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On LPC2103: Can I short VBat to V18?

Started by unity0724 February 22, 2006
Hi,
On LPC2103, Can I short VBat to V18?
The 2 pins are next to each other.
=> Simplify my PCB layout
=> Simplify my RTC backup circuit also, if V18 does not take too
   much current when power down. Single micropower 1.8V LDO used.

Vbat requires 3.3V for normal Operation. 
I do not fully understand the datasheet, does VBat work from 2.0V to
3.6V any time from chip operation to battery backup mode?
On PLCC44, It seems like VBat and V18 are bonded to same pin (read
from previous post) ??

I'm not using the full RTC section at the moment, may be will be 
just using the RTC's second tick interrupt as 1mS interval timer 
(Re-program prescaler to very fast "1 second").

Thanks
	

An Engineer's Guide to the LPC2100 Series

unity0724 wrote:

>Hi,
>On LPC2103, Can I short VBat to V18?
>  
>
No

>The 2 pins are next to each other.
>=> Simplify my PCB layout
>=> Simplify my RTC backup circuit also, if V18 does not take too
>   much current when power down. Single micropower 1.8V LDO used.
>
>Vbat requires 3.3V for normal Operation. 
>I do not fully understand the datasheet, does VBat work from 2.0V to
>3.6V any time from chip operation to battery backup mode?
>  
>
The 32KHz oscillator and clock circuitry (counters) operate over the 2.0 
.. 3.6volt range.  This is the typical discharge life of a lithium 
cell.  As the data sheet says: 2.0..3.6v.  If you connect it to 1.8v 
then it is too low a voltage to run the electronics (RTC).
	PCB layout can be a PITA, but ....

Regards,

TomW
	>On PLCC44, It seems like VBat and V18 are bonded to same pin (read
>from previous post) ??
>
>I'm not using the full RTC section at the moment, may be will be 
>just using the RTC's second tick interrupt as 1mS interval timer 
>(Re-program prescaler to very fast "1 second").
>
>Thanks
>
>
>
>
>
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>  
>
	-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------
	
Hi,

if you don't want to use a battery backup, you can leave Vbat open but
don't short it to V18. 
IMHO the PLCC44 does not connect the second V18, next to Vbat at all.
It can not be connected to Vbat internally because this would cause
V18 to go up to 3.6V with a new battery. 

Bob

--- In lpc2000@lpc2..., "unity0724" <unity0724@...> wrote:
>
> Hi,
> On LPC2103, Can I short VBat to V18?
> The 2 pins are next to each other.
> => Simplify my PCB layout
> => Simplify my RTC backup circuit also, if V18 does not take too
>    much current when power down. Single micropower 1.8V LDO used.
> 
> Vbat requires 3.3V for normal Operation. 
> I do not fully understand the datasheet, does VBat work from 2.0V to
> 3.6V any time from chip operation to battery backup mode?
> On PLCC44, It seems like VBat and V18 are bonded to same pin (read
> from previous post) ??
> 
> I'm not using the full RTC section at the moment, may be will be 
> just using the RTC's second tick interrupt as 1mS interval timer 
> (Re-program prescaler to very fast "1 second").
> 
> Thanks
>
	
Hi, Thanks to your reply.

From Post/Message #9400:
Quote: {{We combined the pins VBAT and V18 and made it just a V18. 
This limits the ability to buffer the RealTimeClock with a battery
but if the device is in power down mode with V18 applied, the RTC
will keep running and the RAM contents remains. Current in power
down is expected typically in the 10 uAs range. }}

=> My interpretation is different, I think they are using same
LPC2103 silicon and only bond both the VBat and V18 pads together to
single pin and bring out as single V18. The RTC is tested to run at
voltage of 1.8V on PLCC44. We are still able to backup the RTC+RAM
provided the backup supply is regulated at 1.8V (using some
micropower 1.8V LDO). 

Shorting of VBat to V18 on LQFP48 could save me lots of trouble.
Look like we could only figure out what's happening when PLCC44 user 
manual ready.  :)

Regards

--- In lpc2000@lpc2..., "lpc2100_fan" <lpc2100_fan@...> 
wrote:
>
> Hi,
> 
> if you don't want to use a battery backup, you can leave Vbat open
> but don't short it to V18. 
> IMHO the PLCC44 does not connect the second V18, next to Vbat at
> all.
> It can not be connected to Vbat internally because this would cause
> V18 to go up to 3.6V with a new battery. 
> 
> Bob
> 
> --- In lpc2000@lpc2..., "unity0724" <unity0724@> wrote:
> >
> > Hi,
> > On LPC2103, Can I short VBat to V18?
> > The 2 pins are next to each other.
> > => Simplify my PCB layout
> > => Simplify my RTC backup circuit also, if V18 does not take too
> >    much current when power down. Single micropower 1.8V LDO used.
> > 
> > Vbat requires 3.3V for normal Operation. 
> > I do not fully understand the datasheet, does VBat work from 
2.0V to
> > 3.6V any time from chip operation to battery
backup mode?
> > On PLCC44, It seems like VBat and V18 are bonded to same pin 
(read
> > from previous post) ??
> > 
> > I'm not using the full RTC section at the moment, may be will be 
> > just using the RTC's second tick interrupt as 1mS interval timer 
> > (Re-program prescaler to very fast "1 second").
> > 
> > Thanks
> >
>
	
Very good points, guess I will have to check this one out myself and
as you said wait for the Um that includes the PLCC44 description.

Bob

--- In lpc2000@lpc2..., "unity0724" <unity0724@...> wrote:
>
> Hi, Thanks to your reply.
> 
> From Post/Message #9400:
> Quote: {{We combined the pins VBAT and V18 and made it just a V18. 
> This limits the ability to buffer the RealTimeClock with a battery
> but if the device is in power down mode with V18 applied, the RTC
> will keep running and the RAM contents remains. Current in power
> down is expected typically in the 10 uAs range. }}
> 
> => My interpretation is different, I think they are using same
> LPC2103 silicon and only bond both the VBat and V18 pads together to
> single pin and bring out as single V18. The RTC is tested to run at
> voltage of 1.8V on PLCC44. We are still able to backup the RTC+RAM
> provided the backup supply is regulated at 1.8V (using some
> micropower 1.8V LDO). 
> 
> Shorting of VBat to V18 on LQFP48 could save me lots of trouble.
> Look like we could only figure out what's happening when PLCC44 user 
> manual ready.  :)
> 
> Regards
> 
> --- In lpc2000@lpc2..., "lpc2100_fan" <lpc2100_fan@> 
> wrote:
> >
> > Hi,
> > 
> > if you don't want to use a battery backup, you can leave Vbat open
> > but don't short it to V18. 
> > IMHO the PLCC44 does not connect the second V18, next to Vbat at
> > all.
> > It can not be connected to Vbat internally because this would cause
> > V18 to go up to 3.6V with a new battery. 
> > 
> > Bob
> > 
> > --- In lpc2000@lpc2..., "unity0724" <unity0724@>
wrote:
> > >
> > > Hi,
> > > On LPC2103, Can I short VBat to V18?
> > > The 2 pins are next to each other.
> > > => Simplify my PCB layout
> > > => Simplify my RTC backup circuit also, if V18 does not take
too
> > >    much current when power down. Single micropower 1.8V LDO used.
> > > 
> > > Vbat requires 3.3V for normal Operation. 
> > > I do not fully understand the datasheet, does VBat work from 
> 2.0V to
> > > 3.6V any time from chip operation to battery backup mode?
> > > On PLCC44, It seems like VBat and V18 are bonded to same pin 
> (read
> > > from previous post) ??
> > > 
> > > I'm not using the full RTC section at the moment, may be will be 
> > > just using the RTC's second tick interrupt as 1mS interval timer 
> > > (Re-program prescaler to very fast "1 second").
> > > 
> > > Thanks
> > >
> >
>