battery connections for RTC

[YahooArchive]

> The LPC does not have any special VCC BAT inputs, how do you keep just the RTC
alive? do you just keep power on the VCC18 cpu core? using a little battery?
>
> How does the LPC2106 know to go into idle mode when the normal power is taken
away?
>
> The datasheet/user manual does not seam to explain any of this
>

The LPC2106 is one of the first ARMs that NXP designed. It does not have a
battery domain, so to keep its RTC running requires power to the whole part.

The LPC2103 was designed later and added the battery domain, just for the RTC.
It wasn't until the more recent parts that even a small RAM with battery backup
was added (not the whole RAM)

[YahooArchive]

I see, the 2106 has 1.8v for the core and 3.3v for the IO im guessing you can
turn the IO 3.3v off and just keep the 1.8v core going to keep the RTC alive?

and maybe monitor the IO input voltage and if this turns off put the cpu into
idle mode?


Thanks

[YahooArchive]

NXP does not spec this, but I doubt you can let the 3.3V supply go below 1.8.
There are internal level translators that would probably crowbar. Maybe a diode
from 1.8 to 3.3V supply?? But you're really on your own on this one.

Better to switch parts and use one of the Cortex M0 parts that NXP is doing
quite a bit to get power consumption to a minimum with very low standby
currents.

We just received the first of the XBsensor PCBs that use an LPC1114 and have
battery backup (pictured as wireless2 in the photos section). Shipments will
begin next month (maybe sooner, the CMSIS C conversion is taking a lot of time,
but is usable at this point).