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LM5145-Q1: LM5145-Q1

Venu Gopal
Prodigy 90 points
Part Number: LM5145-Q1
Other Parts Discussed in Thread: LM5145, LM5146

Dear Team,

Previously I have asked few questions on the LM5145 IC, and we performed testing all most all the issues. Now I have prepared new layout as per guidelines given in the datasheet and suggestions given by David baba from Texas support team. Now, my gate pulse is very clear, and IC is turning on, but I am not getting expected output voltage as per design calculations. for 24V output voltage I have selected feedback resistors of 2.49K and 72.3K but I am getting output voltage of 9.5V. Could you please provide what will be the maximum current provided by this particular IC: LM5145? I am attaching schematic files below kindly look into it.

Thanks in Advance

  • 0
    TI__Guru 68757 points

    Hi Venu,

    Please send a completed quickstart file for this design.

    --

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Guru 68757 points

    Here are some quick comments on the schematic:

    1. Remove the 0.1uF snubber caps - the vlaue is way too high. 220pF is a good starting point (and if the layout is good, snubbers are not required).
    2. the ILIM time constant is typically 6ns per the datasheet.
    3. Remove the 5Ω on the low-side gate - such resistor is neve needed and may cause issues related to Cdv/dt shoot-through.
    4. Change the gate-source pulldown resistors to 10k.
    5. Add an electrolytic input cap for stability.
  • 0 in reply to Timothy Hegarty
    Prodigy 90 points

    Dear sir,

    I have resolved that output voltage issue by adjusting the feedback resistor (calculated as per datasheet equation). Now the issue is at one point of time the output voltage is dropping to 10V from 24V. What may be the reason for this sudden voltage drop. I have attached oscilloscope image below kindly let me know your valuable comments.

    Thanks in advance

  • 0 in reply to Venu Gopal
    TI__Guru 68757 points

    Hi Venu,

    So Vout drops to 10V and stays there? Check the FB pin is at its nominal value of 0.8V.

    This sounds like a PCB layout issue. Ensure that the FB trace is as short as possible and that the lower feedback resistor is directly across the FB and AGND pins. See the layouts for the LM5145 and LM5146 EVMs for reference.

    --

    Tim