STA1295 datasheet(84/109 Pages) STMICROELECTRONICS

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Electrical characteristics

STA1295, STA1275

84/109

DS12586 Rev 5

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 in Figure 4.

Figure 4. 32.768 kHz crystal connection

The specifications of a typical external crystal are shown in the table below.

Table 39. Oscillator amplifier specifications

Symbol

Parameter

Limit values

Unit

Min.

Typ.

Max.

TSXTAL

V Startup time

× Lm/Rm

1.5

Tduty cycle(Zi & NZi) V Duty cycle

—V

Amplitude of oscillation at

M3_SXTALO

1.6

2.6

PSXTAL

Power consumption during

stable oscillation

—10

—

μA

GM0-SXTAL

P Transconductance

—

μA/V

Rneg

S Negative resistance

350

500

S Frequency stability

PPM

Table 40. 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

—

COSXTAL

—

Shunt capacitance

—

3.5

—

CLSXTAL

—

Load capacitance(1)

1. Total capacitance, including board and package parasitics.

—22

—

32.768 kHz

Crystal

SXTALI

SXTALO

Device

LMSXTAL RMSXTAL CMSXTAL

COSXTAL

Crystal Model

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