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AN1519Recommended Crystals for Microchip
Stand-Alone Real-Time Clock/Calendar Devices
This document is designed to serve as a starting pointwhen choosing a crystal to operate alongside theMicrochip Stand-Alone Real-Time Clock/Calendardevices (Figure 1).
FIGURE 1: OSCILLATOR DIAGRAM
To oscillate as closely as possible to the desired fre-quency, a crystal must have load capacitors that matchthe value recommended by the crystal manufacturer,according to Equation 1.
Also, the oscillator pin capacitance (available in thedevice data sheet as COSC) must be included in CX1and CX2, and stray board capacitance (Cstray) must betaken into consideration when choosing the capacitors.
EQUATION 1:
CONSIDERATIONSThe Microchip stand-alone RTCC’s have beendesigned to work with 32.768 kHz tuning fork crystalswith a load capacitance (CLOAD or CL) of 6-9pF. Fortuning fork crystals, the frequency has a parabolicdependence on temperature. Therefore, when itchanges, the frequency decreases accordingly, asshown in Equation 2 and Figure 2. See AN1413, “Tem-perature Compensation of a Tuning Fork Crystal Basedon MCP79410” (DS01413).
EQUATION 2:
FIGURE 2: PARABOLIC CURVE FOR TUNING FORK CRYSTALS
Author: Florian GheorgheMicrochip Technology Inc.
X1
X2RTCC
CX1
CX2
CloadCx2 Cx1Cx2 Cx1+-------------------------+Cstray=
Where:Cx1 = Capacitor value on pin X1 + CpinCx2 = Capacitor value on pin X2 + CpinCstray = Trace capacitanceCpin = 3 pF typical
f f0 [1-Tc T T0– 2 =
Where: f0 = Frequency at turnover pointTc = Temperature coefficientT-T0 = Deviation from turnover pointT = Current temperature (°C)T0 = Turnover point (°C)
2013 Microchip Technology Inc. DS00001519B-page 1
AN1519
For best results, it is recommended that a ground ringshould encompass the crystal and the X1 and X2 pins.See AN1365, “Recommended Usage of MicrochipSerial RTCC Devices” (DS01365). Also, the tracesfrom the RTCC to the capacitors and crystal should beas short as possible in order to minimize the strayboard capacitance (CSTRAY). See AN1288, “DesignPractices for Low-Power External Oscillators”(DS01288).Table 2 shows recommended crystals and loadcapacitors.
Some crystal vendors use the term oscillation allow-ance as the sum of negative R value and ESR(Equation 3). The negative R (-R) which has been mea-
sured on the AC164140 RTCC PICtail™ board is ameasure of the ability of the oscillator to drive the crys-tal over temperature (Figure 3). An oscillation allow-ance value of three to five times the crystal ESR willprovide an acceptable margin. See AN943, “PracticalPICmicro® Oscillator Analysis and Design” (DS00943)and AN949, “Making Your Oscillator Work” (DS00949).
CRYSTAL TEST RESULTSThe crystals listed in Table 1 have been tested on theAC164140 RTCC PICtail board (unless noted). Theresults are in Table 2.
TABLE 1: CRYSTAL TEST RESULTS
EQUATION 3:
FIGURE 3: NEGATIVE RESISTANCE TEST SETUP
Crystal Appendix
Citizen CMR200T-32.768KDZB-UT Appendix A: “CMR200T-32.768KDZB-UT”Citizen CFS206-32.768KDZB-UB Appendix B: “CMR-32.768KDZB-UB”ECS ECS.327-6-13X Appendix C: “ECS327-6-13X”ECS ECS.327-6-17X-TR Appendix D: “ECS.327-6-17X-TR”Epson MC405-32.7KE3R Appendix E: “EPSON MC405-32.7KE3R”Epson C002RX32.76K-EPB Appendix F: “EPSON C002RX32.76K-EPB”AVX ST3215SB32768C0HPWBB Appendix G: “AVX ST3215SB32768C0HPWBB”FOX NC38LF-32.768kHz Appendix H: “FOX MC38LF-32.768kHz”HK Crystals Appendix I: “HK Crystals”
Oscillation Allowance = |-R| + ESR []
X1 X2
RTCC
CX1 CX2
RTEST
DS00001519B-page 2 2013 Microchip Technology Inc.
AN
1519
DS
00001519B-page 3
2013 M
icrochip Technology Inc.
s/ Oscillation Allowance
Oscillation Allowance/ESR Ratio
Start-up Time
(seconds)
480 kΩ 9.6 1.3780 kΩ 22.28 1.25360 kΩ 10.28 1540 kΩ 13.5 1300 kΩ 6 1.5370 kΩ 6.16 1.6800 kΩ 11.42 1600 kΩ 17.14 1390 kΩ 9.75 0.85400 kΩ 10 1.1
1600 kΩ 32 11370 kΩ 19.57 0.5250 kΩ 3.57 0.75300 kΩ 6 1.4340 kΩ 8.5 1.7220 kΩ 5.5 1.2300 kΩ 4.28480 kΩ 9.6390 kΩ 6460 kΩ 9.2
TABLE 2: CRYSTALS
Crystal Vendor
Crystal PartNumber
ESR(Max.)
CLOAD (pF)
C1 Capacitor
Value (pF)
C2 Capacitor Value (pF)
PPM Error
(at 25°C)
SecondDay
Citizen CMR200T-32.768KDZB-UT 50 kΩ 6 10 10 -3.17 -0.274Citizen CFS206-32.768KDZB-UB 35 kΩ 6 10 12 -9.60 -0.829ECS ECS.327-6-13X 35 kΩ 6 12 10 1.07 0.092ECS ECS.327-6-17X-TR 40 kΩ 6 10 8.2 10.93 0.944Epson Crystals MC405-32.7KE3R 50 kΩ 6 10 10 -1.71 -0.148Epson Crystals C002RX32.76K-EPB 60 kΩ 6 12 10 -0.66 -0.057AVX Crystals ST3215SB32768C0HPWBB 70 kΩ 7 10 12 -1.22 -0.105FOX Crystals MC38LF-32.768kHz 35 kΩ 6 8.2 8.2 1.47 0.127HK Crystals 3T 40k 6 8.2 8.2 -4.36 -0.377HK Crystals 2T 40k 6 8.2 10 1.64 0.142HK Crystals M3 50k 6 8.2 10 3.21 0.277HK Crystals M8 70k 7 10 12 -4.98 -0.430HK Crystals M8 70k 9 15 12 2.78 0.240HK Crystals M3 50k 8 12 12 -1.96 -0.169HK Crystals 2T 40k 8 12 12 3.89 0.336HK Crystals 3T 40k 8 12 15 4.65 0.402Micro Crystal (Note) CM7V-T1A 70 kΩ 7 10 12 3 0.259Citizen (Note) CM200S32.768KDZB-UT 50 kΩ 6 10 8 1.2 0.104Seiko (Note) SSP-T7-F 65 kΩ 7 10 12 -0.76 0.066Seiko (Note) VT-200-F 50 kΩ 6 9 9 -2.14 0.185
Note: Not included in this document.
AN1519
APPENDIX A: CMR200T-32.768KDZB-UT
FIGURE 4: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 10 PF; C2 = 10 PF
APPENDIX B: CMR-32.768KDZB-UB
FIGURE 5: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 10 PF; C2 = 12 PF
32,767.890
32,767.892
32,767.894
32,767.896
32,767.898
32,767.900
32,767.902
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 10 pF, C2 = 10 pF
32,767.60
32,767.62
32,767.64
32,767.66
32,767.68
32,767.70
32,767.72
32,767.74
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 10 pF, C2 = 12 pF
DS00001519B-page 4 2013 Microchip Technology Inc.
AN1519
APPENDIX C: ECS327-6-13X
FIGURE 6: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 12 PF; C2 = 10 PF
APPENDIX D: ECS.327-6-17X-TR
FIGURE 7: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 10 PF; C2 = 8.2 PF
32,768.025
32,768.030
32,768.035
32,768.040
32,768.045
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 12 pF, C2 = 10 pF
32,768.335
32,768.340
32,768.345
32,768.350
32,768.355
32,768.360
32,768.365
32,768.370
32,768.375
32,768.380
32,768.385
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 10 pF, C2 = 8.2 pF
2013 Microchip Technology Inc. DS00001519B-page 5
AN1519
APPENDIX E: EPSON MC405-32.7KE3R
FIGURE 8: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 10 PF; C2 = 10 PF
APPENDIX F: EPSON C002RX32.76K-EPB
FIGURE 9: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 12 PF; C2 = 10 PF
32,767.936
32,767.938
32,767.940
32,767.942
32,767.944
32,767.946
32,767.948
32,767.950
32,767.952
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 10 pF, C2 = 10 pF
32,767.965
32,767.970
32,767.975
32,767.980
32,767.985
32,767.990
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 12 pF, C2 = 10 pF
DS00001519B-page 6 2013 Microchip Technology Inc.
AN1519
APPENDIX G: AVX ST3215SB32768C0HPWBB
FIGURE 10: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 10 PF; C2 = 12 PF
APPENDIX H: FOX MC38LF-32.768KHZ
FIGURE 11: FREQUENCY/VOLTAGE CHARACTERISTIC FOR C1 = 8.2 PF; C2 = 8.2 PF
32,767.92
32,767.93
32,767.94
32,767.95
32,767.96
32,767.97
32,767.98
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 10 pF, C2 = 12 pF
32,768.040
32,768.042
32,768.044
32,768.046
32,768.048
32,768.050
32,768.052
32,768.054
32,768.056
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 8.2 pF, C2 = 8.2 pF
2013 Microchip Technology Inc. DS00001519B-page 7
AN1519
APPENDIX I: HK CRYSTALS
I.1 HK 3T 6PF
FIGURE 12: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 8.2 PF, C2 = 8.2 PF
I.2 HK 2T 6PF
FIGURE 13: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 8.2 PF, C2 = 10 PF
32,767.850
32,767.852
32,767.854
32,767.856
32,767.858
32,767.860
32,767.862
32,767.864
32,767.866
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 8.2 pF C2 = 8.2 pF
32,768.042
32,768.044
32,768.046
32,768.048
32,768.050
32,768.052
32,768.054
32,768.056
32,768.058
32,768.060
32,768.062
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 8.2 pF C2 = 10 pF
DS00001519B-page 8 2013 Microchip Technology Inc.
AN1519
I.3 HK M3 6PFFIGURE 14: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 8.2 PF, C2 = 10 PF
I.4 HK M8 7PF
FIGURE 15: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 10 PF, C2 = 12 PF
32,768.1040
32,768.1045
32,768.1050
32,768.1055
32,768.1060
32,768.1065
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 8.2 pF C2 = 10 pF
32,767.74
32,767.76
32,767.78
32,767.80
32,767.82
32,767.84
32,767.86
32,767.88
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 10 pF C2 = 12 pF
2013 Microchip Technology Inc. DS00001519B-page 9
AN1519
I.5 HK M8 9PFFIGURE 16: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 15 PF, C2 = 12 PF
I.6 HK M3 8PF
FIGURE 17: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 12 PF, C2 = 12 PF
32,768.02
32,768.04
32,768.06
32,768.08
32,768.10
32,768.12
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 15 pF C2 = 12 pF
32,767.920
32,767.925
32,767.930
32,767.935
32,767.940
32,767.945
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 12 pF C2 = 12 pF
DS00001519B-page 10 2013 Microchip Technology Inc.
AN1519
I.7 HK 2T 8PFFIGURE 18: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 12 PF, C2 = 12 PF
I.8 HK 3T 8PF
FIGURE 19: FREQUENCY VOLTAGE CHARACTERISTIC FOR C1 = 12 PF, C2 = 15 PF
32,768.110
32,768.115
32,768.120
32,768.125
32,768.130
32,768.135
32,768.140
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 12 pF C2 = 12 pF
32,768.142
32,768.144
32,768.146
32,768.148
32,768.150
32,768.152
32,768.154
32,768.156
32,768.158
32,768.160
32,768.162
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Freq
uenc
y (H
z)
Voltage (V)
C1 = 12 pF 2 = 15 pF
2013 Microchip Technology Inc. DS00001519B-page 11
Note the following details of the code protection feature on Microchip devices:• Microchip products meet the specification contained in their particular Microchip Data Sheet.
• Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions.
• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
• Microchip is willing to work with the customer who is concerned about the integrity of their code.
• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of ourproducts. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such actsallow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding deviceapplications and the like is provided only for your convenienceand may be superseded by updates. It is your responsibility toensure that your application meets with your specifications.MICROCHIP MAKES NO REPRESENTATIONS ORWARRANTIES OF ANY KIND WHETHER EXPRESS ORIMPLIED, WRITTEN OR ORAL, STATUTORY OROTHERWISE, RELATED TO THE INFORMATION,INCLUDING BUT NOT LIMITED TO ITS CONDITION,QUALITY, PERFORMANCE, MERCHANTABILITY ORFITNESS FOR PURPOSE. Microchip disclaims all liabilityarising from this information and its use. Use of Microchipdevices in life support and/or safety applications is entirely atthe buyer’s risk, and the buyer agrees to defend, indemnify andhold harmless Microchip from any and all damages, claims,suits, or expenses resulting from such use. No licenses areconveyed, implicitly or otherwise, under any Microchipintellectual property rights.
2013 Microchip Technology Inc.
QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV
== ISO/TS 16949 ==
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC, FlashFlex, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART, PIC32 logo, rfPIC, SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.
FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor, MTP, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A.
Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries.
Analog-for-the-Digital Age, Application Maestro, BodyCom, chipKIT, chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN, ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP, Mindi, MiWi, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, mTouch, Omniscient Code Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE, rfLAB, Select Mode, SQI, Serial Quad I/O, Total Endurance, TSHARC, UniWinDriver, WiperLock, ZENA and Z-Scale are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated in the U.S.A.
GestIC and ULPP are registered trademarks of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in other countries.
All other trademarks mentioned herein are property of their respective companies.
© 2013, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 9781620774601
Microchip received ISO/TS-16949:2009 certification for its worldwide
DS00001519B-page 13
headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona; Gresham, Oregon and design centers in California and India. The Company’s quality system processes and procedures are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified.
DS00001519B-page 14 2013 Microchip Technology Inc.
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