I'm using the LM2678-ADJ and have the output set to 4.4V. This is a somewhat arbitrary value during my course of testing a circuit including this regulator. I'm connecting a litte more than a 2ohm resistive load across the output, so it should draw less than 2.5 amps; well within the regulators 5 amp rating. I'm using a 100uH toroid inductor, rated for >8 amps, a 1000uF cap at the input, and 470uF at the output. Voltage is set with a 1K and 2.7K resistance.
Here's the problem: when I raise the input voltage to more than about
17V, the regulator's output starts to reduce. At 25V input, the output drops to about 3V. The output is still pretty clean. This seems like a feature, but it's a bad one in my design, and I can't find anything in the datasheet regarding it.Any ideas?