SAM3A4C Atmel Corporation, SAM3A4C Datasheet - Page 1409

• Manufacturer Part Number: SAM3A4C
• Manufacturer: Atmel Corporation

45.4.9
45.4.9.1
45.4.9.2
11057A–ATARM–17-Feb-12
Crystal Oscillators Design Consideration Information
Choosing a Crystal
Printed Circuit Board (PCB)
When choosing a crystal for the 32768 Hz 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:
SAM3 Oscillators are low power oscillators requiring particular attention when designing PCB
systems. A board design example is given on Atmel’s website in the MCU Technical Center
Section.
• Load Capacitance
• Drive Level
• Equivalent Series Resistor (ESR)
• Shunt Capacitance
– This is the equivalent capacitor value the oscillator must “show” to the crystal in
– Crystal drive level >= Oscillator Drive Level. Having a crystal drive level number
– Crystal ESR <= Oscillator ESR Max. Having a crystal with ESR value higher than
– Max. crystal Shunt capacitance <= Oscillator Shunt Capacitance (
order to oscillate at the target frequency. Crystal must be chosen according to the
internal load capacitance (C
load capacitance will result in a frequency drift.
lower than the oscillator specification may damage the crystal.
the oscillator may cause the oscillator to not start.
Having a crystal with ESR value higher than the oscillator may cause the
oscillator to not start.
L
)of the on-chip oscillator. Having a mismatch for the
SAM3X/A
C
SHUNT
).
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