STM32F765II datasheet(143/255 Pages) STMICROELECTRONICS

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STM32F765xx STM32F767xx STM32F768Ax STM32F769xx

Electrical characteristics

224

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 30). 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. The 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 30. 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 44. 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 44. LSE oscillator characteristics (fLSE = 32.768 kHz) (1)

Symbol

Parameter

Conditions

Min

Typ

Max Unit

IDD

LSE current consumption

LSEDRV[1:0]=00

Low drive capability

250

LSEDRV[1:0]=10

Medium low drive capability

300

LSEDRV[1:0]=01

Medium high drive capability

370

LSEDRV[1:0]=11

High drive capability

480

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