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LM5155: Adjustable High Voltage Design

Christopher Hess
Prodigy 95 points
Part Number: LM5155
Other Parts Discussed in Thread: TIDA-020013, PMP21781

I have a need for an adjustable boost converter that can output up to 150V at 0.100 mA.  The input voltage would be off a 14.4V nominal lithium ion pack.  Ideally this rail would work all the way down to 25V at 0.6A.  The design needs to be able to supply 15W at any voltage level.  I have been looking into both the PMP21781 and TIDA-020013 designs to base my design off, but I am having trouble getting my design stable across my full output range.  Which topology would be better for increased output current?  

  • 0
    TI__Guru 58225 points

    Hello Christopher,

    Please specify your full input voltage range. Please share your design.

    Your parameters, I know:

    VOUT = 25V to 150V

    POUT = 15W (what is the minimum power?)

    Especially when looking at the extreme cases, it might be a duty cycle issue as there is a minimum on-time of the transistors. I wonder if a flyback design would be the better solution in this case, but for this decision, I need to understand your system more in detail.

  • 0 in reply to Brigitte
    Prodigy 95 points

    Full input range is 12.8V to 16.8V.  

    Minimum power would be around 0.25W.

    I have been using the PMP21781  design with some modifications.  I changed the switching frequency to 440k with a 48.7k pull down on the Rt pin.  I changed the inductor to a 22uH and Rsl to 2.8k.

    I would be open to using a flyback design, but if at all possible I would prefer to use an off the shelf transformer.  

  • 0 in reply to Christopher Hess
    TI__Guru 58225 points

    Hello Christopher,

    Ok, then let's try if we can get the PMP21781 design stable for your conditions.

    You increased the frequency, changed the slope compensation and reduced the inductor. These changes would mean that you most probable need to change the compensation network as well.

    Please try if you can stabilize the design by reverting the changes you did. A converter that has a very wide output voltage range is normally very hard to stabilize especially at higher switching frequencies. So if we can stabilize the design at the lower frequency, we can then get to the next step and solve the issues you are seeing in your application with this design.

    Please send your schematic, either here or send me a friendship request then you can send it privately to me.