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TPS23750 HPA107 Evaluation board power limit

jack64
Prodigy 20 points
Other Parts Discussed in Thread: TPS23750

Hello.

I'm using HPA107 Evaluation board for the TPS23750 part.

With a load resistance of 50ohm all is right, but if i try to use a lower resistance to obtain an high current the TPS23750 enter in an infinite softstart loop.

Documentation assert that is possible an output of  2A@ 5V but I can't obtain this power.

Any help will be greatly appreciated! 

Best regards,

Jack

  • 0
    TI__Expert 7990 points

    Three possibilities come to mind.

    1)  Your load is not what you think it is.  If you are using an active load (electronic load), they have a bad habit of looking like a very low resistance when the requested loading (current) cannot be met.  This often interferes with the allowed time to start as the output is shorted until the load comes into regulation.  The cure is to try a real resistor directly across the output is you are not currently doing that.   Another thing to check for is the grounding in your setup, and especially parasitic shorts from the 5V return to the TPS23750 RTN through oscilloscope probe grounds or other sneak paths.

    2)  Your source supply is overloaded and collapsing. Either the input supply current limit is too low, or some artifact of the output loading (per 1) is causing the TPS23750 hotswap to current limit.  I assume that you are using a nominal "48V" input and it comes through a properly built cable.

    3)  You may have a bad board.  If all else fails, try replacing the TPS23750. 

    As an aside, the TPS23750 has a protective mode that monitors the current sense for several very high pulses in succesion, then it shuts off for the duration of the softstart / recover cycle.  If this is happening (due to something like a shorted output rectifier), it is hard to see unless you remember to look for it.

  • 0 in reply to Martin Patoka
    Prodigy 20 points

    Martin Patoka said:

    Three possibilities come to mind.

    1)  Your load is not what you think it is.  If you are using an active load (electronic load), they have a bad habit of looking like a very low resistance when the requested loading (current) cannot be met.  This often interferes with the allowed time to start as the output is shorted until the load comes into regulation.  The cure is to try a real resistor directly across the output is you are not currently doing that.   Another thing to check for is the grounding in your setup, and especially parasitic shorts from the 5V return to the TPS23750 RTN through oscilloscope probe grounds or other sneak paths.

    2)  Your source supply is overloaded and collapsing. Either the input supply current limit is too low, or some artifact of the output loading (per 1) is causing the TPS23750 hotswap to current limit.  I assume that you are using a nominal "48V" input and it comes through a properly built cable.

    3)  You may have a bad board.  If all else fails, try replacing the TPS23750. 

    As an aside, the TPS23750 has a protective mode that monitors the current sense for several very high pulses in succesion, then it shuts off for the duration of the softstart / recover cycle.  If this is happening (due to something like a shorted output rectifier), it is hard to see unless you remember to look for it.

    You are reason with the first option. The load wasn't what I think. It is a very heavy load and so the controller is correctly limiting the current. At the end of the soft start time, when CTR reach 3V, COMP voltage isn't in the control range and a shut down is started. Now with a correct load all is right.

    Thanks a lot  for your suggestion.

    Jack