STA8090EXGA datasheet(35/42 Pages) STMICROELECTRONICS

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DS11733 Rev 3

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STA8090EXGA

Electrical characteristics

32.768 kHz OSCI32 oscillator specifications

The 32.768 kHz OSCI32 oscillator is connected between RTC_XTI (oscillator amplifier

input) and RTC_XTO (oscillator amplifier output). It also requires two external capacitors of

18 pF(a), as shown on Figure 2.

OSCI32 is disabled by default and must be enabled by setting bit28-OSCI_EN of

PRCC_BACKUP_REG0 to have 32.768KHz oscillation when an XTAL pi-network is

connected to RTC_XTI/RTC_XTO pins.

The recommended oscillator specifications are shown in Table 27:

The oscillator amplifier specifications are shown in following table:

a. Using crystal with recommended characteristics as per Table 27.

Table 27. Crystal recommended specifications

Symbol

Parameter

Min.

Typ.

Max.

Unit

FSXTAL

Crystal frequency(1)

1. Not tested in production.

—

32.768

—

kHz

LMSXTAL

Motion inductance(1)

—5

—

CMSXTAL

Motional capacitance(1)

—5.0

—

COSXTAL

Shunt capacitance(1)

—1.3

—

ESR

Resonance resistance(1)

——

kΩ

External load capacitance(1)

—18

—

Table 28. Oscillator amplifier specifications

Symbol

Parameter

Min.

Typ.

Max.

Unit

Startup time(1)

1. Not tested in production.

—0.3

0.6

Drive level(1)

——

<0.1

µW

RLC

Required load capacitance(1)

—

12.5

—

Startup transconductance

22.5

33.6

—

µA/V

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