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BQ51025: bq51025 doesn't start-up with load connected

Michael Casey
Prodigy 150 points
Part Number: BQ51025

I am using the bq51025 wireless Receiver chip, the design based on the evm circuit diagram. I cannot get it to start up with a load connected. It starts o.k without a load and then after start up I can connect the load but i can only draw about 300mA max which is much less than it should deliver

  • 0
    Prodigy 150 points

    I haven't had a reply yet but have made some progress: I removed the connection from TS/CTRL to my msp microcontroller and the bq51025 now starts correctly with a load connected, looks like the undefined status switches off the bq51025 at startup.
    The connections from the bq51025 to the microcontroller also cause problems because they are powered before V-OUT is active, the microcontroller uses a 3v3 reg from V-OUT. The uC inputs are powered by the bg51025 before the uC power and this stops the microcontroller from starting correctly.
    I removed the series resistor to the green led (the only connection i could reach) on /WPG and the uC powers up correctly but now with no load it switches on and off every aprox 4 secs for a few minutes and then stays on, with a load it is fine.
    Attached is a pdf of my diagram, I still can only get about 500mA max from V-OUT I have Rfod of 470R and the series resistor to ILIM was initialy 270R, V ilim was aprox 0.55v at 500mA so I lowered the resistor to 140R, V ilim decreases to about 0.4v but I still only get about 500mA, any lower resistor value and the bq51025 shuts down.

    I3857.BQ51025YFP_Receiver.pdf am still confused about Rilim and Rfod, there are no defualt values for this and the tool did not include the bq51025 (as far as I could see). Some help would be really appreciated.