Rev 1.1, August 7, 2008

Page 10 of 12

SL38000

PCin(pF) =PCout(pF)= [(CL(pF) – Cp(pF)/2)] x 2

Where CL is crystal load capacitor as given by the crystal datasheet and Cp(pF) is the compensation factor for the

total parasitic capacitance at XIN or XOUT pin including PCB related parasitic capacitance.

As an example; if a crystal with CL=18pF is used and Cp=4pF, by using the above formula, PCin=PCout=[(18-(4/2)] x

2 = 32pF. Programming PCin and PCout to 32pF assures that this crystal sees an equivalent load of 18pF and no

other external crystal load capacitor is needed. Deviating from the crystal load specification could cause an increase

in frequency accuracy in ppm. Refer to the Table 5 for the recommended crystal specifications.

Recommended External Crystal Specifications (XO Version)

Parameter

Description

Min

Typ

Max

Unit

Comments

FNOM

Nominal Crystal

Frequency Range

8

-

48

MHz

Fundamental Mode – AT Cut

CL

Nominal Crystal Load

6

12

18

pF

Load for +/-0 ppm Fo resonance

value

R1,1

Equivalent Series

Resistance

20

40

100

Ohm

F-Range: 8.0 to 12.999 MHz

R1,2

Equivalent Series

Resistance

12.5

25

60

Ohm

F-Range: 13.0 to 19.999 MHz

R1,3

Equivalent Series

Resistance

10

20

50

Ohm

F-Range: 20.0 to 48.000 MHz

DL1,1

Crystal Drive Level

-

-

200

µW

F-Range: 8.0 to 19.999 MHz

DL1,2

Crystal Drive Level

-

-

150

µW

F-Range: 20.0 to 48.000 MHz

Co1

Shunt Capacitance

-

4

5.4

pF

SMD Xtals

Co2

Shunt Capacitance

-

5

7.2

pF

Through Hole (Leaded) Xtals

Table 3. Recommended Crystal Specifications