STM32F405 datasheet(102/204 Pages) STMICROELECTRONICS

102 / 204 page

Electrical characteristics

STM32F405xx, STM32F407xx

102/203

DS8626 Rev 9

Note:

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

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

Figure 32. 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 33. 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 electing the crystal, refer to the application note AN2867 “Oscillator

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

Table 33. LSE oscillator characteristics (fLSE = 32.768 kHz) (1)

1. Guaranteed by design.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC_IN Oscillator frequency

32.768

MHz

Feedback resistor

18.4

IDD

LSE current consumption

µA

Oscillator transconductance

Startup

2.8

µA/V

Gmcritmax Maximum critical crystal Gm

0.56

tSU(LSE)(2)

2. Guaranteed by characterization. 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

startup time

VDD is stabilized

ai17530

OSC_OU T

OSC_IN

fHSE

CL1

STM32F

8 MHz

resonator

Resonator with

integrated capacitors

Bias

controlled

gain

REXT(1)

CL2

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