hi,
in my project i am using isl12057 RTC for a date and time,the VT-200-F crystal provide 32.768KHz frequency. my circuit have stray capacitance of 7.5+pf, and parallel capacitance for crystal is 5 pf, Now in this circuit condition i got an increment delay of 3 sec after every 24 hours. we can't change the board design also
pleases guide me how can i fix this problem and delay reduces to zero. and also reduce the stray capacitance of the board.

 

hi PT,
What is the ambient temperature variation of the crystal.?
E

 

hi,
in my project i am using isl12057 RTC for a date and time,the VT-200-F crystal provide 32.768KHz frequency. my circuit have stray capacitance of 7.5+pf, and parallel capacitance for crystal is 5 pf, Now in this circuit condition i got an increment delay of 3 sec after every 24 hours. we can't change the board design also
pleases guide me how can i fix this problem and delay reduces to zero. and also reduce the stray capacitance of the board.

The simple answer is that you are unlikely to get to zero unless you build your own Cesium clock. As has been pointed out operating in a temperature stable environment will be a big help.

 

If it is always off in the same direction, trimming the capacitors might help.

Bob

 

Just get out your eraser, bite the bullet and admit your design is 20 years out of date.

Looking on Digikey for single quantities the Renesas part is $2.60, then you have to add your crystal and other comps.

For an additional $1.42 ($4.02 each) you get a MAX31328, a complete timing chip with an internal temperature compensated crystal good for a "Timekeeping Accuracy ±3.5ppm(±0.302 seconds/day) from -40°C to +85°C" right out of the box with no twiddling or fiddling with trimming anything.