AN2867 datasheet(25/41 Pages) STMICROELECTRONICS

Part #	AN2867

Description	Oscillator design guide for STM8S

PDF	41 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

Logo

25 / 41 page

DocID15287 Rev 9

25/41

AN2867

Guidelines for selecting suitable crystal and external components

Step 5 (optional): Calculate the PPM accuracy budget

Finally, you can use the formula below to estimate the PPM accuracy budget for the whole

application:

where:

PPMBudget is the estimated accuracy for the oscillation frequency.

PPMcrystal is the crystal PPM accuracy specified in the datasheet.

Deviation (CL) is expressed in pF. It measures the deviation of the load capacitance

(CL) due to tolerances on load capacitor values and the variation of the stray

capacitance (CS) due to PCB manufacturing process deviation.

Pullabilty is expressed in PPM/pF (refer to Section 3.7: Crystal pullability).

Note:

The PPM budget calculated above does not take into account the temperature variation

which may make the PPM budget bigger.

PPMBudget PPMcrystal Deviation CL

() Pullabilitycrystal

AN2867 Datasheet(PDF) 25 Page - STMicroelectronics