STM32F334C8U6TR datasheet(69/125 Pages) STMICROELECTRONICS

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DS9994 Rev 9

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STM32F334x4 STM32F334x6 STM32F334x8

Electrical characteristics

103

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 17). 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 17. 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 design

simulation results obtained with typical external components specified in Table 39. In the

application, the resonator and the load capacitors have to be placed as close as possible to

the oscillator pins 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 39. LSE oscillator characteristics (fLSE = 32.768 kHz)

Symbol

Parameter

Conditions(1)

Min.(2)

Typ. Max.(2)

Unit

IDD

LSE current consumption

LSEDRV[1:0]=00

lower driving capability

-0.5

0.9

µA

LSEDRV[1:0]=10

medium low driving

capability

LSEDRV[1:0]=01

medium high-driving

capability

1.3

LSEDRV[1:0]=11

higher-driving capability

1.6

MS19876V1

(1)

OSC_IN

OSC_OUT

Bias

controlled

gain

fHSE

REXT

8 MHz

resonator

Resonator with integrated

capacitors

CL1

CL2

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