Spread-Spectrum Clock Generators

Transcription

1 ; Rev 0; 4/10 Spread-Spectrum Clock Generators General Description The are spread-spectrum clock generators that contain a phase-locked loop (PLL) that generates a 2MHz to 134MHz clock from an input clock or crystal. The PLL can provide a spread-spectrum down-dithered (MAX31D80) or center-dithered (MAX31C80) frequency-modulated clock. The devices also buffer the incoming clock and provide this output on a separate pin. The are provided in a 10-pin TDFN package and operate over a full -40NC to +125NC automotive temperature range. Devices can be factory programmed for multiple combinations of input and output frequencies (see the Ordering Information table). A low-cost, low-frequency crystal can be used at the input to generate frequencies up to 134MHz. Typical Application Circuit f IN = 27MHz S 2MHz to 134MHz Spread-Spectrum Clock Generator Features S Input Can Be Either an 8MHz to 34MHz Crystal or 8MHz to 134MHz Clock S Factory-Programmable Output Frequencies in 2MHz to 134MHz Range S Low-Cost Crystal at Low Frequency Used to Generate High Frequencies S On-Board PLL is Capable of Spread-Spectrum Frequency Modulation S Down- or Center-Dither Spread-Spectrum Frequency Modulation S User-Configurable Spread-Spectrum Dither Magnitude S Low Cycle-to-Cycle Jitter S 3.3 Supply oltage S Temperature Range: -40NC to +125NC S Small Package: 10-Pin TDFN (3mm x 3mm x 0.8mm) f IN = 27MHz X1 MAX31D80 X2 XOUT 27MHz CLOCK Graphics Cards Applications GND CLKOUT 1.5% DOWN DITHERED DECOUPLING CAPACITOR Set-Top Boxes Automotive Infotainment Printers xxx = Factory-programmable output frequency and dither rate (see the Selector Guide table). +Denotes a lead(pb)-free/rohs-compliant package. T = Tape and reel. *EP = Exposed pad. Ordering Information PART TEMP RANGE DITHER MODE PIN-PACKAGE MAX31C80T-xxx+ -40NC to +125NC Center 10 TDFN-EP* MAX31C80T-xxx+T -40NC to +125NC Center 10 TDFN-EP* MAX31D80T-xxx+ -40NC to +125NC Down 10 TDFN-EP* MAX31D80T-xxx+T -40NC to +125NC Down 10 TDFN-EP* Selector Guide appears at end of data sheet. Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at , or visit Maxim s website at

2 ABSOLUTE MAXIMUM RATINGS oltage Range on Relative to GND to +4.3 oltage Range on Any Other Pin Relative to GND to ( + 0.3)* Continuous Power Dissipation (T A = +70 C) 10-Pin TDFN (derate 24.4mW/ C above +70 C) mW *Not to exceed Storage Temperature Range NC to +135NC Lead Temperature (soldering, 10s) NC Soldering Temperature (reflow) nc 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. RECOMMENDED OPERATING CONDITIONS (T A = -40NC to +125NC.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply oltage Input Logic 0 ( and ) Input Logic 1 ( and ) Input Logic Unconnected ( and ) IL -0.3 IH IF Limits are in case user wants to force voltage instead of unconnecting this pin Input Logic 0 for X1 IL:X x 0.75 x x 0.55 x 0.7 x + Input Logic 1 for X1 IH:X1 0.3 XOUT Load C L:XOUT 15 pf CLKOUT Load C L:CLKOUT 67MHz P f CLKOUT < 101MHz 10 2MHz P f CLKOUT < 67MHz MHz P f CLKOUT P 134MHz 7 Crystal Frequency f IN 8 34 MHz Clock Input Frequency f IN MHz Crystal ESR X ESR 90 I Clock Input Duty Cycle f INDC % Crystal Parallel Load Capacitance 0.3 x C CL 18 pf pf 2

3 DC ELECTRICAL CHARACTERISTICS (3.0 P P 3.6, T A = -40NC to +125NC, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Current I DD f IN = 27MHz,, down dithered, C L = 10pF Input Leakage ( and ) Low-Level Output oltage (XOUT and CLKOUT) High-Level Output oltage (XOUT and CLKOUT) Input Capacitance (X1 and X2) AC ELECTRICAL CHARACTERISTICS (3.0 P P 3.6, T A = -40NC to +125NC, unless otherwise noted.) 22 ma I IL SMSEL_ = GND or Q15 FA OL I OL = 10mA 0.2 OH I OH = -10mA C IN 5 pf PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CLKOUT Duty Cycle f CLKOUT:DC C L:CLKOUT = 7pF XOUT Duty Cycle f XOUT:DC C L:XOUT = 7pF, T A = +25NC, = Rise Time t R C L:CLKOUT = 7pF 1.6 ns Fall Time t F C L:CLKOUT = 7pF 1.6 ns Dither Rate Range f DR Factory programmable khz Dither Rate Accuracy % Peak Cycle-to-Cycle Jitter t J CLKOUT = 100MHz, 10,000 cycles, T A = +25NC Power-Up Time t PUP valid to output active, T A = +25NC, = 3.3 % 75 ps 1 ms 3

4 ( = +3.3, T A = +25 C, unless otherwise noted.) SUPPLY CURRENT (ma) SUPPLY CURRENT vs. SUPPLY OLTAGE f IN = 27MHz T A = -40 C DUTY CYCLE (%) T A = +25 C SUPPLY OLTAGE () T A = +125 C DUTY CYCLE vs. SUPPLY OLTAGE T A = +25 C MAX31C80 toc01 T A = +125 C T A = -40 C SUPPLY CURRENT (ma) SUPPLY OLTAGE () MAX31C80 toc04 SUPPLY CURRENT vs. TEMPERATURE f IN = 27MHz = 3.6 = TEMPERATURE ( C) Typical Operating Characteristics = 3.3 DUTY CYCLE (%) MAX31C80 toc02 SUPPLY CURRENT (ma) DUTY CYCLE vs. TEMPERATURE = = 3.0 = TEMPERATURE ( C) SUPPLY CURRENT vs. OUTPUT FREQUENCY 32 = 3.3 OUTPUT FREQUENCY (MHz) MAX31C80 toc MAX31C80 toc FREQUENCY SPECTRUM AT 122MHz WITH CENTER SPREAD f CLKOUT = 122MHz CENTER DITHER = ±1.5% dB MAX31C80 toc FREQUENCY SPECTRUM AT 100MHz WITH DOWN DITHER CENTER DITHER = -3% dB MAX31C80 toc07 ATTENUATION (db) ATTENUATION (db) FREQUENCY (MHz) FREQUENCY (MHz) 100 4

5 8MHz TO 134MHz CLOCK OR 8MHz TO 34MHz CRYSTAL f IN X1 X2 CRYSTAL OSCILLATOR TOP IEW MAX31C80 MAX31D80 X2 PROGRAMMABLE PLL WITH SPREAD SPECTRUM SPREAD-SPECTRUM MAGNITUDE CONTROL CC GND XOUT Block Diagram CLKOUT (f CLKOUT = 2MHz TO 134MHz) XOUT (f XOUT = f IN ) GND Pin Configuration MAX31C80 MAX31D80 + EP X1 CC TDFN GND CLKOUT Pin Description PIN NAME FUNCTION 1 X1 2, 9, Crystal Drive/Clock Input. A crystal with the proper loading is connected across X1 and X2. Instead of a crystal, a clock can be applied at the X1 input. If no clock or crystal is present, then no clock is output at either XOUT or CLKOUT. Spread-Spectrum Magnitude Select. These are three-state digital inputs to determine the spread-spectrum magnitude. Tables 1 and 2 provide details for configuration of these pins for down and center dither, respectively. PIN NAME FUNCTION 3, 8 Supply oltage 4, 7 GND Ground 5 CLKOUT Clock Output. Spread-spectrum-capable digital output clock from the PLL. 6 XOUT 10 X2 Crystal Buffered Output. Buffered digital output of the input crystal or clock. Crystal Drive Output. A crystal with the proper loading is connected across X1 and X2. If a clock is applied at the X1 input, then X2 should be left open circuit. EP Exposed Pad. Connect to GND. 5

6 Detailed Description The modulate an input clock to generate a center-dithered or down-dithered spreadspectrum output. An 8MHz to 27MHz crystal or 8MHz to 134MHz oscillator input is applied to the device. An internal PLL dithers the output clock at a user-selectable magnitude to produce a down-dithered or centerdithered output clock. The output clock s frequency is programmable from 2MHz to 134MHz. The devices also buffer the incoming clock and provide this output on a separate pin. Spread-Spectrum Dither Magnitude The MAX31D80 can generate down-dithered magnitudes up to -3%. The MAX31C80 can generate center-dithered magnitudes up to P 1.5%. The desired magnitude is selected using the input pins and as shown in Tables 1 and 2. A power cycle is required after each change of the dither magnitude for the changes to take effect. Table 1. Spread-Spectrum Mode and Magnitude Select (for Down Dither) SPREAD-SPECTRUM MAGNITUDE SELECTED (%) 0 0 Spread-Spectrum Disabled 0 Unconnected 0 to to Unconnected 0 0 to -0.5 Unconnected Unconnected 0 to Unconnected 1 0 to to Unconnected 0 to to -3.0 SPREAD-SPECTRUM DITHER MODE SELECTED Down Dither Table 2. Spread-Spectrum Mode and Magnitude Select (for Center Dither) SPREAD-SPECTRUM MAGNITUDE SELECTED (%) 0 0 Spread-Spectrum Disabled 0 Unconnected to to Unconnected to +0.5 Unconnected Unconnected to Unconnected to to Unconnected N/A 1 1 N/A SPREAD-SPECTRUM DITHER MODE SELECTED Center Dither 6

7 DOWN DITHERED (MAX31D80) f CLKOUT f CLKOUT - (0.25% TO 3%) FREQUENCY 1 DITHER CYCLE RATE Figure 1. Spread-Spectrum Frequency Modulation (Down Dithered) IF = = 0 DITHER AMOUNT (-0.25% TO -3.0%) TIME CENTER DITHERED (MAX31C80) FREQUENCY f CLKOUT + (0.25% TO 1.5%) f IN f CLKOUT - (0.25% TO 1.5%) IF = = 0 DITHER AMOUNT (±0.25% TO ±1.5%) 1 DITHER CYCLE RATE TIME Figure 2. Spread-Spectrum Frequency Modulation (Center Dithered) 7

8 CC ALID XOUT CLKOUT Figure 3. Power-Up Timing t PUP OUTPUT ALID OUTPUT ALID Factory Programmability The can provide a variety of frequencies, which are available to users by ordering the device according to specifications listed in the Selector Guide table. the factory at custom.oscillators@maxim-ic.com to obtain custom output frequencies for specific input frequencies not mentioned in the Selector Guide table. Applications Information Power-Supply Decoupling To achieve best results, it is highly recommended that a decoupling capacitor be used on the IC power-supply pins. Typical values of decoupling capacitors are 0.01FF and 0.1FF. Use a high-quality, ceramic, surface-mount capacitor and mount it as close as possible to the CC pins of the IC to minimize lead inductance. Selector Guide PART INPUT FREQUENCY (MHz) +Denotes a lead(pb)-free/rohs-compliant package. OUTPUT FREQUENCY (MHz) DITHER RATE (khz) DITHER TYPE MAX31C80T-UGQ Center MAX31C80T Center MAX31D80T-UGQ Down MAX31D80T Down Package Information For the latest package outline information and land patterns, go to Note that a +, #, or - in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 10 TDFN-EP T

9 REISION NUMBER REISION DATE DESCRIPTION Revision History PAGES CHANGED 0 4/10 Initial release 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.