For customers designing "BD71815AGW" ROHM Semiconductor

We are pleased to introduce you to our crystal unit.
Crystal Recommendations for ROHM Semiconductor "BD71815AGW ".

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.

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 3.2 x 1.5 x 0.9 Consumer, Industrial FC135
MC-146 7.0 x 1.5 x 1.4 Consumer, Industrial MC146

Oscillation Circuit and Selection Guidance of Crystal Unit for BD71815AGW

32 kHz Crystal

Product Name Normal Frequency Range
[Hz]
CL *1
[pF]
Product Code *2 External Parts*3
Size
[mm]
Cg
[pF]
Cd
[pF]
FC-135 32.768k 12.5 Q13FC13500004** 22 18 3.2 x 1.5 x 0.9
MC-146 32.768k 12.5 Q13MC14620002** 18 18 7.0 x 1.5 x 1.4

Notes:

*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 BD71815AGW as far as possible.
-Please connect pins within 20mm length, and do not cross other signal lines.

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.