For customers designing "nRF51x22 family" Nordic Semiconductors

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.
• Precautions for designing of PCB Board

Crystal Recommendations for Nordic Semiconductors nRF51x22 family".

• Recommendations nRF51x22 family.

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
Please refer to our web site:
https://www5.epsondevice.com/en/information/precaution/design.html
Support information > Precautions in Designing oscillation circuits > 2. Allowance for oscillation

Drive Level:
You need to confirm if oscillation is stable, and if the drive level is within the specification.
Please refer to our web site:
https://www5.epsondevice.com/en/information/precaution/design.html
Support information > Precautions in Designing oscillation circuits > 1. Drive level

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.
Please refer to our web site:
https://www5.epsondevice.com/en/information/precaution/design.html
Support information > Precautions in Designing oscillation circuits > 3. Load capacitance

* frequency stability: frequency deviation out of circuit conditions.

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

Oscillation Circuit and Selection Guidance of Crystal Unit for nRF51x22

Notes:*

1. Load capacitance.
2. Two digits of the product code is packing specification,please refer here for the detail.
3. Above recommendations are based on actual evaluation results and intended to support users in picking the right components. And the results are only according to the sample set that received from our customers, so it is not including the dispersion trend of IC and the external parts.
   As the actual board layout and choice of external components influences the best suitable crystal load capacitance, We do not assume any responsibility and grant warranty for above recommendations. Users design must be verified and decided by own and individual evaluation.

Precautions for designing of PCB Board

<Layout of pins, Crystal unit, Capacitor and Resistor>
-Please lay out crystal unit, capacitor and resistor near nRF51x22 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-layered PCB board, do not lay out other signal lines under crystal unit.