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BQ25703A: OTG over current (no load attached)

Matej Planinsek
Prodigy 20 points
Part Number: BQ25703A

Hi,

I'm having some problems getting OTG mode to work on my design using BQ25703A. With any OTG voltage/current setting, I get a short voltage burst on VBUS, then OTG mode turns off (ChargeOption3, bit 4 returns to 0) and OTG_OCP flag is set to 1 (ChargerStatus, bit 0). This is happening with no load attached to VBUS rail. I can read back correct voltage/current set values from OTGVoltage and OTGCurrent registers. EN_OTG pin is set to high. I have tried OTG voltages above and below my battery voltage (3S lithium) and many different current limits.

I should also note that I have had some problems with power-up from VBUS (5V) and no battery attached. In this configuration, regulator was outputting short bursts of voltage to VSYS while audible clicking was coming from the inductor. This problem was solved with a capacitor parallel to R17 resistor to pull ILIM_HIZ high during power-up. I don't now if these two problems are related.

  • 0
    TI__Mastermind 25800 points

    Matej,

    As far as the schematic, I would have you compare to this FAQ to review the components.You will need to add capacitance on some of these nodes, such as between the RSR resistor is a 1uF missing, and more capacitance on the SYS node. 

    The next thing we will need a startup waveform of OTG mode. We would want to see the VBUS pin voltage, SW2 voltage (if OTG would be in Buck Mode) or SW1 voltage (if OTG would be in Boost Mode). I would also like to capture the REGN voltage and the SRN voltage at the same time.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 20 points

    Hi,

    Thanks for help. I will make sure to compare my components with this document. I will provide waveforms as soon as I can get access to an oscilloscope. Meanwhile, could you clarify what conditions can cause OTG over current protection to kick in (OTG_OCP, ChargerStatus, bit 0)? Can any other current/voltage drop measurements beside current measured on RAC resistor cause this over-current event?

    Regards!

  • 0 in reply to Matej Planinsek
    TI__Mastermind 25800 points

    Hey Matej,

    The OTG_OCP function occurs when you exceed the OTGCurrent() register setting or whenever the VBUS voltage falls too low (see EC table parameter: VVBUS_OTG_UV). A similar condition occurs if OTG never rises up to the programmed setting.

    Regards,

    Joel H