Microchip Technology SA5 Series User manual

2019 Microchip Technology Inc. DS50002938A
Miniature Atomic Clock (MAC)
SA5X
User’s Guide

DS50002938A-page 2 2019 Microchip Technology Inc.
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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,
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Prochip Designer, QTouch, SAM-BA, SenGenuity, SpyNIC, SST,
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are registered trademarks of Microchip Technology Incorporated in
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Edge, ProASIC, ProASIC Plus, ProASIC Plus logo, Quiet-Wire,
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CryptoController, dsPICDEM, dsPICDEM.net, Dynamic Average
Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial
Programming, ICSP, INICnet, Inter-Chip Connectivity, JitterBlocker,
KleerNet, KleerNet logo, 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, SAM-ICE, Serial Quad I/O, SMART-I.S., SQI,
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ZENA are trademarks of Microchip Technology Incorporated in the
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II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in
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© 2019, Microchip Technology Incorporated, All Rights Reserved.
ISBN: 978-1-5224-5327-7
For information regarding Microchip’s Quality Management Systems,
please visit www.microchip.com/quality.

MAC-SA5X USER’S GUIDE
2019 Microchip Technology Inc. DS50002938A-page 3
Preface
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.
PURPOSE OF THIS GUIDE
The MAC-SA5X User's Guide provides basic recommendations for designing products
to use Microchip's Miniature Atomic Clock (MAC) SA5X. The guidelines in the docu-
ment are generic because specific product requirements vary between applications.
This material consists of a brief description of SA5X design supported by block dia-
grams, description of environmental issues, installation guidelines, and unit operation.
WHO SHOULD READ THIS GUIDE
This document is intended for engineers and telecommunications professionals who
are designing, installing, operating, or maintaining time, frequency, and synchroniza-
tion systems that require a low profile and highly precise frequency generator.
To use this document effectively, you must have a good understanding of digital tele-
communications technologies, analog frequency generation, and synthesis tech-
niques.
DOCUMENT LAYOUT
This guide contains the following sections and appendixes:
•Chapter 1. “Product Overview”: Provides an overview of the product, describes
the major hardware and software features, and lists the system specifications.
•Chapter 2. “Installation”: Contains procedures for unpacking and installing the
system, and for powering up the unit.
•Chapter 3. “Operation”: Describes procedures for frequency adjustment and
toggling on/off various features.
•Chapter 4. “Command Line Interface”: Describes the CLI command conven-
tions, functions, and features.
•Chapter 5. “Maintenance and Troubleshooting”: Contains maintenance and
troubleshooting procedures for the product. Also contains procedures for return-
ing the MAC.
•Appendix A. “Principle of Operation”: Briefly explains Atomic Interrogation and

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Coherent Population Trapping
•Appendix B. “Legacy Command Set (SA.3Xm)”: Describes the Legacy CLI
command conventions, functions, and features. For backwards compatibility.
•Appendix C. “Reference Designs”: Provides generic sample schematics for
converting MAC input/output signals.
•Appendix D. “Evaluation Kit”: Describes the evaluation kit for use with the
MAC.
•Appendix E. “Software License Agreements”: Describes the open source soft-
ware that portions of the SA5X software makes use of.
CONVENTIONS USED IN THIS GUIDE
This manual uses the following documentation conventions:
• Acronyms and Abbreviations: Terms are spelled out the first time they appear in
text. Thereafter, only the acronym or abbreviation is used. This guide uses “SA5X”
and “MAC” interchangeably. SA5X is the latest generation of Miniature Atomic
Clock (MAC).
• Unless explicitly labeled with Hz, MHz, etc, all references to “frequency offset”
throughout this document imply the industry-standard fractional frequency ∆f/f,
where “∆f” is the difference between nominal and measured value (in Hz), and “f”
is the nominal frequency (in Hz).
WARNINGS, CAUTIONS, RECOMMENDATIONS, AND NOTES
Warnings, Cautions, Recommendations, and Notes attract attention to essential or crit-
ical information in this guide. The types of information included in each are displayed
in a style consistent with the examples below.
WARNING
To avoid serious personal injury or death, do not disregard warnings. All warnings use
this style. Warnings are installation, operation, or maintenance procedures, practices,
or statements that, if not strictly observed, may result in serious personal injury or
even death.
CAUTION
To avoid personal injury, do not disregard cautions. All cautions use this style. Cau-
tions are installation, operation, or maintenance procedures, practices, or statements
that, if not strictly observed, may result in damage to, or destruction of, the equipment.
Cautions are also used to indicate long-term health hazards.
Note: All notes use this style. Notes contain installation, operation, or mainte-
nance procedures, practices, conditions, or statements that alert you to
important information that may make your task easier or increase your
understanding.

Preface
2019 Microchip Technology Inc. DS50002938A-page 5
WHERE TO FIND ANSWERS TO PRODUCT AND DOCUMENT QUESTIONS
For additional information about the products described in this guide, please contact
your Microchip representative or your local sales office. You can also contact us on the
web at www.microsemi.com/ftdsupport.
When this manual is updated the latest version will be available for downloading from
Microchip’s web site. Manuals are provided in PDF format for ease of use. After down-
loading, you can view the manual on a computer or print it using Adobe Acrobat
Reader.
Manual updates are available at: www.microsemi.com/ftdsupport
RELATED DOCUMENTS AND INFORMATION
See your Microchip representative or sales office for a complete list of available docu-
mentation. To order any accessory, contact the Microchip Sales Department. See
www.microsemi.com/sales-contacts/0 for sales support contact information. If you
encounter any difficulties installing or using the product, contact Microchip Frequency
and Time Systems (FTS) Services and Support:
U.S.A. Call Center: including Americas, Asia and Pacific Rim
Frequency and Time Systems
3870 N 1st St.
San Jose, CA 95134
Toll-free in North America: 1-888-367-7966
Telephone: [phone]
Fax: [phone]
email: [email protected]
Internet: www.microsemi.com/ftdsupport
Europe, Middle East, and Africa (EMEA)
Microchip FTS Services and Support EMEA
Altlaufstrasse 42
85635 Hoehenkirchen-Siegertsbrunn
Germany
Telephone: [phone]
Fax: [phone]
email: [email protected]
email: [email protected]
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

MAC-SA5X User’s Guide
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•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 (November 2019)
• Initial release of this document as Microchip DS50002938A.
- Under Microsemi’s literature system, this document is number
900-44500-000, Rev. A.

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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............................................. 4
Where to Find Answers to Product and Document Questions .............................. 5
Related Documents and Information..................................................................... 5
The Microchip Website.......................................................................................... 5
Customer Support ................................................................................................. 6
Document Revision History ................................................................................... 6
Chapter 1. Product Overview
1.1 MAC-SA5X Overview ...................................................................................... 9
1.1.1 Key Features .............................................................................................. 10
1.2 Physical Description ...................................................................................... 10
1.2.1 Communications Connections.................................................................... 11
1.2.2 Input Connections....................................................................................... 11
1.2.3 Output Connections.................................................................................... 11
1.2.4 Power and Ground Connections ................................................................ 12
1.3 Functional Description................................................................................... 12
1.4 Configuration Management ........................................................................... 13
1.5 Alarms ........................................................................................................... 13
Chapter 2. Installation
2.1 Handling Considerations .............................................................................. 15
2.2 Mounting Considerations .............................................................................. 15
2.21 Absolute Minimum and Maximum Ratings .................................................. 19
2.3 Start-Up Sequence ....................................................................................... 19
Chapter 3. Operation
3.1 Configure the Serial Port ............................................................................... 21
3.2 Analog Tuning ............................................................................................... 21
3.3 Digital Tuning ................................................................................................ 22
3.3.1 Calibration .................................................................................................. 22
3.4 1PPS Disciplining .......................................................................................... 23
3.4.1 Theory ........................................................................................................ 23
3.4.2 Selection of Disciplining Time Constant, “Tau”........................................... 25
3.4.3 JamSync..................................................................................................... 26
3.4.4 1PPS Phase Measurement Mode .............................................................. 26
3.4.5 Cable Length Compensation...................................................................... 26

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3.4.6 PPS Quantization Error Correction .............................................................27
3.5 Device Information and Status ...................................................................... 27
3.6 Time of Day (TOD) ........................................................................................ 27
Chapter 4. Command Line Interface
4.1 Command Structure ...................................................................................... 30
4.1.1 Sequence Number ......................................................................................30
4.1.2 Arguments...................................................................................................30
4.1.3 Command Checksum .................................................................................31
4.2 Response Structure....................................................................................... 31
4.2.1 Error Response...........................................................................................31
4.2.2 Response Checksum..................................................................................32
4.3 Announcement Structure............................................................................... 33
4.4 Parameters.................................................................................................... 33
4.4.1 Parameter Index .........................................................................................33
4.4.2 Parameter Attributes ...................................................................................35
4.4.2.1 Parameter Units Attribute............................................................35
4.4.3 Alarms Parameter .......................................................................................36
4.5 Commands .................................................................................................... 37
4.5.1 Command Index..........................................................................................37
4.5.2 Command Usage ........................................................................................38
Chapter 5. Maintenance and Troubleshooting
5.1 Preventative Maintenance............................................................................. 43
5.2 Electrostatic Discharge (ESD) Considerations.............................................. 43
5.3 Troubleshooting............................................................................................. 43
5.4 Repairing the MAC ........................................................................................ 43
5.5 Upgrading the Firmware................................................................................ 43
5.6 Returning the MAC........................................................................................ 43
Appendix A. Principle of Operation ............................................................................45
Appendix B. Legacy Command Set (SA.3Xm)
B.1 Legacy Command Structure ......................................................................... 47
B.2 Legacy Command Index ............................................................................... 48
B.3 Legacy Command Usage ............................................................................. 48
Appendix C. Reference Designs .................................................................................51
Appendix D. Evaluation Kit
D.1 Overview and Key Features ......................................................................... 55
D.2 Physical Description ..................................................................................... 56
D.2.1 Communications Connections....................................................................57
D.2.2 Input Connections ......................................................................................58
D.2.3 Output Connections....................................................................................58
D.2.4 Power Connections ....................................................................................58
D.2.5 Functional Description and Operation ........................................................58
D.2.5.1 Troubleshooting..........................................................................59
Appendix E. Software License Agreements ..............................................................61
Worldwide Sales and Service .....................................................................................63

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Chapter 1. Product Overview
1.1 MAC-SA5X OVERVIEW
The MAC is a source of stable output frequency. Because it relies on the Atomic reso-
nance of Rubidium Isotope 87 (87Rb) gas to generate the RF output, it is less suscep-
tible to instabilities produced from the mechanical and thermal stresses inherent in
Quartz oscillators, enabling superior mid- to long-term accuracy. This stability makes it
suitable as a holdover reference in GPS denied environments. Frequency errors can
be corrected by applying a digital command or external correction voltage to the MAC.
(See Frequency steering and Section 3.2 “Analog Tuning”). Frequency drift (Aging
rate) can also be corrected by implementing the 1PPS disciplining feature of the MAC.
When combined with a GNSS receiver, this feature allows the system designer to com-
bine the short-term stability of a Rb reference with the long-term stability of the GNSS,
approaching the performance of laboratory-grade Cesium Beam Tube frequency stan-
dards (see Section 3.4 “1PPS Disciplining”).
The Miniature Atomic Clock (MAC) SA5X is Microchip's seventh generation gas cell
atomic oscillator technology product. It was designed to accommodate a variety of tim-
ing applications as well as to replace several legacy Rubidium products (SA.22c, x72
and MAC-SA.3Xm). The footprint is compatible with the SA.3Xm, but with several
advancements in technology and features. Users of the previous generation (SA.3Xm)
can now expect improvements to frequency stability, warm-up time, input voltage
range, and operational temperature range. Additionally, 1PPS disciplining and USB
connections via a new embedded Molex™ connector allow greater design capabilities.
The 1PPS input allows users to quickly calibrate frequency and phase of the MAC to a
primary clock such as GPS, while the RF and 1PPS outputs provide highly stable hold-
over references.
FIGURE 1-1: The Miniature Atomic Clock (MAC) SA5X.

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The MAC reflects significant advances in physics miniaturization and atomic interroga-
tion algorithms that serve to reduce size and power while providing a stable reference
frequency that is resistant to environmental perturbation. The SA5X comes in several
performance levels to meet a range of system requirements. The SA5X offers a low
height (18.3 mm/0.72 in), a small footprint (50.8 mm × 50.8 mm, or 2 in × 2 in), and an
industrial operating temperature range of –40°C to +75°C (measured at the baseplate).
It is refined for cost effective mass production and can be easily integrated into time,
frequency, and synchronization systems. The SA5X requires a single supply voltage
and can be mounted directly onto a circuit board as a component of a module used in
20 mm (0.8 in) wide card slots. The design produces a stable frequency with good
short and long term stability, and excellent phase noise performance.
This user guide provides engineering information for use of the SA5X. It also provides
supporting information for use of the Evaluation Kit (p/n 090-44500-000). Furthermore,
the design details of the Evaluation Kit can be used to assist with host system design
(for example, power conditioning, signal buffering, and so on). This user guide must be
used in conjunction with the current data sheet for the SA5X, which is available on the
Microchip web site.
1.1.1 Key Features
•10MHz CMOS Output
• 1PPS Disciplining
• 1PPS LVDS Inputs and Output
• –40°C to +75°C Operating Temperature (Baseplate)
• –55°C to +100°C Storage Temperature
• USB 2.0-Compatible Communication Pins
• Wide Range Allowable DC Input (4.5 to 32V)
• Fast Warm-Up Time (<7 Minutes from –10°C to +75°C)
• <5x10-11 Monthly Aging Rate (On for 30 Days Prior)
• <100 ns Time Error in 24 hrs (Calculated Based on 5x10-11/mo. Aging Rate,
Assuming Zero Initial Phase/Frequency Offset, Static Environment, On for 30
Days Prior to Holdover)
• Serial/USB Interface for Digital Steering, Configuration, and Diagnostics
1.2 PHYSICAL DESCRIPTION
Labels will contain information about the part number and the serial number. The serial
number indicates the initial time of manufacture in the following manner. The first two
digits of serial number indicate the year of manufacture (18 = 2018). Digits three and
four indicate the month of manufacture (01 = January).
The MAC consists of a 2 in x 2 in x 0.7 in PCB-mountable chassis, consisting of a
Nickel-plated Aluminum baseplate and black anodized Aluminum cover. All connec-
tions for the MAC are on the baseplate. Figure 1-2 shows the top cover on the left and
the bottom baseplate on the right.
See Figure 2-1 for a complete mechanical drawing.

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FIGURE 1-2: Top Cover and Bottom Baseplate.
The baseplate consists of eight backwards-compatible gold-plated pins and recessed
20-lead Molex™ connector for new features (1PPS, USB, etc).
FIGURE 1-3: Pinout.
1.2.1 Communications Connections
The MAC is controlled either by the legacy serial port pins or with the high speed
USB-compatible pins on the Molex connector.
•Serial Console Port: The serial port connection is made through pins 7 and 8 on
the baseplate of the MAC. This port allows a user to connect to a terminal or com-
puter using a terminal emulation software package. When connecting to this port,
use an appropriate converter chip such as the TRS3122E or similar to attain the
required LVCMOS levels. Figure 1-2 shows the serial port pins 7 and 8 in the
lower-right region of the baseplate. The default speed is 57600 bps and higher
speeds of 230400 bps and 921600 bps are available.
•USB Port: The USB port is capable of making high speed communication with the
MAC though the Molex (J1) connector pins J-2, 4, and 6.
Note: “Compatibility” commands are not supported when communicating via USB
port. See Appendix B. “Legacy Command Set (SA.3Xm)”.
1.2.2 Input Connections
•Analog Tuning: Analog Tuning is available on pin 1 for steering the MAC output
frequency by means of an externally supplied DC voltage. This method is for leg-
acy applications that cannot steer the MAC digitally via the serial/USB interface.
•1PPS Input (x2): Two selectable LVDS 1PPS inputs can be provided on pins
J1-5,7 (PPS0-IN) or J1-1,3 (PPS1-IN) for aligning the MAC’s frequency and timing

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output with an externally applied 1PPS reference signal. The PPS input is
selected via digital interface. Default input is PPS0-IN.
1.2.3 Output Connections
•10 MHz RF Output: One CMOS output is available on pin 3.
•1PPS Output: A single differential LVDS 1PPS output is available on pins
J1-17, 19.
•Built-In Test Equipment (BITE): An active-low CMOS output on pin 6 signifies
that the MAC has achieved atomic lock.
•Alarm Output: An active-low CMOS output on pin J1-20 indicates if an alarm
condition is present. The user can read the Alarm bits through the USB/Serial
interface to determine which alarm was triggered.
1.2.4 Power and Ground Connections
The MAC is not equipped with a power switch. DC power is applied on pin 5 with
ground pins located on pins 2 and 4. If the J1 connector is used, pins J1-8, J1-9, and
J1-15 should be grounded. Remaining pins should remain as “No Connect” (NC)
unless indicated otherwise in Figure 1-3. If J1 connector is unused, all pins should
remain as “No Connect”.
Recommendation: It is recommended to tie ground (Pin 4) to same node as the
baseplate ground Pin 2.
1.3 FUNCTIONAL DESCRIPTION
Communication Ports
These ports can be used to configure the MAC with Microchip’s C3 software com-
mands using a terminal or a computer with terminal emulation software. The default
settings for the serial port are:
• Baud = 57.6K
• Data Bits = 8 bits
• Parity = None
• Stop bits = 1
• Flow Control = None
Commands allow the user to:
• Turn Analog tuning on or off
• Digitally adjust the output frequency
• Configure 1PPS Disciplining settings
• Query the MAC’s health/lock/alarm status
• Configure the Time of Day
Analog Tuning Input
Analog tuning is a means of steering the MAC's output frequency by applying a DC tun-
ing voltage to Pin 1. This is useful for legacy applications where digital frequency steer-
ing is not possible.
1PPS Inputs
The MAC offers two selectable 1PPS inputs for use in steering the output RF (and
1PPS Output, simultaneously). PPS_Input_0 (pins J1-5,7) and PPS_Input_1 (pin
J1-1,3) are selectable with the PpsSource parameter. Their 1PPS Disciplining set-

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tings can be adjusted independently, however, the MAC can only discipline to one input
at a time. If a valid PPS signal on the selected input is present, then the parameter
PpsInDetected = 1. See Section 3.4 “1PPS Disciplining” for more details.
CAUTION
An LVDS square wave 1PPS is the allowable input.
10 MHz Output
The 10 MHz RF output appears on Pin 3 as soon as the MAC is switched ON and is
always present, regardless of the lock status. When the MAC is out of lock
(Locked = 0/Logic-High BITE pin), the output frequency is provided by the free-running
TCXO, which has frequency accuracy specification of ±2 ppm over its operating range.
The output format is 3.3V LVCMOS compatible.
Note: If a high-level (high-power) output driver is required, a driver circuit must be
implemented external to the MAC.
1PPS Output
An LVDS 1 pulse-per-second (1PPS) square wave output is available on pins J1-17,19
upon power-up. The 1PPS output is derived by digital division of the RF reference fre-
quency and cannot be de-coupled. Therefore, the 1PPS and 10 MHz outputs are
always synchronized (within ±50 nanoseconds, regardless of Lock status).
PPS output timing relative to average PPS input timing is adjustable via the digital inter-
face with 10 ns steps using PpsOffset parameter.
Default PPS Pulse Width is 20 μs. Pulse width may be modified via the PpsWidth
parameter.
BITE Output
The SA5X provides an active logic low indication through Pin 6, the BITE signal, when
the internal quartz oscillator is frequency-locked to the rubidium atomic resonance. As
long as the BITE signal is low, the user can be assured that the short-term stability
specifications are satisfied. The lock status is also available through the C3 Protocol
Locked parameter.
If the BITE signal is high (Locked = 0), then atomic Lock is not attained (or is lost) and
the SA5X is in its start-up sequence. During this sequence, signal output amplitude is
maintained but the stability performance is driven by the internal TCXO. Lock acquisi-
tion typically takes 5 minutes at room temperature.
Alarm Output
The Alarm Output provides an indication if an alarm is present (active logic low). It will
persist until cleared with the ackalm software command. A user can learn the exact
alarm condition from the value of the Alarms parameter (See Section 4.4.3 “Alarms
Parameter”).
1.4 CONFIGURATION MANAGEMENT
The Command Line Interface can be used to control specific functions of the MAC from
a terminal connected to the RS-232 serial port or the USB port.
Refer to Chapter 4. “Command Line Interface” for further details.

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1.5 ALARMS
The MAC uses alarms to notify the user when certain conditions are deteriorating
below specified levels or when issues arise, such as failure to acquire Lock or tempera-
ture warning. These alarms are indicated by CLI status and the alarm pin. For more
information, see Section 3.5 “Device Information and Status” and
Section 4.4.3 “Alarms Parameter”.

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Chapter 2. Installation
2.1 HANDLING CONSIDERATIONS
CAUTION
To avoid electrostatic discharge (ESD) damage, proper ESD handling procedures must
be observed in unpacking, assembling, and testing the MAC.
The MAC is delivered in ESD-safe packaging. The MAC must be removed from the
ESD-protective bag in an ESD-safe environment. Once installed on the test fixture, it
is recommended that the entire assembly be treated as ESD-sensitive.
Retain the original MAC ESD-safe packaging material in the event that the device
needs to be returned to Microchip for service.
2.2 MOUNTING CONSIDERATIONS
For initial testing and evaluation, it is recommended that the pins not be modified or sol-
dered to a PCB. The recommended socket for PCB attachment is Mill-Max
0332-0-43-80-18-27-10-0. After evaluation, the pins can be hand-soldered to a PCB.
Below is the mechanical drawing (ICD). Contact Microchip for latest revision.
FIGURE 2-1: ICD 697-00498-000 for MAC.

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DS50002938A-page 16 2019 Microchip Technology Inc.
Solder
The MAC is a lead-free device. See the data sheet for RoHS compliance. Use SAC305
solder Sn96.5/Ag3.0/Cu0.5 or similar for hand-soldering to a PCB.
Heat Sink and Thermal Management
To allow the highest ambient operating temperature for the SA5X, it is recommended
that the bottom (baseplate) of the SA5X have good thermal contact with the mounting
surface (no air gap between baseplate and external PCB/heat sink etc). To ensure
good thermal contact, Microchip recommends that the SA5X is secured using (4) 2-56
screws. The location of the four screw holes is shown in Figure 2-1.
If the baseplate temperature rises above +75°C, the physics package heater shuts
down as control point temperatures are exceeded and the unit temperature coefficients
increase. The unit eventually loses lock above +75°C.
When practical, it is recommended to monitor the baseplate temperature with a ther-
mocouple to ensure it remains below +75°C. Alternatively, one may query the telemetry
parameter Temperature to get a rough estimate of the external baseplate tempera-
ture. The Temperature parameter is measured internally on the PCB and is generally
~10°C to 15°C warmer than the actual baseplate temperature.
It is also important to maintain a uniform temperature into the baseplate of the SA5X
through its mounting points. A thermal pad or thermal grease may improve thermal
conductivity between a heat sink and the MAC's outer case. Figure 2-2 shows the
mechanical drawing for a thermal pad.
FIGURE 2-2: ICD 172-00054-000 Thermal Pad.
CAUTION
To avoid damage to the SA5X, the mounting screws must not penetrate the unit by
more than 0.11 in. (2.79 mm).
WARNING
To avoid the possibility of a burn, mount the SA5X to a heat-dissipating surface. The
SA5X operates at a temperature that is hot to the touch and may cause handling dis-
tress.

Installation
2019 Microchip Technology Inc. DS50002938A-page 17
RF Noise Mitigation
If the system that the MAC is designed into is sensitive to RF or microwave frequencies
(especially 3.417 GHz and its harmonics), care must be taken to dampen those fre-
quencies at locations that might be adversely affected. One way to do this is to deter-
mine the appropriate capacitor that has its "zero-ohm" characteristic at the frequency
of interest and use that capacitor to effectively short that frequency to ground where it
might a problem. For example, it has been determined that at 3.417 GHz, the
"zero-ohm" capacitor value for an 0603-sized SMT component is 4.3 pF; for an
0402-sized capacitor, the value must be 6.8 pF; and for an 0201-sized capacitor, 8.2 pF
is ideal.
From this, it is recommended to place the appropriate-valued capacitor at the node of
interest. It is important that this cap be exactly on the node where the noise must be
squelched, and is grounded right at the cap as well. In addition, a good RF ground
plane is required, otherwise the improvement can be nullified.
The nulling capacitors are placed as close to the MAC I/O pins as possible. Because
the 3.417 GHz frequency is used within the MAC, the above mentioned nulling capac-
itors are recommended to be installed on pins 1,3,5-8.
EMI and Noise Considerations
When a user has an application where the phase noise and spur integrity are crucial,
the SA5X must be provided with a clean source of DC power (free of spurious current
or voltage noise). Connecting fans, heaters, and other switching devices to the DC sup-
ply powering the SA5X can result in degraded performance.
This noise is coupled through the power line to cause modulation spurs on the output
signal. Special care must be taken to avoid noise at 100 Hz and its harmonics (roughly
up to the tenth harmonic).
If power line filtering is added at the power input pin of the SA5X, this filtering cannot
have any resonance points greater than the specified impedance of less than 0.1Ω
from DC to 100 kHz in order to avoid the potential for noise peaking or oscillations in
the internal power regulators.
In addition, the input operating voltage range specified for the SA5X during turn-on
must continue to be met during operation of the unit. For example, using a 0.3ΩDC
source resistance for the input supply line may not be appropriate because the voltage
drop resulting from this resistance (caused by the turn-on current or quiescent operat-
ing current) could cause the input voltage to drop below the specified allowable value.
Signal Connections
The SA5X pinout is shown in Figure 2-3.
FIGURE 2-3: Pinout.

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The electrical function of each pin is shown in Table 2-1.
TABLE 2-1: PIN FUNCTION TABLE
Connector Pin
Number Function Range/Format Note
OCXO Style 1 Analog tuning
input 0V to 5.0V Note 1, Note 2
OCXO Style 2 Baseplate — Note 3
OCXO Style 3 RF output CMOS 3.3VPP nominal Note 4
OCXO Style 4 GND — Note 5
OCXO Style 5 Supply voltage
(VCC)
4.5VDC to 32VDC
(5VDC recommended) —
OCXO Style 6 Built-In Test
Equipment (BITE)
CMOS: Logic_H > 3V,
Logic_L < 0.3V Note 6
OCXO Style 7, 8 Serial
communication
2.8V < Logic_H < 3.8V
0V < Logic_L < 0.3V Note 7
J1 Molex 1, 3 PPS1-IN LVDS —
J1 Molex 5, 7 PPS0-IN LVDS —
J1 Molex 8, 9, 15 GND — —
J1 Molex 17, 19 PPS-OUT –,+ LVDS square wave, 4 ns, 100Ω—
J1 Molex 20 Alarm CMOS: Logic_H > 3V,
Logic_L < 0.3V —
J1 Molex 2, 4, 6 USB USB —
Note 1: Analog tuning input sensitivity is 0V to 5V into 5 kΩ, 2.5V for no pull.
2: Analog tuning is disabled by default. Digital tuning is recommended instead.
3: Shall be connected to GND externally.
4: 10 MHz, CMOS square wave, VL < 0.3V, VH > 3V. Amplitude is dependent on load.
5: Signal and Supply. It is recommended to tie this ground to same node as baseplate
ground Pin 2.
6: BITE output (active-low):
0 = Normal Operation
1 = Unlock Condition
7: If connecting to COM port of a computer, a TTL/RS-232 (or HCMOS/RS-232)
adapter is necessary.

Installation
2019 Microchip Technology Inc. DS50002938A-page 19
2.2.1 Absolute Minimum and Maximum Ratings
Table 2-2 indicates the absolute minimum and maximum ratings to which the MAC can
be subjected without permanent unrecoverable damage.
TABLE 2-2: MINIMUM AND MAXIMUM RATINGS
Parameter Rating
Supply Voltage (VCC) 0VDC to +32VDC
1PPS Inputs –0.5V to +3.6V
Analog Tuning Voltage 0V to +5V (into 5 kΩ)
Maximum Current Draw RS-232, BITE, Alarm: ±8 mA
RF output: ±8 mA
Storage Temperature –55°C to +100°C
Note: The MAC cannot be expected to perform normally when operated outside
of the recommended operating conditions noted on the product data sheet.
All ratings apply at +25°C, unless otherwise noted.
2.3 START-UP SEQUENCE
CAUTION
To avoid severe damage to the unit, do not apply power to the incorrect terminals. The
SA5X does not have reverse voltage protection.
When the MAC is initially powered on, it performs an acquisition sequence, which
includes stabilizing the temperature of the physics package, optimizing physics pack-
age operating parameters, and acquiring frequency lock to the atomic resonance.
A typical warm-up sequence is shown in Figure 2-4. When power is connected to the
MAC, its RF and 1PPS output signals (orange dashed line) will appear immediately.
The short-term stability specification of these signals will not be satisfied until the Lock
sequence is completed (after ~300 seconds in this example). Prior to Lock, the output
signal will have an inaccuracy of several ppm and drift per the MAC’s internal TCXO.
All MAC’s have their (Locked) output frequency calibrated to within ±5x10-11 Hz/Hz
prior to shipment. However, environmental conditions and transit time will affect the cal-
ibration to an unknown degree. Therefore, some additional frequency offset should be
expected when the MAC is first powered on by the user. Offsets may be corrected, as
explained in the Frequency Steering section. The re-trace specification provides some
guidance for frequency offsets due to powering off the unit; however, the specification
is not comprehensive.
Power consumption is displayed as a solid black trace. Initially, the power consumption
will draw >10W to bring the internal unit temperature up to operational level. Once the
temperature has stabilized, the steady state power consumption will drop to ~6W.
Steady state power consumption will be higher for colder ambient temperatures
because more heating will be required to maintain the correct internal temperature.
Similarly, the duration of the heat-up period (maximum power consumption) will be lon-
ger for colder ambient temperatures.
The baseplate temperature (solid orange trace) will generally rise ~15°C during the
start-up sequence, but this varies greatly with thermal management (heat sink, airflow,
etc). Generally, the temperature rise will be smaller at warmer temperatures, larger at
colder temperatures.

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DS50002938A-page 20 2019 Microchip Technology Inc.
Care should be used to ensure that the maximum operating temperature is not violated.
For instance, a MAC that is powered up in a 70°C ambient environment will likely rise
above the maximum operating temperature during the start-up period unless careful
thermal management is employed. (See Section 2.2 “Mounting Considerations”)
The LockProgress parameter (not pictured) will reveal the Lock acquisition status in
terms of percentage-complete. Once the unit finishes the sequence, the BITE pin
(black dashed trace) will indicate Lock (logic low). Generally, Lock acquisition times will
be shorter at warmer temperatures, longer at colder temperatures. If this sequence
should fail, the Alarms parameter will signify “Acquisition Failed”. If this should occur,
check that the environmental specifications have not been violated (operating tempera-
ture, input voltage, magnetic field exposure, etc) and reboot the device. Contact Cus-
tomer support if the alarm persists.
Note: Sequence times and power levels vary according to environmental condi-
tions, especially temperature.
FIGURE 2-4: Start-Up Sequence.
Once power is supplied to the unit, it will output the following strings on the serial port:
[>Loading...]
[>Microchip SA5X]
After a typical warm-up time of 5 to 7 minutes, the oscillator is fully operational and the
operator may choose to adjust the device parameters. The MAC meets all short-term
stability specifications as soon as Lock is achieved. Long-term stability specifications
(Monthly Aging frequency drift rate) is satisfied within 30 days of continuous power at
room temperature. There are no maintenance procedures or adjustments needed,
aside from frequency adjustment which is described in a later section.