STM32F103CBU6XXX datasheet(52/116 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F103x8, STM32F103xB

52/116

DS5319 Rev 18

Figure 23. 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 16 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).

ai14144b

OSC32_IN

EXTER NAL

STM32F103xx

CLOCK SOURC E

VLSEH

tf(LSE)

tW(LSE)

90%

10%

TLSE

tr(LSE)

tW(LSE)

fLSE_ext

VLSEL

Table 22. HSE 4-16 MHz oscillator characteristics(1) (2)

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC_IN Oscillator frequency

MHz

Feedback resistor

200

kΩ

Recommended load capacitance

versus equivalent serial

resistance of the crystal (RS)(3)

RS = 30Ω

-30-

HSE driving current

VDD = 3.3 V, VIN = VSS

with 30 pF load

Oscillator transconductance

Startup

mA/V

tSU(HSE(4) Startup time

VDD is stabilized

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

2. Evaluated by characterization, not tested in production, unless otherwise specified.

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.

4. tSU(HSE) is the startu.p 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

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