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I am confused about OCP protection

user6091462
Prodigy 130 points
Part Number: TLV62569

Hi, e2e

Currently, I am measuring TLV62569DBVR, but its operation is strange.

I read its datasheet, but it don't have simulation about performance curve.

Thus, I can't verify my measurement whether is correct or not

Please help me check measurement result, its operation is in normal.

The below picture is my measurement result:

Thank you for your assistance.

  • 0
    TI__Mastermind 31751 points

    Hello,

    The device is working properly based on the waveform provided above. It only shows that the device is operating in peak current control because the current limit (ILIM) on the high-side FET was reached. Please see part of the datasheet below which describe its operation.

    In addition, the device will NOT work in hiccup mode during OCP or short circuit conditions.

    Best regards,

    Excel

  • 0 in reply to Excel Regidor
    TI__Prodigy 130 points

    Hi, 

    Thanks for your answer, but I want to ask further why device can still operation properly.

    Because its datasheet describe current limit is 3A and I test this one in output current is 3A, 

    In additional, my measurement shows output voltage drop very much in the waveform, why?

    Thank you for your assistance.

  • 0 in reply to user6091462
    TI__Guru 52745 points

    user6091462 ,

    There are a number of different schemes for Over Current Protection.  In the case of the TLV62569DBVR, the OCP is a current limit with a cycle by cycle peak current limit.  Rather than shutting the output down and restarting, the TLV62569DBVR limits the current it can deliver, if the external load draws more current than the TLV62569DBVR can deliver, the difference is made up by the output capacitor, which is discharged until the load current drawn out of the output matches the current sourced by the TLV62569DBVR.

    Because the Current Limit is a cycle by cycle peak current limit, the average switch node current into the output will be less than the current limit.

    If you are using a constant current load, that will draw the output voltage down to the compliance voltage of the electronic load, below which the load can not sink that constant current.

  • 0 in reply to Peter James Miller
    TI__Prodigy 130 points

    Hi Peter,

    Thank you so much for your answer.

    And I further want to ask that different schemes for OCP.

    How should I choose cycle by cycle or shutting the output down for end-device?

    What is advantage or disadvantage of them respectively?

    I'm studying about this application, if you have free time, please give me some advise or reference.

    Thank you for your assistance.

  • 0 in reply to user6091462
    TI__Guru 52745 points

    user6091462,

    Cycle by Cycle current limit, where a power converter becomes a constant current source rather than a constant voltage source has the advantage of allowing a converter to continue operating and deliver an output voltage, even if it's lower than intended, during an over-load condition.  In many application, that can allow the power converter to operate through short periods of over-load while protecting the power devices from excessive current damage.  This can be extremely useful in applications where there could be a sudden load on the converter that doesn't need to trigger a shut-down, but could be damaging if the current is not controlled.

    As a couple of examples:

    Hot plugging or connecting a device with a large input capacitor to the output.  The input capacitors apply a sudden, high load current on the output, but you don't want to shut the rail down, just allow it to charge the capacitors with a controlled current until hey come up to the intended voltage.

    A motor or light might initially try to draw a very high current as it starts up, but then reduce that current once it is running.  Constant Current Limits, like cycle by cycle current limits prevent these "in-rush" or surge currents from shutting down the rail.

    There main disadvantage is that they will continually drive that current for a very long time.  If the device they are powering experiences a fault that causes them to draw excessive current, the power converter will continue to provide the current, which could result in damage to the powered device.

    Over Current Protection that imposes a shut-down requirement is the opposite.  In response to an unexpectedly high load current, they terminate switching and shutdown.  Some will restart after a short "cooling" period often called "hiccup" or "time-out"

    This prevents the converter from operating through a short, mild over-current condition that might not require a shut-down, but it provides more protection to the load by resetting its output in response to the excessive load.  In some fault cases, this can give the device the converter is powering a chance to reset whatever fault is causing the over-current without actually the device.