Li ion battery charging problem

[spelter]

Hi,
We are building a charger for Li ion battery using

the LP3947 IC from national semiconducor.

Presently i have read the application notes from its

datasheet but still i have the following doubts in

general -
1.how can i use a controller (atmega 8 in my case) to

make lp3947 switch from one mode to anther For eg

-in the datasheet it is written that "As soon as pack

terminal reaches 4.2V (or 4.1V), the controller starts

operating in constant voltage mode ".What i mean

to say is how would i source different currents to the

battery (during the different stages of

charging).Have i to build seperate circuits

supplying different ranges of currrent and control

them through the controller.OR something else

needs to be done

2.In the flowchart given in the datasheet it compares

the voltage at the Ts pin to monitor battery

temperature.But a microcontroller understands only

two logic levels so how can i compare a voltage at a

pin to lie within a particular range.(as in this case

the voltage at Ts pin should lie between 1.39 and

2.42 volts).
as it would be clear basically i have a problem how to interface the microcontroller with LP3947 to control its various stages of operation and monitor the battery temperature.

These questions may sound stupid but still i hope

someone would try n clear my doubts
regards
atul

 

[Papabravo]

Are you sure the word "controller" refers to a microcontroller? Most Li Ion battery charger chips ARE the controller.

Microprocessors are allowed to have Analog to Digital converters that allow them to look at a voltage as 256, 1024, 4096 or more distinct levels.

I will check the datasheet.
Edit: I checked the datasheet and it looks like the part can be used without a controller. The I2C interface provides a soupcon of parameter capability but very little it would seem. Do you understand what the chip is trying to do with the Li Ion battery and why?

 

[justDIY]

i'm not sure I understand your problem, your post is very difficult to read for some reason ... did you type it on a cell phone or some other device with a very small screen? and why is it double spaced?

anyway ... a good Lion or LiPo charger should be fully automatic, no microcontroller required or desired even... to leave such things in the hands of firmware could result in a catastrophy. From my quick read of the datasheet, your chip is fully automatic, and doesn't require a microcontroller to manage anything. Their i2c interface only provides a few basic commands, hardly worth the effort in my humble opinion.

I recommend starting with something a bit simpler, such as Maxim's MAX1551, MAX1811 or MAX1898. Analog Micro also has a simple LiPo charger similar to the 1811.

 

[Papabravo]

i'm not sure I understand your problem, your post is very difficult to read for some reason ... did you type it on a cell phone or some other device with a very small screen? and why is it double spaced?

anyway ... a good Lion or LiPo charger should be fully automatic, no microcontroller required or desired even... to leave such things in the hands of firmware could result in a catastrophy. From my quick read of the datasheet, your chip is fully automatic, and doesn't require a microcontroller to manage anything. Their i2c interface only provides a few basic commands, hardly worth the effort in my humble opinion.

I recommend starting with something a bit simpler, such as Maxim's MAX1551, MAX1811 or MAX1898. Analog Micro also has a simple LiPo charger similar to the 1811.

In Michigan we just know these things. Go Blue!
:LOL: