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Bidirectional Load Switch with optional current limiting

matt holland
Intellectual 260 points
Other Parts Discussed in Thread: TPS2552, BQ25606, TPS2500

I am designing a product and am looking for a bidirectional load switch between VBUS and CHGIN of a battery charger used in the following three modes.

Mode 1) Charging from USB, switch closed, no current limiting

Mode 2) Nothing connected to USB, switch can be closed or not

Mode 3) Supplying current to USB (OTG mode), switch closed, current limited to ~150mA.

So perhaps I don't need a load-switch at all, but optional current-limiting via an enable pin, though i'm not sure if such a part exists, or if it does, what it would be called. 

Any help appreciated,

Matt

  • 0
    Prodigy 5 points

    Hello Matt,

    This sounds like a PowerBank design, USB OTG on the go.
    I do not know of a power switch that will allow bidirectional current but only limit current in one direction.

    There are several ways to do OTG, I will mention a few to get dialogue started.

    One way is having 2 paths, charge path (buck or linear step down charger), OTG boost path (boost converter for 5Vout)
    In this case the boost circuit output could have a current limit switch like the TPS2552.
    This would limit the current during OTG boost mode, and block current back into the boost stage when charging.
         -charging phase would turn off the boost, thus would present reverse voltage across the TPS2552 activating its reverse blocking mode.

    This blog article shows how to implement boost current limit discretely.
    Make your power bank more reliable with output short-circuit protection

    TI has several USB OTG and PowerBank integrated IC solutions.
    An OTG design may use 2 connectors, however it is common to use one USB connector.
    bq25606 is a new device that uses one connector for charging/OTG.

    OTG current may not need to be tightly controlled, as long as the source has current limit functions.

    TPS2500 however is a integrated USB OTG boost with USB current limited switch.
    Since you must boost anyway for OTG, this part has adjustable USB switch inside for OTG.

    If you can provide a block diagram of what your system would look like it would help.