RTC Battery Backup

lpcware · ‎06-15-2016

Content originally posted in LPCWare by mike31416 on Thu Jun 09 05:25:39 MST 2011
Hi,

The LPCXpresso Base Board has provisions for a coin cell to backup the RTC. Looking at the base board schematic the battery would also power the base board unless J3 is removed. That helps, but the battery is also connect to J4-28 which is the 3.3V input to the LPCXpresso LPC1768 in addition to VBAT on J4-3.

I think if D2 were removed, then the battery would only be connected to VBAT on J4-3. I am not sure why D2 is there unless they expected to power the LPC1768 with the coin battery. The battery will not last very long doing that.

Mike

lpcware · ‎06-15-2016

Content originally posted in LPCWare by R2D2 on Tue Feb 17 04:01:55 MST 2015
Explain what :quest:

LPC_RTC->GPREG[0] = 1;
LPC_RTC->GPREG[1] = 2;
LPC_RTC->GPREG[2] = 3;
LPC_RTC->GPREG[3] = 4;
LPC_RTC->GPREG[4] = 5;

lpcware · ‎06-15-2016

Content originally posted in LPCWare by venuchitiki on Tue Feb 17 03:49:50 MST 2015
hai,

How to store the data in RTC back up registers, can any one explain please.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by mike31416 on Thu Aug 16 03:01:21 MST 2012
Hi djlegge,

Let me clarify my setup... I am using the LPC1769 rev B CPU board which is plugged into the LPCXpresso Base Board rev B. The CPU schematic has 7 sheets and the base board has 11 sheets. In my configuration, the coin battery is on the base board. I removed D2 from the base board.

It seems you are not using the base board.

Sorry for the confusion,
Mike

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Thu Aug 16 01:43:16 MST 2012

Quote: djlegge
It is confusing that the boards all seem to have the same name !

No :)

We are talking about LPCXpresso1769RevB :D

It can be divided in LPC-link board and LPC1769 target board and it's actual schematic can be found at EA. That's all :eek:

BTW: Your picture shows an LPCXpresso1768RevA, like shown on Embedded Artists LPCXpresso1769 page. That's confusing :confused:

lpcware · ‎06-15-2016

Content originally posted in LPCWare by djlegge on Thu Aug 16 01:34:14 MST 2012
Thanks Mike but I want to be sure because I am using the single board version. This one :
[IMG]http://www.embeddedartists.com/sites/default/files/image/product/xpr_lpc176x_banner.png[/IMG]
- J4 only has 16 pins so J4-28 does not exist.:confused:
- The schematics are only 7 pages, not 11 !

It is confusing that the boards all seem to have the same name !

lpcware · ‎06-15-2016

Content originally posted in LPCWare by mike31416 on Wed Aug 15 13:20:39 MST 2012
Hi djlegge,

I am also using the LPC1769 and rev B base board.

It's D2 on the baseboard not the CPU board. D2 will allow current to flow from the positive side of the battery to J4-28 which is the +3.3V input.

I am looking at the schematic for the LPCXpresso Base Board rev B sheet 2 of 11.

Here is the response from Anders Rosvall near the start of this tread:

[I]Hi,
The LPCXpresso Base Board has been designed to be compatible with many different boards. It was actually designed before the LPCXpresso LPC176x was even considered.
Powering of the RTC (via the coin cell) is not optimal and is only included for test purposes. In retrospect the powering structure of both the LPCXpresso boards and the base board could have been done a little better and smoother.
When running a LPC176x board, D2 can be removed in order not to drain the battery too quick.
D2 is there for the LPCXpresso LPC11xx boards, which can operate are very deep power down modes. These boards do not have a separate VBAT input.

Kind Regards,
Anders Rosvall
Embedded Artists
[/I]

Mike

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Wed Aug 15 07:16:29 MST 2012
IIRC LPC1768RevA board was sold out at the end of 2010 and 1769RevB was introduced 2011.

So this PDF is just a renamed version of LPC1768 (which does not include R91;)), lost in NXP-land :eek:

lpcware · ‎06-15-2016

Content originally posted in LPCWare by djlegge on Wed Aug 15 06:59:37 MST 2012
Thanks zero - that is more recent than the one I was looking at.
http://ics.nxp.com/support/documents/microcontrollers/pdf/lpcxpresso.lpc1769.schematic.pdf
Which does not show R91 !

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Wed Aug 15 06:49:17 MST 2012

Quote: djlegge
... there is a 100k resistor R91 in series with the RTC crystal that does not appear on the schematic I have.

:confused:

Wrong schematic?

http://www.embeddedartists.com/sites/default/files/docs/schematics/LPCXpressoLPC1769revB.pdf

All RevB Boards include this resistor (Page 5) ;)

lpcware · ‎06-15-2016

Content originally posted in LPCWare by djlegge on Wed Aug 15 06:33:40 MST 2012
Thanks Mike but I think I must have a different board to you since D2 is in the USB supply circuit of the LPC3154 which provides the JTAG functionality. It is nothing to to with the RTC on the LPC1769.
Interestingly though, there is a 100k resistor R91 in series with the RTC crystal that does not appear on the schematic I have.
If I feel brave later I will cut the track to try to determine if the 1769 is really pulling the current, as zero suggested.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by mike31416 on Wed Aug 15 05:01:36 MST 2012
I removed D2 and the problem is gone.

Mike

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Wed Aug 15 03:41:44 MST 2012
It's a long way from J6-3 to Pin 19. Perhaps a cut at C49 could help you to find something abnormal :confused:

lpcware · ‎06-15-2016

Content originally posted in LPCWare by djlegge on Wed Aug 15 03:22:44 MST 2012
Thanks zero.
I have removed D7 and the problem remains (except now the current is drawn even when the rest of the board is powered).
If I remove D8 then of course there is no current so the RTC does not run.
I think I need to get another LPC board :(

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Wed Aug 15 03:05:04 MST 2012
VB should source < 1µA, so if you are measuring 25mA there's of course a hardware problem :mad:

Either D7/D8 are damaged or there's a short circuit somewhere. My LPCXpresso1769 isn't drawing this huge current :)

lpcware · ‎06-15-2016

Content originally posted in LPCWare by djlegge on Wed Aug 15 02:43:26 MST 2012
I am using an LPCXpresso LPC1769 REV B development board and I find that the current drawn from VB (J6-3) is over 25mA (when the board is not powered otherwise) which is clearly wrong. The RTC battery must be trying to power the board somehow but looking at the schematic, I can't see how.
I think this is a different board to the one referred to so far in this thread ?
Any ideas ?

lpcware · ‎06-15-2016

Content originally posted in LPCWare by mike31416 on Sat Jun 11 04:35:31 MST 2011
Thank you Anders.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by andersrosvall on Fri Jun 10 13:39:44 MST 2011
Hi,
The LPCXpresso Base Board has been designed to be compatible with many different boards. It was actually designed before the LPCXpresso LPC176x was even considered.
Powering of the RTC (via the coin cell) is not optimal and is only included for test purposes. In retrospect the powering structure of both the LPCXpresso boards and the base board could have been done a little better and smoother.
When running a LPC176x board, D2 can be removed in order not to drain the battery too quick.
D2 is there for the LPCXpresso LPC11xx boards, which can operate are very deep power down modes. These boards do not have a separate VBAT input.

Kind Regards,
Anders Rosvall
Embedded Artists