• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 451 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25886: BQ25886 - Some questions

Marcelo garcia
Prodigy 20 points
Part Number: BQ25886

Hi,
I'm newbie and I have some questions about the BQ25886. I have studied the datasheet and the evaluation module.
I want to use 5V-2A input and 2 Li-poly battery (3.7V each one):
1) I have connected ILIM to ground. It's correct?
2) I have set Rvset=220k to limit the battery charge voltage at 8.4V. It's correct? I have read that I need 4.2V x 2 to charge the battery;
3)I would like to have 5V in SYS pin (output-load). I don't understand how BQ25886 can switch between the main source (connected to VBUS) and the battery source without LDO because they have different voltages. Is there an output LDO regulator (or something similar) before SYS pin?
4)What is Vref? I don't think it is VBUS because STAT and PG pins have to work even without the main power source.
Could you help me, please?

Marcelo

  • 0
    TI__Genius 10385 points

    Marcelo,

    1. Shorting ILIM to current will set the input current limit to its maximum value of 3 A.
    2. A 220k resistor will set an 8.4 V charge voltage limit
    3. The BQ25886 is a boost mode battery charger. The output voltage (VSYS) must be higher than the input voltage (VBUS). The minimum system regulation voltage for this device is 6.4 V typical. If you would like 5 V system rail, you will have to buck the voltage down externally using an appropriate DC-DC converter or LDO depending on your system requirements.
    4. VREF is a constant voltage source. You are correct in saying that it cannot be VBUS. I would suggest you have VREF be tied to the output of an LDO. The input of this LDO could be the SYS pin or the BAT pin.

     

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 20 points

    Thanks for answer.

    I got one last question:

    the switch between main supply and battery supply is automatic? if one  is not available the load will be fed instantly and automatically by the other? if the main power supply is reconnected the load is fed by it or by the battery (causing their discharge)?

  • 0 in reply to Marcelo garcia
    TI__Genius 10385 points

    Marcelo,

     

    The BQ25886 prioritizes the system load (SYS) above battery charging. For example if there is a battery charging utilizing a majority of the output power and the system suddenly requires more power than VBUS can provide, the power will be redirected to SYS. The device will try to maintain the system load with no battery connected at all. Additionally, the battery can supplement the system load when the input source is overloaded and the charge current has already been reduced to zero.

     

    These power management features are described in further detail in section 8.3 and presented graphically in the functional block diagram in section 8.2 of the datasheet.

     

    Thanks,

    Ricardo