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LM25145: The current consumption when there is no load on the output side.

seungpum kang
Prodigy 120 points
Part Number: LM25145
Other Parts Discussed in Thread: LM25148

Tool/software:

HI sir.

I am using LM25145 to generate a 12V output. The input voltage is from a battery (13~17V).

The LM25145 consumes around 70mA of current when there is no load on the output.

All output stage components were removed to eliminate the load.

Inquiring about the cause of power consumption when there is no load.

The circuit diagram is as follows.

Thanks.

  • 0
    TI__Mastermind 22300 points

    Hello,

    When measuring input current to the device, make sure that the EN divider is disconnected and the enable pin is being driven manually. The EN divider can pull some current to GND from the battery. Are you measuring directly on the Vin pin of the device? Is the device enabled or disabled when you make this measurement?

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Prodigy 120 points

    Hellow Ridge.

    The EN pin is not divided and is directly connected to Vin or ground. The current measurement was taken at Vin. When enabled, a current of 70mA was measured, and when disabled, the current measured was 0mA.

    Thanks.

    Kang.

  • 0 in reply to seungpum kang
    TI__Mastermind 35210 points

    Hi Kang,

    The quiescent current specification is provided in the datasheet and for your convivence supplied below.

    70mA does seem high. If you are seeing this behavior across multiple devices even when recreating the test condtion below, then we need to further understand how the measurement is being done. 

  • 0 in reply to Marshall_Beck
    Prodigy 120 points

    Hi Marshall_Beck,

    I measured the current of the LM25145's input (BATT_B+) voltage using a multimeter as shown in the diagram below.

    The current measured when enabled is 69mA and when disabled is 0A

    All output stage components were removed to eliminate the load.

    Is there any problem with the circuit diagram?

    Thanks,

    Kang.

  • 0 in reply to seungpum kang
    TI__Mastermind 22300 points

    Hello,

    It looks like the output voltage is still active and the controller is still driving the FETs. I think the next step to test this would be to replicate the measurement in the datasheet if you are trying to understand if the behavior is expected. Some current will be required to drive the switches when the device is enabled. Are you trying to understand the behavior of the device or improve the no load input current?

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Prodigy 120 points

    Hello,

    To prevent battery discharge, I am trying to improve the no-load input current.

    I have set the device to no-load for testing, but it is actually used as the input for a 5V output DC-DC converter to generate standby voltage. The device(msp430) that uses 5V consumes about 1mA, but the current measured at the battery input is 71mA. As a result, even with only a 1mA load, an additional 70mA of current is consumed.

    In this case, even without any other devices besides the MSP430, the battery will discharge within a week.

    Thanks.

    Kang.

     

  • +1 in reply to seungpum kang
    TI__Mastermind 22300 points

    Hi Kang,

    The LM25145 is a device that operates in FPWM mode. This means that even when there is no load, the device switches at the set frequency in order to regulate the output voltage. As a result, the device has poor light load efficiency. 

    The best option to improve this would be to use a device that has PFM mode at light load. PFM provides increased efficiency at light load by modulating the switching frequency of the device. Newer controllers such as the LM25148:https://www.ti.com/product/LM25148

    Using a device that has PFM at light load will significantly improve your efficiency in this condition. I think this is the best option for significantly reducing your standby current.

    Best regards,

    Ridge