How is a crystal circuit's oscillation allowance determined to ensure that it provides adequate stability?
The AM0805 RTC crystal oscillator circuit's negative resistance can be measured to ensure it is within the XT Oscillation Allowance? The XT Oscillator Allowance value (related to negative resistance) is measured by adding additional series resistance to the oscillator circuit until it stops oscillating.
The minimum and typical values of the AM0805 XT Oscillation Allowance is specified as OAXT in "Table7 Oscillator Parameters" of the AM08X5 Datasheet, and is shown below.
Please see this link for a detailed explanation from a crystal manufacturer (Seiko): https://www.sii.co.jp/en/quartz/circuit-design/