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BQ24072T: BQ2407xT RIterm setting

craig
Intellectual 510 points
Part Number: BQ24072T
Other Parts Discussed in Thread: BQ24074

Tool/software:

Hello,

We're looking at the BQ2407xT charger. 

Looks like ITerm is based of IChg which is modified with Iset, But the Iterm comes in too low for us when using this value alone. It looks like RIterm should should let you modify by the Iterm value??? But where is this set--It's not indicated in the data sheet:

I calculato a cutoff of 400mA for the inr-18650-35E cell in 4p arrangment  (100mA cutoff for cycle life charge):


KIset = 890 k*Ohms 'typically'

 

IChg = KIset/RIset

 

RIset is settable from 590 Ohms to 3kOhm, 

 

Iterm = .1*IChg  'typically'

 

 

------------>

 

RIset = 1kOhm--->IChg = 890/1000 = .89A --->.1*.89 = 89mA 

 

Which is too low.

Where does the RIterm get set? Am I missing something?

  • 0
    TI__Mastermind 31840 points

    Hi Craig, 

    Apologies for any confusion caused by the reference to RIterm in the recommended operating conditions table. The BQ24074 device is the only version from this product family which has a dedicated ITERM pin where termination threshold is set by RIterm resistor. None of the BQ2407xT device have the ITERM pin. Please ignore the mention of RIterm in BQ2407xT datasheet. 

    On all BQ2407xT devices termination threshold will be typical 10% of ICHG setting unless input current limit is set to 100mA via EN1=EN2=low. When input current limit is 100mA termination threshold will be 33% of ICHG setting. 

    I recommend you look into BQ24074 if you require a termination threshold higher than 10% of ICHG. 

    Best Regards,

    Garrett