STM32F205VGT6 Datasheet, PDF(77/163 Page) STMicroelectronics – ARM-based 32-bit MCU, 150DMIPs, up to 1 MB Flash/128+4KB RAM, USB OTG HS/FS, Ethernet, 17 TIMs, 3 ADCs, 15 comm. interfaces & camera

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STM32F205VGT6 Datasheet, PDF (77/163 Pages) STMicroelectronics – ARM-based 32-bit MCU, 150DMIPs, up to 1 MB Flash/128+4KB RAM, USB OTG HS/FS, Ethernet, 17 TIMs, 3 ADCs, 15 comm. interfaces & camera

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STM32F205xx, STM32F207xx

Electrical characteristics

Table 25. HSE 4-26 MHz oscillator characteristics(1) (2)

Symbol

Parameter

Conditions

Min Typ Max Unit

fOSC_IN Oscillator frequency

RF Feedback resistor

Recommended load capacitance

versus equivalent serial

RS = 30 Î©

resistance of the crystal (RS)(3)

HSE driving current

VDD = 3.3 V, VIN = VSS

with 30 pF load

26 MHz

200 -

kÎ©

1 mA

gm Oscillator transconductance

tSU(HSE(4) Startup time

Startup

- mA/V

VDD is stabilized

- ms

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

2. Based on characterization, not tested in production.

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 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

For CL1 and CL2, it is recommended to use high-quality external ceramic capacitors in the

5 pF to 25 pF range (typ.), designed for high-frequency applications, and selected to match

the requirements of the crystal or resonator (see Figure 30). CL1 and CL2 are usually the

same size. The crystal manufacturer typically specifies a load capacitance which is the

series combination of CL1 and CL2. PCB and MCU pin capacitance must be included (10 pF

can be used as a rough estimate of the combined pin and board capacitance) when sizing

CL1 and CL2. Refer to the application note AN2867 âOscillator design guide for ST

microcontrollersâ available from the ST website www.st.com.

Figure 30. Typical application with an 8 MHz crystal

Resonator with

integrated capacitors

CL1

8 MH z

resonator

OSC_IN

Bias

controlled

gain

CL2

REXT(1)

OSC_OU T

fHS E

STM32F

ai17530

1. REXT value depends on the crystal characteristics.

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 26. 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).

Doc ID 15818 Rev 7

77/163

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