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Original question:

TPS54360B: Split-Rail Power Supply

TPS54360B: Unable to achieve simultaneous Vout for +/-3.3V

Pang
Expert 2415 points
Part Number: TPS54360B
Other Parts Discussed in Thread: TPS54360, LM5160, TPS55010

Hi,

There are some minor issue on the split rail regulator. Based on the waveform attached, channel 1 probes on positive supply & channel 2 probes on negative supply. Positive side supplies only +3.29V whereas negative side supplies -3.65V.  The difference is quite huge at negative side if we expect -3.3V supply. 

 

Based on what I understand from the circuit, the supply at positive side & negative side should be equal as the positive side is "mirrored" from negative side using coupled inductor.

Can you help to provide the advise how could this be resolved?

  • 0
    TI__Expert 6245 points

    Hello Electrobud,

    While it is true that the two taps are mirrored off each other, there is stray inductance to be considered. In effect, in series with each winding of the inductor there is an inductance that is typically as few percent of the mutual inductance. This inductance causes ringing on each winding. Since the +3.3 V output is used to provide feedback, it will be well regulated. If the -3.3V output is not loaded, its voltage may increase. Also if the +3.3 V supply is not loaded but the -3.3 V is loaded, the -3.3 V supply may decrease below 3.3 V. To prevent collapse of the -3.3 V supply, a synchronous converter should be used. Please go to TI’s website and search for “flybuck” for more information.  The flybuck topology has a similar limitation. 

    Regards, Robert

  • 0 in reply to Robert Blattner
    Expert 2415 points

    Hi Robert,

    Thanks for the advise. Do you mean that need a post regulator to prevent the collapse of -3.3V supply? Can you take a look on the below part which I have seen from Ti website whether is it suitable to use? If not you may recommend.

    http://www.ti.com/lit/ds/symlink/tps55010.pdf

  • 0 in reply to Pang
    TI__Mastermind 35210 points

    Sorry for the delay. We are working on this.

  • 0 in reply to Marshall_Beck
    TI__Expert 6245 points

    Hello Electrobud,

    Sorry for the delayed response.

    For this type of application, we typically recommend the LM5160. It can operate in FPWM mode and is comfortable with your input voltage. It is the possibility of the TPS54360 entering skip mode and failing to regulate the primary that I am concerned with. There is also a lot of literature concerning the LM5160 in this topology.

    While the TPS55010 can be used as a post regulator, since rails should only be out of regulation when loads are light, I recommend an LDO for post regulation.  Also, voltage error can be minimized by preloading the primary.   

    Regards, Robert

  • 0 in reply to Robert Blattner
    TI__Mastermind 35210 points

    Are you still seeing this issue? If not, I will close this thread so it is no longer being monitored.

    Please let us know if you need more help.