Hi,
I happen to be experiencing a very similar issue with the same boost controller. Found the original question but sadly, no answer.
In my case, I have two boards prototyped, one is working fine, the output voltage is 5.15v as expected. The other board has the same layout, but is only outputting 3.4x volts while the input voltage from a battery is 3.8x volts. I've also tried other input voltages/batteries found that output voltage is always 0.4x volts less then the input voltage (ex: tried a battery with 2.66v and would output 2.21 volts). At the moment, there is almost no load (only powering a controller that is doing nothing).
If it helps, attached is my schematic and layout.
*In my layout, I though perhaps an issue might be the ground connection from the input capacitors, C1 and C2 are "far", but I've temporally made a much shorter connection from those pads to the power ground to see if it was the issue. It didn't make any difference. On the working board, it seems to be functioning okay despite this.
Assembly-wise, I've also made sure that there are no shorts and pin connections are correct.
Tim
