BD71815GW

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For customers designing "BD71815GW" ROHM Semiconductor

We are pleased to introduce you to our crystal unit.
Please refer to ROHM Semiconductor BD71815GW official site for additional information.

· 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 ROHM Semiconductor "BD71815GW ".

· Recommendations BD71815GW.

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.
* 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.

StrongFirst Crystal Product Lineups

Product	Size [mm]	Applications	Images
S3215	3.2×1.5×0.8t	Consumer,Industrial
SM146	7.0×1.5×0.8t	Consumer,Industrial

Oscillation Circuit and Selection Guidance of Crystal Unit for BD71815GW

32.768 kHz Crystal

Product Name	Normal Frequency Range[Hz]	CL*1 [pF]	Product code*2	External parts*3		Size WxDxH [mm]
				Cg[pF]	Cd[pF]
S3215	32.768k	12.5	S3215-32.768K-12.5-20-E	22	18	3.2×1.5×0.8t
SM146	32.768k	12.5	SM146-32.768K-12.5-20-E	18	18	7.0×1.5×0.8t

Notes:

· *1 Load Capacitance

· *2 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.
Users design must be verified and decided by own and individual evaluation.

Precautions for designing of PCB Board

-Please lay out crystal unit, capacitor and resistor near BD71815GW as far as possible.
-Please connect pins within 20mm length, and do not cross other signal lines.

-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.

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