User manual for I²C-bus RTC demo board OM13515
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© NXP B.V. 2014. All rights reserved.
3. Hardware set-up
3.1 General requirements for the RTCs PCx85063A
The RTC circuit just requires one external part: a tuning fork quartz as resonator. The
oscillation capacitors are integrated and therefore there is no need for external
capacitors. The quartz crystal must be placed close to the RTC circuit, avoiding long
lines which may pick up noise. Avoid any tracks with high frequency signals (fast edges)
close to the RTC, quartz, or quartz interconnect.
The interface is the standard Fast Mode I
2
C-bus, operating up to 400 kHz. Adjust the
values of the pull-up resistors to match the required interface speed keeping them as
high impedance as possible for power savings reasons. Ensure that the specified
minimum requirements of the hold times t
LOW
and t
HIGH
are fulfilled.
Supply voltage: The RTC is specified from 0.9 V to 5.5 V. The I
2
C-bus interface is
specified from 1.8 V to 5.5 V. It is recommended to have a decoupling capacitor on the
V
DD
-V
SS
rails close by.
Due to the low power consumption of below 1 μW, no precautions for heat dissipations
are required.
CLKOUT can be used to measure the frequency or be used as reference for frequency
generation with a PLL.
Fig 2. Interfacing to the microcontroller
