JN516X Datasheet, PDF (19/94 Pages) NXP Semiconductors – IEEE802.15.4 Wireless Microcontroller

Section 19.3.10. Please refer to Appendix B for development support with the crystal oscillator circuit. The oscillator
includes a function which flags when the amplitude of oscillation has reached a satisfactory level for full operation,
and this is checked before the source of the high-speed system clock is changed to the 32MHz crystal oscillator
JN516x
XTALIN
R1
XTALOUT
C1
C2
Figure 8: 32MHz Crystal Oscillator Connections
For operation over the extended temperature range, 85 to 125 deg C, special care is required; this is because the
temperature characteristics of crystal resonators are generally in excess of +/-40ppm frequency tolerance defined by
the IEEE802.15.4 standard. The oscillator cell contains additional circuitry to compensate for the poor performance of
the crystal resonators above 100 deg C. Full details, including the software API function, can be found in the
application note JN516x Temperature-dependent Operating Guidelines [2]
5.1.2 High-Speed RC Oscillator
An on-chip High-Speed RC oscillator is provided in addition to the 32MHz crystal oscillator for two purposes, to allow
a fast start-up from reset or sleep and to provide a lower current alternative to the crystal oscillator for non-timing
critical applications. By default the oscillator will run at 27MHz typically with a wide tolerance. It can be calibrated,
using a software API function, which will result in a nominal frequency of 32MHz with a +/-1.6% tolerance at 3v and
25 deg C. However, it should be noted that over the full operating range of voltage and temperature this will increase
to +/-5%. The calibration information is retained through speed cycles and when the oscillator is disabled, so typically
the calibration function only needs to be called once. No external components are required for this oscillator. The
electrical specification of the oscillator can be found in Section 19.3.11.
5.2 Low-speed (32kHz) System Clock
The 32kHz system clock is used for timing the length of a sleep period (see Section 18). The clock can be selected
from one of three sources through the application software:
• 32kHz RC Oscillator
• 32kHz Crystal Oscillator
• 32kHz External Clock
Upon a chip reset or power-up the JN516x defaults to using the internal 32kHz RC Oscillator. If another clock source
is selected then it will remain in use for all 32kHz timing until a chip reset is performed.
5.2.1 32kHz RC Oscillator
The internal 32kHz RC oscillator requires no external components. The internal timing components of the oscillator
have a wide tolerance due to manufacturing process variation and so the oscillator runs nominally at 32kHz ±30%. To
make this useful as a timing source for accurate wakeup from sleep, a frequency calibration factor derived from the
more accurate 16MHz clock may be applied. The calibration factor is derived through software, details can be found
in Section 11.3.1. Software must check that the 32kHz RC oscillator is running before using it. For detailed electrical
specifications, see Section 19.3.8.
© NXP Laboratories UK 2013
JN-DS-JN516x v1.1 Production
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