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BQ24079: What is Vin(low) value or Vin(low) loop?

Jeff Zhang22
Prodigy 170 points
Part Number: BQ24079

Hi,

In the datasheet of BQ24079, there are two places mentioned Vin(low), page 23 and 26. But there is no place to specify the value of the Vin(low). My first question is, what is the Vin(low) value and what is the Vin(low) loop?

My second question is, if I set the EN2=1, EN1=0, which means the input current limit is set by external resistor connected to ISET pin. what happens if the Vin drop below Vbat(reg) (4.1V for BQ24079)? The device should not get into DPPM mode because it is not USB100 or USB500 mode. is that right? What is about charging in this case? the fast-charge will stop or back to pre-charge?

Thanks, 

  • 0
    TI__Mastermind 21590 points
    Hello Jeff,
    1) VIN(low) is VIN-DPM which is typically 4.5V. I'll look into clarifying this.
    2) I think you're confusing VIN-DPM mode with DPPM mode. Take a look at this App Note to get a better explanation www.ti.com/.../slua400a.pdf
    When VIN drops below 4.1V, the device will enter DPPM mode because the output will drop below 4.3V(VDPPM voltage). When this happens, charging is reduced and eventually stopped because priority is given to OUT and the IC tries to get the OUT voltage above 4.3V. Eventually, you go into supplement mode and the output will be powered from the battery.
  • 0 in reply to Raheem
    Prodigy 170 points
    Hi Raheem,

    On one of my board, I found the Vout dropped below 4.3V with EN2=1 EN1=0 setting but it didn't go to DPPM mode or Battery Supplement mode. But it went to Battery Supplement mode when I switch to USB500 mode. So I'm wondering the DPPM mode may be only apply for USB500 and USB100 mode. Please confirm this.
    Another thing I would like to know is, if the Vin drops below 4.3V, even 4.1V for BQ24079, in fast-charge phase and non USB500 or USB100 mode, what will happen for battery charging? Does it get into DPPM mode or some other mode?
    Thanks,
  • 0 in reply to Jeff Zhang22
    TI__Mastermind 21590 points
    Hello Jeff,
    DPPM mode is always present regardless of the EN1 and EN2 setting. The DPPM voltage can be as low as 4.2V in certain conditions.
    In non USB500 or USB100 mode, you'll get into DPPM mode if VIN drops below 4.3V. VIN dropping will cause VOUT to drop which will cause reduction in charge current in DPPM mode.