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Power Supply design help - 5V @ 3A and +/- 6V @ 20 mA

Kyle Aven
Intellectual 950 points
Other Parts Discussed in Thread: TPS54331, TPS54332, TPS54040, TPS54231

Hello,

I have two power supply challenges ahead of me that i need some help with.

1). Vin=6-18V, Vout=5V @ ~3A.

2). Vin=6-18V, Vout=+/-6V @ ~+/-20mA

The first supply is for power multiple subsystems with the use of regulators(1.8V, 3.3V...). It should be relatively clean but can always be filtered after the linear regulators.

The second supply is for an ADC analog front end and should be as clean as possible.

Any suggestions or help?

thanks

kyle

  • 0
    TI__Guru**** 150750 points

    For the first output, the TPS54331 or TPS54332 is your simplest solution.

    For the second, you should definitely post filter with LDOs as the power loss at 20 mA will be minimal.  I would recommend a +/- 7 or 8V supply to the LDOs to give them plenty of headroom to accomplish some great filtering.  The complementary TPS7A4901 and TPS7A3001 are perfect.

    To get the +/- 8V from a 6V to 18V source, you can use another TPS5433x like this app note: http://focus.ti.com/lit/an/slva369/slva369.pdf  Of course, the TPS54040 or TPS54231 also provide enough current, but you could use the same IC as for your +5V output.

     

  • 0 in reply to Chris Glaser
    Intellectual 950 points

    Once the voltages have been created using the coupled inductor, can the new GND created be connected back to the Vin GND using ferrite beads without any issues? Sorry for my ignorance on this topic. I do not have much experience in power supply design

  • 0 in reply to Kyle Aven
    TI__Guru**** 150750 points

    I'm not sure what you mean by 'new ground'.  The ground between the output voltage potentials is the same ground as Vin ground.  It should be a direct connection without ferrite beads in between.

    The GND of -8V is 8V of potential separate from GND.  These cannot be connected.

  • 0 in reply to Chris Glaser
    Intellectual 950 points

    I was just thrown off i guess due to the fact that the app note shows the use of two different ground symbols in the schematic

  • 0 in reply to Kyle Aven
    TI__Guru**** 150750 points

    Yes, the IC's ground is different from system ground (input supply return). 

  • 0 in reply to Chris Glaser
    Intellectual 950 points

    Ok, back to my last question then.

    My design has a battery voltage Vin.  The negative battery terminal is attached to the PCB GND plane so that after linear regulators are used to create my other required voltages, the entire design will operate from the same system GND. Should the GND of the TPS54331 (depicted in the app note as a triangle) be tied to system GND using vias like in the PCB layout example of the TPS54331 data sheet or handled in a different matter.

  • 0 in reply to Kyle Aven
    TI__Guru**** 150750 points

    No, because the ground of the TPS54331 is different than your system ground.  The triangle ground is your -7 or -8V that feeds the LDO to get -6V.  The other ground symbol, the one with 3 horizontal lines, is your system ground.

    The layout of the TPS54331 in its datasheet is for the IC as a buck converter.  That is the typical application for it.  In a split rail supply or inverting buck boost, the connections are as shown in the app note.

    You will need to make a -8V heat sink for the TPS54331--its ground potential reference.  However, it doesn't need top be big at all as you won't have hardly any power lost in the IC.