For customers designing Texas Instruments "CC430 Family" applications
We are pleased to introduce you to our 32.768 kHz crystal unit for Texas Instruments CC430 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
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 |
|---|---|---|---|
| MC-306 | 8.0 x 3.8 x 2.54 | Electronic, Gas, Water meter, Flow meter, Intelligent sensor, Measurement equipment, Blood pressure meter, Blood-sugar monitor, Security systems |  |
| MC-146 | 7.0 x 1.5 x 1.4 | DSC, Consumer equipment, Radio equipment, Blood pressure meter, Blood-sugar monitor, Security systems |  |
| FC-135 |
3.2 x 1.5 x 0.9 |
PMP, DSC, Portable equipment |  |
Oscillation Circuit and Selection Guidance of Crystal Unit for CC430 family
CC430 F5137, F6137 crystal oscillator setting and equivalent crystal CL values
| XCAPx value (integrated effective load) |
Crystal unit equivalent CL values (pF) |
32.768 kHz Crystal Product Code *1 | |||
|---|---|---|---|---|---|
| CL (pF) |
MC-306 | MC-146 | FC-135 | ||
| XCAPx=0 (2 pF Typ.) |
External capacitors are required | - | Customer can select crystal products with external capacitor combination. | ||
| XCAPx=1 (5.5 pF typ) |
7 | 7 | Q13MC30610004** | Q13MC14610001** | Q13FC13500002** |
| XCAPx=2 (8.5 pF typ) |
12.5 | 12.5 | Q13MC30610003** | Q13MC14610002** | Q13FC13500004** |
| XCAPx=3 default (12 pF typ) |
- | - | - | - | - |
* Product Code: encoded numbers of crystal specifications
Choosing a suitable XCAPx setting of CC430 F5137, F6137
| No. | Crystal CL Value | XCAP value (integrated effective load typ.) |
Advantage | Drawback |
|---|---|---|---|---|
| 1 | 12.5 pF | XCAPx=2 (8.5 pF) | High frequency stability | Higher current consumption, slower oscillation startup |
| 2 | 7 pF | XCAPx=1 (5.5 pF) | Low current consumption | Lower stability due to load capacitance variation of externalcomponents and the layout. |
Remarks:
By tuning CC430 XT1DRIVE, oscillation allowance and current consumption will be controlled.
Notes:
- 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.
Please refer to Texas Instruments CC430 manual for setting XCAPx and other parameters.
Precautions for designing of PCB Board
Layout of XIN, XOUT, Crystal unit, Capacitor and Resistor
-Please lay out crystal unit, capacitor and resistor near CC430 as far as possible.
-Please connect XIN and XOUT within 20mm length, and do not cross other signal lines.
For 32 kHz crystal unit
If Vcc drops to below 2.5V, insert a resistor of 5.1 ohms between XOUT and GND.
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.
