STM8L151F3 datasheet(74/122 Pages) STMICROELECTRONICS

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Electrical parameters

STM8L151x2, STM8L151x3

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DocID018780 Rev 9

HSE oscillator critical gm formula

gmcrit

fHSE

()2 Rm

2Co C

()

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

LSE crystal/ceramic resonator oscillator

The LSE clock can be supplied with a 32.768 kHz 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...).

Table 31. LSE oscillator characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fLSE

Low speed external oscillator

frequency

32.768

kHz

Feedback resistor

ΔV = 200 mV

1.2

C(1)

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

Recommended load capacitance (2)

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

small Rm value. Refer to crystal manufacturer for more details.

IDD(LSE) LSE oscillator power consumption

1.4(3)

3. Guaranteed by design.

µA

VDD = 1.8 V

450

VDD = 3 V

600

VDD = 3.6 V

750

Oscillator transconductance

3(3)

µA/V

tSU(LSE)(4)

tSU(LSE) is the startup time measured from the moment it is enabled (by software) to a stabilized

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

with the crystal manufacturer.

Startup time

VDD is stabilized

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