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LMR16030: 5V Drops to ~600mV when 100mA load applied and is very noisy

Oliver George
Prodigy 10 points
Part Number: LMR16030

Tool/software:

I am having issues with a LMR16030S, the output is noisy even under no load, and then when load is applied (using a resistor) the voltage drops to ~600mV. The circuit is very noisy - both on the scope output and audibly

If the soft-start capacitor (C12) is removed, the voltage will stay at 5V, but the noise is increased to around 1V p-p, likewise if the inductor is reduced to 6.8uH the same behaviour occurs.

The schematic (pictured), is the same as the recommended circuit using the TI power designer/datasheet. Vin is 24V and max load is ~500mA  

  • 0
    TI__Guru* 78370 points

    Hi Oliver,

    Thank you for designing with LMR16030S. Could you clarify the following, so we can better understand your issue?

    • Do you build a Printed Circuit Board referring to our EVM, or you are using a bread board with loose wire connections? Can you show a photo picture of your circuit, 
    •  What is your input power source's current limit?
    • What is your inductor part number?
    • Could you capture a SW waveform, along with Vin and Vout, under  100mA, 250mA, and 500mA, respectively?

    Also please note that we will be out of office for the rest of the week (Independence Day holiday), and return to work next week. 

    Best Regards,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 10 points

    Hi Youhao,

    I have a PCB, see photo:

    I realise the GND plane is not as recommended on the EPAD, I have also tried to resolve the issue by filling in the thermal relief.

    Below are the waveforms you requested, blue is Vin, Pink is Vout, Yellow is SW:

    No Load:

    100mA:

    250mA:

    500mA:

    The inductor is WE 74405042100

    Thanks

  • 0 in reply to Oliver George
    TI__Guru* 78370 points

    I will get back to you next week.  Currently we are off for the holiday and please do not post here until next week.  I am writing this on my mobile phone. Thank you for understanding.

  • 0 in reply to Youhao Xi
    TI__Guru* 78370 points

    Sorry for the delay due to holidays.  Thank you for sharing the info.  I worry your layout may cause the noise issue because the input switching current takes a long way to close.  Please also refer to our EVM in which the input switching current closes in a very small loop.  

    Vs EVM input switching current loop (white)

    When you update your layout, please move your C8 away to allow the direct gnd connection between the IC under-pad and C9-11 gnd polygon. Also pay attention to your Feedback signal trace, which should be away from the switch node polygon. 

    You may also order an EVM and modify it to fit your design, and get a quick test.

    Hope this helps. 

    Regards,

    Youhao