STM32F412RGH7PTR datasheet(110/201 Pages) STMICROELECTRONICS

110 / 201 page

Electrical characteristics

STM32F412xE/G

110/201

DocID028087 Rev 7

For CL1 and CL2, it is recommended to use high-quality external ceramic capacitors in the

5 pF to 25 pF range (Typ.), designed for high-frequency applications, and selected to match

the requirements of the crystal or resonator (see Figure 29). CL1 and CL2 are usually the

same size. The crystal manufacturer typically specifies a load capacitance which is the

series combination of CL1 and CL2. PCB and MCU pin capacitance must be included (10 pF

can be used as a rough estimate of the combined pin and board capacitance) when sizing

CL1 and CL2.

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 29. 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 42. 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).

The LSE high-power mode allows to cover a wider range of possible crystals but with a cost

of higher power consumption.

Table 42. LSE oscillator characteristics (fLSE = 32.768 kHz) (1)

1. Guaranteed by design, not tested in production.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Feedback resistor

18.4

IDD

LSE current consumption

Low-power mode

(default)

µA

High-drive mode

ACCLSE(2)

LSE accuracy

-500

500

ppm

Gm_crit_max Maximum critical crystal gm

Startup, low-power

mode

0.56

µA/V

Startup, high-drive

mode

1.50

tSU(LSE)(3)

startup time

VDD is stabilized

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