For customers using NXP Semiconductors "PCF85263"

Contents

We are pleased to introduce you to our crystal unit.

Items to Confirm (designing of oscillation circuit)

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.

For details of each characteristic, please refer to the PDF file.

Precautions for Oscillation Circuit Design PDF

Selection Guidance for crystal unit

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.

Epson Crystal Product Lineups

Product Size[mm] Applications Images
FC-135
FC-135R 		3.2 x 1.5 x 0.9 Portable equipment
MC-146 7.0 x 1.5 x 1.4 Portable equipment

Oscillation Circuit and Selection Guidance of Crystal Unit for PCF85263

PCF85263
Registers Setting		 32.768 kHz Crystal Product Code
CL [pF] OSCD CL [pF] FC-135R FC-135 MC-146
7.0 Low 6 Go to Low CL page
Normal
High
12.5 High 12.5 X1A0001410003** Q13FC13500004** Q13MC14620002**

Cautions

*1. Load Capacitance
*2. Two digits of the product code is packing specification, please refer here for the detail.
*3. The evaluation board is the OM13510 evaluation board.
*4. 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.

Precautions for designing of PCB Board

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 32 kHz Crystal Unit

GND Line Pattern and Interconnection of PCB

- Please lay out GND line pattern under crystal unit. - In case of multi-layered PCB board, do not lay out other signal lines under crystal unit.