STA1085 datasheet(60/127 Pages) STMICROELECTRONICS

60 / 127 page

Electrical Characteristics

STA108x, STA109x

60/127

DS13319 Rev 2

4.7

AC Characteristics

4.7.1

Oscillator Electrical Specifications

This device contains two oscillators:



a 32.768 kHz oscillator



a 24-26 MHz oscillator

Each requires a specific crystal, with parameters that must be as close as possible to the

following recommended values.

Clock from external source can also be applied on input pins.

4.7.2

32.768 kHz Oscillator Specifications

The internal oscillator amplifier specifications are shown in Table 24:

The 32.768 kHz oscillator is connected between M3_SXTALI (oscillator amplifier input) and

M3_SXTALO (oscillator amplifier output). It also requires two external capacitors of CL pF,

as shown on Figure 4.

The specifications of a typical external crystal are shown in Table 25:

Table 24. Oscillator Amplifier Specifications

Symbol

Parameter

Limit Values

Unit

Min

Typ

Max

TSXTAL

Startup Time

15 x Lm/Rm

1.5

Tduty

cycle(Zi &

NZi)

Duty Cycle

ASXTALO

Amplitude of OSCILLATION at

M3_SXTALO

1.6

2.6

PSXTAL

Power Consumption during

Stable Oscillation

-10

µA

GM0-SXTAL

Transconductance

A/V

Rneg

Negative Resistance

350

500



Frequency Stability

PPM

Table 25. Typical Crystal Recommended Specifications

Symbol

Parameter

Limit values

Unit

Min

Typ

Max

FSXTAL

Crystal frequency

32.768

kHz

LMSXTAL

Motion inductance

11.8

CMSXTAL

Motional capacitance

2.0

RMSXTAL

Motional resistance



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