STM32F479AI datasheet(114/217 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F479xx

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DocID028010 Rev 3

5.3.9

External clock source characteristics

High-speed external user clock generated from an external source

In bypass mode the HSE oscillator is switched off and the input pin is a standard I/O. The

external clock signal has to respect the Table 58. However, the recommended clock input

waveform is shown in Figure 29.

The characteristics given in Table 35 result from tests performed using an high-speed

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

summarized in Table 17.

Low-speed external user clock generated from an external source

In bypass mode the LSE oscillator is switched off and the input pin is a standard I/O. The

external clock signal has to respect the Table 58: I/O static characteristics. However, the

recommended clock input waveform is shown in Figure 30.

The characteristics given in Table 36 result from tests performed using an low-speed

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

summarized in Table 17.

Table 35. High-speed external user clock characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fHSE_ext

External user clock source

frequency(1)

MHz

VHSEH

OSC_IN input pin high level voltage

0.7VDD

-VDD

VHSEL

OSC_IN input pin low level voltage

VSS

-0.3VDD

tw(HSE)

OSC_IN high or low time(1)

1. Guaranteed by design.

tr(HSE)

tf(HSE)

OSC_IN rise or fall time(1)

Cin(HSE) OSC_IN input capacitance(1)

DuCy(HSE) Duty cycle

OSC_IN Input leakage current

VSS ≤VIN ≤VDD

±1

µA

Table 36. Low-speed external user clock characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fLSE_ext

User External clock source frequency(1)

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)

tf(LSE)

OSC32_IN high or low time(1)

450

tr(LSE)

tf(LSE)

OSC32_IN rise or fall time(1)

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