LM3481: LM3481 SEPICE Eval board measurments

Part Number: LM3481


I have the LM3481SEPICEVAL board and I was doing some measurements and have a few questions/concerns.

1) The datasheet for the eval board has a graph on page 5 for "Efficiency at Vout = 12V. With an input of 12V it says it has almost 90% efficiency.  When I powered it up, I have 12V in the input and it reads 12.11 volts on the output. I have an electronic load with a constant current set for 1Amp. But the input current from my power supply is 1.48Amps.

Vin = 12V

Iin = 1.48Amps

Vout = 12.11V

Iout = 1Amp

Power in = 17.76W

Power out = 12.11W

Efficiency = 12.11/17.76 = 0.68 or 68% efficiency.  I must be missing something. Could you help me out? 

2) Eval board datasheet also says on page 1 that the 12V output option can have a input voltage range of 4.5-18V. With an output current of 0-1.25 Amps

Even with no load, and 4.5V on the input, it does not output 12V. It is not able to do it. The only way I can get it to output 12V is to start with a higher input, wait for it to get to 12V then lower it to 4.5V.

3) With a 5V input on power up, it is able to see the full 12V output. But this won't work with any load. I put a 100mA load on there and the voltage drops down to almost 2V.

I need reliable operation at 5. I need to boost it to 12V with 600mA. Which will be an input current of about 2Amps. Also this is a battery application, so this low efficiency is no good.

Please let me know your thoughts on this.