STM8AF6268ITCU datasheet(58/99 Pages) STMICROELECTRONICS

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Electrical characteristics

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DocID14952 Rev 11

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...).

Table 29. 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

1. 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.

2. 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.

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