STM8L051F3 datasheet(61/96 Pages) STMICROELECTRONICS

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DS9178 Rev 4

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STM8L051F3

Electrical parameters

HSE crystal/ceramic resonator oscillator

The HSE clock can be supplied with a 1 to 16 MHz crystal/ceramic resonator oscillator. All

the information given in this paragraph is based on characterization results with specified

typical external components. 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

(frequency, package, accuracy...).

Figure 12. HSE oscillator circuit diagram

HSE oscillator critical gm formula

Rm: Motional resistance (see crystal specification), Lm: Motional inductance (see crystal specification),

Cm: Motional capacitance (see crystal specification), Co: Shunt capacitance (see crystal specification),

CL1=CL2=C: Grounded external capacitance

gm >> gmcrit

Table 28. HSE oscillator characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fHSE

High speed external oscillator

frequency

-1

MHz

Feedback resistor

200

C(1)

Recommended load capacitance (2)

IDD(HSE) HSE oscillator power consumption

C = 20 pF,

fOSC = 16 MHz

2.5 (startup)

0.7 (stabilized)(3)

C = 10 pF,

fOSC =16 MHz

2.5 (startup)

0.46 (stabilized)(3)

Oscillator transconductance

3.5(3)

mA/V

tSU(HSE)(4) Startup time

VDD is stabilized

1. C=CL1=CL2 is approximately equivalent to 2 x crystal CLOAD.

2. The oscillator selection can be optimized in terms of supply current using a high quality resonator with small Rm value.

Refer to crystal manufacturer for more details

3. Guaranteed by design.

4. tSU(HSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 16 MHz oscillation. This

value is measured for a standard crystal resonator and it can vary significantly with the crystal manufacturer.

gmcrit

fHSE

()2 Rm

2Co C

()

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