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2021 Microchip Technology Inc. DS50003049A
X-PRO High-Performance
Rubidium Oscillator
User’s Guide
DS50003049A-page 2 2021 Microchip Technology Inc.
Information contained in this publication is provided for the sole
purpose of designing with and using Microchip products. Infor-
mation regarding device applications and the like is provided
only for your convenience and may be superseded by updates.
It is your responsibility to ensure that your application meets
with your specifications.
THIS INFORMATION IS PROVIDED BY MICROCHIP "AS IS".
MICROCHIP MAKES NO REPRESENTATIONS OR WAR-
RANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED,
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RELATED TO THE INFORMATION INCLUDING BUT NOT
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WHATSOEVER RELATED TO THE INFORMATION OR ITS
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ALLOWED BY LAW, MICROCHIP'S TOTAL LIABILITY ON
ALL CLAIMS IN ANY WAY RELATED TO THE INFORMATION
OR ITS USE WILL NOT EXCEED THE AMOUNT OF FEES, IF
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the buyer agrees to defend, indemnify and hold harmless
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Note the following details of the code protection feature on Microchip devices:
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• There are dishonest and possibly illegal methods being used in attempts to breach the code protection features of the Microchip
devices. We believe that these methods require using the Microchip products in a manner outside the operating specifications
contained in Microchip's Data Sheets. Attempts to breach th likely, cannot be accomplished ese code protection features, most
without violating Microchip's intellectual property rights.
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Trademarks
The Microchip name and logo, the Microchip logo, Adaptec,
AnyRate, AVR, AVR logo, AVR Freaks, BesTime, BitCloud, chipKIT,
chipKIT logo, CryptoMemory, CryptoRF, dsPIC, FlashFlex,
flexPWR, HELDO, IGLOO, JukeBlox, KeeLoq, Kleer, LANCheck,
LinkMD, maXStylus, maXTouch, MediaLB, megaAVR, Microsemi,
Microsemi logo, MOST, MOST logo, MPLAB, OptoLyzer,
PackeTime, PIC, picoPower, PICSTART, PIC32 logo, PolarFire,
Prochip Designer, QTouch, SAM-BA, SenGenuity, SpyNIC, SST,
SST Logo, SuperFlash, Symmetricom, SyncServer, Tachyon,
TimeSource, tinyAVR, UNI/O, Vectron, and XMEGA are registered
trademarks of Microchip Technology Incorporated in the U.S.A. and
other countries.
AgileSwitch, APT, ClockWorks, The Embedded Control Solutions
Company, EtherSynch, FlashTec, Hyper Speed Control, HyperLight
Load, IntelliMOS, Libero, motorBench, mTouch, Powermite 3,
Precision Edge, ProASIC, ProASIC Plus, ProASIC Plus logo, Quiet-
Wire, SmartFusion, SyncWorld, Temux, TimeCesium, TimeHub,
TimePictra, TimeProvider, WinPath, and ZL are registered
trademarks of Microchip Technology Incorporated in the U.S.A.
Adjacent Key Suppression, AKS, Analog-for-the-Digital Age, Any
Capacitor, AnyIn, AnyOut, Augmented Switching, BlueSky,
BodyCom, CodeGuard, CryptoAuthentication, CryptoAutomotive,
CryptoCompanion, CryptoController, dsPICDEM, dsPICDEM.net,
Dynamic Average Matching, DAM, ECAN, Espresso T1S,
EtherGREEN, IdealBridge, In-Circuit Serial Programming, ICSP,
INICnet, Intelligent Paralleling, Inter-Chip Connectivity,
JitterBlocker, maxCrypto, maxView, memBrain, Mindi, MiWi,
MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, MultiTRAK,
NetDetach, Omniscient Code Generation, PICDEM, PICDEM.net,
PICkit, PICtail, PowerSmart, PureSilicon, QMatrix, REAL ICE,
Ripple Blocker, RTAX, RTG4, SAM-ICE, Serial Quad I/O,
simpleMAP, SimpliPHY, SmartBuffer, SMART-I.S., storClad, SQI,
SuperSwitcher, SuperSwitcher II, Switchtec, SynchroPHY, Total
Endurance, TSHARC, USBCheck, VariSense, VectorBlox, VeriPHY,
ViewSpan, WiperLock, XpressConnect, and ZENA 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.
The Adaptec logo, Frequency on Demand, Silicon Storage
Technology, and Symmcom are registered trademarks of Microchip
Technology Inc. in other countries.
GestIC is a registered trademark 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.
© 2021, Microchip Technology Incorporated, All Rights Reserved.
ISBN: 978-1-5224-7671-9
For information regarding Microchip’s Quality Management Systems,
please visit www.microchip.com/quality.
XPRO USER’S GUIDE
2021 Microchip Technology Inc. DS50003049A-page 3
Preface
PURPOSE OF THIS GUIDE
This guide provides basic recommendations for designing products that use Micro-
chip's XPRO rubidium oscillators. The guidelines provided are generic because spe-
cific product requirements vary from application to application.
WHO SHOULD READ THIS GUIDE
This document is intended for professionals who are design operating, or ing, installing,
maintaining time, frequency, and synchronization systems having a requirement for a
low-profile and highly-precise frequency generator.
To use this document effectively, a good understanding of digital technologies, analog
frequency generation, and synthesis techniques is helpful.
DOCUMENT LAYOUT
This guide contains the following sections:
•Chapter 1. “Functional Descriptions”: Provides an overview of the product,
describes the major hardware and software features, and lists the system specifi-
cations.
•Chapter 2. “Operation and Installation”: Contains the Principle of Operation,
Start-Up Sequence, and aspects related to first power-up.
•Chapter 3. “Design Integration Considerations”: Provides details on the
design integration considerations for the XPRO device, including thermal consid-
erations, interfaces and grounding, and EMI considerations.
NOTICE TO CUSTOMERS
All documentation becomes dated, and this manual is no exception. Microchip tools and
documentation are constantly evolving to meet customer needs, so some actual dialogs
and/or tool descriptions may differ from those in this document. Please refer to our website
(www.microchip.com) to obtain the latest documentation available.
Documents are identified with a “DS” number. This number is located on the bottom of each
page, in front of the page number. The numbering convention for the DS number is
“DSXXXXXXXXA”, where “XXXXXXXX” is the document number and “A” is the revision level
of the document.
For the most up-to-date information on development tools, see the MPLAB® IDE online help.
Select the Help menu, and then Topics, to open a list of available online help files.
XPRO User’s Guide
DS50003049A-page 4 2021 Microchip Technology Inc.
CONVENTIONS USED IN THIS GUIDE
This manual uses the following documentation conventions:
DOCUMENTATION CONVENTIONS
Description Represents Examples
Arial font:
Italic characters Referenced books MPLAB® IDE User’s Guide
Emphasized text ...is the only compiler...
Initial caps A window the Output window
A dialog the Settings dialog
A menu selection select Enable Programmer
Quotes A field name in a window or
dialog
“Save project before build”
Underlined, italic text with
right angle bracket
A menu path File>Save
Bold characters A dialog button Click OK
A tab Click the Power tab
N‘Rnnnn A number in verilog format,
where N is the total number of
digits, R is the radix and n is a
digit.
4‘b0010, 2‘hF1
Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>
Courier New font:
Plain Courier New Sample source code #define START
Filenames autoexec.bat
File paths c:\mcc18\h
Keywords _asm, _endasm, static
Command-line options -Opa+, -Opa-
Bit values 0, 1
Constants 0xFF, ‘A’
Italic Courier New A variable argument file.o, where file can be
any valid filename
Square brackets [ ] Optional arguments mcc18 [options] file
[options]
Curly brackets and pipe
character: { | }
Choice of mutually exclusive
arguments; an OR selection
errorlevel {0|1}
Ellipses... Replaces repeated text var_name [,
var_name...]
Represents code supplied by
user
void main (void)
{ ...
}
XPRO User’s Guide
DS50003049A-page 6 2021 Microchip Technology Inc.
email: SJO-FTD.GBUTechSupport@microchip.com
Internet: www.microsemi.com/ftdsupport
Europe, Middle East, and Africa (EMEA)
Microchip FTS Services and Support EMEA
Altlaufstrasse 42
85635 Hoehenkirchen-Siegertsbrunn
Germany
Telephone: +49 700 3288 6435
Fax: +49 8102 8961 533
email: ftd.emeasupport@microsemi.com
email: ftd.emea_sales@microsemi.com
THE MICROCHIP WEBSITE
Microchip provides online support via our website at www.microchip.com. This website
is used as a means to make files and information easily available to customers.
Accessible by using your favorite Internet browser, the website contains the following
information:
•Product Support – Data sheets and errata, application notes and sample
programs, design resources, user’s guides and hardware support documents,
latest software releases and archived software
•General Technical Support – Frequently Asked Questions (FAQs), technical
support requests, online discussion groups, Microchip consultant program
member listing
•Business of Microchip – Product selector and ordering guides, latest Microchip
press releases, listing of seminars and events, listings of Microchip sales offices,
distributors and factory representatives
CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Technical Support
Customers should contact their distributor, representative or field application engineer
(FAE) for support. Local sales offices are also available to help customers. A listing of
sales offices and locations is included in the back of this document.
Technical support is available through the website at:
http://www.microchip.com/support.
DOCUMENT REVISION HISTORY
Revision A (February 2021)
• Initial release of this document as Microchip DS50003049A.
XPRO USER’S GUIDE
2021 Microchip Technology Inc. DS50003049A-page 7
Table of Contents
Preface ........................................................................................................................... 3
Purpose of This Guide........................................................................................... 3
Who Should Read This Guide............................................................................... 3
Document Layout .................................................................................................. 3
Conventions Used in this Guide ............................................................................ 4
Warnings, Cautions, Recommendations, and Notes............................................. 5
Where to Find Answers to Product and Document Questions .............................. 5
Related Documents and Information..................................................................... 5
The Microchip Website.......................................................................................... 6
Customer Support ................................................................................................. 6
Document Revision History ................................................................................... 6
Chapter 1. Product Overview
1.1 Typical Applications......................................................................................... 9
1.2 Specifications ................................................................................................ 10
1.2.1 XPRO Electrical Specifications................................................................... 10
1.2.2 XPRO Connectors...................................................................................... 11
1.2.3 XPRO MTBF: Ground Benign (GB) Prediction........................................... 12
Chapter 2. Operation and Installation
2.1 Theory of Operation ...................................................................................... 13
2.2 Installation ..................................................................................................... 14
2.2.1 Site Selection ............................................................................................. 14
2.2.2 Cabling ....................................................................................................... 14
2.2.3 Turn-On Procedure .................................................................................... 14
2.2.4 Frequency Adjustment Procedure .............................................................. 15
2.2.5 Synchronizing to an External 1PPS Signal ................................................ 16
2.2.6 Maintenance and Repairs .......................................................................... 16
Chapter 3. Design Integration Considerations
3.1 XPRO Mechanical Drawings ......................................................................... 17
3.2 Thermal Considerations ................................................................................ 17
3.2.1 Thermal Tape Use...................................................................................... 17
3.2.2 Heat Sink .................................................................................................... 17
3.2.3 Impact of External Ambient Air Temperature on Unit Operation ................ 17
3.2.4 Unit Operating Temperature Range ........................................................... 18
3.2.5 Frequency Offset from Water Condensation.............................................. 19
3.3 External Interfacing and Grounding............................................................... 19
3.3.1 XPRO Serial Port Protocol ......................................................................... 20
3.3.2 Lock (BITE) Signal ..................................................................................... 21
3.3.3 Service Signal ............................................................................................ 21
3.3.4 Frequency Control ...................................................................................... 21
XPRO User’s Guide
DS50003049A-page 8 2021 Microchip Technology Inc.
3.4 Temperature Compensation of Frequency.................................................... 21
3.5 EMI Considerations....................................................................................... 22
3.5.1 Outer Mu-Metal Cover ................................................................................22
3.6 XPRO Susceptibility to Input Noise............................................................... 22
3.7 XPRO Maintenance....................................................................................... 23
3.7.1 XPRO Design Goal .....................................................................................23
Worldwide Sales and Service .....................................................................................25
XPRO USER’S GUIDE
2021 Microchip Technology Inc. DS50003049A-page 9
Chapter 1. Functional Descriptions
The XPRO is part of Microchip's family of precision frequency generator components.
It is designed to easily integrate into a system, requiring only one input supply voltage
and allowing direct plug-in connection into another circuit board. It offers the reliability
of a design that has been refined over many years from the experience gained in field-
ing tens of thousands of Microchip oscillators.
The following illustration shows the XPRO high-performance rubidium oscillator.
FIGURE 1-1: XPRO High-Performance Rubidium Oscillator.
1.1 TYPICAL APPLICATIONS
The XPRO is a product that Microchip offers for those who require a high-performance
rubidium atomic frequency standard in their system design. The XPRO is designed for
ease of integration into time and frequency systems because of its low-profile and sin-
gle-circuit board design. The height and footprint are designed to accommodate a 1U
VME application, or a 3U VME application. Great care has been taken in the design to
minimize EMI emissions and susceptibility, including the use of an outer mu-metal
cover. The XPRO complies with the FCC Article 47, Code of Federal Rules, Part 15,
Class B. The operation is subject to the following two conditions.
XPRO User’s Guide
DS50003049A-page 10 2021 Microchip Technology Inc.
• This device may not cause harmful interference.
• This device must accept any interference received, including interference that
may cause undesired operation.
The XPRO also complies with EN55022B and EN50082-1. For more information, see
the XPRO data sheet.
The technology utilized in the design of the XPRO has been successfully applied to
telecom networks, such as digital cellular/PCS base stations, SONET/SDH digital net-
work timing, and aerospace and defense applications (such as secure communications
systems and satellite ground-stations). Linked with a GPS receiver, the XPRO provides
the necessary timing requirements for CDMA cellular and PCS systems. The low-tem-
perature coefficient and excellent frequency stability extend holdover performance
when the GPS signal is not available.
The XPRO is designed for long operating periods without maintenance (long-life Rb
lamp, extended crystal control range) with a goal to exceed 10 years. The design pro-
vides a stable frequency with go ability, and excellent spur od short- and long-term st
performance.
The XPRO provides a 5V CMOS-compatible alarm signal derived from the basic phys-
ics operation, which indicates when the output frequency is outside roughly ±5 × 10–8
of absolute frequency offset.
1.2 SPECIFICATIONS
The following sections provide details on the specifications for the XPRO device.
1.2.1 XPRO Electrical Specifications
The following are outputs for the XPRO electrical specifications.
• 10 MHz Sine Wave
- Level: 7.8 dBm ±0.8 dBm (0.55VRMS ±0.05VRMS)
- Impedance load: 50Ω
• 1PPS
- Polarity: Positive
- Pulse width: 20 μs
- Rise/fall time: ≤5 ns (with a 15 pF load)
- Logic level: VL < 0.55V, VH > 4.2V (with a 15 pF load)
- RMS jitter: ≤1 ns
- JamSync accuracy: 10 ns
• Lock status (BITE) 5V CMOS
- Lock: 0V to <0.55V
- Unlock: 4.2V to 5V
• Service status 5V CMOS
- Low: 0V to <0.55V
- High: 4.2V to 5V
The following are inputs for the XPRO electrical specifications.
• 1PPS Sync
- VIL: 0V to 0.8V
- VIH: 2.2V to 3.8V
Note: This information is subject to change. Consult the XPRO data sheet for the
most up-to-date list of specifications.
Functional Descriptions
2021 Microchip Technology Inc. DS50003049A-page 11
• Analog range (±1.5 × 10–9)
- 0VDC to 5VDC
• Input voltage range
- 19VDC to 32VDC
RS-232 control/monitor interface
- Baud rate: 57,600
- Data bits: 8
- Parity: None
- Stop bits: 1
- Flow control: None
1.2.2 XPRO Connectors
The following illustration shows the J1 connector.
FIGURE 1-2: J1 Connector.
The following table lists the J1 signals.
The following illustration shows the J4 connector for the 10 MHz sine output (SMA
FEMALE, MIL-PRF-39012).
Note: Voltage levels are 3.3V CMOS. A “level-shift” device should be employed
to achieve true RS-232 levels.
TABLE 1-1: J1 SIGNALS
Pin
Number Signal Name Type Signal Function
1 24V RTN GND Power return to chassis ground
2 1PPS IN — Sync to external 1PPS input
3 SERIAL DATA OUT 3.3V CMOS Digital steer and control
4 SERIAL DATA IN 3.3V CMOS Digital steer and control
5 LOCKBITE 5V CMOS Indication of lock status
6 24VDC PWR Power input
7 1PPS OUT 5V CMOS 1PPS output
8 SERVICE 5V CMOS Indication of service status
9 FREQCTL DC Analog steer
XPRO User’s Guide
DS50003049A-page 12 2021 Microchip Technology Inc.
FIGURE 1-3: J4 Connector.
Functional Descriptions
2021 Microchip Technology Inc. DS50003049A-page 13
1.2.3 XPRO MTBF: Ground Benign (GB) Prediction
The following table lists the predicted mean time between failure (MTBF) for the XPRO
in a ground benign (GB) environment.
TABLE 1-2: XPRO PREDICTED MTBF, GB
Temperature XPRO MTBF XPRO MTBF
20°C 950,976 hours 109 years
25°C 808,510 hours 92 years
30°C 679,036 hours 78 years
35°C 536,669 hours 64 years
40°C 462,792 hours 53 years
45°C 376,112 hours 43 years
50°C 302,799 hours 35 years
55°C 241,655 hours 28 years
60°C 191,277 hours 22 years
XPRO USER’S GUIDE
2021 Microchip Technology Inc. DS50003049A-page 15
Chapter 2. Operation and Installation
The following sections describe the operation and installation of the XPRO device.
2.1 THEORY OF OPERATION
The XPRO makes use of the atomic-resonance property of rubidium (87Rb) to control
the frequency of an unheated voltage-controlled crystal oscillator (VCXO) through a
frequency-locked loop (FLL).
The following illustration shows a simplified function block diagram for the FLL.
FIGURE 2-1: XPRO Simplified Function Block Diagram.
A microwave signal is derived from a 20 MHz VCXO and applied to the 87Rb vapor
within a glass container or cell. The light of a rubidium spectral lamp also passes
through this cell and illuminates a photo detector. When the frequency of the applied
RF signal corresponds to the frequency of the ground-state hyperfine transition of the
87Rb atom (an ultra-stable high-Q rubidium atomic resonator), light is absorbed caus-
ing a change (decrease) in photo detector current (IPH).
As the change in current is small, modulation techniques are required to extract the
desired signal out of the noise background.
The dip in photo detector current is used to generate a control signal with phase and
amplitude information, which permits continuous atomic regulation of the VCXO fre-
quency. The servo section converts the photo detector current into a voltage, then
amplifies, digitizes, demodulates, and integrates it for high DC-servo loop gain.
The VCXO output signal is divided by two and is buffered to provide the standard fre-
quency output at 10 MHz. This signal is also frequency multiplied to microwave at
6.8346875 GHz through an offset locked phase lock loop (PLL) to interrogate the rubid-
XPRO User’s Guide
DS50003049A-page 16 2021 Microchip Technology Inc.
ium reference. The offset frequency is generated by a high-resolution direct digital syn-
thesizer (DDS) for tuning ability and the microwave power level is servo controlled to
minimize frequency instability caused by microwave power fluctuations.
2.2 INSTALLATION
The following sections provide details on installation for the XPRO device.
2.2.1 Site Selection
The XPRO installation site should be selected to maintain supply voltage and baseplate
temperatures in the product specifications range.
Make sure there are no strong magnetic fields at the site because XPRO is sensitive
to external DC- and AC-magnetic fields (see Section 1.2 “Specifications”). An exter-
nal magnetic field under 2 gauss should not result in measurable permanent frequency
offsets for XPRO.
2.2.2 Cabling
If desired, the XPRO is designed to directly mate to a user's interface board, saving the
cost and associated issues of interconnect cabling.
2.2.3 Turn-On Procedure
The XPRO does not have an on/off switch. The unit is powered up by plugging in the
unit's J1 connector to a properly terminated cable or the user's interface board. The fol-
lowing illustration shows a block diagram of a suggested hookup.
FIGURE 2-2: Block Diagram of Suggested XPRO Hookup.
The mating connector must provide power to J1-6 and power return to J1-1. The sys-
tem power supply must be capable of providing a peak source current of >1.5A during
the warm-up period. After warm-up, this power requirement drops to ~0.5A (room tem-
perature).
If the power supply is unable to provide the required peak amperage, then the XPRO
warm-up times will be degraded. If insufficient power is provided, the unit may be
unable to complete warm-up and a latch-up condition will result. This does not over
stress the electronics of the unit. However, it prevents the unit from achieving lock. It
can also cause rubidium migration in the lamp, which could prevent the unit from oper-
ating properly (it would require servicing).
The following are steps for turning on the XPRO:
1. Connect the RF load to the SMA female connector, J4.
2. Monitor the BITE signal at J1-5 with respect to chassis ground at J1-1, using a
high-impedance meter (recommended >1 MΩ input resistance).
3. Once the XPRO is plugged in and receiving power, wait 3 to 6 minutes while the
unit achieves atomic lock. During this period, the monitored BITE signal should
Note: Always use shielded cable and connectors to minimize EMI emissions.
XPRO User’s Guide
DS50003049A-page 18 2021 Microchip Technology Inc.
2.2.5 Synchronizing to an External 1PPS Signal
The following steps show how to synchronize to an external 1PPS signal.
1. Wait for clock to lock (see Lock (BITE) Signal (see page 13)).
2. Connect external 1PPS in (see XPRO Connectors (see page 5)).
3. Send command J (see XPRO Serial Port Protocol (see page 12)).
2.2.6 Maintenance and Repairs
The XPRO is not field repairable. If the unit should fail, do not remove the cover of the
unit and attempt to make repairs. Instead, call Microchip for the return procedure from
the Customer Support Group before returning the unit to Microchip.
XPRO USER’S GUIDE
2021 Microchip Technology Inc. DS50003049A-page 19
Chapter 3. Design Integration Considerations
The following sections provide details on the design integration considerations for the
XPRO device.
3.1 XPRO MECHANICAL DRAWINGS
The following illustration shows the XPRO mechanical drawing.
FIGURE 3-1: XPRO Mechanical Drawing.
3.2 THERMAL CONSIDERATIONS
The following sections describe the thermal considerations for the XPRO device.
3.2.1 Thermal Tape Use
It is critical to obtain a good thermal contact from the bottom (baseplate) of the XPRO
to the mounting surface in order to achieve the highest ambient operating temperature
for the specified XPRO operating baseplate temperature. It is also very important to
maintain a uniform heat sink temperature because of uneven heat flow into the base-
plate of the XPRO through its various mounting points.
3.2.2 Heat Sink
A heat sink or mounting baseplate is required to keep the baseplate temperature under
70°C. Internal self heating of the XPRO will cause local internal temperatures to exceed
Microchip’s part de-rating guidelines when used without a heat sink or forced air
(although the maximum manufacturer’s operating temperature ratings will not be
exceeded). A heat sink with thermal resistance to ambient of less than 2°C/W is
required for ambient of 50°C maximum.
3.2.3 Impact of External Ambient Air Temperature on Unit Operation
The power consumption for XPRO versus baseplate temperature is dominated by the
following mechanisms.
• The resonator heater power
XPRO User’s Guide
DS50003049A-page 20 2021 Microchip Technology Inc.
• The lamp heater power
• The electronics power
The resonator heater power is determined primarily by the resonator control tempera-
ture of 82°C, the baseplate temperature, and the 15.3°C/W thermal resistance from the
resonator to baseplate. The lamp heater power is determined primarily by the lamp
control temperature of 114°C, the baseplate temperature, and the 53°C/W thermal
resistance from the lamp to baseplate. Due to the unit’s internal 17V regulator, the elec-
tronics power reflects a fixed electronic current that is independent of input voltage. It
is roughly independent of baseplate temperature. The heater powers are roughly inde-
pendent of input voltage.
The XPRO maximum baseplate temperature described in the specifications was based
on a model where the unit was covered on 5 sides with 1-inch foam to simulate free
convection in air as the heat sink/baseplate was exposed to forced air.
The maximum operating baseplate temperature will be lower by several degrees Cel-
sius if the external air is hotter than the baseplate mounting. For example, a situation
where the baseplate is being cooled by a thermoelectric cooler, but the unit is exposed
to nearby heat-producing equipment.
If there is air flow over the unit’s top cover, the XPRO’s maximum operating baseplate
temperature will increase by 1°C or 2°C and its power consumption at a given base-
plate temperature will also increase by a few tens of milliwatts.
3.2.4 Unit Operating Temperature Range
There are three scenarios of interest concerning the operating temperature range for
XPRO (operating range –25°C to +70°C baseplate).
These three scenarios are differentiated by performance for the following conditions:
• The turn-on/warm-up period
• Standard operation after warm up is completed
• Emergency operation after warm up is completed
The turn-on/warm-up period includes the time for the internal heater circuits to obtain
thermal equilibrium, for the lamp to ignite into a plasma discharge, for the standard to
achieve atomic lock, and for the crystal operating temperature to reach its normal oper-
ating temperature range.
The following are the three scenarios:
• Scenario 1: The operating temperature range below the normal temperature
range without guaranteed warm up, but with full frequency control. Not recom-
mended and performance/specifications are not guaranteed.
• Scenario 2: The normal temperature range with full performance, including warm
up.
• Scenario 3: The operating temperature range above the normal temperature
range, excluding guaranteed warm up, but without loss of lock. Not recommended
and performance/specifications are not guaranteed.
The following describe all scenarios defined in terms of the unit’s baseplate tempera-
ture (the bottom surface of the bottom cover):
• Scenario 1 (not recommended) Temperature Range: –35°C to –25°C baseplate.
This operating temperature range allows full-frequency control, but excludes nor-
mal warm up. The cold-temperature limit is based on the use of a –30°C/+85°C
unheated crystal, and an internal temperature rise at the crystal of ~6°C.
• Scenario 2 Temperature Range: –25°C to +70°C baseplate. The normal operating
temperature range with specified warm-up capability included. This temperature
range excludes that of scenario 1, because of the unheated crystal used in the

Tuotetiedot

Merkki: Microchip
Kategoria: Ei luokiteltu
Malli: XPRO-Base-Perf-AT

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