STM32L431 datasheet(111/200 Pages) STMICROELECTRONICS

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STM32L431xx

Electrical characteristics

168

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.

Figure 22. Typical application with an 8 MHz crystal

1. 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 46. 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).

Table 46. LSE oscillator characteristics (fLSE = 32.768 kHz)(1)

Symbol

Parameter

Conditions(2)

Min

Typ

Max

Unit

IDD(LSE) LSE current consumption

LSEDRV[1:0] = 00

Low drive capability

-250

LSEDRV[1:0] = 01

Medium low drive capability

-315

LSEDRV[1:0] = 10

Medium high drive capability

-500

LSEDRV[1:0] = 11

High drive capability

-630

Gmcritmax

Maximum critical crystal

LSEDRV[1:0] = 00

Low drive capability

0.5

µA/V

LSEDRV[1:0] = 01

Medium low drive capability

0.75

LSEDRV[1:0] = 10

Medium high drive capability

1.7

LSEDRV[1:0] = 11

High drive capability

2.7

tSU(LSE)(3) Startup time

VDD is stabilized

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