Low Power Battery Development Issues

[leomecma]

I have a question: I'm development a product that use a battery (CR2032) and this has a RTC(real time clock). This is all implemented on PIC18LF2455. When my device is connected to USB it works at the USB voltage (5V) and the application software run at 48MHz. But when disconnected it works with the 32768Hz crystal, that is the source for TMR1 and for program and source is battery (the product is stand alone without connections to nothing). My RTC is so bad about 10 sec/day of error when use battery, but when it's connected to USB it works well. I have doing some tests, and I'm thinking that can be any type of induction, because it's under tests and when I connect the battery minus to USB shield it seems works too, running at 3V battery and 32768Hz crystal. If is it my problem, how can I solve it, because it doesn't has a reference to ground, how can I reduced the induction effects? I can see that when I put my hand closer to them the current rises, because it's works at 18,4uA and when I put my hand closer it rise to 40 to 50uA unstable.

I use only a 470nF capacitor at battery 3V, if I put a greater capacitor it will works better?

What issues I have to observe in this type of project, with very low power with battery without ground reference


Any suggestion?

leomecma

 

[sensor_ua]

Crystal type must be choise by DataSheet of microcontroller. Capacitors must be set as crystal recommend. Oscillator may be run if capacity wrong but not haved a stability of frequency.