ST10F272M datasheet(149/175 Pages) STMICROELECTRONICS

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ST10F272M

Electrical characteristics

149/176

24.8.12

32 kHz oscillator specifications

VDD = 5V ± 10%, VSS = 0V, TA = -40 to +125°C

Figure 48.

32 kHz crystal oscillator connection diagram

The given values of CA do not include the stray capacitance of the package and of the

printed circuit board: the negative resistance values are calculated assuming additional 5pF

to the values in the table. The crystal shunt capacitance (C0) and the package capacitance

between XTAL3 and XTAL4 pins is globally assumed equal to 4pF. The external resistance

between XTAL3 and XTAL4 is not necessary, since already present on the silicon.

Warning:

Direct driving on XTAL3 pin is not supported. Always use a

32 kHz crystal oscillator.

Table 66.

32 kHz oscillator characteristics

Symbol

Parameter

Conditions

Value

Unit

Min

Typ

Max

gm32

Oscillator Transconductance(1)

At power-on a high current biasing is applied for faster oscillation start-up. Once the oscillation is started,

the current biasing is reduced to lower the power consumption of the system.

Start-up

µA/V

Normal run

µA/V

VOSC32 Oscillation Amplitude

(2)

Not 100% tested, guaranteed by design characterization.

Peak to Peak

0.5

1.0

2.4

VAV32

Oscillation Voltage level(2)

Sine wave middle

0.7

0.9

1.2

tSTUP32 Oscillator Start-up Time

(2)

Stable VDD

–15

Table 67.

Minimum values of negative resistance (module) for 32 kHz oscillator

Frequency

CA = 6pF CA = 12pF CA = 15pF CA = 18pF CA = 22pF CA = 27pF CA = 33pF

32 kHz

150 k

Ω

120 k

Ω

90 k

Ω

Crystal

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