Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet
Product codes
ATSAM4S-WPIR-RD
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
1148
44.5.8 Crystal Oscillator Design Considerations Information
44.5.8.1 Choosing a Crystal
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 of crystal and SAM4S 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. The crystal must be chosen according to the internal load capacitance (C
L
) of the
on-chip oscillator. Any mismatch in 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.
44.5.8.2 Printed Circuit Board (PCB)
SAM4S oscillators are low-power oscillators requiring particular attention when designing PCB systems.