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ISL12059IBZ 数据表(PDF) 10 Page - Intersil Corporation |
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ISL12059IBZ 数据表(HTML) 10 Page - Intersil Corporation |
10 / 11 page 10 FN6757.0 June 15, 2009 Application Section Oscillator Crystal Requirements The ISL12059 uses a standard 32.768kHz crystal. Either through hole or surface mount crystals can be used. Table 6 lists some recommended surface mount crystals and the parameters of each. This list is not exhaustive and other surface mount devices can be used with the ISL12059 if their specifications are very similar to the devices listed. The crystal should have a required parallel load capacitance of 12.5pF and an equivalent series resistance of less than 50k. The crystal’s temperature range specification should match the application. Many crystals are rated for -10°C to +60°C (especially through-hole and tuning fork types), so an appropriate crystal should be selected if extended temperature range is required. Layout Considerations The crystal input at X1 has a very high impedance, and oscillator circuits operating at low frequencies such as 32.768kHz are known to pick up noise very easily if layout precautions are not followed. Most instances of erratic clocking or large accuracy errors can be traced to the susceptibility of the oscillator circuit to interference from adjacent high speed clock or data lines. Careful layout of the RTC circuit will avoid noise pickup and insure accurate clocking. Figure 10 shows a suggested layout for the ISL12059 device using a surface mount crystal. Two main precautions should be followed: Do not run the serial bus lines or any high speed logic lines in the vicinity of the crystal. These logic level lines can induce noise in the oscillator circuit to cause misclocking. Add a ground trace around the crystal with one end terminated at the chip ground. This will provide termination for emitted noise in the vicinity of the RTC device. In addition, it is a good idea to avoid a ground plane under the X1 and X2 pins and the crystal, as this will affect the load capacitance and therefore the oscillator accuracy of the circuit. If the FT/OUT pin is used as a clock, it should be routed away from the RTC device as well. The traces for the VDD pins can be treated as a ground, and should be routed around the crystal. FIGURE 9. MULTIPLE BYTES READ SEQUENCE SIGNALS FROM THE MASTER SIGNALS FROM THE SLAVE SIGNAL AT SDA S T A R T IDENTIFICATION BYTE WITH R/W = 0 ADDRESS BYTE A C K A C K 0 S T O P A C K 1 IDENTIFICATION BYTE WITH R/W = 1 A C K S T A R T LAST READ DATA BYTE FIRST READ DATA BYTE A C K 10 1 1000 10 1 10 00 R/W BIT = “0” R/W BIT = “1” TABLE 3. SUGGESTED SURFACE MOUNT CRYSTALS MANUFACTURER PART NUMBER Citizen CM200S MicroCrystal MS3V Raltron RSM-200S SaRonix 32S12 Ecliptek ECPSM29T-32.768K ECS ECX-306 Fox FSM-327 FIGURE 10. SUGGESTED LAYOUT FOR ISL12059 AND ISL12059 |
类似零件编号 - ISL12059IBZ |
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类似说明 - ISL12059IBZ |
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