topic Re: Problem with using PCF85063A in Other NXP Products

Problem with using PCF85063A

uveuvenouve — Mon, 28 Jul 2025 09:47:38 GMT

i am trying to use PCF85063ATT to acquire and set time

my problem:
can read and set date(repower the mcu can still read the last set date time)

the time not running

can't set most of the register, like reg0 12-24hrs, reg1 clk output(set 0x1 but no 16kHz output)

my circuit:

power supply 3.3v, have super cap of 0.33F at it

have 32.768kHz crystal , with 2 15pF capacitors connecting osc in and out to the ground

between osc in and out have 1M ohms resistor

clkout floating

reg 0 value always 0x08(stop bit =0)

reg 4 OS flag is 0 too

what could be the problem?
software? i saw some arduino example is just setting the time and display the time in loop
seems no specific code needed

hardware?
is the capacitor cause the problem ? what capacitors is needed
or can i just try without the crystal and capacitors?

Re: Problem with using PCF85063A

JozefKozon — Mon, 28 Jul 2025 11:18:17 GMT

Dear Uveuve,

from the hardware point, I see the issue in using external capacitors for the crystal. The PCF85063A has internal capacitors. Selected can be 7pF or 12.5pF. You need to select a quartz crystal with one of these load options and then either left the default 7pF or change it to the 12.5pF.

Please check the PCF85063AT-ARD design files attached. In the Bill Of Materials you can find what crystal had been used. It is CM7V-T1A with 12.5pF load capacitance. There is also a 7pF option. Please consider to use this crystal.

Please check the board schematic.

With Best Regards,

Jozef

Re: Problem with using PCF85063A

uveuvenouve — Wed, 30 Jul 2025 05:28:56 GMT

Hi Jozef,

Thanks for replying
i am using quartz crystal in this circuit.
in other project in my company , they are using the same way to design the PCF85063ATT circuit. and it works.
So weird.

i think i could just try without any capacitor and resistor belong to the crystal?
and connect sda scl gnd vcc only ?

Re: Problem with using PCF85063A

JozefKozon — Wed, 30 Jul 2025 10:59:45 GMT

Hi Uveuve,

i am using quartz crystal in this circuit.
in other project in my company , they are using the same way to design the PCF85063ATT circuit. and it works.
So weird.

[A] If they have used a crystal with difference capacitance, than default 7pF in the datasheet. Then adding external capacitors could work. E.g. if they have used crystal with required capacitance of 5pF, the internal capacitors are 7pF and they will use 18pF, then overall capacitance will be 5pF.

But why to use additional external components if you don't have to. Saving cost and room.

i think i could just try without any capacitor and resistor belong to the crystal?
and connect sda scl gnd vcc only ?

[A] For the recommended schematic please refer to the Figure 31. in the PCF85063A datasheet.

With Best Regards,

Jozef