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Multiple outputs (one inverting)

Rob Coker
Intellectual 390 points
Other Parts Discussed in Thread: TPS60400, TPS82740B

 I have a 5 VDC input and am trying to generate 3.3V @ 200 mA and -5V @ 10 mA.  This is not a lot of power, but I need to have a very small footprint (< 50 mm^2) so I'm trying to minimize the size and number of converters.  The outputs don't have to be isolated from the input and don't strictly speaking have to be dc/dc either, but I'm assuming that will give best efficiency.  Is there a single chip that can create both outputs?  Is there a better approach than using 2 DC-DC converter chips?

  • 0
    TI__Guru**** 150950 points
    I've not seen a single chip with a negative voltage but 2 discretes can do.

    The TPS60400 family can easily make your -5V.

    For the 3.3, the TPS82740B is the absolute smallest device. TPS62237 would be a discrete version but still small.
  • 0
    TI__Guru 66590 points

    Hello Rob,

    A possible solution with just one switcher would be a buck converter and in addition a charge pump driven from the switch node of the buck converter. Due to your input voltage being 5V and the low current on the -5V, the inverting charge pump should be ok. But this depends on the accuracy needs on the -5V and on the accuracy of the +5V.

    I would recommend Schottky diodes for the charge pump to reduce the voltage drop in the diodes. BAT54S could be a useful Schottky diode pair.

    Best regards,
    Brigitte