ST10F276 datasheet(203/229 Pages) STMICROELECTRONICS

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ST10F276

Electrical characteristics

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Figure 55.

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), the package and the stray

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.

23.8.15

External clock drive XTAL1

When Direct Drive configuration is selected during reset, it is possible to drive the CPU clock

directly from the XTAL1 pin, without particular restrictions on the maximum frequency, since

the on-chip oscillator amplifier is bypassed. The speed limit is imposed by internal logic that

targets a maximum CPU frequency of 64 MHz.

In all other clock configurations (Direct Drive with Prescaler or PLL usage) the on-chip

oscillator amplifier is not bypassed, so it determines the input clock speed limit. Then an

external clock source can be used but limited in the range of frequencies defined for the

usage of crystal and resonator (refer also to Table 95 on page 196).

External clock drive timing conditions: VDD = 5V ±10%, VSS = 0V, TA = –40 to +125°C

Table 101.

Minimum values of negative resistance (module)

CA = 6pF

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

32 kHz

----

150 k

Ω

120 k

Ω

90 kW

Crystal

ST10F276

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