RTC Current Draw

NETMF & Gadgeteer
1

I have looked through the docs and forum and I can’t find information on how much current the RTC uses on the G120.

I am trying to estimate battery life so I know how big of a battery I need to put on my PCB.

So, does anyone know how many amps the TC draws, or where it is documented?

Thanks

2

You need to look at the MCU datasheet for that information. You can find it on NXP site.

3

@ stevepx - here’s a direct link http://www.nxp.com/documents/data_sheet/LPC178X_7X.pdf

1 Like
4

Page 78:

1 Like
5

Thanks, I should have thought of that.

I looked in the manual before I saw the picture, I think page 78 only applies when main (VDD) 3.3V power is on and the microcontroller is not drawing power from the RTC battery.

It looks like Page 72 applies to the RTC battery and it says the uC pulls 1uA when main power is off, and less than 1 nA when power is on.

The bottom line is that a 48 mAH coin cell should last well over 3 years.

1 Like
6

Good to know!