Datasheet

DRAFT
1399
SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
45.4.9 Crystal Oscillator Design Consideration Information
45.4.9.1 Choosing a Crystal
When choosing a crystal for the 32.768 kHz Slow Clock Oscillator or for the 3–20 MHz Oscillator, several
parameters must be taken into account. Important parameters between crystal and SAM3 specifications are as
follows:
 Load Capacitance
C
crystal
is the equivalent capacitor value the oscillator must “show” to the crystal in order to oscillate at the
target frequency. Crystal must be chosen according to the internal load capacitance (C
LOAD
) of the on-chip
oscillator. Having a mismatch for the load capacitance will result in a frequency drift.
 Drive Level
Crystal drive level ≥ Oscillator Drive Level. Having a crystal drive level number lower than the oscillator
specification may damage the crystal.
 Equivalent Series Resistor (ESR)
Crystal ESR ≤ Oscillator ESR Max. Having a crystal with ESR value higher than the oscillator may cause the
oscillator to not start.
 Shunt Capacitance
Max. crystal Shunt capacitance ≤ Oscillator Shunt Capacitance (C
SHUNT
). Having a crystal with ESR value
higher than the oscillator may cause the oscillator to not start.
45.4.9.2 Printed Circuit Board (PCB)
SAM3 oscillators are low-power oscillators requiring particular attention when designing PCB systems.