CHG pin of max1555

Kit Morton

Hi all,
I am using a max1555 Polymer Lithium Ion battery charger to charge the battery of a propeller project I am working on. I am trying to use the CHG pin to get the charging state of the chip. The datasheet says:

max1555 datasheet said...

The MAX1555’s CHG is an active-low, open-drain charge status indicator. CHG pulls low when the battery is charging (whenever USB or DC are powered) and charge current is greater than 50mA. CHG indicates when the battery is fully charged by going high impedance when the charger is in voltage mode and charge current falls below 50mA. Charging does not stop when CHG goes high. CHG is low in precharge mode.

I have CHG connected to a pin of my propeller with a pull-up to VDD. I can detect when the charger is plugged in, but I can't figure out how to tell if the battery is done charging.

Does anyone have any tips on how to detect when the battery is charged?

Thanks
-Kit

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Paul Sr.

Datasheet said...

CHG indicates when the battery is fully charged by going high impedance when the charger is in voltage mode and charge current falls below 50mA

Interesting statement!

If it were going from a Low to High LEVEL, a pullDOWN resistor to GND might be a better choice.

Post Edited (Paul Sr.) : 6/4/2008 12:33:52 PM GMT

Ken Peterson

Kit: The output is active-low, open-drain, which indicates you need a pull-up resistor. You should read a low when the battery is charging, and it should go high when charge is complete. The data sheet says "high impedance" which means it no longer drives the line (high or low) - therefore you need the pull-up resistor to produce a high level.· Open-drain outputs only actively drive low.

It says charging does not stop when CHG goes high. It only indicates that the current has dropped below 50mA. The assumption here is that the battery is sufficiently charged when the charge current drops below 50mA. You would need to detect when CHG goes high and then shut it down by other means if you want to stop charging when the charging is complete.

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Post Edited (Ken Peterson) : 6/4/2008 2:58:50 PM GMT