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BQ21040: I need a LED on to indicate the charge process is completed.

SeaFesse
Expert 2690 points
Part Number: BQ21040

Hello TI employee,

  I have a probem need your help. 

I use polymer li-ion battery(40mah) as the power of the system. 

I want a RED led【LED01】 to indicate the charge process is ongoing ，and at the same time, GREEN led (LED02）is OFF.

When the battery gets a full charge, the charge process is  terminal , I need  RED  turn off ，and the GREEN led  turn on.

Any software solution involve is not my option.

Is there anything wrong with this schematic? For it does't work as my expectation. Thanks. :)

B.R

Seafesse.

  • 0
    TI__Guru* 75656 points
    Hi Seafesse
    A couple of things to look at:
    1.) The diode D1 will add a voltage drop to OUT that will prevent full charge, voltage taper and termination start at lower battery voltage.
    2.) Need a capacitor at OUT before D1
    3.) Check voltage at Q1 gate during charge complete ( CHG ), it will be High Z and the voltage may not rise high enough to turn on Q1. May need a pull up resistor on Gate of Q1.
    4.) CHG will indicate a charge is in progress but if battery completes charge then enters recharge it is not indicated by CHG.