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LM5018: Efficiency comparison of LM5018 and LM5008A

Pawan Nayak
Expert 3245 points
Other Parts Discussed in Thread: LM5018, LM5008A

Hi,

I was comparing the efficiency of LM5018 and LM5008A at an output load of 120mA. LM5018 has efficiency of ~78% and LM5008A has ~85% efficiency. Why is the efficiency of synchronous buck converter(LM5018) lower than a normal buck (LM5008A)? I want to use the LM5018 as it is a newer part but it seems to have comparitively lesser efficiency


Power converter specifications:

Vin = 48Vdc battery (Vinmax = 56V)

Vout = 12V @ 120mA output current


Thanks,

Pawan

  • 0
    TI__Intellectual 2320 points
    Hello Pawan,

    What is the value of the inductor on your boards when you are working with the LM5008a and the LM5018?
    LM5008A is a non-synchronous Buck converter which can enter into the discontinuous mode (DCM) of operation depending on the value of the input voltage, output voltage, frequency and your load current. At 120mA , if the value of the inductor is rather low, the LM5008A will enter into DCM which reduces the Fsw (the pulse skipping mode is enabled). This helps in improving the efficiency of the part at lighter loads.

    The LM5018 is a synchronous buck converter which continues to have fixed frequency continuous conduction mode operation, even at light loads. This leads to increased switching frequency losses which leads to reduction in efficiency.

    Regards,
    Sourav
  • 0 in reply to Sourav.Sen
    TI__Expert 3245 points
    Hi Sourav,

    I will be using an inductor of 470uH along with LM5008A. Even at higher load of 300mA, the LM5008A seems to have ~88% efficiency compared to ~85% for LM5018.

    I an having a standby load of 12V,20mA and operational load of 12V, 120mA. I decided to use LM5008A because of its better efficiency at light loads.

    Thanks,
    Pawan