I have a system that is powered by a 7.4V Lithium-Ion battery. The system, which is a combination of processor module and sensors, draws a varying amount of current at varying voltages (5V, 12V, -12V, 6V...) but pulls about 10 watts. The battery I chose is quite a hefty 10 amp-hour one.
This started off with a simple off-line charger which is no problem. Then feature creep set in (sigh) and now I'm tasked with a dual battery + charger with gas gauges. That means there are up to 3 DC sources to be managed - two batteries and a charging port. And I've two months.
One way to do this is use a fully featured chip like the LTC1760. This has support for dual smart batteries and a power path architecture, all managed from SMBUS. It's in TSSOP-48. That creates another issue - you have to come up with the smart batteries but they can be bought off the shelf (example). I don't believe it's reasonable to make smart batteries from scratch in this case!
The question is:
- Is this adding complexity where it isn't warranted? If I have to put in a gas gauge type system, the smart battery has that but really requires a smart battery charger chip.
- I can't see how to (simply) support two batteries, multiplexed with on-line charging, except by using the LTC1760. Is this really a common scenario?
- The LTC will switch-mode large currents. This easily leads to RFI issues and supply noise. Is it a requirement for a TSSOP-48 chip like this that I should go to a 4-layer board? Or could I get by with 2-layer? I haven't done 4 layer before but there's some good information on stackexchange!