STM32L021D4 datasheet(66/114 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32L021x4

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DocID027982 Rev 5

time. Refer to the crystal resonator manufacturer for more details on the resonator

characteristics (frequency, package, accuracy).

Note:

For information on selecting the crystal, refer to the application note AN2867 “Oscillator

design guide for ST microcontrollers” available from the ST website http://www.st.com.

Figure 20. Typical application with a 32.768 kHz crystal

Note:

An external resistor is not required between OSC32_IN and OSC32_OUT and it is forbidden

to add one.

Table 36. LSE oscillator characteristics(1)

Symbol

Parameter

Conditions(2)

Min(2)

Typ

Max

Unit

fLSE

LSE oscillator frequency

32.768

kHz

Maximum critical crystal

transconductance

LSEDRV[1:0]=00

lower driving capability

0.5

µA/V

LSEDRV[1:0]= 01

medium low driving capability

0.75

LSEDRV[1:0] = 10

medium high driving capability

1.7

LSEDRV[1:0]=11

higher driving capability

2.7

tSU(LSE)(3) Startup time

VDD is stabilized

1. Guaranteed by design, not tested in production.

2. Refer to the note and caution paragraphs below the table, and to the application note AN2867 “Oscillator design guide for ST

microcontrollers”.

3. Guaranteed by characterization results, not tested in production. tSU(LSE) is the startup time measured from the moment it is

enabled (by software) to a stabilized 32.768 kHz oscillation is reached. This value is measured for a standard crystal

resonator and it can vary significantly with the crystal manufacturer. To increase speed, address a lower-drive quartz with a

high- driver mode.

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