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LM5175: Regulator's shutdown during load's very brief current spike

Danilo Smokovitz
Prodigy 10 points
Part Number: LM5175

Hi,

I designed a circuit based on LM5175. The circuit has input voltage of 5-30V and output of 12V-5A.

The main load of my circuit is an Intel NUC computer that consumes up to 50W during steady operation. However, during the computer's boot, it seems to be very briefly spiking over 5A. It is hard to capture the current spike on the scope by measuring the load_output, it is indeed very quick (perhaps under 1ms). When this inrush current occurs, the LM5175 causes a voltage drop on the output, to 5V. then returns after 10ms, to 12V, what causes the shutting down the load.

At first, I thought it was due to the hiccup mode, so I turned it off, without success. I tried also to remove the ISNS resistor, thinking it could be the current limiting, but that did not help.

I have then tried to measure the SLOPE pin of the LM5175, then saw it enters into capacitor discharge at same time of the voltage drop.

I am not sure on the exact cause of the regulator's shutdown, so appreciate any guidance on how to verify what's happening. I'm sharing my design https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=CB2179CAF3BEC9B0

  • 0
    TI__Guru* 78240 points
    It seems you trip the peak current limit. You should reduce the current sense resistor to prevent from hitting the limit. Since you don't know your peak load current, you can reduce the resistor gradually to see the effects. Note that, once your decided a final current sense resistor value, please put that in to the design tool spreadsheet and get the new loop compensation values as well as the newly recommended slope capacitor.