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LMZM23601: Extremely low efficiency when driving light loads

Steve Sanislo
Prodigy 10 points
Part Number: LMZM23601


I have a sensor monitoring application powered by a 12 volt solar charged battery that normally draws about 30uA and occasionally draws 700mA for a short time to transmit data. Minimizing the average current consumption is critical to this application.

I’m using the fixed 5 volt version of LMZM23601 with its MODE pin tied (low for auto PFM operation) and its EN pin tied to Vin. If I’m interpreting the data sheet correctly, LMZM23601 should consume less than 20uA while active with no load attached. I assumed that adding my application would result in a total current consumption from the battery under normal operation of: 20uA(LMZM23601 at no load) + 30uA(application load) + 15uA(50% efficiency loss) = 65uA. The actual current consumption with my 30uA load attached is about 2mA - way higher than expected!

Is it possible (and if so, what can I do) to reduce the input current of the LMZM23601 from 2mA to under 100uA when driving a 30uA load?

  • 0
    TI__Guru 50120 points

    Hi Steve,

    Is it correct to assume that in your application you have a 12V input to 5V output application where you go from idle( relatively no load) to 700mA loading (transmit data)? 

    At no load on the output of the LMZM23601 for 12Vin to 5Vout application, the operating quiescent current is typically 7uA detailed in Section 7.5 Electrical Characteristics. If your voltage source(12V solar battery) naturally draws 30uA being of downstream circuit/IC then the total expected input current drawn from the battery(I_in) during no output load condition is the sum of the two drawn currents 30uA + 7A for a total of 37uA. 

    Are you bench test measuring I_in to be 2mA at a no output load condition?   

    Regards,

    Jimmy  

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Steve,

    Can I get an update on this? If possible please attach the schematic so I can review.

    Regards,
    Jimmy