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BQ24075 : What append if input voltage is under VOUT(reg)

olivier.guedat
Prodigy 40 points
Other Parts Discussed in Thread: BQ24079, BQ24074, BQ24075, BQ24072, BQ24073

I'm trying to choose the best battery charger for my application, and my choice is the BQ2407X serie (72/73/74/75/79).

But after having read all the documentation about this chip's serie, I'm still trying to anderstand which chip is the best one for my application.

As mentionned in the datasheet, the differences among these chips are : VOVP ; VBAT(REG) ; VOUT(REG) ; VDPPM ; OPTIONAL FONCTION

Here are the different steps I took into account to choose the right one :

1 ) VBAT(REG)

Because the battery li-ion voltage is 4.2V, I can exlude the BQ24079.

2 ) VOVP

Overvoltage protection input is preferred to be as low as possible to prevent the chip over-heat, because of the high current charge for my battery ~1A. So I exlude the BQ24074 (even if I use VUSB as input source, and I'm sure that the Input voltage will not exceed the VUSB max = 5.25V )

3 )  VOUT(REG) and VDPPM

The input voltage for my application is 2.5-5.5V tolerant. So I have the choice among the BQ24072 / BQ24073 / BQ24075. Ideally, I prefer to have a VOUT as high as possible, because I use charge-pump buck/boost at the input of my application. So the more efficient the be better, and the BQ2407X chip's will minimze its power dissipation.

So, I think the best choice is the BQ24075, because if I use a usb port at the charger input which supplies 5V, the regulator is switched fully on to deliver what voltage is available (as mentionned in the document "Analog applications Journal" article "Designing a linear Li-Ion battery charger with power-path control" one page 15).

So VOUT will be approximately  VIN ( less VDO).

But what happens with the VDPPM ? Does it remain at 4.3V or does it decrease ?

Because in the worst case, if the voltage on the usb connector is 4.4V (value mention in the USB Spec rev. 2 under Supply Voltage in Low-Port) does the DPPM mode will be enable all the time ?


 


 

 

 

  • 0
    TI__Genius 17610 points

    BQ24075 has VIN-DPM mode and it limits input voltage no less than 4.5V typically when using USB. Thus, input current trys to reduce to keep input voltage regulated. If system current is smaller than input current limitation and Vdo acceptable, Vout will be regulated at 4.3V. Or else, it will be pulled down even to around VBAT voltage and run into supplement mode. During supplement mode, battery provides additional current.