STM32F050C4 datasheet(55/97 Pages) STMICROELECTRONICS

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STM32F050xx

Electrical characteristics

Doc ID 023683 Rev 1

55/97

Figure 14.

Typical application with an 8 MHz crystal

REXT value depends on the crystal characteristics.

Low-speed external clock generated from a crystal resonator

The low-speed external (LSE) clock can be supplied with a 32.768 kHz crystal resonator

oscillator. All the information given in this paragraph are based on design simulation results

obtained with typical external components specified in Table 32. In the application, the

resonator and the load capacitors have to be placed as close as possible to the oscillator

pins in order to minimize output distortion and startup stabilization 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 www.st.com.

Table 32.

LSE oscillator characteristics (fLSE = 32.768 kHz)

Symbol

Parameter

Conditions(1)

Min(2)

Typ

Max(2)

Unit

IDD

LSE current consumption

LSEDRV[1:0]=00

lower driving capability

-0.5

0.9

µA

LSEDRV[1:0]= 01

medium low driving capability

LSEDRV[1:0] = 10

medium high driving capability

1.3

LSEDRV[1:0]=11

higher driving capability

1.6

Oscillator

transconductance

LSEDRV[1:0]=00

lower driving capability

µA/V

LSEDRV[1:0]= 01

medium low driving capability

LSEDRV[1:0] = 10

medium high driving capability

LSEDRV[1:0]=11

higher driving capability

tSU(LSE)

(3)

Startup time

VDD is stabilized

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

ST microcontrollers”.

Guaranteed by design, 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 and it can vary significantly with the crystal manufacturer

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