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BQ25601EVM-877: otg output 5.1V and connect to DC power source

Part Number: BQ25601EVM-877
Other Parts Discussed in Thread: BQSTUDIO, EV2400


my customer is using our EVM to test the behavior when the OTG is mistakenly connected to DC source.

First, they enable the OTG mode and 5.15V is presented on VBUS.

Then they connect VBUS to 5.2V DC source, now the current consumption is about 3mA shown on DC source.

Then they increase DC source voltage gradually to 6.5V.

Before the DC source voltage reaches 5.8V, the current consumption is always 3mA.

After it crosses 5.8V, the current consumption will be 36mA and will still be 36mA when DC source reaches 6.5V.

The datasheet only says the device will exit boost mode when VBUS rises above 5.8V boost_ovp threshold, but will it enter buck mode?

Is it the buck mode which causes the larger power consumption of DC source?

  • Hey Howard,

    If the device exits OTG mode, and a valid input source is present on VBUS, it will enter buck mode.

    It is likely that buck mode is causing the charger power consumption. Do you see current flowing into the battery? Is charging disabled?


    Joel H

  • Joel,

    we've monitored the registers with EV2400 and BQSTUDIO, finding that BOOST_FAULT is never set when DC source rises from 5.2V till 6.5V, which means VOTG_OVP is not working.

    MOSFETS stop switching at the first time we connect VBUS to 5.2V DC source. And it's not switching along with DC source rises from 5.2V to 6.5V.

    In datasheet:

    When the VBUS voltage rises above regulation target and exceeds VOTG_OVP, the device enters overvoltage protection which stops switching, clears OTG_CONFIG bit and exits boost mode. At Boost overvoltage duration, the fault register bit (BOOST_FAULT) is set high to indicate fault in boost operation. An INT is also asserted to the host.

    So the 30mA is not caused by buck mode. And the phenomenon is hard to explain.

  • To be more specific, the question could be concluded as:

    1. Why current from DC source increase from 3mA to 36mA at 5.8V?

    2. Why BOOST_FAULT is not set at 5.8V? and it's never set (even when the voltage increases to 6.5V).

  • Hey Howard,

    I am posting my comments from our offline conversation here:

    1) Once the VBUS voltage rises above the OVP threshold for OTG mode, there is a pull down circuit that becomes active, which tries to bring the VBUS voltage back down with a current of 30mA.

    2) For BOOST_FAULT to occur, the charger is waiting for 4 consecutive and distinct occurrences of VOTG_OVP within a 4 second window. This means entering and exiting VOTG_OVP four times.


    Joel H