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数据搜索系统，热门电子元器件搜索 |
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数据搜索系统，热门电子元器件搜索 |
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STM8AF5269 数据表(PDF) 69 Page - STMicroelectronics |
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STM8AF5269 数据表(HTML) 69 Page - STMicroelectronics |
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69 / 125 page  DocID14395 Rev 15 69/125 STM8AF526x/8x/Ax STM8AF6269/8x/Ax Electrical characteristics 114 Figure 20. HSE oscillator circuit diagram HSE oscillator critical gm formula The crystal characteristics have to be checked with the following formula: Equation 1 where gmcrit can be calculated with the crystal parameters as follows: Equation 2 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 Table 32. HSE oscillator characteristics Symbol Parameter Conditions Min Typ Max Unit RF Feedback resistor - - 220 - k Ω CL1/CL2(1) Recommended load capacitance - - - 20 pF gm Oscillator trans conductance - 5 - - mA/V tSU(HSE)(2) Startup time VDD is stabilized -2.8 - ms 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 24 MHz oscillation is reached. It can vary with the crystal type that is used. gm gmcrit » gmcrit 2 Π × HSE f × () 2 Rm × 2Co C + () 2 = |
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