STM32L021D4 datasheet(65/114 Pages) STMICROELECTRONICS

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STM32L021x4

Electrical characteristics

Low-speed external user clock generated from an external source

The characteristics given in the following table result from tests performed using a low-

speed external clock source, and under ambient temperature and supply voltage conditions

summarized in Table 17.

Figure 19. Low-speed external clock source AC timing diagram

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 36. 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

Table 35. Low-speed external user clock characteristics(1)

1. Guaranteed by design, not tested in production

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fLSE_ext

User external clock source

frequency

32.768

1000

kHz

VLSEH

OSC32_IN input pin high level

voltage

0.7VDD

-VDD

VLSEL

OSC32_IN input pin low level

voltage

VSS

-0.3VDD

tw(LSE)

OSC32_IN high or low time

465

tr(LSE)

tf(LSE)

OSC32_IN rise or fall time

CIN(LSE) OSC32_IN input capacitance

0.6

DuCy(LSE) Duty cycle

OSC32_IN Input leakage current VSS ≤ VIN ≤ VDD

±1

µA

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