• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 1137 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

BQ51003 Design Questions

Michael M
Prodigy 50 points
Other Parts Discussed in Thread: BQ51003, BQ25100, BQ51050B

Hey All,

I'm designing a Qi compliant inductive charger Rx circuit using the BQ51003 for a wearable.  Here are the questions I have:

1)     Can the FOD pin be used as an internal signal to monitor the output current?

2)     What is the ratio between RFOD and R1 supposed to be to ensure the proper FOD voltage is measured?  My output current is 50mA

3)     Can the 3 state driving circuit also be used with the temperature limiting circuit on the TS-CTRL pin?

4)     I need to regulate the output from 5V to 4.2V to meet the maximum battery charging voltage specifications.  How would an LDO or zener diode effect the current limiting/battery charging capabilities of the device?

Thanks!

  • 0
    TI__Expert 7730 points

    Michael,

    Please see my comments below.

    1) The FOD is only used to determine the offset for FOD and to do FOD calibration. It cannot be used for anything else.

    2) It is not a ratio. You need to use the FOD tool to calculate both value.

    www.ti.com/.../sluc577

    3) Yes. Refer to page#26 of the datasheet.

    4) BQ51003 only serves as a power supply to provide the 5V input to the charger. You will also need a charger IC to charge your battery. If your charge current is 50mA, I recommend bq25100 low power battery charger to you. It supports charge current from 10mA to 250mA and can terminate at as low as 1mA. If you want a integrated solution which includes both RX and charger, you can consider bq51050B, however, it cannot terminate accurately below 100mA.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Prodigy 50 points

    Thanks for the feedback.  I have another question regarding the Ros1 and Ros2 resistors.  The datasheet says only one is needed, but I can't find any information as to what the benefit of one over the other is or what the value should be.  What is the difference between populating these two resistors.

    Thanks!

  • 0 in reply to Michael M
    TI__Expert 7730 points

    Ros1 is from FOD to OUT.

    Ros2 is from FOD to RECT. 

    Yes you will only need one of them in your design. Most applications use FOD to RECT.  If the resistor is tied to OUT, then it’s always in the circuit since OUT is likely tied to the charger or possibly the battery.  Using RECT removes that concern plus since RECT is an indication of power. Using Ros2 tracks the power a bit more precisely resulting in better FOD tracking.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Prodigy 50 points

    I'm looking at using the BQ51050B instead.  Can you tell me what you mean by "it cannot terminate accurately below 100mA"?  The datasheet says that the battery charge current can be programmed to anything <1.5A so what termination current are you referring to?

    My battery specs have also changed.  The max charge current is around 15 mA.  The BQ51050B seems like it's meant for higher currents, but can this device accurately charge the battery with that type of charge current?

    Thanks,

    Mike

  • 0 in reply to Michael M
    TI__Genius 14890 points

    Mike,

    You are correct in that the bq51050B is targeted towards higher currents (2-5W).  

    The charge current (IBULK) is set by the ratio represented by KILIM (IBULK = KILIM / RILIM).  The ratio, KILIM, is accurate for IBULK above 500mA.  Below 500mA, the "typical" KILIM is still close to the target, however the standard deviation begins to increase and some units will reside outside the limits.  This includes all process and temperature variation.

    For 15mA charge current, I strongly recommend the bq51003+bq25100 as a very good option.

    Regards,

    Dick