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LM5116: 15mA power consumption during no load operation

Sarath Vijayan1
Prodigy 40 points
Part Number: LM5116

Hi,

We have designed a 5V O/P regulator using LM5116. It works great, but at no load condition, there is a ~15mA current consumption. I was reading through the datasheet and it mentioned that DEMB pin should be grounded for diode emulation mode and this should increase the efficiency in light load condition. I have done exactly same in my design, but yet have 15mA current consumption at no load. 

IS this expected? If not, what I am doing wrong for the higher power consumption at no load?

Please find the attached screen shot of the schematics. Hope to hear from someone soon and thank you in advance. 

  • 0
    TI__Expert 3835 points

    Hi Sarath,

    The DEMB pin is for light-load efficiency and not for Iq. It looks like you have a couple feedback resistors that is causing some leakage current. Try increasing them an order of magnitude. For UVLO, try just pulling it up to Vin.

    Regards,

    Ethan

  • 0 in reply to Ethan T
    Prodigy 40 points

    Hi Ethan,

    Than you for answering, but I still have queries. 

    The DEMB pin is for light-load efficiency and not for Iq - what do you mean by Iq?

    It looks like you have a couple feedback resistors that is causing some leakage current  - with 3.92K and 1.2K for feedback resistor, leakage should be <1mA at 5V O/P. But what I am getting is 15mA. DO you think the issue is with feedback resistor?

    For UVLO, try just pulling it up to Vin. - how does this make a difference for high power consumption at zero load?

    Thank you in advance. 

  • 0 in reply to Sarath Vijayan1
    Prodigy 40 points

    I changed the feedback resistor value by one order higher, but only improved by 1.2mA i.e. my current consumption at no load is ~13mA. 

    Is there any way this can be improved? Or is this expected? 13mA seems to be high current for battery powered application. 

    Thank you

  • 0 in reply to Sarath Vijayan1
    TI__Expert 3835 points

    Hi Sarath,

    Iq is your measured input current at no load. The UVLO feedback resistor will also consume some power. I have forwarded this to a product expert for this feedback. To me it does seem 13mA is high.

    Regards,

    Ethan

  • 0 in reply to Ethan T
    Prodigy 40 points

    Thanks Ethan. I was doing some more study and I believe this loss is due to the gate charge of the Mosfet used. For 600Khz frequency and for the gate charge of the mosfet that we have, loss comes to around 12mA. I tried to use lower frequency to test this theory and used 300Khz instead and saw the input current drop to 6mA.