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SM840021
125MHz Ultra-Low Jitter Clock Synthesizer
General Description
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. Datasheets and support documentation can be found on Micrel's web site at: www.micrel.com.
Features
* * * * * * * * * * 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: -40C to +75C Green, RoHS-compliant and PFOS-compliant Available in 8-pin TSSOP package
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
March 2010
M9999-031810-B hbwhelp@micrel.com or (408) 955-1690
Micrel, Inc.
SM840021
Ordering Information(1)
Part Number SM840021KA SM840021KA TR
Note: 1. Devices are Green, RoHS-compliant and PFOS-compliant. 2. Tape and Reel
(2)
Package Type K-8 K-8
Operating Range -40C to +75C -40C to +75C
Package Marking 840021 840021
Lead Finish NiPdAu NiPdAu
Pin Configuration
8-Pin TSSOP (K-8)
Pin Description
Pin Number 1 2 3 4 5 6 7 8 Pin Name VDDA OE XTAL OUT XTAL IN NC GND Q0 VDD P O P Type P I O I Pull-up Level Pin Function Analog Power. Output Enable: 1 = Enable, 0 = Disable. Crystal Output. Crystal Input. No Connect. Ground. Single Ended LVCMOS Clock Out. Core Power.
Output Enable
OE 0 1 Output Disable Enable
March 2010
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Micrel, Inc.
SM840021
Absolute Maximum Ratings(1)
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.)....................... 260C Storage Temperature (Ts) .........................-65C to +150C
Operating Ratings(2)
Supply Voltage (VIN)............................. +2.375V to +3.465V Ambient Temperature (TA) .......................... -40C to +75C Junction Thermal Resistance TSSOP (JA).....................................................150C/W
DC Electrical Characteristics
VDD = 2.5V 5%; TA = -40C to +75C, unless noted.
Symbol VDD VDDA IDD IDDA Parameter Core Supply Voltage Analog Supply Voltage Core Supply Current Analog Supply Current No load Condition Min 2.375 2.375 Typ 2.50 2.50 12 48 Max 2.625 2.625 20 55 Units V V mA mA
DC Electrical Characteristics
VDD = 3.3V 5%; TA = -40C to +75C, unless noted.
Symbol VDD VDDA IDD IDDA Parameter Core Supply Voltage Analog Supply Voltage Core Supply Current Analog Supply Current No load Condition Min 3.135 3.135 Typ 3.30 3.30 15 49 Max 3.465 3.465 22 55 Units V V mA mA
LVCMOS DC Characteristics
VDD = 2.5V 5% and 3.3V 5%; TA = -40C to +75C, unless noted.
Symbol VIH VIL IIH IIL VOH VOL
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 50 to VDD/2. See Parameters measurements 3.3V load test circuit.
Parameter Input HIGH Voltage Input LOW Voltage Input HIGH Current Input LOW Current Output HIGH Voltage(3) Output LOW Voltage(3)
Condition 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 = 2.5V 5% VDD = 3.3V 5% or VDD = 2.5V 5%
Min 2 1.7 -0.3 -0.3 -150 2.6 1.8
Typ
Max VDD +0.3 VDD + 0.3 0.8 0.7 5
Units V V V V A A V V
0.5
V
March 2010
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Micrel, Inc.
SM840021
AC Electrical Characteristics
VDD = 2.5V 5% and 3.3V 5%; TA = -40C to +75C, unless noted.
Symbol FOUT tJITTER t R / tF ODC Parameter Output Frequency RMS phase jitter @ 125MHz Output Rise/Fall Time Output Duty Cycle Condition 25MHz Crystal Integration Range: 1.875MHz to 20MHz 20% to 80% 100 48 50 Min Typ 125 250 350 52 Max Units MHz fs ps %
Test Circuit
3.3V Carrier Frequency, 125MHz
Offset from Carrier 100Hz 1kHz 10kHz 100kHz 1MHz 1.875MHz 10MHz 20MHz Measured Phase Noise -103 -126 -134 -130 -143 -152 -166 -167 Unit dBc/Hz dBc/Hz dBc/Hz dBc/Hz dBc/Hz dBc/Hz dBc/Hz dBc/Hz
March 2010
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M9999-031810-B hbwhelp@micrel.com or (408) 955-1690
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. 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 providing a precision clock at 125MHz. Duty Cycle is inherently improved to provide a tight control and stability on this critical specification. 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.
March 2010
5
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Micrel, Inc.
SM840021
RMS Phase Noise/Jitter
Phase Noise Plot: 125MHz @ 3.3V
March 2010
6
M9999-031810-B hbwhelp@micrel.com or (408) 955-1690
Micrel, Inc.
SM840021
Switching Waveforms
March 2010
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Micrel, Inc. Power Supply Filtering 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 Loading
SM840021
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. 70 Cut Load Cap. Shunt Cap. Max. 7pF Drive Max. 0.1mW
Figure 2.
AT
Crystal Input Interface
March 2010
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M9999-031810-B hbwhelp@micrel.com or (408) 955-1690
Micrel, Inc. Total capacitance seen by crystal = CL = 1 1 (Ct1 + Cb1 + Cd1) + 1 (Ct2 + Cb2 + Cd2)
SM840021 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. 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.
Board Layout
March 2010
9
M9999-031810-B hbwhelp@micrel.com or (408) 955-1690
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. (c) 2010 Micrel, Incorporated.
March 2010
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