• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 544 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.

BQ25616: Power Distribution and DC-DC conversion questions

AI31
Expert 1600 points
Part Number: BQ25616

Hello, 

I have a system that uses a 1S re-chargeable battery to deliver: 5V, 3V3, and 1V8 Power Rails. Here are a few questions

1- Is the BQ256x6 the optimal chip for my application given that the maximum charging current of the battery is 1.25A (Fast mode)?

2- The Max discharge current allowed by the battery PCM is 2.5A, If I used BQ256x6, what setting should I set VSYS to so that I can get maximum current  at the VDD_3V3 rail?

3- How to calculate the maximum allowable load of the BQ256x6? the datasheet says 3.2A but won't the current be limited by the PCM?

Thanks,

  • 0
    TI__Expert 5590 points

    5V and 3V3 is your output rail. You charge the battery using 5V input?

    1. What is your battery voltage? BQ25616 can charge battery up to 3A.

    2. From battery to your 3.3V rail, your 3.3V rail is connected to battery through internal FET. VSYS is not programmable.

    3. BQ256x6 is a charger, 3.2A is from VBUS not from battery. PCM current will limit the battery discharge current.

  • 0 in reply to Hong Mao
    Expert 1600 points

    Sorry for some reason the system block diagram was hidden from the original post, I edited it, please have a look.

    1- Battery voltage as seen in the diagram is 3.7-3.9V, I'm ok with the charging current, I'm mainly concerned about how much current can I take out of VSYS when the battery is discharging
    2- But the datasheet says from 3.5 to 4.35V, how is that voltage set then? does it depend on the battery only? what will it be for 3.7-3.9 1S Battery?

    3- So you mean Q4 doesn't have a limit on the current withdrawn from the battery when the charger is not plugged?

    Thanks

  • 0 in reply to AI31
    TI__Expert 5590 points

    1- Battery voltage as seen in the diagram is 3.7-3.9V, I'm ok with the charging current, I'm mainly concerned about how much current can I take out of VSYS when the battery is discharging

    A: Battery voltage could be 3V to 4.4V depending on what battery you use. If you have adaptor connected, on SYS you can take up to 3A from inductor and more current from your battery during transient. For steady state, your charge current + SYS current should be less than 3A. If no adaptor is connected, the current you take should be limited by battery itself.


    2- But the datasheet says from 3.5 to 4.35V, how is that voltage set then? does it depend on the battery only? what will it be for 3.7-3.9 1S Battery?

    3.5V to 4.35V is the VSYS operation range. When battery is below 3.5V, VSYS operates at 3.5V, if battery voltage is higher than 3.5V, the SYS tracks battery voltage. If battery voltage is 3.7V to 3.9V, then the SYS voltage tracks battery voltage 3.7V to 3.9V. Please read the datasheet to understand how the power path works.