STM32U535NET3QTR datasheet(187/278 Pages) STMICROELECTRONICS

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DS14217 Rev 1

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STM32U535xx

Electrical characteristics

253

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

5 pF to 20 pF range (typ.), designed for high-frequency applications, and selected to match

the requirements of the crystal or resonator (see the figure below). CL1 and CL2 are usually

the same size. The crystal manufacturer typically specifies a load capacitance that 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 ‘Oscillator design guide

for STM8AF/AL/S, STM32 MCUs and MPUs’ (AN2867).

Figure 31. Typical application with a 8 MHz crystal

1. REXT value depends on the crystal characteristics.

Low-speed external clock generated from a crystal resonator

The low-speed external (LSE) clock can be supplied with a 32.768 kHz crystal resonator

oscillator. All the information given in this paragraph are based on design simulation results

obtained with typical external components specified in the table below. 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).

2. Resonator characteristics given by the crystal/ceramic resonator manufacturer.

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.

MS19876V1

(1)

OSC_IN

OSC_OUT

Bias

controlled

gain

fHSE

REXT

8 MHz

resonator

Resonator with integrated

capacitors

CL1

CL2

Table 79. LSE oscillator characteristics (fLSE = 32.768 kHz)(1)

Symbol

Parameter

Conditions(2)

Min

Typ

Max

Unit

IDD(LSE)

LSE current

consumption

LSEDRV[1:0] = 00, low-drive capability

410

LSEDRV[1:0] = 01, medium low-drive capability

450

LSEDRV[1:0] = 10, medium high-drive capability

590

LSEDRV[1:0] = 11, high-drive capability

700

STM32U535NET3QTR Datasheet(PDF) 187 Page - STMicroelectronics

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