4
2.2
RTC
RTC is usually driven by 32.768 kHz oscillator, which needs to connect external 32.768
kHz crystal.
If GNSS hot start function is not needed, RTC crystal can be omitted. Under this condition,
RTC_O should be grounded, and RTC_I should be floating.
UC6226 also supports external 32.768 kHz digital clock signal directly input RTC_I pin to
replace the crystal. When using external digital clock signal input RTC_I, be sure that the
high level of the signal must be less than 1.05 V, or it may lead to UC6226 getting burned.
Level requirement for the input signal: high level 0.9 V ~ 1.05 V, low level 0 V~0.2 V.
Waveform requirement for the clock: duty cycle range should be 45% ~ 55%, clock error
range should be ± 0.6 Hz, ± 20 ppm.
RTC layout and routing should follow the general rules of RTC layout and routing, with
special attention to:
1)
Use a proper GND concept;
2)
The RTC crystal shall be placed as close to the chip as possible, and there shall be
no other devices between the two;
3)
Devices, signals, wiring, etc. with high power or strong interference should be avoided
around RTC crystal;
4)
It is recommended to ground shield with the relevant circuits of RTC.
