STM32F107RB datasheet(49/108 Pages) STMICROELECTRONICS

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STM32F105xx, STM32F107xx

Electrical characteristics

107

Figure 15. 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 3 to 25 MHz crystal/ceramic

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

characterization results obtained with typical external components specified in Table 22. 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 22. HSE 3-25 MHz oscillator characteristics(1) (2)

1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.

2. Based on characterization, not tested in production.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC_IN Oscillator frequency

MHz

Feedback resistor

200

Recommended load capacitance

versus equivalent serial

resistance of the crystal (RS)(3)

3. The relatively low value of the RF resistor offers a good protection against issues resulting from use in a

humid environment, due to the induced leakage and the bias condition change. However, it is

recommended to take this point into account if the MCU is used in tough humidity conditions.

RS = 30 Ω

HSE driving current

VDD = 3.3 V, VIN =VSS

with 30 pF load

Oscillator transconductance

Startup

mA/V

tSU(HSE(4)

4. tSU(HSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz

oscillation is reached. This value is measured for a standard crystal resonator and it can vary significantly

with the crystal manufacturer

Startup time

VDD is stabilized

ai14140c

OSC32_IN

External

STM32F10xxx

clock source

VLSEH

tf(LSE)

tW(LSE)

90%

10%

TLSE

tr(LSE)

tW(LSE)

fLSE_ext

VLSEL

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