SPRSP85A April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
PRODMIX
Start-up time is an important consideration when selecting the components of the crystal circuit. As mentioned in the Rneg – Negative Resistance section, for reliable start-up across all conditions, it is recommended that the Rneg > 3x ESR to 5x ESR of the crystal.
Crystal ESR and the dampening resistor (Rd) greatly affect the start-up time. The higher the two values, the longer the crystal takes to start up. Longer start-up times are usually a sign that the crystal and components are not a correct match.
Refer to Crystal Oscillator Specifications for the typical start-up times. Note that the numbers specified here are typical numbers provided for guidance only. Actual start-up time depends heavily on the crystal in question and the external components.