STM32F101X6 datasheet(41/74 Pages) STMICROELECTRONICS

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STM32F101xx

Electrical characteristics

41/74

Figure 18.

Low-speed external clock source AC timing diagram

High-speed external clock

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 21. 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).

ai14140b

OSC32_IN

EXTER NAL

STM32F101

CLOCK SOURC E

VLSEH

tf(LSE)

tW(LSE)

90%

10%

TLSE

tr(LSE)

tW(LSE)

fLSE_ext

VLSEL

Table 21.

HSE 4-16 MHz oscillator characteristics(1)

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fOSC_IN

Oscillator frequency

MHz

Feedback resistor

200

Ω

CL1

CL2

(2)

Recommended load capacitance versus

equivalent serial resistance of the crystal (RS)

(3) RS = 30 Ω

HSE driving current

VDD = 3.3 V

VIN = VSS with 30 pF

load

1mA

(4)

Oscillator transconductance

Startup

mA/V

tSU(HSE)

(5)

Startup time

VDD is stabilized

Resonator characteristics given by the crystal/ceramic resonator manufacturer.

For CL1 and CL2 it is recommended to use high-quality 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. 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 when sizing CL1 and CL2 (10 pF can be used as a rough estimate of

the combined pin and board capacitance).

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.

Based on characterization results, not tested in production.

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

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