CC3200_15 Datasheet, PDF (37/71 Pages) Texas Instruments – CC3200 SimpleLink™ Wi-Fi® and Internet-of-Things Solution, a Single-Chip Wireless MCU

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CC3200
SWAS032F – JULY 2013 – REVISED FEBRUARY 2015
4.11.3 Clock Specifications
The CC3200 device requires two separate clocks for its operation:
• A slow clock running at 32.768 kHz is used for the RTC.
• A fast clock running at 40 MHz is used by the device for the internal processor and the WLAN subsystem.
The device features internal oscillators that enable the use of cheaper crystals rather than dedicated TCXOs for
these clocks. The RTC can also be fed externally to provide reuse of an existing clock on the system and reduce
overall cost.
4.11.3.1 Slow Clock Using Internal Oscillator
The RTC crystal connected on the device supplies the free-running slow clock. The accuracy of the slow clock
frequency must be 32.768 kHz ±150 ppm. In this mode of operation, the crystal is tied between RTC_XTAL_P
(pin 51) and RTC_XTAL_N (pin 52) with a suitable load capacitance.
Figure 4-9 shows the crystal connections for the slow clock.
51
RTC_XTAL_P
32.768 kHz
10 pF
GND
RTC_XTAL_N ⁵²
10 pF
GND
SWAS031-028
Figure 4-9. RTC Crystal Connections
4.11.3.2 Slow Clock Using an External Clock
When an RTC clock oscillator is present in the system, the CC3200 device can accept this clock directly as an
input. The clock is fed on the RTC_XTAL_P line and the RTC_XTAL_N line is held to VIO. The clock must be a
CMOS-level clock compatible with VIO fed to the device.
Figure 4-10 shows the external RTC clock input connection.
RTC_XTAL_P
RTC_XTAL_N
32.768 kHz
VIO
100 K
Host system
SWAS031-029
Figure 4-10. External RTC Clock Input
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