For customers designing "BD71850MWV" ROHM Semiconductor

We are pleased to introduce you to our crystal unit.
Please refer to ROHM Semiconductor BD71850MWV official site for additional information.

Crystal Recommendations for ROHM Semiconductor "BD71850MWV ".

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:
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:
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:
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.

Selection Guidance for crystal unit

Epson Crystal Product Lineups

Product Size [mm] Applications Images
FC-12M 2.05×1.2×0.6t Consumer,Industrial FC12M
FC-135 3.2×1.5×0.8t Consumer,Industrial FC135

Oscillation Circuit and Selection Guidance of Crystal Unit for BD71850MWV

32.768 kHz Crystal

Product code*2 External parts*3
Cg[pF] Cd[pF]
FC-12M 32.768k 12.5 X1A0000610002 18 18 2.05x1.2x0.6t
FC-135 32.768k 12.5 Q13FC13500004 18 18 3.2x1.5x0.8t


  • *1 Load Capacitance
  • *2 Two digits of the product code is packing specification,please refer here the detail.
  • *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.
    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 BD71850MWV as far as possible.
-Please connect pins within 20mm length, and do not cross other signal lines.

TOP View

<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.

Cross-seection View(Multi-layered PCB Board)

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