ST7LITE20F2 datasheet(34/166 Pages) STMICROELECTRONICS

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Supply, reset and clock management

ST7LITE20F2 ST7LITE25F2 ST7LITE29F2

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Doc ID 8349 Rev 5

Note:

See Section 13: Electrical characteristics for more information on the frequency and

accuracy of the RC oscillator.

To improve clock stability and frequency accuracy, it is recommended to place a decoupling

capacitor, typically 100nF, between the VDD and VSS pins as close as possible to the ST7

device.

These two bytes are systematically programmed by ST, including on FASTROM devices.

Consequently, customers intending to use FASTROM service must not use these two bytes.

RCCR0 and RCCR1 calibration values will be erased if the Read-out protection bit is reset

after it has been set. See Section 4.5.1: Read-out protection.

Caution:

If the voltage or temperature conditions change in the application, the frequency may need

to be recalibrated.

Refer to application note AN1324 for information on how to calibrate the RC frequency using

an external reference signal.

7.2

Phase locked loop (PLL)

The PLL can be used to multiply a 1 MHz frequency from the RC oscillator or the external

clock by 4 or 8 to obtain fOSC of 4 or 8 MHz. The PLL is enabled and the multiplication factor

of 4 or 8 is selected by 2 option bits.

●

The x4 PLL is intended for operation with VDD in the 2.4 V to 3.3 V range

●

The x8 PLL is intended for operation with VDD in the 3.3 V to 5.5 V range

Note:

Refer to Section 15.1: Option bytes for the option byte description.

If the PLL is disabled and the RC oscillator is enabled, then fOSC = 1 MHz.

If both the RC oscillator and the PLL are disabled, fOSC is driven by the external clock.

Figure 12. PLL output frequency timing diagram

When the PLL is started, after reset or wakeup from HALT mode or AWUF mode, it outputs

the clock after a delay of tSTARTUP.

When the PLL output signal reaches the operating frequency, the LOCKED bit in the

SICSCR register is set. Full PLL accuracy (ACCPLL) is reached after a stabilization time of

4/8 x

freq.

LOCKED bit set

tSTAB

tLOCK

input

tSTARTUP

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