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LMR62014:LMR62014 Heat generation issue when boosting

kim dayoung
Prodigy 20 points
Other Parts Discussed in Thread: LMR62014, LM3405A

Using your LMR62014, we designed a circuit that boosts to 5V -> 12V.

It is designed in the same way as the connection plot on the two pages of the datasheet. (10uF added to input)

However, when the LED bars (Diode turn-on 3.7V, 250mA, two series) are connected and turned on, heat of more than 100 degrees toward the DCDC circuit is generated.

In the case of LEDs, an LED driver is used and PWM control is performed by receiving a 12V input.

I received a reply from the TI chat that there is nothing wrong with the circuit.

There seems to be a problem with the LMR62014 circuit currently designed because there is no problem with heating when outputting 12V by connecting the LMR62014 demo board to the PCB.

The reason is
1. Artwork Problems
(5V, 12V adjacent to or different power lines)

2. Part selection problem (size, internal pressure, etc.)

Could you tell me why the heat is generated?

Also, I would like to know the difference from Demoboard Schematic, not Datasheet connectivity.

 

     

  • 0
    TI__Expert 8735 points

    Hi dayoung,

    Thanks for reaching out. Could you pls describe your question in English, we do not understand Korean... Thanks.

    Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 20 points

    I'm sorry. I posted it in Korean because I was mistaken while translating it into English. I fixed it. Thank you.

  • 0 in reply to kim dayoung
    TI__Expert 8735 points

    Hi dayoung,

    From my understanding, in your application, the output of LMR62014 is connected to a LED driver, then the LED driver is connected to LED bars. And there is no problem when it's not connected to the LED driver, right?

    So I want to know what is the output current of LMR62014 in your application? Have you measured the VOUT, SW or any other waveforms?  Thanks.

    Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 20 points

    Hi, Nathan

    Thank you for your quick reply.

    Yes, there is no problem even if it is not connected to the LED driver. Currently, LED drivers consume more current than I thought.

    When the LED bar is connected and measured in my application, 760mA is measured at the 5V input.

    A 0.4 resistance current limiting resistor was inserted using the LED driver (LM3405A) of TI to allow a maximum IF to output 500 mA.

    Currently, it is set to output 350 mA current through PWM control.

    When the maximum value of Load Current vs Vin was checked in the datasheet, it was confirmed that 500 to 550mA was Max when Vin = 5V and Vout = 12V.

    It is thought that heat is generated because the load current exceeds the allowable value.

    I don't understand that I consume more current than I currently set.

    What part should I check? Also, I'm attaching the measurement waveform, so please check it.

    Thank you.

    Dayoung

      

       

  • 0 in reply to kim dayoung
    TI__Expert 8735 points

    Hi dayoung,

    It seems that VOUT of LMR62014 is a little abnormal, but I am not sure it is caused by LMR62014 itself or by load.

    Have you tested post staged circuit of LMR62014 separately? I mean you can connect a 12V DC voltage source to the LED driver, by this way you can test weather the LED driver works well and you can also measure the input current of LED driver, this current is also the output current of LMR62014, you can check weather this current is larger than the maximum output current of LMR62014.

    Best Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 20 points

    Hi, Nathan.
    I appreciate your prompt reply.
    The LED wire connected to the TP3 (VLED) end of the LED driver was disconnected and the current was measured with a multimeter.
    At this time, it was confirmed that ~290mA was measured.
    I understand that the load current of LMR62014 is ~530mA, so I don't think 290mA is a problem.
    However, when 5V is input and verified through the power supply, the current flows about 760mA.


    Could you please let me know part am I mistaken about?

    Thanks.

  • 0 in reply to kim dayoung
    TI__Expert 8735 points

    Hi Dayoung,

    Thanks for your update. I  found that there is a little problem about your layout. The path of SW-diode-C7-GND is too long, this path should be as short as possible, otherwise it will work unexpectedly. You can take this guidelines in datasheet as reference. Thanks.

    Best Regards,

    Nathan