Lpc2000

The battery will be recharged after... 21 days of continuous 
operation!!!! You can imagine how big a deal is a couple of mAmps in 
such a long time... The battery must not get below 10.5V or else it 
would become unusable. Even worse, acid-lead batteries, though less 
than other kinds of rechargeable batteries, do self-discharge 
considerably in such 'long' periods. I also have a limit on how big 
the battery can be (we're targetting a 12V 12A/H battery as the 
heavier one we can carry).

The devices are pretty much what I listed below, LPC + GPS + RM, plus 
obvious control circuitery, serial ports, an occasional led flash, 
etc. (no display, no keyboard). The worst part comes from the 
radiomodem, which draws from <5 mA when standby to 200-300 mA 
operating (sending/receiving) and with 1.6A peaks.

Maximum acceptable price for the power supply part of the circuit 
(including inductors, etc.) would be around $15.

Guille

--- In lpc2000@yahoogroups.com, Sean <embeddedrelated@w...> wrote:
>
> 
> Is this for use in an automotive environment?
> 
> Is 4.3mA or 50% efficiency when at low currents that big a deal?  
What's 
> the amp-hour rating of the battery, and how many other devices are 
using 
> it?  How often does it get recharged?
> 
> What's your target price range for this setup?
> 
> -- Sean
> 
> At 07:49 PM 12/1/2005, Guillermo Prandi wrote:
> >Hi! I am in trouble trying to find a voltage regulator suitable 
for my
> >project; my project features an LPC2138, a GPS and a radiomodem. 
When
> >idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> >working hard and with short (50 mS) peaks of up to 1.8A. The 
supply is
> >a lead-acid 12V battery (can't change that), and occasionally, 
when the
> >battery is charging, the input voltage will rise up to ~20V. The
> >problem is the regulator efficiency. We were going for the LM2676-
3.3V
> >switching regulator, because it seemed simple and in range, but two
> >things made it a poor choice: it draws about 4.3 mA from the 
battery
> >just for its own supply, and its efficiency when the load is in 
the 20-
> >25 mA range is awful (less than 50%, not counting Iquiescent). I 
looked
> >everywhere but I couldn't find any other switcher with better
> >performance in these conditions (12V in, 3.3V out, 20-25 mA average
> >load, but >1.5A capability). And there's a catch! The radiomodem is
> >extremely sensitive to VCC getting lower than 3.3V especially in 
the
> >current peaks! Also, it should be relatively easy to find in ~400
> >quantities (i.e., Digikey, Mouser or your suggestion).
> >
> >Any ideas?
> >
> >Guille
>