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LM5170-Q1: Using in a low power application

Craig Duncan
Prodigy 80 points
Part Number: LM5170-Q1
Other Parts Discussed in Thread: LM5170, LM5176, LM5155, LM5088, TPS43060, LM5117

I require an adaptive design solution for a product where either a 12V or 48V input may be present and 12V and 48V outputs are always both required. A bidirectional supply such as one based on  a LM5170 appears at first inspection to be attractive.

The output current requirement at 12V is 2A or at 48V just 0.5A. Can anyone offer comments on:

  1. Whether this is a reasonable use of the controller. Is there any reason that would preclude scaling the output capacity for this lower current.
  2. I note the Buck Mode efficiency of the EVM  drops rapidly for 14.5V  loads below 10A (Figure 4 of EVM user guide). What is the driving factor(s) behind this knee in the efficiency curve? Is it something that will likely scale with a design based on the output parameters above?
  3. Why might  I use just one side of the convertor, rather than both phases?

To date we have been looking at developing a LM5176 based design with two exclusive conversion modes (12V -> 48V or 48V -> 12V), but the LM5170  will potentially also  allow us to avoid the complications of  matrix switching such a convertor between 12V and 48V input and output connections.

Thanks in advance for any assistance.

Craig

  • 0
    TI__Guru 58781 points
    Hi
    The responsible engineer is out now. We will reply by 4/12
    Regards,
    EL
  • 0
    TI__Guru* 78270 points
    Hi Craig,

    Thank you for reaching out. Sorry I have been on the business trip.

    Yes the LM5170 can support your application, but I do feel your power level is on the low side, because the LM5170 can process 1kW or more. It may be more cost effective if you consider the LM5155 to perform boost from 12V to 48V, and use a buck controller like the LM5088 to convert 48V down to 12V.

    However, you can still use it, and you can refer to the design tool at the following link to
    www.ti.com/.../snvc205

    Regarding the efficiency, the EVM's full load current is 60A. At 10A or lower, the lower level is less than 15% of rated power level, and the switching losses become more significant. If you scale the circuit for your 24W, you will see the efficiency may start to drop for <3~4W.

    Yes, you can use only one channel of the LM5170, and leave the other disabled.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Prodigy 80 points

    Thank you Youhao for completely answering all my questions. I have had a look at the alternate components you suggested and I can see there is a definite price advantage when considering the total BOM costs.

    Additionally I have be investigating sync convertor such as LM5117 and TPS43060 to get greater efficiency comparable to what I expect from the LM5170.  It would seem that with these there is still a total cost advantage in my low power application.

    The LM5170 appears to be a great component but as you have suggested perhaps not best suited to my design.

    Thanks once again for you assistance.

    Regards

    Craig