Main Site Documentation

Fez Raptor and real time clock


#1

Hi guys,

I want to use the RTC so, What should I do to enable it? I just found that connector 5 pin 5 is called VBat.
Does it need a battery between this pin and ground?
Is an external circuit required?
What kind of battery do I have to use?

Thanks

Crespi Juan


#2

The G400 Real Time Clock will require a voltage source of between 1.8V ~ 3.6V, typically a button battery, to be connected to the VDDBU/VBAT pin.


#3

Excellent!!!

Do you know if the battery will be charged by the g400 circuit?


#4

@ crespi - not sure about that.


#5

I don’t believe so. Normally a button cell is used, and the RTC draws so little current, it lasts for years.

You’d have to check the processor’s datasheet for exact numbers.

Often a supercap can be used as well, and I think it will be charged but I’d want confirmation from GHI before I tried that.


#6

Supercap, resistor and diode will do the trick.


#7

https://www.ghielectronics.com/community/forum/topic?id=620


#8

Indeed. I’m going for the supercap.

Thanks guys.


#9

Remember that the Supercap is only designed for short term power off use. This can range from hours to x days. After this time the clock will not be backed up.

The coin cell provides a much longer backup period and can be years depending on the current draw and battery capacity.

Here’s a handy little calculator from Maxim for the supercap.

http://www.maximintegrated.com/design/tools/calculators/product-design/supercap.cfm