STM8S207MB datasheet(65/103 Pages) STMICROELECTRONICS

65 / 103 page

STM8S207xx, STM8S208xx

Electrical characteristics

Doc ID 14733 Rev 12

65/103

Figure 17.

HSE oscillator circuit diagram

HSE oscillator critical gm formula

Rm: Notional resistance (see crystal specification)

Lm: Notional inductance (see crystal specification)

Cm: Notional capacitance (see crystal specification)

Co: Shunt capacitance (see crystal specification)

CL1=CL2=C: Grounded external capacitance

gm >> gmcrit

Table 32.

HSE oscillator characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fHSE

External high speed oscillator

frequency

124

MHz

Feedback resistor

220

C(1)

Recommended load capacitance (2)

IDD(HSE)

HSE oscillator power consumption

C = 20 pF,

fOSC = 24 MHz

6 (startup)

2 (stabilized)(3)

C = 10 pF,

fOSC = 24 MHz

6 (startup)

1.5 (stabilized)(3)

Oscillator transconductance

mA/V

tSU(HSE)

(4) Startup time

VDD is stabilized

C is approximately equivalent to 2 x crystal Cload.

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

Data based on characterization results, not tested in production.

tSU(HSE) is the start-up time measured from the moment it is enabled (by software) to a stabilized 24 MHz oscillation is

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

OSCOUT

OSCIN

fHSE to core

CL1

CL2

STM8

Resonator

Consumption

control

Resonator

mcrit

HSE

()2 R

2Co

()

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