STLC60134 datasheet(13/22 Pages) STMICROELECTRONICS

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Table 21. VCXO circuit Characteristics

Symbol

Parameter

Min.

Nominal

Max.

Note

fabs

Absolute frequency accuracy

-15ppm

35.328MHz

+15ppm

frange

Frequency Tuning Range

±50ppm

VCXO Output Current

100

µA

Rref = 16.5k

Ω

AVDD = 3.3V

Reference Input Current

100

µA

1mA

AVDD = 3.3V

N.B: frequency tuning range is proportional to the crystal dynamic capacitance Cm.

DAC

AGND

XTALO

XTALI

VCXOUT

IVCO

RREF

IO=Ii

AVDD

AVDD/22

÷AVDD/2

Filtered VCXO

(se e CTRLIN table)

VCOCX

AVDD

Ω

Clk35

±30%

-1 5V

CTRLIN

8 bits

D98TL364mod

Figure 11. Principle of VCXO control

The tuning must be monotonic with 8-bit resolution with the worst-case tuning step of <2ppm/LSB (8-bit).

The time constant of the tuning must be variable from 5s to 10s through an external capacitor Cs (R =

Ω ±30%). This determines the speed of the VCXO in normal operation (slow speed in ”show time”)

with filtered VCXO. For faster tracking, the previous filter is not used and the speed depends on CtRt.

STLC60134S

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