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TPS2358: Functionality with 3.3V and no 12V

JDJ
Expert 4526 points
Part Number: TPS2358


Hello! 

We are having issues with an AMC site in which an overcurrent is being reported on the +3.3V A Channel (the A channel is used for the AMC site). The SETA resistor is populated as 3.32k, to comply with the AMC.0 standard.  However, this only seems to happen when +12V is not present (IN12A is not there).  If +12V is present, the AMC seems to power up as normal.

My question is in regard to functionality of the TPS2358 when +3.3V is present but +12V is not.  The electrical characteristics in the datasheet are given assuming both +3.3V and +12V are present. 

Is it expected the +3.3V hot swap channel should function in the absence of +12V? 

They appear to be independent but is there some internal leakage path that could be causing a lower current limit trip of +3.3V when +12V is not present? 

 According to the AMC.0 spec, this is a valid scenario:


 

Thanks!

  • 0
    TI__Guru 57737 points

    Hi JDJ,

    1. TPS2358 can draw power from any of four inputs (IN12A, IN12B, IN3A, or IN3B) or from any of four outputs (OUT12A, OUT12B, OUT3A, or OUT3B). This feature allows the internal circuitry to function regardless of which channels receive power, or from what source.
      1. So, the +3.3V hot swap channel will function even in the absence of +12V rail 
    2. The current limit functionality of each channel is independent of the other channel.
      1. Do you have waveform captures which prove the current limit of 3.3V rail has reduced in the absence of 12V rail ? Can you please share the waveforms ?