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.

For detail product information of CC430 Family, please refer to Texas Instruments web site.

Items to Confirm (designing of oscillation circuit)

Please note: to design oscillation circuit for CC430 Family, 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, lload 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
MC-306 8×3.8×2.5t Electronic, Gas, Water meter, Flow meter, Intelligent sensor,
Measurement equipment, Blood pressure meter,
Blood-sugar monitor, Security systems
MC-146 7×1.5×1.4t DSC, Consumer equipment, Radio equipment,
Blood pressure meter, Blood-sugar monitor, Security systems
FC-135 3.2×1.5×0.8t PMP, DSC, Portable equipment FC135

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
32.768 kHz Crystal Product Code
MC-306 MC-146 FC-135
(2pF Typ.)
External capacitors are required
Customer can select crystal products
with external capacitor combination.
(5.5pF typ)
(8.5pF typ)
default (12pF 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
12.5 pF
XCAPx=2 (8.5pF)
High frequency stability
Higher current consumption,
slower oscillation startup
7 pF
XCAPx=1 (5.5pF)
Low current consumption
Lower stability due to load capacitance variation of
externalcomponents and the layout.

By tuning CC430 XT1DRIVE, oscillation allowance and current consumption will be controlled.

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 32kHz crystal unit
TOP View
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.

Cross-seection View(Multi-layered PCB Board)

Page Top