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ST72321R7-Auto Datasheet(PDF) 196 Page - STMicroelectronics |
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ST72321R7-Auto Datasheet(HTML) 196 Page - STMicroelectronics |
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196 / 243 page  Electrical characteristics ST72321xx-Auto 196/243 Doc ID 13829 Rev 1 19.5.3 Crystal and ceramic resonator oscillators The ST7 internal clock can be supplied with four different crystal/ceramic resonator oscillators. 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 start-up stabilization time. Refer to the crystal/ceramic resonator manufacturer for more details (such as frequency, package or accuracy). Figure 79. Typical application with a crystal or ceramic resonator) Table 116. Crystal and ceramic resonator oscillators Symbol Parameter Conditions Min Typ Max Unit fOSC Oscillator frequency(1) 1. The oscillator selection can be optimized in terms of supply current using a high-quality resonator with small RS value. Refer to crystal/ceramic resonator manufacturer for more details. LP: Low power oscillator MP: Medium power oscillator MS: Medium speed oscillator HS: High speed oscillator 1 >2 >4 >8 - 2 4 8 16 MHz RF Feedback resistor(2) 2. Data based on characterization results, not tested in production. The relatively low value of the RF resistor offers a good protection against issues resulting from use in a humid environment, due to the induced leakage and the bias condition change. However, it is recommended to take this point into account if the microcontroller is used in tough humidity conditions. -20 - 40 k CL1 CL2 Recommended load capacitance versus equivalent serial resistance of the crystal or ceramic resonator (RS) (3) 3. For CL1 and CL2 it is recommended to use high-quality ceramic capacitors in the 5pF to 25pF range (typ.) designed for high-frequency applications and selected to match the requirements of the crystal or resonator. CL1 and CL2, are usually the same size. The crystal manufacturer typically specifies a load capacitance which is the series combination of CL1 and CL2. PCB and MCU pin capacitance must be included when sizing CL1 and CL2 (10pF can be used as a rough estimate of the combined pin and board capacitance). RS =200 RS =200 RS =200 RS =100 LP oscillator MP oscillator MS oscillator HS oscillator 22 22 18 15 - 56 46 33 33 pF i2 OSC2 driving current VDD =5V, VIN =VSS LP oscillator MP oscillator MS oscillator HS oscillator - 80 160 310 610 150 250 460 910 µA OSC2 OSC1 fOSC CL1 CL2 i2 RF ST72XXX RESONATOR WHEN RESONATOR WITH INTEGRATED CAPACITORS |
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