Hi,
I need some help with the schematics of an RTC and a crystal!
It is a PCF8563 RTC (datasheet) and I think it is wired right from the datasheet but I do not know with the FC-135 (datasheet) crystal?
I have tried to google but can not find any concrete answers, so is there anyone here who can help with that?
No, just follow the circuit given in the application section of the datasheet and checkout the trimmer
capacitance specification too.
Without the supercap as shown in the application circuit you won't have a non-volatile clock.
Its more usual to use a coin-cell battery backup and the DS1307 or related chips that support this -
this can keep time over extended periods of power-down (years). A supercap will self-discharge
much quicker than this.
MarkT:
No, just follow the circuit given in the application section of the datasheet and checkout the trimmer
capacitance specification too.Without the supercap as shown in the application circuit you won't have a non-volatile clock.
Its more usual to use a coin-cell battery backup and the DS1307 or related chips that support this -
this can keep time over extended periods of power-down (years). A supercap will self-discharge
much quicker than this.
Thank you, but, power outages are not an issue in my setup.
My problem is mostly the crystal. I do not know how to wiring it?
Its an SMD component with 2 pads! What are you confused about?
missdrew:
Its an SMD component with 2 pads! What are you confused about?
How to wire it?
Should I use capacitors etc. and how big should they be? Or is what I have on my schematics now, correct?
The datasheet says 12.5pF for the capacitors. I would of just bought a preloaded 'can' type and saved the hastle.
The RTC data sheet calls for one capacitor on the OSCO pin, between 12 pF and 35 pF (typically 25 pF). Adjust this for best clock accuracy.
jremington:
The RTC data sheet calls for one capacitor on the OSCO pin, between 12 pF and 35 pF (typically 25 pF). Adjust this for best clock accuracy.
Tanks you!
So something like this will work?
No, that's wrong.
As I said go to the "application information" section of the datasheet (section 14) and the recommended
circuit is there as I said.
The capacitor does NOT go on the OSC0 pin.
The data sheet states in several places that the capacitor should be connected to OSCO, but the suggested application circuit shows it connected to OSCI.
Table 30 clearly states the range of values on OSCO, and this diagram shows it connected to OSCO (for some reason, internally). So try your way first and if that doesn't work, try OSCI. Let us know what you find.
That's an internal capacitor, provided for convenience, which is why you only need one external
capacitor instead of the usual two. Anything in the box is on the die, not the application circuit.
Chip designers are very keen to reduce the external parts count as that effectively increases the
value of the chip to application engineers.
If trimmability wasn't useful, they'd have put both capacitors on the die.
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