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BQ25883: [/BQ2588x] Not power good loop when using mains USB charger

Jan Penterman
Prodigy 180 points
Part Number: BQ25883

Hi,

We are using BQ25883 in one of our designs. The charger works fine when we have it connected to a laptop port. Also when we short D+/D- on a stock USB cable and attach the power lines to a 5V lab supply, the ICO settles at ±1.2A (ICO_STAT=0b10) But when we use any off the shelf wall charger, the device gets into a continuous loop of "Not power good", then it becomes good and it detects a Fast charge adapter (VBUS_STAT = 0b011), it enters ICO (ICO_STAT = 0b01) but it never settles. It seems that ICO_ILIM is ramping up or at least the values vary. Then Power goes to "Not good" and I get an interrupt. This happens both standalone and it host mode. When in host mode (Android), this is interpreted as the cable being plugged in and out continuously. We have an LED on the STAT pin and it flashes about twice a second. Not sure how to interpret this behavior. Is this intended behaviour or are we doing something wrong?

--edit--

When we disable EN_ICO, the LED pin flashes even faster (with equally fast interruots happening) and the charger won't even begin charging. However in this case Power is always "good".

We have !PG pin floating.

Thanks. 

  • 0
    TI__Mastermind 20570 points

    This can be a combination of adapters rating and cable resistance. 

    Could you please try to set ICHG current register to lower setting, for example, 100mA, and slowly ramp it up to your programmed current?

  • 0 in reply to Jing Zou
    Prodigy 180 points

    I am now running the charger without a driver loaded and controlling the registers via Linux i2c-tools. I have opened up one of the unstable stoch USB cables and put an Ampere meter on the 5V line. I have disbaled the Watchdog timer as it tends to reset the device after 40 seconds. I can get more or less stable charging with an ICHG setting of 600mA (0Ch), which corresponds to about 1.5A on the Ampere meter. Sometimes it drops to 0 but then it stabilizes again. When I increase the ICHG further, the higher I set it, the quicker it drops out. 

    I thought the whole I idea of ICO was to find the sweet sport and then settle there. I, mean when I would find an ideal cable and wall charger, I wouldn't want to have limited ICHG to only 600mA? Or is this limit a result of my circuit design and parts selection?

  • 0 in reply to Jan Penterman
    TI__Mastermind 20570 points

    This problem is mainly due to the high resistance at the input path. Some high resistance cables can be higher than 500mOhm resistance. Imaging you have a 5-V adapter and the input current gets >1.5A once the charging turns on, the voltage drop from your adapter output to the input our the IC is going to be > 0.75V. If you look at the waveform at VBUS of the IC, you will see the bus voltage drop really fast. 

    Adding more caps at VBUS should help with this issue. We also recommend to add 40uF at PMID for optimized performance.

  • 0 in reply to Jing Zou
    Prodigy 180 points

    We found that we had installed caps with too low voltage rating at PMID, BAT and SYS. After having those replaced with 25V rating caps, the problem went away. We still only have 10uF at PMID and 1uF at VBUS, whcih we copied from the EV kit schematics.

    I'm still facing another problem but I will open another topic for this as it is probably related to something else.