CC3220 Datasheet, PDF (39/84 Pages) Texas Instruments – SimpleLink Wi-Fi Wireless and Internet-of-Things Solution, a Single-Chip Wireless MCU

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CC3220
SWAS035A – SEPTEMBER 2016 – REVISED FEBRUARY 2017
Table 4-6 lists the external RTC digital clock requirements.
Table 4-6. External RTC Digital Clock Requirements
CHARACTERISTICS
TEST CONDITIONS
Frequency
Frequency accuracy
(Initial plus temperature plus aging)
t_r, t_f
Input transition time t_r, t_f (10% to
90%)
Frequency input duty cycle
V_ih
Slow clock input voltage limits
V_il
Square wave, DC coupled
Input impedance
MIN
TYP
32768
±150
20%
0.65 × VIO
0
1
50%
MAX
UNIT
Hz
ppm
100
80%
VIO
0.35 × VIO
5
ns
V
V_peak
MΩ
pF
4.14.4.3 Fast Clock (F_ref) Using an External Crystal
The CC3220x device also incorporates an internal crystal oscillator to support a crystal-based fast clock.
The XTAL is fed directly between WLAN_XTAL_P (pin 23) and WLAN_XTAL_N (pin 22) with suitable
loading capacitors.
Figure 4-11 shows the crystal connections for the fast clock.
23
WLAN_XTAL_P
40 MHz
6.2 pF
GND
WLAN_XTAL_N ²²
6.2 pF
GND
SWAS031-030
NOTE: The XTAL capacitance must be tuned to ensure that the PPM requirement is met. See CC31xx & CC32xx Frequency
Tuning for information on frequency tuning.
Figure 4-11. Fast Clock Crystal Connections
Table 4-7 lists the WLAN fast-clock crystal requirements.
Table 4-7. WLAN Fast-Clock Crystal Requirements
CHARACTERISTICS
TEST CONDITIONS
MIN
Frequency
Frequency accuracy
Initial plus temperature plus aging
Crystal ESR
40 MHz
TYP
MAX UNIT
40
MHz
±25 ppm
60 Ω
4.14.4.4 Fast Clock (F_ref) Using an External Oscillator
The CC3220x device can accept an external TCXO/XO for the 40-MHz clock. In this mode of operation,
the clock is connected to WLAN_XTAL_P (pin 23). WLAN_XTAL_N (pin 22) is connected to GND. The
external TCXO/XO can be enabled by TCXO_EN (pin 21) from the device to optimize the power
consumption of the system.
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