Implementing battery charger using Li-ion.
I have used Linear Technologies battery chargers for Li-Ion and Li-Poly. They work great. Using digital pots in place of fixed resistors for the charging voltage and charging current. These of course controlled with a micro-controller. life doesn't get any better than that. The micro allows for charging algorithms to suit different battery chemistry's and provides for status flexibility. It doesn't get any simpler than that. Piece of cake.
In Part One of this two-part article, Cypress describes different types of rechargeable batteries, their differences and how to select a battery technology for a specific application.
The article is available here: http://www.eetimes.com/design/smart-energy-design/4375627/Battery--The-source-of-a-device---Part-1?Ecosystem=smart-energy-design
I don't think they mean to use the PSoC strictly for this function, but as a part of the overall PSoC system function. The battery health can be judged by a gas gage IC. They generate pulses proportional to the current versus time of the charge. Use it with a processor and you can make decisions about battery life.
Sometimes a regulator with a current limiting resistor on the input side is used as a cheap coin cell charger. The precharge time is very short, under a minute, on a Li-Ion battery. I think if the resistor was on the output side, it would be hard to top off the battery. You can use a simple 2 transistor circuit to up the current when the cell voltage goes up.
Now a question about simplification of the process: would a current limited constant voltage charge work as well? It would not be as fast, it may take overnight to recharge completely, but it would certainly be simpler. Most importantly, would it damage the cells to start out with a current limited constant voltage charge? Or is it a situation that must have the higher voltage at the beginning?
Another possibility for being able to use a single-ended ADC in this system would be to simply put a small-value resistor in series with the negative terminal of the battery pack, before its ground connection. This way the microcontroller system and the power supply can share the same ground. There is a small efficiency cost, but this can be mitigated by using a very small-value resistor, (for example, a 0.1 ohm resistor at 100mA would drop 10mV, at a power cost of only 1 mW).
Unless a sophisticated charging circuit is needed, using a PSoC would be an overkill. In general standard charging ICs will need a lot less design efforts.
But some time, the user might need to know the health life of the battery, how many charging cycles took place etc. In that case this will be helpful.
NASA's Orion Flight Software Production Systems Manager Darrel G. Raines joins Planet Analog Editor Steve Taranovich and Embedded.com Editor Max Maxfield to talk about embedded flight software used in Orion Spacecraft, part of NASA's Mars mission. Live radio show and live chat. Get your questions ready.
Brought to you by