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LM25148: Initially design this device for up to a 12A load. But having issues starting up the regulator with a light load. I need a reliable start up with a low power load of 30-40 mA.

Robert Correllus
Prodigy 50 points
Part Number: LM25148

Tool/software:

Initially design this device for up to a 12A load.  But having issues starting up the regulator with a light load.

I need a reliable start up with a low power load of 30-40 mA.  Is that possible?  I can start up with 130mA and once started I can lower the load down to 10 mA or even no load.

Any ideas.

  • 0
    TI__Genius 12255 points

    Hi Robert,

    Please send more information as to what issues you are seeing at startup so I can better assist you. The following should be sufficient for now:

    • This calculator filled out with your application parameters
    • Startup waveforms with VIN, VOUT, SW, IOUT
    • Test setup (how the application is hooked up to the oscilloscope, equipment details, etc.)

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 50 points

    LM5148-LM25148 Quickstart Calculator_rev4_RMC20240808.xlsm

    I will capture the start up with 130mA and with less and send along it will be a few minutes to get the wave forms.

  • 0 in reply to Robert Correllus
    TI__Genius 12255 points

    Hi Robert, 

    Sounds good. I will review these once all the information is sent.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 50 points

    C313696-NFC.pdf

    Find working (130mA or more load) test set up and scope plots Vin at TP13 and vout at TP3. and non start-up at 100 mA.  I have changed the Enable voltage via the new design workbook to 50k and 2.9K ohms.  which is different than the schematic attached.

  • 0 in reply to Robert Correllus
    TI__Genius 12255 points

    Hi Robert,

    I will review these today and get back to you at the latest by next Tuesday.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    TI__Genius 12255 points

    Hi Robert,

    I reviewed your information and noted that it is generally not recommended to keep PFM/SYNC floating. Either connect this pin to GND for FPWM or to VDDA for PFM operation. Please note section 8.4.2 of the datasheet for more information.

    It also looks like the CNFG pin is a bit far from the configuration values provided in Table 8-2 and the ranges given in the EC table under "Configuration." I have included the excerpt in the datasheet below for your convenience:

    Please ensure that R27 is within the correct ranges for your desired operation.

    If these two items still do not resolve your issue, I have a couple more questions to be answered for us to better assist you:

    • Have you tried starting up the device without a load attached, i.e. disconnecting the E-load. In this case does the device properly start up?
    • Is this device in isolation? Are there other circuits or schematics connected upstream/downstream of the power supply/load respectively. If this is the case, can you please test the circuit in isolation?
    • Can you probe EN and the VCC pin as well when conducting these tests?

    Thank you,

    Joshua Austria