ISL12022M Oscillator Accuracy APPLICATION NOTE
The ISL12022M devices are high-accuracy, temperature compensated Real Time Clock (RTC) modules that incorporate the RTC die and the quartz crystal. The RTC contains an internal temperature sensor and state machine to adjust the oscillator frequency and allow factory calibration to less than ±5ppm error over the -40°C to +85°C ambient operating temperature range. There are numerous items that affect the final accuracy of the module once assembled on a PC board, including handling and shock, reflow temperature profile, maximum temperature, number of reflows (or wave solder) and if ultrasound is used (note that the ISL12022M family refers to the ISL12022M, ISL12022MA and ISL12022MR5421 products).This application note will discuss the expected accuracy of the device when mounted on a board, at room temperature and as temperature varies. Also discussed will be the measurement techniques and analyzing the results.
The ISL12022M provides a high accuracy 3-in-1 RTC solution for real time clock timing requirements. The oscillator accuracy is guaranteed for the device shipped from the factory. The PCB assembly process adds environmental factors, such as heat and vibration that will cause the accuracy error to increase after assembly. This change will be evident when testing the final assembled PC board RTC oscillator frequency. The major contributors to additional accuracy error are solder reflow, board cutting or routing, ultrasound cleaning and mechanical handling shocks or vibrations.For final product oscillator accuracy, the customer must consider the assembly effects and the resulting board mounted module device may not be within the expected accuracy limits shown on the datasheet. The customer can adjust their system to address this change in accuracy or look into other ways of adjusting final oscillator accuracy.
NOTE: If the customer has the capability to test, access the serial interface, make adjustments and test again, there are methods to readjust the device for better accuracy after assembly. Please contact Intersil applications about this possibility.The customer needs to read and understand the environmental effects on the crystal oscillator accuracy and make every effort to minimize these effects, which will result in the highest possible accuracy of the board mounted RTC. In some cases, the customer may be forced to use an assembly process that is known to cause additional accuracy error as listed in this document. They should immediately contact Intersil to verify the hazard and possible impact and to identify alternative procedures that may be possible.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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October 17, 2014 |
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Rev 0.00 |
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AN1744 |
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383 KB |
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