STM32WB15CC datasheet(87/127 Pages) STMICROELECTRONICS

87 / 127 page

DS13258 Rev 4

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STM32WB15CC

Electrical characteristics

115

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 16. 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 6.3.16.

The recommend clock input waveform is shown in Figure 17.

Figure 17. Low-speed external clock source AC timing diagram

1. Specified by design, not tested in production.

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

MS19215V2

VLSEH

tf(LSE)

90%

10%

TLSE

tr(LSE)

VLSEL

tw(LSEH)

tw(LSEL)

Table 51. 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

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