STM32MP157C datasheet(152/258 Pages) STMICROELECTRONICS

152 / 258 page

Electrical characteristics

STM32MP157C

152/258

DS12505 Rev 2

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

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

match the requirements of the crystal or resonator (see Figure 19). 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 19. Typical application with a 24 MHz crystal

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 34. 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).

3. This consumption level occurs during the first 2/3 of the tSU(HSE) startup time.

4. tSU(HSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz oscillation is

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

MSv63062V1

STM32

OSC_OUT

fHSE

CL1

24 MHz

crystal

Bias

controlled

gain

OSC_IN

CL2

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