Internal Oscillator Design Considerations
Guideline: Connectivity Restrictions
You cannot drive the PLLs with internal oscillator.
PLLs Design Considerations
Guideline: PLL Control Signals
You must include the
areset
signal in your designs if one of the following conditions is true:
• PLL reconfiguration or clock switchover is enabled in your design.
• Phase relationships between the PLL input clock and output clocks must be maintained after a loss-of-
lock condition.
• The input clock to the PLL is toggling or unstable at power-up.
• The
areset
signal is asserted after the input clock is stable and within specifications.
Related Information
PLL Control Signals
on page 2-13
Guideline: Connectivity Restrictions
To comply with simultaneous switching noise (SSN) design guideline, Altera recommends that you do
not use unterminated I/O in the same bank as the input clock signal to the PLL.
Related Information
Guidelines: Clock and Asynchronous Control Input Signal
Provides more information about using I/O connectivity restrictions.
Guideline: Self-Reset
The lock time of a PLL is the amount of time required by the PLL to attain the target frequency and phase
relationship after device power-up, after a change in the PLL output frequency, or after resetting the PLL.
A PLL might lose lock for a number of reasons, such as the following causes:
• Excessive jitter on the input clock.
• Excessive switching noise on the clock inputs of the PLL.
• Excessive noise from the power supply, causing high output jitter and possible loss of lock.
• A glitch or stopping of the input clock to the PLL.
• Resetting the PLL by asserting the
areset
port of the PLL.
• An attempt to reconfigure the PLL might cause the
M
counter,
N
counter, or phase shift to change,
causing the PLL to lose lock. However, changes to the post-scale counters do not affect the PLL
locked
signal.
• PLL input clock frequency drifts outside the lock range specification.
• The PFD is disabled using the
pfdena
port. When this happens, the PLL output phase and frequency
tend to drift outside of the lock window.
3-2
Internal Oscillator Design Considerations
UG-M10CLKPLL
2015.06.12
Altera Corporation
MAX 10 Clocking and PLL Design Considerations
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