STM8AF6168 datasheet(55/89 Pages) STMICROELECTRONICS

55 / 89 page

STM8AF61xx, STM8AF62xx

Electrical characteristics

Doc ID 14952 Rev 6

55/89

Figure 16.

HSE external clock source

HSE crystal/ceramic resonator oscillator

The HSE clock can be supplied using a crystal/ceramic resonator oscillator of up to 16 MHz.

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 17.

HSE oscillator circuit diagram

OSCIN

fHSE

External clock

STM8A

source

VHSEL

VHSEH

Table 31.

HSE oscillator characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Feedback resistor

220

CL1/CL2

(1)

Recommended load capacitance

Oscillator transconductance

mA/V

tSU(HSE)

(2)

Startup time

VDD is

stabilized

-2.8

The oscillator needs two load capacitors, CL1 and CL2, to act as load for the crystal. The total load capacitance (Cload) is

(CL1 * CL2)/(CL1 + CL2). If CL1 = CL2, Cload = CL1 / 2. Some oscillators have built-in load capacitors, CL1 and CL2.

This value is the startup time, measured from the moment it is enabled (by software) until a stabilized 16 MHz oscillation is

reached. It can vary with the crystal type that is used.

OSCOUT

OSCIN

fHSE to core

CL1

CL2

STM8A

Resonator

Current control

Resonator

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