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BQ25620: OTG OCP Mechanism

Yishan Chen
Intellectual 1730 points
Part Number: BQ25620
Other Parts Discussed in Thread: BQ25638

Tool/software:

Hi,

What is the OCP Mechanism of BQ25620 when it works in OTG mode?

Will it detect the output current to do the protection or detect the peak current in inductor or the current flow though Q3?

What is the exactly current limit?

In customer working condition, they might be 4 to 5A output current with 200uS duration time, is that ok for customer using BQ25620?

If BQ25620 can't cover this scenario, Could BQ25638 cover this scenario?

Thank you,

Yishan Chen.

  • 0
    TI__Mastermind 31720 points

    Hi Yishan, 

    Please see my comments below. 

    There are a few different current protections in place when in OTG mode.

    • If VBUS pin is used as OTG output an OTG mode current limit can be set in REG0x0A. The allowable range is 100mA to 2.4A. Please be aware if PMID pin is used as OTG output rather than VBUS then IOTG setting will have no effect.
    • There is a cycle by cycle current limit at Q3 of 6.5A.
    • There is also a battery discharge overcurrent protection described in datasheet section 8.3.10.1.2 which applies to battery discharge current shared between OTG output and SYS current draw. 
    Yishan Chen said:
    What is the exactly current limit?

    There is not a fixed current limit because OTG mode voltage regulation point can be modified. For OTG mode with ~5V output continuous load should not be greater than 2.4A. 

    Yishan Chen said:
    In customer working condition, they might be 4 to 5A output current with 200uS duration time, is that ok for customer using BQ25620

    It is recommended that the customer perform prototype testing with their unique load profile, but in general 4 to 5A current draw for < 200uS should be okay on the BQ25620. Customer will need to ensure IBAT_PK setting (REG0x19[7:6])  is set to either 6A or 12A (12A is default). 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    TI__Intellectual 1730 points

    Hi Garrett,

    Thank you for your reply.

    How do we understand that?

    Garrett Kreger said:
    It is recommended that the customer perform prototype testing with their unique load profile, but in general 4 to 5A current draw for < 200uS should be okay on the BQ25620.

    If the output current limit is 2.4A, why BQ25620 can cover 4-5A current draw for <200us in Vbus pin?

    Another question is, what is the trigger time for upper mentioned three protection mechanism?

    Thank you,

    Yishan Chen

  • 0 in reply to Yishan Chen
    TI__Mastermind 31720 points

    Hi Yishan, 

    The BQ25620 can support a continuous load of up to 2.4A in boost mode. When PMID pin is used as output rather than VBUS the device can briefly support current spikes higher than 2.4A.

    Please allow me to correct my previous statement based on lab testing the BQ25620 can not support 4A to 5A current spikes in boost mode with VBUS as output. I am unable to test the exact load condition as my hardware setup limits me to minimum current pulse width of ~500uS. 

    Yishan Chen said:
    Another question is, what is the trigger time for upper mentioned three protection mechanism?

    The cycle by cycle protection is immediate. Converter will be turned off as fast as possible after detection. trigger time for battery discharge overcurrent protection is listed in datasheet section 8.3.10.1.2.

    Customer will need to use a higher current rated IC for a load that will reach 5A. It may also make sense to use an external boost converter rather than one built into the charger IC I mention this because while BQ25638 is a higher rated charger it can support up to 3A boost load at 5V output. It similarly is not designed to support 5A boost load. 

    Best Regards,

    Garrett