STA8100GA datasheet(28/42 Pages) STMICROELECTRONICS

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Electrical specifications

STA8100GA

28/42

DS13006 Rev 4

4.4

RTC 32.768 kHz 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 in Figure 5.

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

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

connected to RTC_XTI/RTC_XTO pins.

The recommended oscillator specifications are shown in the table below:

The oscillator amplifier specifications are shown in the following table:

tFALL(1)

CMOS output fall time

with CL = 15 pF, from 10

to 90 %; 3.3 V

2 mA max. current

drive

—3

—

4 mA max. current

drive

—2

—

1. Specified by design

Table 21. Electrical characteristics of digital input and output buffers (continued)

Symbol

Parameter

Test conditions

Min.

Typ.

Max.

Unit

a. Using crystal with recommended characteristics as per Table 22.

Table 22. Crystal recommended specifications

Symbol

Parameter

Min.

Typ.

Max.

Unit

FSXTAL

Crystal frequency

—

32.768

—

kHz

LMSXTAL

Motion inductance

3500

6500

CMSXTAL

Motional capacitance

4.0

5.0

6.0

COSXTAL

Shunt capacitance

1.0

1.3

1.6

ESR

Resonance resistance

—

kOhm

External load capacitance

—

18 + / - 2 %

—pF

External load capacitance

(frequency variation < 80 ppm)

18 + / - 2 %

Table 23. 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

RLC

Required load capacitance(1)

—

12.5

—

Startup conductance

22.5

33.6

uA/V

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