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LM25117 without Rsns (sense resistor)

Tomas Pelka
Prodigy 100 points
Other Parts Discussed in Thread: LM25117

Hi.

I am designing power supply with following parameters:

  • Input voltage: 10 - 30 V DC
  • Output voltage: 5 V DC
  • Max. output current: 12 A

I used Webench design for LM25117 with one modification - I omitted Rsns resistor (instead there is a short).

Problem is, that my power supply doesn't work with heavier loads (tested only with resistive load - bulbs) - I mean something about 10 A, 5 V. In this case the power supply starts to be noisy (you can hear whinning) and doesn't provide enough power.

Is there any other purpose of Rsns except output current sensing and limiting.

Do you have any advice where to look at first?

Thank you for your help.

Here is the schematic and board:

  • 0
    TI__Mastermind 21720 points
    Tomas,

    The current sense resistor is imperative as the LM25117 is a current mode controller. Effectively, without the sense resistor the converter is in voltage mode control which is not how the IC was designed to operate. Please add the sense resistor back to the circuit from proper operation.

    -Garrett