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LMR14030SDDAR (8 pin SOIC) power supply IC

Shankar Raj
Prodigy 80 points

Dear Sir/Madam,
I am using LMR14030SDDAR (8 pin SOIC) power supply IC in my prototype project.If everything is fine i need to immediately go for mass production. My input will be 7.5V to 36V and i have design to get an output of fixed 5V. But the output is already only 4.7 to 4.8V. From this i will be generating 3.3V, 1.2V, 8V.Since LMR IC supports and output current of 3A.With 3.3V only enabled the performance is OK, but when i start using 1.2V the 5V output is unstable and 5V drops down to 4.5V or less. Please help me out. I have nearly followed the same design as the EVM board. If needed i will share the schematics of the power supply section with you. This is very critical phase of the project.

Thanks and Regards

Shankar.R

  • 0
    TI__Genius 10095 points
    Can you please share the schematics for your design? It sounds like you might be hitting the current limit. How much is being drawn from your input supply and what voltage are you testing at for these tests?

    Marc
  • 0 in reply to Marc Davis-Marsh
    Prodigy 80 points

    Hi Marc,

    Please find attached the schematics of the power supply design. When powered from my DC variable supply, i can see 500 mA is being drawn from my board. But my board should not draw more than 300 mA max.

    I am testing for wide range of input right from 8V to 36V.

    Thanks and Regards

    Shankar.R2350.Power supply.pdf

  • 0 in reply to Shankar Raj
    TI__Mastermind 23825 points

    Hi Shankar,

    Do you have the screenshot of the waveform of the switch node and the inductor current when you apply the 1.2V rail?

    Also, what happen when you just apply the 1.2V rail by itself? Does it still unstable?

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Prodigy 80 points

    Hi Arief,

    Thanks a lot for the response. I have not checked the waveform.

    But the 1.2V generation happens in 2 places, one gets generated from the microcontroller internal 1.2V regulator when 3.3V is applied to the micro.

    I am currently using the same. The other external 1.2V is being generated by the FAN2558S12X regulator, which i am planning to use whenever the internally generated 1.2V is not sufficient.

    I need to check the condition that you have mentioned (Also, what happen when you just apply the 1.2V rail by itself? Does it still unstable?). Let me check it out.

    Thanks and Regards

    Shankar.R

  • 0 in reply to Shankar Raj
    TI__Mastermind 23825 points
    Yes, i am a little bit suspicious with the boost section on your power supply. How much load current on the 8V rail?
    I am thinking of removing R98 and just run the 5V supply to get the 1.2V and see if the stability issue still there.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Prodigy 80 points

    Hi Arief,

    I have currently isolated the 8V supply, i am not using it. 8V section will draw a mx current of 150mA to 200mA. I have checked by enabling the internal micro 1.2V. The external 1.2V gets generated but it is not used. I am planning to use the external and stop using internal 1.2V from micro. Let me check the performance.

    I see a drop of 2V to 3V at the 50 ohms/4W resistor that is placed just before the 36V zener diode. Because of this my input voltage from the DC variable power supply should be kept at 9.5V to get proper 5V output from the LMR13040 IC.

    Thanks and Regards

    Shankar.R

  • 0 in reply to Shankar Raj
    TI__Mastermind 23825 points
    Hi Shankar,

    Yes you are correct the drop caused by the 50 ohm resistor will affect your minimum input voltage. You can try to bypass it too just for debugging purpose to eliminate the drop caused by it. Is the zener only used for transient?
    We have an app note for automotive line transient but you might be able to change the zener with the combination of FET and zener as an OVP circuit
    www.ti.com/.../snva717.pdf

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Prodigy 80 points

    Hi Arief,

    For now i am using by shorting the resistor in place of 50 ohms. I have given the board for testing all other interfaces, and to identify if there are any heating issues. Total board is consuming 100 mA current. I will update you further with my other testing.

    Thanks and Regards

    Shankar.R