We are pleased to introduce you to our crystal unit
· Items to Confirm (designing of oscillation circuit)
· Selection Guidance for crystal unit
· Crystal Products Lineup
· Oscillation Circuit and Selection Guidance of Crystal Unit for PCF85263.
· Precautions for designing of PCB Board
Please note: to design oscillation circuit, you need to confirm the electronic characteristics as follows:
Oscillation allowance and Negative resistance (-R):
You need to confirm oscillation capability.
We recommend the condition: (-R) / ESR > 5
* -R: Negative resistance, ESR: Equivalent Series Resistance
Drive Level:
You need to confirm if oscillation is stable, and if the drive level is within the specification.
Load Capacitance:
Load capacitance affects frequency stability, oscillation allowance, negative resistance, and start-up time of oscillation.
In addition the load capacitance is determinative factor of crystal unit's load capacitance (CL value) directly.
* frequency stability: frequency deviation out of circuit conditions.
When Customer selects crystal unit, load capacitance (CL value) is an important factor of the selection.
For instance, crystal with small CL(7.0 pF) makes larger oscillation allowance, smaller current consumption and worse frequency stability,
like below table. Oppositely, crystal with large CL(12.5 pF) makes smaller oscillation allowance, larger current consumption and better frequency stability. Please select it in consideration of these characteristics.
Product
Size [mm]
Applications
Images
S3215
3.2x1.5x0.8t
Portable equipment
SM146
7x1.5x1.4t
Portable equipment
PCF85263
Registers Setting
32.768 kHz Crystal Product Code
CL[pF]*1
OSCD
CL[pF]*1
S3215
S3215
SM146
7.0
Low
6
Go to Low CL page
Normal
High
12.5
High
12.5
S3215R-32.768K-12.5-20-E
S3215-32.768K-12.5-20-E
SM146-32.768K-12.5-20-E
· *1.Load Capacitance
· *2.The evaluation board is the OM13510 evaluation board.
· *3.Above recommendations are based on actual evaluation results and intended to support users in picking the right components. As the actual board layout and choice of external components influences the best suitable crystal load capacitance, We does not assume any responsibility and grant warranty for above recommendations.
Layout of pins, Crystal unit, Capacitor and Resistor
- Please lay out crystal unit, capacitor and resistor near PCF85263 as far as possible.
- The length of signal patterns in oscillation circuit should be as short as possible, and do not cross other signal lines.
For 32kHz Crystal Unit
GND Line Pattern and Interconnection of PCB
- Please lay out GND line pattern under crystal unit.
- In case of multi-layer PCB board, do not lay out other signal lines under crystal unit.
