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BQ51025: Custom board is only able to give 550 mA Max

Javier Pena Gonzalez
Prodigy 20 points
Part Number: BQ51025
Other Parts Discussed in Thread: BQ500215, BQ501210, BQ51013B, BQ51021

Dear technical support,

I recently started working as an R&D engineer and my first job is to debug a board containing the BQ51025 the former engineer made.

The problem comes when i have started to try the board and while it works fine connecting with the transmitter it starts to limit itself to 540 mA.

I have tried adding potentiometers in Rfod (0-1000 ohm) and in Rlim (0-2000 ohm), calculating all possible solutions and getting a regression of the current that should be flowing thought the load, It works fine between 300-550 mA but when i ask the board for more power(lowering resistor load from 20 ohm to 10 ohm at 5 V) it starts to limit power.

Later I had another potentiometer added in the voltage feedback circuit to be able to change the voltage and therefore finding out where the limit was,  with this i am able to set the circuit in the full voltage range(0-8V roughly), and then  i found that i am not able to go up of 5.5V (550 mA ) with a 10 ohm load even if Rfod is (200 ohm) and Rlim is only 100 ohm(by my calculations that should be 1.5A limit.

Also I have disabled all power limiting and FOD systems in the emitter and is connected to a power supply so it should be delivering 5 watts but i'm only getting 2.7 Watts at best.

Any idea of why this can be happening?,

  • 0
    TI__Guru 66276 points
    Hello
    BQ51025 is NRND (Not Recommended for New Design), I would discourage you from designing with the device.

    The TX would need to be the BQ500215 or BQ501210 to get 10W out, other wise the unit will default to 5W mode.
    Also if the two units have FOD detection disabled they will default to 5W mode.

    Check the TX LED_A, Green it will blink fast for 10W power transfer. If it is slow blink the TX is in 5W mode, see table 3.
  • 0 in reply to Bill Johns
    Prodigy 20 points

    Hello Bill,

    All the process I'm talking about is in 5 Watt mode and the application is not designed for 10 watt mode, the problem is that I'm only being able to get around 2.8 Watt at best in the output, Sorry for not detailing that.

    What chip do you recommend for a 5 Watt application in the case we decide to change this chip?, we are evaluating It but we need:

    • an adjustable voltage output.
    • Current limiting

    And would be nice to have but not necessary:

    • I2C or some way to control it from micro controller.
    • QFN PAD or similar if possible (would simplify production a lot and size is not critical for our application), also it would help with thermal issues.

    I have seen bq5105xB and bq51013B  with 20-VFQFN  package but they are fixed voltage, any idea of what to choose?

    Thank you.

     

  • 0 in reply to Javier Pena Gonzalez
    TI__Guru 66276 points
    Hello
    For 5 Watt application with adjustable output and I2C take a look at the BQ51021.
    Sorry only have a few devices that are QFN.