STM32H747AI datasheet(142/252 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32H747xI/G

132/242

DS12930 Rev 1

Figure 23. Typical application with an 8 MHz crystal

1. REXT value depends on the crystal characteristics.

Low-speed external clock generated from a crystal/ceramic resonator

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

resonator oscillator. All the information given in this paragraph are based on

characterization results obtained with typical external components specified in Table 53. 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).

ai17530b

OSC_OU T

OSC_IN

fHSE

CL1

STM32

8 MHz

resonator

Resonator with

integrated capacitors

Bias

controlled

gain

REXT(1)

CL2

Table 53. Low-speed external user clock characteristics(1)

Symbol

Parameter

Operating conditions(2)

Min

Typ

Max

Unit

Oscillator frequency

32.768

kHz

IDD

LSE current

consumption

LSEDRV[1:0] = 00,

Low drive capability

-290

LSEDRV[1:0] = 01,

Medium Low drive capability

-390

LSEDRV[1:0] = 10,

Medium high drive capability

-550

LSEDRV[1:0] = 11,

High drive capability

-900

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(3)

Startup time

VDD is stabilized

1. Guaranteed by design.

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

ST microcontrollers.

3. tSU is the startup time measured from the moment it is enabled (by software) to a stabilized 32.768k Hz oscillation is

reached. This value is measured for a standard crystal resonator and it can vary significantly with the crystal manufacturer.

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