5mhz Crystal Substitute in SMC?
JBWolf
Posts: 405
Just wanted to make sure I'm not missing something before ordering....
I need a smaller SMC solution.
Is this a suitable substitute for the 5mhz crystal?
http://www.digikey.com/product-detail/en/NX8045GB-5MHZ-STD-CSF-3/644-1202-1-ND/3894081
I need a smaller SMC solution.
Is this a suitable substitute for the 5mhz crystal?
http://www.digikey.com/product-detail/en/NX8045GB-5MHZ-STD-CSF-3/644-1202-1-ND/3894081
Comments
-Phil
Phil, I thought it was 6 pf per page 25 of the data sheet. Would 8 pf be close enough?
Another option is a ceramic resonator - slightly lower precision than a Crystal.
http://www.digikey.com/product-detail/en/CSTCR5M00G53Z-R0/490-4720-1-ND/1219380
and if Size matters more than price, the Si504 Prog Osc comes as small as 2x2.5mm SMD, and you can define any Freq you like.
As to ceramic resonators: okay if you're not doing video. The BASIC Stamps all use ceramic resonators, BTW.
Personally, if size is a problem (and I know jmg will disagree), I would use (and have used without issue) a 10 MHz crystal at PLL8x. It is outside the 4-8 MHz stated spec for PLL locking, though.
-Phil
Just to clarify a bit more, you should be looking for a crystal with 18-20pF of capacitance.
http://www.digikey.com/product-search/en?pv183=6185&pv139=564&pv35=10&pv35=6&pv69=3&FV=fff4000d%2Cfff8016d&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
The crystal 'sees' the two Pin C values in series., so that makes 36pF/Pin -> 18pF ideal Crystal operating point.
A crystal with a different operating point will still oscillate, but not precisely at the factory trim mean value.
The other XTAL options will likely also oscillate, and you could try a series R on XOUT to improve the phase margin if using the higher F settings at 5MHz.
How many ppm do you actually need ?
eg I've found some notes here, on a CMOS inverter oscillator
(Note the pins are not quite the same in ppm/pF)
HC49U/4 Xtal, 11.0592MHz Pull-ability
One Pin is ~ -2.3328ppm/pF pull and the other is ~ -7.052ppm/pF, on HC49U Xtal.
A 24MHz Murata crystal gave -0.332ppm/pF, & -3.132ppm/pF.
Looks like more products are now available.
Only difference I see is the ESR (equivalent series resistance).... is there a critical value needed for use with the prop?
Digikey list of SMC & Through Hole 5mhz 20pf Crystals
There is a diagram of a Pierce oscillator showing the series arrangement of the capacitors here, How-does-the-load-capacitance-of-a-crystal-effect-its-clock?
I couldnt find anything at digikey relating to product id JXG75P2... can you find it there by chance?
http://www.mouser.com/ProductDetail/ABRACON/ABM3C-10000MHZ-D4Y-T/?qs=sGAEpiMZZMsPDM5321osT8c7QnCB39Ur
Of course 10MHz is "outside" the range but that isn't normally a problem unless you are running at the extremes of the Prop operating conditions anyway. Besides Hydra used 10MHz and I have dozens of designs in the field using 10MHz.
-Phil
And having crashes due to forgetting to change the clkfreq when you trying a few demo codes is not fun.
I'm checking mouser/digikey once a month to see if that 7x4mm 5mhz crystal will show up one day, if it does I will post it.
{ ┌──────────────────────────────────────────────────────────┐ │ CLKSET │ │(c) Copyright 2009 Philip C. Pilgrim (propeller@phipi.com)│ │ See end of file for terms of use. │ └──────────────────────────────────────────────────────────┘ This object determines whether a 5MHz or 10MHz crystal is being used and sets the PLL accordingly for 80MHz operation. The main program should use the following settings: CON _clkmode = xtal1 + pll8x _xinfreq = 10_000_000 OBJ clk : "clkset" Then clk.set should be called first in the toplevel program. If the crystal is determined to be 5MHz, the clkmode will be changed to xtal1 + pll16x. clkfreq will still return 80_000_000. Version History ─────────────── 2009.05.23: WARNING: Trial, tentative, very alpha release! } PUB set '' Automatically set the pll mode for a 5MHz or 10MHz crystal. cognew(@setpll, 0) DAT org 0 setpll movi ctra,#%0_00001_011 'Set ctra for pll on no pin at x1. movi frqa,#%0100_0000_0 'Set frqa for clk / 4 (= 20MHz w/ 10MHz crystal, i.e. too high). add x,cnt 'Give PLL time to lock (if it can) and stabilize. waitcnt x,#0 movi vcfg,#$40 'Configure video for discrete pins, but no pins enabled. mov vscl,#$10 'Set for 16 clocks per frame. waitvid 0,0 'Wait once to clear time. neg x,cnt 'Read -cnt. waitvid 0,0 'Wait 16 pll clocks = 64 processor clks. add x,cnt 'Compute elapsed time. cmp x,#$40 wz 'Is it really 64 clocks? if_z mov x,#$6f ' Yes: Crystal is 5MHz. Set clock mode to XTAL1 and PLL16X. if_z clkset x cogid x 'Stop the cog: we're done. cogstop x x long $1_0000 '65536 clks for pll to stabilize. {{ ┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ │ TERMS OF USE: MIT License │ ├──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤ │Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation │ │files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, │ │modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software│ │is furnished to do so, subject to the following conditions: │ │ │ │The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.│ │ │ │THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE │ │WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR │ │COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, │ │ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. │ └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘ }}It allows you to use either a 5 MHz or 10 MHz crystal and handles the details of figuring which crystal is being used and doing the appropriate clock settings. No other programmer or user intervention is required.-Phil
Hundreds of times lower accuracy than a quartz crystal - I'd never choose a ceramic resonator myself, there are
many things that want accurate frequencies and low jitter.
Ceramic resonator - +/-5000 ppm typical spec (0.5%, 7 minutes a day, sensitive to temperature)
Quartz crystal - +/-30ppm typical spec. (0.003%, 3 secs/day)
TCXO - +/- 2ppm typical spec. (0.0002%)
Peter can you give a link or product number for the 5x3mm SMD packs? I would like to look at those, that size is just perfect.
The official range for the crystal is 4 to 8 MHz, which gives PLL operation from 64 to 128MHz. 10MHz is a bit outside that range, PLL at 160MHz and prop operation at 80MHz on PLL8. It seems to be working okay for many designs now, but I wonder about extended temperature ranges. Has anyone been using them at extreme temperatures?
I've used a couple of different ones, here are some links to Digikey.
10MHz 12pF 30ppm 48c @100
10MHz 8pF 50ppm 48c @100