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LM5088-2 strange behaviour

carlo agrusti
Prodigy 40 points
Other Parts Discussed in Thread: LM5088

Hi,

I have prototyped a board with a mcu-selectable buck converter; the circuit is as follows:

and it should work with an input voltage of 45-54 V and an output at 24 V/ 6A. The problem is that it does not work at all, or better, when enable by mcu, the LM5088 starts working, but the output voltage is stuck at about 12 V without load, but it falls down to 1~2 V with 1~2 A loads. The ramp signal doesn't seem to be valid, since all I get is a noise:

Any clue is greatly appreciated.

TIA,

Carlo

  • 0
    TI__Guru 59001 points

    Hi

    It looks like false current limiting.

    I could not find anything wrong on your schematic. Probably, the issue is caused by wrong component population (especially, R202, R207, C207, R23) or noise injection  at CS-CSG pins. CS-CSG pins should be kelvin-connected to the sense resistor.

    Regards,

  • 0 in reply to EricLee
    Prodigy 40 points

    Thank you Eric for the fast answer. It seems that the Vout drop when under load is due to false overcurrent protection: I have short-circuited sense resistor and now Vout remains constant and regulated but at the wrong value (13 V instead of 24 V). Moreover, the ramp signal is still flat, but maybe this is due to the absence of signal on sense circuitry.

    Anyway, it seems that LM5088 is not well suited for my application, since it seems very sensible to noise and on my board there are a lot of different switching sections that interfere badly with it.

    Thank you again for uour answer,

    Carlo.