SM840021 [MICREL]
125MHz Ultra-Low Jitter Clock Synthesizer; 125MHz的超低抖动时钟合成器
| 型号： | SM840021 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | 125MHz Ultra-Low Jitter Clock Synthesizer |
| 文件： | 总10页 (文件大小：342K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SM840021
125MHz Ultra-Low Jitter Clock Synthesizer
General Description
Features
The SM840021 synthesizer was designed for Ethernet
applications. This clock synthesizer is optimized for
125MHz using a standard 25MHz fundamental parallel
resonant crystal, with unparalleled stability and accuracy
over the full operating range. The SM840021 design
includes a unique power reduction methodology, along
with a patented RotaryWaveTM architecture that provides a
very stable clock with very low noise for optimized
performance yielding an overall improved Bit Error Rate
(BER) and improved waveform integrity.
• Generates an optimized 125MHz LVCMOS Output
• Integrated loop filter components
• RMS Phase Jitter: 250 fs (typ)
• Operates with either a 3.3V or 2.5V supply
• Power consumption is <77mA @ 3.3V
• Input frequency: 25MHz parallel resonant crystal
• Output frequency: 125MHz
• Temperature range: –40°C to +75°C
• Green, RoHS-compliant and PFOS-compliant
• Available in 8-pin TSSOP package
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Applications
• Gigabit Ethernet
• Datacom/Telecom
• Ethernet Switch
___________________________________________________________________________________________________________
Block Diagram
RotaryWave is a registered trademark of Multigig, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
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March 2010
Micrel, Inc.
SM840021
Ordering Information(1)
Part Number
Package
Type
Operating Range
Package Marking
Lead
Finish
SM840021KA
SM840021KA TR(2)
Note:
K-8
K-8
-40°C to +75°C
-40°C to +75°C
840021
840021
NiPdAu
NiPdAu
1. Devices are Green, RoHS-compliant and PFOS-compliant.
2. Tape and Reel
Pin Configuration
8-Pin TSSOP (K-8)
Pin Description
Pin Number
Pin Name
VDDA
Type
Level
Pin Function
Analog Power.
1
2
3
4
5
6
7
8
P
I
OE
Pull-up
Output Enable: 1 = Enable, 0 = Disable.
Crystal Output.
XTAL OUT
XTAL IN
NC
O
I
Crystal Input.
No Connect.
GND
P
O
P
Ground.
Q0
Single Ended LVCMOS Clock Out.
Core Power.
VDD
Output Enable
OE
0
Output
Disable
Enable
1
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Micrel, Inc.
SM840021
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VDD)...................................................+4.6V
Input Voltage (VIN)................................ –0.50V to VDD+0.5V
Output Voltage (VOUT) .......................... –0.50V to VDD+0.5V
Lead Temperature (soldering, 20sec.)....................... 260°C
Storage Temperature (Ts) .........................–65°C to +150°C
Supply Voltage (VIN)............................. +2.375V to +3.465V
Ambient Temperature (TA) ..........................–40°C to +75°C
Junction Thermal Resistance
TSSOP (θJA).....................................................150°C/W
DC Electrical Characteristics
VDD = 2.5V ±5%; TA = –40°C to +75°C, unless noted.
Symbol
Parameter
Core Supply Voltage
Analog Supply Voltage
Core Supply Current
Analog Supply Current
Condition
Min
Typ
2.50
2.50
12
Max
2.625
2.625
20
Units
V
VDD
VDDA
IDD
2.375
2.375
V
No load
mA
mA
IDDA
48
55
DC Electrical Characteristics
VDD = 3.3V ±5%; TA = -40°C to +75°C, unless noted.
Symbol
Parameter
Condition
Min
Typ
3.30
3.30
15
Max
3.465
3.465
22
Units
V
VDD
VDDA
IDD
Core Supply Voltage
Analog Supply Voltage
Core Supply Current
Analog Supply Current
3.135
3.135
V
No load
mA
mA
IDDA
49
55
LVCMOS DC Characteristics
VDD = 2.5V ±5% and 3.3V ±5%; TA = -40°C to +75°C, unless noted.
Symbol
Parameter
Condition
Min
2
Typ
Max
Units
V
3.3V Operation
2.5V Operation
3.3V Operation
2.5V Operation
VDD = VIN = 3.465V
VDD = 3.465V; VIN = 0V
VDD = 3.3V ±5%
VDD +0.3
VIH
VIL
Input HIGH Voltage
1.7
-0.3
-0.3
V
DD + 0.3
0.8
V
V
Input LOW Voltage
0.7
V
IIH
IIL
Input HIGH Current
Input LOW Current
5
µA
µA
V
-150
2.6
VOH
Output HIGH Voltage(3)
Output LOW Voltage(3)
VDD = 2.5V ±5%
1.8
V
VOL
VDD = 3.3V ±5% or VDD = 2.5V ±5%
0.5
V
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Outputs terminated with 50Ω to VDD/2. See Parameters measurements 3.3V load test circuit.
M9999-031810-B
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Micrel, Inc.
SM840021
AC Electrical Characteristics
VDD = 2.5V ±5% and 3.3V ±5%; TA = -40°C to +75°C, unless noted.
Symbol
FOUT
Parameter
Condition
Min
Typ
125
250
Max
Units
MHz
fs
Output Frequency
RMS phase jitter @ 125MHz
Output Rise/Fall Time
Output Duty Cycle
25MHz Crystal
tJITTER
tR / tF
Integration Range: 1.875MHz to 20MHz
20% to 80%
100
48
350
52
ps
ODC
50
%
Test Circuit
3.3V Carrier Frequency, 125MHz
Offset from Carrier
100Hz
Measured Phase Noise
Unit
-103
-126
-134
-130
-143
-152
-166
-167
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
1kHz
10kHz
100kHz
1MHz
1.875MHz
10MHz
20MHz
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Micrel, Inc.
SM840021
Functional Description
The SM840021 provides a high performance and high
accuracy solution for a precision clock source at
125MHz derived, from a low cost 25MHz Xtal.
providing a precision clock at 125MHz. Duty Cycle is
inherently improved to provide a tight control and
stability on this critical specification.
The design of the SM840021 consumes very low power
in the PLL due to a proprietary technology in the VCO
and the associated dividers. The output divider is fixed at
÷26, and the feedback divider is also fixed at ÷130
The device provides improved specifications for Duty
Cycle, Jitter, Phase Noise, Power Consumption, and
noise sensitivity.
Additionally, the SM840021 will
operate at either 3.3V or 2.5V supplies.
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March 2010
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Micrel, Inc.
SM840021
RMS Phase Noise/Jitter
Phase Noise Plot: 125MHz @ 3.3V
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Micrel, Inc.
SM840021
Switching Waveforms
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SM840021
Power Supply Filtering
Crystal Loading
The SM840021 provides separate power supply pins to
isolate any high switching noise from outputs to internal
core blocks. VDD and VDDA should be individually
connected to the power plane through vias. Bypass
capacitors should be used for each pin. Figure 2
illustrates how the power supply filter for 3.3 V and 2.5 V
is configured.
Crystal Recommendations
This device requires a parallel resonance crystal.
Substituting a series resonance crystal will cause this
device to operate at the wrong frequency and violate the
ppm specifications.
To achieve low ppm error, the total capacitance of the
crystal must be considered in order to calculate
appropriate capacitive loading (CL).
Load Capacitance at each side: Trim Capacitance = Ct =
(2*CL-(Cb + Cd))
CL: Crystal load capacitance. Defined by manufacturer
Ct: External trim capacitors. (Trimmed CL Load
capacitance to get the right ppm)
Cb: Board capacitance (vias, traces, etc.)
Cd: Internal capacitance of the device (lead frame, bond
wires, pin, etc.)
Equivalent Series
Resistance (ESR)
Max.
Cut
Load
Cap.
Shunt
Cap.
Max.
Drive
Max.
Figure 2.
70Ω
AT
7pF
0.1mW
Crystal Input Interface
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Micrel, Inc.
SM840021
Total capacitance seen by crystal = CL =
1
Example:
CL = 18pF, Cb = 2pF, Cd = 4pF
Trim Cap = Ct = 2 (18pF) - (2pF +4pF) = 30pF
The SM840021 has been characterized with 25MHz,
18pF parallel resonant crystal. The trim capacitors Ct1
and Ct2 were optimized to minimize the ppm error.
1
+
1
To minimize the board capacitance, a short trace from
pin to crystal footprint without vias is desirable. It is
preferable to have ground shielding or distance between
the crystal traces and noisy signals on the board.
(Ct1 + Cb1 + Cd1)
(Ct2 + Cb2 + Cd2)
Board Layout
M9999-031810-B
hbwhelp@micrel.com or (408) 955-1690
March 2010
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Micrel, Inc.
SM840021
Package Information
8-Pin TSSOP (K-8)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2010 Micrel, Incorporated.
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March 2010
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