PCF8563TS (i2c RTC) time not increasing?

Thread Starter

akke

Joined Dec 17, 2015
77
I have a circuit as shown here:

rtc.jpg


The board was assembled via JLCPCB with the following parts:

C37+C38 = https://jlcpcb.com/partdetail/2000-CL10C200JB8NNNC/C1648 (info + datasheet link)
Y2 = https://jlcpcb.com/partdetail/SeikoEpson-Q13FC1350000400/C32346 (info + datasheet link)
U17 = https://jlcpcb.com/partdetail/NxpSemicon-PCF8563TS_5118/C27397 (info + datasheet link)
C36 = https://jlcpcb.com/partdetail/53938-CL05A105KA5NQNC/C52923 (info + datasheet link)


The problem is: when I set the RTC time and date it stays there forever. It's not incrementing.
I have multiple boards assembled by JLCPCB and tried 3 of them. They all 3 have the same issue.
So it must be a design error I'm afraid.

Any thoughts?
 

geekoftheweek

Joined Oct 6, 2013
1,214
I have to admit I have never worked with crystals myself as I have always used internal clocks or oscillators for my clock sources so I may be wrong.

The application diagram on page 36 of the RTC datasheet looks nothing like your circuit. Most times those diagrams are the bare minimum to success with any IC. Other than that I would say you have too much capacitance on your crystal from what I gather... too much will make it run slow and too little will make it run too fast.
 

Thread Starter

akke

Joined Dec 17, 2015
77
I'm using Adafruit's library and even the included example ( https://github.com/adafruit/RTClib/blob/master/examples/pcf8563/pcf8563.ino ) doesn't work here. I assume they are correctly setting the register bits as it's supposed to be a working library...



So... maybe I do need to desolder the two capacitors I added? The datasheet does indeed not list those like I added them.
(I actually copied this part from another schematic I found online. Maybe that one was incorrect to start with...)
 

Thread Starter

akke

Joined Dec 17, 2015
77
I tried removing C37 too, same issue.
I even tried several different libraries, they alle have the same issue: time is not increasing.

I'm scratching my head on this.. Can't figure out why it's not working :(
 

Thread Starter

akke

Joined Dec 17, 2015
77
Someone suggested replacing C37 with a 10pF capacitor and removing C38.
I tried this, no luck either :(
 

Thread Starter

akke

Joined Dec 17, 2015
77
I tried replacing C37 with different values (10pF, 15pF, 20pF and 22pF) but I can't get it to work.
The clock output stays flat and measuring the frequency at OSCO I get:

10pF: +- 19kHz
15pF: +- 19.7kHZ
20pF: 17kHz
22pF: Flucutating between 16-17kHz

So I'm unable to get 32.678kHz on the OSCO pin.
Should I try with other different capacitors? I'm not sure what else to try...
 

Thread Starter

akke

Joined Dec 17, 2015
77
I do now wonder if the crystal I'm using is the right one... The one I'm using is one of JLCPCB's basic parts: Seiko Epson Q13FC1350000400 32.768kHz 12.5pF ±20ppm SMD3215-2P Crystal.

This is an SMD Crystal Resonator but that's not a Quartz crystal, right?
So I'm just f*cking using the wrong crystal for this RTC. It might just not work with this SMD crystal resonator?
 

geekoftheweek

Joined Oct 6, 2013
1,214
I do now wonder if the crystal I'm using is the right one... The one I'm using is one of JLCPCB's basic parts: Seiko Epson Q13FC1350000400 32.768kHz 12.5pF ±20ppm SMD3215-2P Crystal.
I had wondered that myself, but without any practical experience with crystals I wasn't sure. I do know there are different ways of cutting the quartz that impact how it works, but was not able to find any details in either the RTC or crystal datasheets. I do notice a formula in the footnotes on page 34 of the RTC datasheet that may be of interest, but I'm not understanding how to apply it exactly. The crystal datasheet isn't making sense to me (probably a lack of experience issue)

At any rate I did dig through my parts box and found a few of the RTC that I had bought a few years back and never managed to get working so now I'm really curious. The part number sounded familiar...
 
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