BQ2002 2V Vbat threshold

Benjamin Zhao

Other Parts Discussed in Thread: BQ2002

Dears

I'm a new guy to use BQ2002. Also I'm not familiar with Nicd and MiMH battery.

As my understanding, Nich and NiMH battery are both 1.2V typical voltage.

But I see from datasheet, Vbat threshold of BQ2002 is 2V to detect if battery is OK to charge. But I think 2V is much higher than 1.2V voltage, if we want to use it as a protection method, why we don't set it to a lower value such as 1.5V and so on?

Thanks a lot!

over 13 years ago

0 Chris Glaser over 13 years ago

TI__Guru**** 151520 points

Yes, this is a basic nickel charging question that has been discussed many times on the forum and on wikipedia:

http://en.wikipedia.org/wiki/Nickel%E2%80%93cadmium_battery#Charging

http://e2e.ti.com/support/power_management/battery_management/f/179/t/150760.aspx

http://e2e.ti.com/support/power_management/battery_management/f/179/t/74822.aspx

Just use the equations in the datasheet to use this IC.

0 Benjamin Zhao over 13 years ago in reply to Chris Glaser

TI__Prodigy 165 points

Dear Chris

I also read above link on our forums. But the highest voltage of Nickel battery is about 1.45V, I still don't understand why we choose 2V as threshold rather than lower value such as 1.6V?

0 Chris Glaser over 13 years ago in reply to Benjamin Zhao

TI__Guru**** 151520 points

To give plenty of margin. This peak voltage (2V) should never be reached during normal charging. But some packs over their lifetimes and/or temperature may reach 1.6V or higher at the end of fast charge. If you confirm with your battery pack manufacturer the highest voltage their pack could reach at the end of fast charge (over life, temperature, process, lot to lot, etc.) and account for the tolerance in your resistors and BAT pin setpoint, then you can certainly set it lower. 2V is a safe level to set it at and is recommended for all nickel packs.

0 Benjamin Zhao over 13 years ago in reply to Chris Glaser

TI__Prodigy 165 points

Dear Chris

It's clear! Thanks a lot!

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BQ2002 2V Vbat threshold