For customers designing "BD71850MWV" ROHM Semiconductor
We are pleased to introduce you to our crystal unit.
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
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
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-12M | 2.05 x 1.2 x 0.6 | Consumer, Industrial |  |
| FC-135 | 3.2 x 1.5 x 0.9 | Consumer, Industrial |  |
Oscillation Circuit and Selection Guidance of Crystal Unit for BD71850MWV
32kHz Crystal
| Product Name | Normal Frequency Range[ [Hz] |
CL *1 [pF] |
Product Code *2 | External Parts*3 |
Size [mm] |
|
|---|---|---|---|---|---|---|
| Cg [pF] |
Cd [pF] |
|||||
| FC-12M | 32.768k | 12.5 | X1A0000610002** | 18 | 18 | 2.05 x 1.2 x 0.6 |
| FC-135 | 32.768k | 12.5 | Q13FC13500004** | 18 | 18 | 3.2 x 1.5 x 0.9 |
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 BD71850MWV 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.
