew rate will degrade the noise floor and jitter. For this reason, a differential signal input is recommended over singleended because it typically provides higher slew rate and
common-mode-rejection. Refer to the “Noise Floor vs. CLKin
Slew Rate” and “RMS Jitter vs. CLKin Slew Rate” plots in
Section 13.0 Typical Performance Characteristics.
While it is recommended to drive the CLKin0 and CLKin1 with
a differential signal input, it is possible to drive them with a
single-ended clock. Again, the single-ended input slew rate
should be as high as possible to minimize performance degradation. The CLKin input has an internal bias voltage of about
1.4 V, so the input can be AC coupled as shown in Figure 3.
30177429
FIGURE 4. Single-Ended LVCMOS Input, DC Coupling
with Common Mode Biasing
If the crystal oscillator circuit is not used, it is possible to drive
the OSCin input with an single-ended external clock as shown
in Figure 5. The input clock should be AC coupled to the OSCin pin, which has an internally-generated input bias voltage,
and the OSCout pin should be left floating. While OSCin provides an alternative input to multiplex an external clock, it is
recommended to use either universal input (CLKinX) since it
offers higher operating frequency, better common mode and
power supply noise rejection, and greater performance over
supply voltage and temperature variations.
30177430
FIGURE 5. Driving OSCin with a Single-Ended Input
14.2 Crystal Interface
The LMK00306 has an integrated crystal oscillator circuit that
supports a fundamental mode, AT-cut crystal. The crystal interface is shown in Figure 6.
30177428
FIGURE 3. Single-Ended LVCMOS Input, AC Coupling
A single-ended clock may also be DC coupled to CLKinX as
shown in Figure 4. If the DC coupled input swing has a common mode level near the device's internal bias voltage of 1.4
V, then only a 0.1 uF bypass cap is required on CLKinX*.
Otherwise, if the input swing is not optimally centered near
the internal bias voltage, then CLKinX* should be externally
biased to the midpoint voltage of the input swing. This can be
achieved using external biasing resistors, RB1 and RB2, or another low-noise voltage reference. The external bias voltage
should be within the specified input common voltage (VCM)
range. This will ensure the input swing crosses the threshold
voltage at a point where the input slew rate is the highest.
30177409
FIGURE 6. Crystal Interface
The load capacitance (CL) is specific to the crystal, but usually
on the order of 18 - 20 pF. While CL is specified for the crystal,
the OSCin input capacitance (CIN = 1 pF typical) of the device
and PCB stray capacitance (CSTRAY ~ 1~3 pF) can affect the
discrete load capacitor values, C1 and C2.
For the parallel resonant circuit, the discrete capacitor values
can be calculated as follows:
CL = (C1 * C2) / (C1 + C2) + CIN + CSTRAY
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16
(1)
LMK00306
Typically, C1 = C2 for optimum symmetry, so Equation 1 can
be rewritten in terms of C1 only:
CL = C12 / (2 * C1) + CIN + CSTRAY
(2)
Finally, solve for C1:
C1 = (CL - CIN - CSTRAY)*2
(3)
30177420
Section 11.0 Electrical Characteristics provides crystal interface specifications with conditions that ensure start-up of the
crystal, but it does not specify crystal power dissipation. The
designer will need to ensure the crystal power dissipation
does not exceed the maximum drive level specified by the
crystal manufacturer. Overdriving the crystal can cause premature aging, frequency shift, and eventual failure. Drive level
should be held at a sufficient level necessary to start-up and
maintain steady-state operation.
The power dissipated in the crystal, PXTAL, can be computed
by:
PXTAL = IRMS2 * RESR*(1 + C0/CL)2
FIGURE 7. Differential LVDS Operation, DC Coupling,
No Biasing by the Receiver
For DC coupled operation of an HCSL driver, terminate with
50 Ω to ground near the driver output as shown in Figure 8.
Series resistors, Rs, may be used to limit overshoot due to
the fast transient current. Because HCSL drivers require a DC
path to ground, AC coupling is not allowed between the output
drivers and the 50 Ω termination resistors.
(4)
Where:
• IRMS is the RMS current through the crystal.
• RESR is the max. equivalent series resistance specified for
the crystal
• CL is the load capacitance specified for the crystal
• C0 is the min. shunt capacitance specified for the crystal
IRMS can be measured using a current probe (e.g. Tektronix
CT-6 or equivalent) placed on the leg of the crystal connected
to OSCout with the oscillation circuit active.
As shown in Figure 6, an external resistor, RLIM, can be used
to limit the crystal drive level, if necessary. If the power dissipated in the selected crystal is higher than the drive level
specified for the crystal with RLIM shorted, then a larger resistor value is mandatory to avoid overdriving the crystal. However, if the power dissipated in the crystal is less than the drive
level with RLIM shorted, then a zero value for RLIM can be used.
As a starting point, a suggested value for RLIM is 1.5 kΩ.
30177490
FIGURE 8. HCSL Operation, DC Coupling
For DC coupled operation of an LVPECL driver, terminate
with 50 Ω to Vcco – 2 V as shown in Figure 9. Alternatively
terminate with a Thevenin equivalent circuit as shown in Figure 10 for Vcco (output driver supply voltage) = 3.3 V and 2.5
V. In the Thevenin equivalent circuit, the resistor dividers set
the output termination voltage (VTT) to Vcco - 2 V.
14.3 Termination and Use of Clock Drivers
When terminating clock drivers keep in mind these guidelines
for optimum phase noise and jitter performance:
• Transmission line theory should be followed for good
impedance matching to prevent reflections.
• Clock drivers should be presented with the proper loads.
— LVDS outputs are current drivers and require a closed
current loop.
— HCSL drivers are switched current outputs and require
a DC path to ground via 50 Ω termination.
— LVPECL outputs are open emitter and require a DC
path to ground.
• Receivers should be presented with a signal biased to
their specified DC bias level (common mode voltage) for
proper operation. Some receivers have self-biasing inputs
that automatically bias to the proper voltage level; in this
case, the signal should normally be AC coupled.
It is possible to drive a non-LVPECL or non-LVDS receiver
with a LVDS or LVPECL driver as long as the above guidelines are followed. Check the datasheet of the receiver or
input being driven to determine the best termination and coupling method to be sure the receiver is biased at the optimum
DC voltage (common mode voltage).
30177421
FIGURE 9. Differential LVPECL Operation, DC Coupling
14.3.1 Termination for DC Coupled Differential Operation
For DC coupled operation of an LVDS driver, terminate with
100 Ω as close as possible to the LVDS receiver as shown in
Figure 7.
17
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LMK00306
DC coupled example in Figure 10, since the voltage divider is
setting the input common mode voltage of the receiver.
30177422
30177424
FIGURE 10. Differential LVPECL Operation, DC Coupling,
Thevenin Equivalent
FIGURE 12. Differential LVPECL Operation, AC Coupling,
Thevenin Equivalent
14.3.2 Termination for AC Coupled Differential Operation
AC coupling allows for shifting the DC bias level (common
mode voltage) when driving different receiver standards.
Since AC coupling prevents the driver from providing a DC
bias voltage at the receiver, it is important to ensure the receiver is biased to its ideal DC level.
When driving non-biased LVDS receivers with an LVDS driver, the signal may be AC coupled by adding DC blocking
capacitors; however the proper DC bias point needs to be
established at the receiver. One way to do this is with the termination circuitry in Figure 11. When driving self-biased
LVDS receivers, the circuit shown in Figure 11 may be modified by replacing the 50 Ω terminations to Vbias with a single
100 Ω resistor across the input pins of the receiver. When
using AC coupling with LVDS outputs, there may be a startup
delay observed in the clock output due to capacitor charging.
The previous example uses a 0.1 μF capacitor, but this may
need to be adjusted to meet the startup requirements for the
particular application. Another variant of AC coupling to a selfbiased LVDS receiver is to move the 0.1 uF capacitors between the 100 Ω differential termination and the receiver
inputs.
14.3.3 Termination for Single-Ended Operation
A balun can be used with either LVDS or LVPECL drivers to
convert the balanced, differential signal into an unbalanced,
single-ended signal.
It is possible to use an LVPECL driver as one or two separate
800 mV p-p signals. When DC coupling one of the LMK00306
LVPECL driver of a CLKoutX/CLKoutX* pair, be sure to properly terminate the unused driver. When DC coupling on of the
LMK00306 LVPECL drivers, the termination should be 50 Ω
to Vcco - 2 V as shown in Figure 13. The Thevenin equivalent
circuit is also a valid termination as shown in Figure 14 for
Vcco = 3.3 V.
30177425
FIGURE 13. Single-Ended LVPECL Operation, DC
Coupling
30177423
FIGURE 11. Differential LVDS Operation, AC Coupling,
No Biasing by the Receiver
LVPECL drivers require a DC path to ground. When AC coupling an LVPECL signal use 160 Ω emitter resistors (or 91
Ω for Vcco = 2.5 V) close to the LVPECL driver to provide a
DC path to ground as shown in Figure 15. For proper receiver
operation, the signal should be biased to the DC bias level
(common mode voltage) specified by the receiver. The typical
DC bias voltage (common mode voltage) for LVPECL receivers is 2 V. Alternatively, a Thevenin equivalent circuit
forms a valid termination as shown in Figure 12 for Vcco = 3.3
V and 2.5 V. Note: this Thevenin circuit is different from the
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30177426
FIGURE 14. Single-Ended LVPECL Operation, DC
Coupling, Thevenin Equivalent
When AC coupling an LVPECL driver use a 160 Ω emitter
resistor (or 91 Ω for Vcco = 2.5 V) to provide a DC path to
ground and ensure a 50 Ω termination with the proper DC bias
level for the receiver. The typical DC bias voltage for LVPECL
18
LMK00306
receivers is 2 V. If the companion driver is not used, it should
be terminated with either a proper AC or DC termination. This
latter example of AC coupling a single-ended LVPECL signal
can be used to measure single-ended LVPECL performance
using a spectrum analyzer or phase noise analyzer. When
using most RF test equipment no DC bias point (0 VDC) is
required for safe and proper operation. The internal 50 Ω termination the test equipment correctly terminates the LVPECL
driver being measured as shown in Figure 15. When using
only one LVPECL driver of a CLKoutX/CLKoutX* pair, be sure
to properly terminated the unused driver.
30177427
FIGURE 15. Single-Ended LVPECL Operation, AC
Coupling
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LMK00306
14.4 Power Supply and Thermal Considerations
14.4.1 Current Consumption and Power Dissipation Calculations
The current consumption values specified in Section 11.0 Electrical Characteristics can be used to calculate the total power dissipation and IC power dissipation for any device configuration. The total VCC core supply current (ICC_TOTAL) can be calculated
using Equation 5:
(5)
ICC_TOTAL = ICC_CORE + ICC_BANK_A + ICC_BANK_B + ICC_CMOS
Where:
•
•
•
•
ICC_CORE is the current for core logic and input blocks and depends on selected input (CLKinX or OSCin).
ICC_BANK_A is the current for Bank A and depends on output type (ICC_PECL, ICC_LVDS, ICC_HCSL, or 0 mA if disabled).
ICC_BANK_B is the current for Bank B and depends on output type (ICC_PECL, ICC_LVDS, ICC_HCSL, or 0 mA if disabled).
ICC_CMOS is the current for the LVCMOS output (or 0 mA if REFout is disabled).
Since the output supplies (VCCOA, VCCOB, VCCOC) can be powered from 3 independent voltages, the respective output supply
currents (ICCO_BANK_A, ICCO_BANK_B, and ICCO_CMOS) should be calculated separately.
ICCO_BANK for either Bank A or B can be directly taken from the corresponding output supply current spec (ICCO_PECL, ICCO_LVDS, or
ICCO_HCSL) provided the output loading matches the specified conditions. Otherwise, ICCO_BANK should be calculated as follows:
ICCO_BANK = IBANK_BIAS + (N * IOUT_LOAD)
(6)
Where:
•
•
•
IBANK_BIAS is the output bank bias current (fixed value).
IOUT_LOAD is the DC load current per loaded output pair.
N is the number of loaded output pairs per bank (N = 0 to 3).
Table 5 shows the typical IBANK_BIAS values and IOUT_LOAD expressions for LVPECL, LVDS, and HCSL.
For LVPECL, it is possible to use a larger termination resistor (RT) to ground instead of terminating with 50 Ω to VTT = Vcco - 2 V;
this technique is commonly used to eliminate the extra termination voltage supply (VTT) and potentially reduce device power
dissipation at the expense of lower output swing. For example, when Vcco is 3.3 V, a RT value of 160 Ω to ground will eliminate
the 1.3 V termination supply without sacrificing much output swing. In this case, the typical IOUT_LOAD is 25 mA, so ICCO_PECL for a
fully-loaded bank reduces to 95 mA (vs. 100 mA with 50 Ω resistors to Vcco – 2 V).
TABLE 5. Typical Output Bank Bias and Load Currents
Current Parameter
LVPECL
LVDS
HCSL
IBANK_BIAS
20 mA
17.4 mA
3.6 mA
IOUT_LOAD
(VOH - VTT)/RT + (VOL - VTT)/RT
0 mA
(No DC load current)
VOH/RT
Once the current consumption is known for each supply, the total power dissipation (PTOTAL) can be calculated as:
PTOTAL = (VCC*ICC_TOTAL) + (VCCOA*ICCO_BANK_A) + (VCCOB*ICCO_BANK_B) + (VCCOC*ICCO_CMOS)
(7)
If the device is configured with LVPECL or HCSL outputs, then it is also necessary to calculate the power dissipated in any
termination resistors (PRT_ PECL and PRT_HCSL) and in any LVPECL termination voltages (PVTT_PECL). The external power dissipation
values can be calculated as follows:
PRT_PECL (per LVPECL pair) = (VOH - VTT)2/RT + (VOL - VTT)2/RT
(8)
PVTT_PECL (per LVPECL pair) = VTT * [(VOH - VTT)/RT + (VOL - VTT)/RT]
(9)
2
PRT_HCSL (per HCSL pair) = VOH / RT
(10)
Finally, the IC power dissipation (PDEVICE) can be computed by subtracting the external power dissipation values from PTOTAL as
follows:
PDEVICE = PTOTAL - N1*(PRT_PECL + PVTT_PECL) - N2*PRT_HCSL
Where:
•
•
N1 is the number of LVPECL output pairs with termination resistors to VTT (usually Vcco - 2 V or GND).
N2 is the number of HCSL output pairs with termination resistors to GND.
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20
(11)
This example shows how to calculate IC power dissipation for a configuration to estimate worst-case power dissipation. In this
case, the maximum supply voltage and supply current values specified in Section 11.0 Electrical Characteristics are used.
•
•
•
•
•
VCC = VCCO = 3.465 V. Max ICC and ICCO values.
CLKin0/CLKin0* input is selected.
Banks A and B are configured for LVPECL: all outputs terminated with 50 Ω to VT = Vcco - 2 V.
REFout is enabled with 5 pF load.
TA = 85 °C
Using the power calculations from the previous section and maximum supply current specifications, we can compute PTOTAL and
PDEVICE.
•
•
•
•
•
•
•
From Equation 5: ICC_TOTAL = 10.5 mA + 22.5 mA + 22.5 mA + 5.5 mA = 61 mA
From ICCO_PECL max spec: ICCO_BANK_A = ICCO_BANK_B = 115 mA
From Equation 7: PTOTAL = 3.465 V * (61 mA + 115 mA + 115 mA + 10 mA) = 1043 mW
From Equation 8: PRT_PECL = ((2.57 V - 1.47 V)2/50 Ω) + ((1.72 V - 1.47 V)2/50 Ω) = 25.5 mW (per output pair)
From Equation 9: PVTT_PECL = 1.47 V * [ ((2.57 V - 1.47 V) / 50 Ω) + ((1.72 V - 1.47 V) / 50 Ω) ] = 39.5 mW (per output pair)
From Equation 10: PRT_HCSL = 0 mW (no HCSL outputs)
From Equation 11: PDEVICE = 1043 mW - (6 * (25.5 mW + 39.5 mW)) - 0 mW = 653 mW
In this worst-case example, the IC device will dissipate about 653 mW or 63% of the total power (1043 mW), while the remaining
37% will be dissipated in the LVPECL emitter resistors (153 mW for 6 pairs) and termination voltage (237 mW into Vcco - 2 V).
Based on θJA of 31.8 °C/W, the estimated die junction temperature would be about 21 °C above ambient, or 106 °C when TA = 85
°C.
21
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LMK00306
14.4.1.1 Power Dissipation Example: Worst-Case Dissipation
LMK00306
phase spur levels for the differential output types at 156.25
MHz and 312.5 MHz . The LMK00306 exhibits very good and
well-behaved PSRR characteristics across the ripple frequency range for all differential output types. The phase spur levels
for LVPECL are below -64 dBc at 156.25 MHz and below -62
dBc at 312.5 MHz. Using Equation 12, these phase spur levels translate to Deterministic Jitter values of 2.57 ps pk-pk at
156.25 MHz and 1.62 ps pk-pk at 312.5 MHz. Testing has
shown that the PSRR performance of the device improves for
Vcco = 3.3 V under the same ripple amplitude and frequency
conditions.
14.4.2 Power Supply Bypassing
The Vcc and Vcco power supplies should have a high-frequency bypass capacitor, such as 0.1 uF or 0.01 uF, placed
very close to each supply pin. 1 uF to 10 uF decoupling capacitors should also be placed nearby the device between the
supply and ground planes. All bypass and decoupling capacitors should have short connections to the supply and ground
plane through a short trace or via to minimize series inductance.
14.4.2.1 Power Supply Ripple Rejection
In practical system applications, power supply noise (ripple)
can be generated from switching power supplies, digital
ASICs or FPGAs, etc. While power supply bypassing will help
filter out some of this noise, it is important to understand the
effect of power supply ripple on the device performance.
When a single-tone sinusoidal signal is applied to the power
supply of a clock distribution device, such as LMK00306, it
can produce narrow-band phase modulation as well as amplitude modulation on the clock output (carrier). In the singleside band phase noise spectrum, the ripple-induced phase
modulation appears as a phase spur level relative to the carrier (measured in dBc).
For the LMK00306, power supply ripple rejection, or PSRR,
was measured as the single-sideband phase spur level (in
dBc) modulated onto the clock output when a ripple signal
was injected onto the Vcco supply. The PSRR test setup is
shown in Figure 16.
14.4.3 Thermal Management
Power dissipation in the LMK00306 device can be high
enough to require attention to thermal management. For reliability and performance reasons the die temperature should
be limited to a maximum of 125 °C. That is, as an estimate,
TA (ambient temperature) plus device power dissipation times
θJA should not exceed 125 °C.
The package of the device has an exposed pad that provides
the primary heat removal path as well as excellent electrical
grounding to the printed circuit board. To maximize the removal of heat from the package a thermal land pattern including multiple vias to a ground plane must be incorporated
on the PCB within the footprint of the package. The exposed
pad must be soldered down to ensure adequate heat conduction out of the package.
A recommended land and via pattern is shown in Figure 17.
More information on soldering LLP packages can be obtained
at: http://www.national.com/analog/packaging/.
A recommended footprint including recommended solder
mask and solder paste layers can be found at: http://
www.national.com/analog/packaging/gerber for the SQA36A
package.
30177440
FIGURE 16. PSRR Test Setup
A signal generator was used to inject a sinusoidal signal onto
the Vcco supply of the DUT board, and the peak-to-peak ripple amplitude was measured at the Vcco pins of the device.
A limiting amplifier was used to remove amplitude modulation
on the differential output clock and convert it to a single-ended
signal for the phase noise analyzer. The phase spur level
measurements were taken for clock frequencies of 156.25
MHz and 312.5 MHz under the following power supply ripple
conditions:
• Ripple amplitude: 100 mVpp on Vcco = 2.5 V
• Ripple frequencies: 100 kHz, 1 MHz, and 10 MHz
Assuming no amplitude modulation effects and small index
modulation, the peak-to-peak deterministic jitter (DJ) can be
calculated using the measured single-sideband phase spur
level (PSRR) as follows:
DJ (ps pk-pk) = [(2*10(PSRR / 20)) / (π*fCLK)] * 1012
30177473
FIGURE 17. Recommended Land and Via Pattern
To minimize junction temperature it is recommended that a
simple heat sink be built into the PCB (if the ground plane
layer is not exposed). This is done by including a copper area
of about 2 square inches on the opposite side of the PCB from
the device. This copper area may be plated or solder coated
to prevent corrosion but should not have conformal coating (if
possible), which could provide thermal insulation. The vias
shown in Figure 17 should connect these top and bottom
copper layers and to the ground layer. These vias act as “heat
pipes” to carry the thermal energy away from the device side
of the board to where it can be more effectively dissipated.
(12)
The “PSRR vs. Ripple Frequency” plots in Section 13.0 Typical Performance Characteristics show the ripple-induced
www.ti.com
22
LMK00306
15.0 Physical Dimensions inches (millimeters) unless otherwise noted
36-Pin LLP (SQA36A) Package
Order Number
Package Marking
LMK00306SQX
LMK00306SQ
Packing
2500 Unit Tape and Reel
LMK00306
1000 Unit Tape and Reel
LMK00306SQE
250 Unit Tape and Reel
23
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LMK00306 3-GHz 6-Output Differential Clock Buffer/Level Translator
Notes
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