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PMP9766: TPS259401A not blocking reverse current under light load on INPUT

Kristián Szalay
Prodigy 20 points
Part Number: PMP9766

I'm working with PMP9766 EV kit and during the testing I found a problem what is probably just an unfortune combination of components. 

There is a DC/DC converter board based on MP1584EN integrated circuit (can't be replaced yet) what is used as a power supply for this kit (5V CV output). 

When the MP1584EN lost input power, the EV kit starts working as a backup PS. But the MP1584 is somehow able to sink current from his output and get in some weird on-state. The problem is that under light load on the input side of PMP9766 the TPS259401A IC do not detect the 66mV voltage drop between IN and OUT and it stays open ("back-supplying" the MP1584EN). 

What I did, that I shorted the INPUT of the TPS259401A through P-MOSFET and it works good but I'm not sure about my solution. 

What do you about this solution? Have you ever tested the the EV Kit under some similar conditions like my case? It is an acceptable behavior for TPS259401A? 

There is no space for using the UVLO and the circuit must act autonomously. 

If there is any more detail you need to know,  I'll be more than happy to share with you.

  • 0
    TI__Intellectual 1425 points

    Hi Kristian,

    If the positive input rail of your pre-regulator becomes 0V, the body-diode of the HS-MOSFET of the pre-regulator is forward biased and you will have a conductive path from the supercap to GND. You need to insert some sort of reverse current protection, e.g. a diode, at the input or output of your pre-regulator.

    Best regards

    Markus

  • 0 in reply to Markus Zehendner
    Prodigy 20 points

    I see now! Thanks! 

    So there is no option to force TPS259401A  block reverse current in my application?

  • 0 in reply to Kristián Szalay
    TI__Intellectual 1425 points

    Hi Kristian,

    Since the TPS259401A has the reverse blocking sense circuit fully integrated, you'd need to make sure that you draw enough current to trigger it or use a diode at the pre-regulator input/output or use a different eFuse. However, the best option would be swapping out the pre-regulator against a device that stays off, when the output is pre-biased with no input voltage available.

    Best regards

    Markus