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LM5123-Q1: 12V to 50V@4A design verification

Bartosz Nowicki
Prodigy 80 points
Part Number: LM5123-Q1
Other Parts Discussed in Thread: LM5121, LM51551

Hi,

I've tried to design boost converter using LM51551 and LM5121 without success and decided to give LM5123 a try. I've used both Webench Power Designer and Power Stage Designer 5 to determine inductor and loop compensation values. I've designed a simple PCB to test the converter, but unfortunately it burned at 200W load, probably due to soldering issues connected with overheating (low side transistor blew up together with the driver). I don't have another driver to test it again (ordered, but not arrived yet), but I've redesigned PCB for better heating management. I've decided to keep crossover frequency as low as possible, therefore I am oscillating around 1 kHz at all load conditions (1 to 4A). Please find schematics and Power Stage Designer files (topology and loop compensation) attached. Inductor in design is PA2248.153NLT. Are you able to cross-check my design?

Regards,

Bart

lm5123_sch.pdf

lm5123_loop.txt 
LOOP_CALCULATOR
12
50
4
15
8
164
10
164
10
240
2
10
1
3
1
1.2
1200
2
10
60
3
0.1
1
0.2
1
4700
24000
150
1000
0
1
2200
22

lm5123_topology.txt 
BOOST
10
26
50
4
240
0.7
50
15

  • 0
    TI__Genius 12885 points

    Hi Bartosz,

    You should choose between the non-synchronous solution (LM51551) and synchronous solution (LM5121, LM5123) first.

    A non-synchronous solution is simpler with lower efficiency.

    You should keep an eye on the SW voltage rating when using LM5123.

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    Prodigy 80 points

    Hi Feng,

    I've already abandoned non-synchronous solution as I need more efficiency, now I am trying to choose between LM5121 and LM5123.

    By keeping an eye on the SW voltage you are saying it shouldn't be exposed to voltages larger than 60V as mentioned in datasheet?

    Regards,

    Bart

  • 0 in reply to Bartosz Nowicki
    TI__Genius 12885 points

    Hi Bartosz,

    Exactly. You should be very careful on the layout.

    So, I think LM5121 will be an easier way for you though the cost may be higher.

    Best Regards,

    Feng Ji