STA8090GA datasheet(25/32 Pages) STMICROELECTRONICS

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DS10820 Rev 5

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STA8090GA

Electrical characteristics

The recommended oscillator specifications are shown in Table 21:

The oscillator amplifier specifications are shown in the following table:

Figure 3. 32.768 kHz crystal connection

To drive the 32.768 kHz crystal pins from an external clock source:



Disable the oscillator (bit28-OSCI_EN = 0b in PRCC_BACKUP_REG0 register). This

disables the internal inverter, thus reducing the power consumption to minimum.



Drive the RTC_XTI pin with a square signal or a sine wave.

Table 21. 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 22. 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

CL = 18 pF

32.768 kHz

Crystal

RTC_XTII

RCT_XTO

Device

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