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LM25149-Q1EVM-2100: At 6Vin, the 5V output is not regulated for output currents greater than 2.5A

Part Number: LM25149-Q1EVM-2100
Other Parts Discussed in Thread: LM25149,

We want to design a 12V->5V circuits that is very efficient from 5mA to 4A. We also want the output to maintain regulation as the input drops down to 5.85V. I looked at the LM25149 and was able to create a design using Webench that seems to fit our requirements. I purchased the LM25149-Q1EVM-2100 so that I could test the IC.

With the unmodified EVM, I took some measurements and recorded the following:

Vin = 12V, Vout=5.05V, Iout=2.72A, efficiency=89%

Vin=6V, Vout=4.87V, Iout=2.59A, efficiency=81%

The efficiency recorded for Iout=10mA was ~80%.

I changed the design to what Webench specified (L=5.6uH and change R13 - RT pin - to 53.6K) and recorded the following:

Vin = 12V, Vout=5.05V, Iout=2.62A, efficiency=93%

Vin=6V, Vout=4.9V, Iout=2.51A, efficiency=81%

Vin=5.85V, Vout=4.77V, Iout=2.44A, efficiency=81%

The efficiency recorded for Iout=10mA was ~90%.

The modified design gives me a much better efficiency as Webench predicted but both versions start to lose regulation at a low Vin for Iout>2.5A. According to Webench, the design should be able to output 5V with a Vin of 5.85V @ Iout=4A. The compensation circuit of the EVM is not the same as Webench and I wanted to know if this is causing the design not to output 5V with a Vin down to 5.85V.

Also, I wanted to double check if the unmodified EVM should also regulate Vout=5V at Vin=5.85V since I am not seeing this.