STM32WB35CCU6ATR datasheet(121/193 Pages) STMICROELECTRONICS

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DS11929 Rev 10

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STM32WB55xx STM32WB35xx

Electrical characteristics

169

Note:

For information on selecting the crystal refer to application note AN2867 “Oscillator design

guide for STM8S, STM8A and STM32 microcontrollers” available from www.st.com.

Figure 22. Typical application with a 32.768 kHz crystal

Note:

No external resistors are required between OSC32_IN and OSC32_OUT, and it is forbidden

to add one.

In bypass mode the LSE oscillator is switched off and the input pin is a standard GPIO.

The external clock signal has to respect the I/O characteristics detailed in Section 6.3.17.

The recommend clock input waveform is shown in Figure 23.

Figure 23. Low-speed external clock source AC timing diagram

1. Guaranteed by design.

2. tSU(LSE) is the startup time measured from the moment it is enabled (by software) until a stable 32 kHz oscillation is

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

MS30253V2

OSC32_IN

OSC32_OUT

Drive

programmable

amplifier

fLSE

32.768 kHz

resonator

Resonator with integrated

capacitors

CL1

CL2

Table 58. Low-speed external user clock characteristics(1) – Bypass mode

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fLSE_ext

User external clock

source frequency

21.2

32.768

44.4

kHz

MS19215V2

VLSEH

tf(LSE)

90%

10%

TLSE

tr(LSE)

VLSEL

tw(LSEH)

tw(LSEL)

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