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TPS54560 - Input ripple in eco-mode

Raul Perez17
Prodigy 20 points
Other Parts Discussed in Thread: TPS54560, LM5160

My application uses TPS54560 to obtain 24V from 50V. 

Load is not allways the same and it is normally 0 as it is used for an auxiliary supply of an external equipment with its own AC/DC. It supply is needed, it can be 0.5 or 1.5 Amp.

The problem we see is that in normla operation with no load, the TPS54560 enters in eco-mode and input ripple is not acceptable as that supply must be stable to be used by other sensitive circuits.

I have seen that eco-mode can not be disabled. Is is correct?

To minimize input ripple (600mVpp) I tried with power inductors and electrolitic capacitors but very poor improvement is achieved (no means to reduce bellow 150mV). Any other suggestion?

As alternative solution I would consider to use other part with same performance but without eco-mode or with the possibility of disable it. Is does exist that part?

Thanks. 

Raúl Pérez

  • 0
    TI__Guru**** 191445 points
    You cannot disable eco-mode. But at light load the input voltage ripple should be quite small, 50 mV or less. At full load of 5 A , the input ripple can get to around 400 mV p-p. Can you post your schematic and waveforms?

    You might look at LM5160 as an alternative.
  • 0 in reply to JohnTucker
    Prodigy 20 points
    Thank you Jonh,

    you are right. It was my fault. The real problem wasn´t in the TPS54560 operation but in the AC/DC that was used to provide the 50V input voltage:
    As in my tests, the TPS54560 was the only circuit connected, when I reduced the output current to test the operation in DCM or eco-mode, the AC/DC was not able to regulate its output correctly as it needs a minimum load. That was the cause of the ripple I observed that erroneously I thought it was due to enter in eco-mode.

    After solving the AC/DC minimum load issue, everything is working as expected. The ripple in eco-mode is about 15mV in the output and is neglegible in the input!

    (I was using the eval board changing feedback resistors to obtain 24V, and input and output capacitors adding some capacitance to reduce ripple)

    Regards.
    Raúl