Silicon Labs Si5332-AM User Manual
AN1292: Si5332-AM SmartClock™ Fault
Detection and Monitoring
What is the Si5332-AM family and why use it in automotive applications?
Automotive electronics
of quartz crystals and quartz crystal oscillators to provide timing references for all the
required system clocks. One of the largest drawbacks to this approach is that quartzbased components have the highest FIT rates of any electronic systems component,
which greatly affects system reliability. As designs continue to adopt processors with
greater functionality with higher speed SerDes, Ethernet connectivity, and PCI-Express
data buses, the need for more reference clocks arises, with both single-ended and differential formats, and lower RMS phase jitter.
The Si5332-AM family of clock generators is designed to overcome the challenges associated with increasingly complex clock tree design in automotive electronics. These
devices are capable of supporting up to 12 unique frequency outputs, all of which can
be individually programmed to its own electrical format (i.e., LVCMOS, LVDS, HCSL,
etc.). By consolidating the functionality of many pieces of quartz-based components into a silicon-based clock generator, system designers can eliminate many points of failure and greatly improve overall system reliability.
In addition to component count reduction and reliability improvements, clock generators
offer numerous additional benefits that are not available from quartz-based timing components. The Si5332-AM clock generators provide in-system programming capability,
spread spectrum modulation, output enable control, and frequency selection capabilities. To help system designers meet system level safety goals, the Si5332-AM devices
also come equipped with SmartClock features that include redundant reference inputs,
health monitoring, fault detection, communication with an external safety manager, primary/back-up reference source switching, and AlwaysON outputs. This application
note provides an overview of the SmartClock features and outlines system level examples on how to implement them.
system designs have traditionally depended on multiple pieces
KEY POINTS
• SmartClock features
• System implementation examples
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AN1292: Si5332-AM SmartClock™ Fault Detection and Monitoring
Focus of this Application Note: Si5332-AM SmartClock Features
1. Focus of this Application Note: Si5332-AM SmartClock Features
This application note will specifically focus on the integrated clock fault detection features of the Si5332- AM Clock Generator family.
For more details on the many other features and benefits of the Si5332-AM device family and other automotive timing products, please
browse the link below.
https://www.silabs.com/timing/automotive-timing-solutions
The Si5332-AM programmable clock generators can be easily customized to individual design clock tree requirements by creating a
configuration file using the ClockBuilder Pro Software Utility. Users can enable the Si5332-AMs SmartClock features during configuration file development. ClockBuilder Pro can be downloaded for free:
https://www.silabs.com/products/development-tools/software/clockbuilder-pro-software
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AN1292: Si5332-AM SmartClock™ Fault Detection and Monitoring
SmartClock Health Monitoring and Fault Detection Features within Si5332-AM
2. SmartClock Health Monitoring and Fault Detection Features within Si5332-AM
Shown below is a generic block diagram of the Si5332-AM clock generator family of devices. The three devices in this family are as
follows:
• Si5332-AM1: 2 input (xtal + 1 CLKIN), 6 output
• Si5332-AM2: 3 input (xtal + 2 CLKIN), 8 output
• Si5332-AM3: 3 input (xtal + 2 CLKIN), 12 output
LDO
OSC
Low
CLKIN_2
Jitter
PLL
CLKIN_3
LOS
FOOF
CLKIN_SEL0
CLKIN_SEL1
GPIs
2.1 Fault Monitor Block Overview
The Si5332-AM
ment in ClockBuilder Pro. System designers can choose to enable SmartClock features using some of the Universal GPIO pins, as
highlighted within the red box in Figure 2.1 Si5332-AM Block Diagram on page 3. When enabling these features, SIlicon Labs recommends the use of a crystal reference source, as well as a backup input clock reference source. The Si5332-AM2 (8-output) and Si5332AM3 (12-output) include a third reference input.
The Fault Monitor continuously monitors the status of the input clock reference to the PLL. If a fault condition is detected, a signal is
provided to an external system safety manager or MCU, which can then direct the Si5332-AM to switch the reference source from the
primary to the backup input source. The Fault Monitor block provides 4 signals, 2 input and 2 output, as follows:
• LOS (Loss of Signal) output: This output asserts when the frequency of the selected input clock falls below a set threshold. This
frequency threshold is set by our CBPro configuration software based on input clock frequency.
• FOOF (Fast Out of Frequency) output: This output asserts when the difference between the PLL input reference frequency and PLL
feedback frequency falls outside of a set band. FOOF assertion is an indication the PLL has either fallen out of lock or other PLL
fault condition has occurred and the PLL may either be unlocked or otherwise not operational. The band limits are automatically set
by CBPro.
• CLKIN_SEL[1:0]: Two logic inputs used to select one of 4 possible input clock sources for PLL reference.
includes a bank of Universal GPIO pins that can be assigned to numerous functions during configuration file develop-
Fault
Monitor
Status /
Control
Figure 2.1. Si5332-AM Block Diagram
Synth
Multi
Synth
÷ INT
÷ INT
÷ INT
÷ INT
÷ INT
÷ INT
÷ INT
6/8/12
Output
Clock
s
Multi
2.2 External Action Required on Either LOS or FOOF Assertion
The LOS and FOOF signal outputs indicate that a fault condition has occurred. No action is automatically taken by the Si5332-AM as a
result of these fault indications. An external device, such as an MCU or other system safety manager, must monitor LOS and FOOF
outputs from the Si5332-AM,and can make a system level decision on potential courses of action for maintaining acceptable levels of
system safety. The external device can then provide instructions back to the Si5332-AM to migrate from the faulted input reference to
the backup input reference, or take action at the system level based on the severity of the detected fault.
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AN1292: Si5332-AM SmartClock™ Fault Detection and Monitoring
SmartClock Health Monitoring and Fault Detection Features within Si5332-AM
2.3 CLKIN_SEL[1:0] Input Clock Selects: Input Clock Selection and Validation
CLKIN_SEL1 CLKIN_SEL0 Clock Selected Note
0 0 Input disabled To test input clock fault condition.
0 1 Crystal Oscillator
1 0 Clock 2 Input
1 1 Clock 3 Input Only on -AM2 and -AM3 devices.
The CLKIN_SEL[1:0] inputs can be used to select which input clock source is to be used by the on-chip PLL for its clock reference.
With this input selection capability an external device, such as an MCU, can be used to intelligently select an alternate (redundant) input
clock reference
can attempt to recover from this fault condition by selecting an alternate clock source.
In addition, when running system power-up or other diagnostics, the MCU software can test the functionality of LOS and FOOF by selecting the Input Disabled setting and then confirming assertion of LOS and FOOF as a result. Similarly, the MCU software can also
confirm proper operation of any alternate clock input sources by selecting the alternate source(s) and confirming LOS and FOOF are
not asserted.
as part of a fault recovery plan. For example, if assertion of the LOS signal is detected by an MCU, the MCU software
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AN1292: Si5332-AM SmartClock™ Fault Detection and Monitoring
System Implementation Examples Of Using Si5332-AM SmartClock Features
3. System Implementation Examples Of Using Si5332-AM SmartClock Features
Several different use-case examples are presented below, complete with system level block diagrams showing how the Si5332-AM device can be implemented with the SmartClock features enabled. When coupled with an external MCU or system safety manager, the
device provides the highest degrees of health monitoring, fault detection, and redundancy. These configurations highlight the flexibility
in tailoring a solution to meet different levels of clocking fault detection and redundancy.
Devices noted in the block diagram that are highlighted in dark orange are the external devices and signals that support the various
fault detection and control scenarios. For each configuration scenario, an associated example software flowchart of operations is provided. These flowcharts are meant to show how the input reference health monitoring and fault detection/recovery plan can be implemented.
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