STM32F070CB datasheet(47/83 Pages) STMICROELECTRONICS

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STM32F070CB/RB/C6/F6

Electrical characteristics

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 GPIO.

The external clock signal has to respect the I/O characteristics in Section 6.3.14. However,

the recommended clock input waveform is shown in Figure 12.

Figure 12. Low-speed external clock source AC timing diagram

High-speed external clock generated from a crystal/ceramic resonator

The high-speed external (HSE) clock can be supplied with a 4 to 32 MHz crystal/ceramic

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

simulation results obtained with typical external components specified in Table 32. 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).

Table 31. Low-speed external user clock characteristics

Symbol

Parameter(1)

1. Guaranteed by design, not tested in production.

Min

Typ

Max

Unit

fLSE_ext User external clock source frequency

32.768

1000

kHz

VLSEH OSC32_IN input pin high level voltage

0.7 VDDIOx

-VDDIOx

VLSEL

OSC32_IN input pin low level voltage

VSS

0.3 VDDIOx

tw(LSEH)

tw(LSEL)

OSC32_IN high or low time

450

tr(LSE)

tf(LSE)

OSC32_IN rise or fall time

Table 32. HSE oscillator characteristics

Symbol

Parameter

Conditions(1)

Min(2)

Typ

Max(2)

Unit

fOSC_IN

Oscillator frequency

MHz

Feedback resistor

200

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