Problems with ISL9120, no Boost, only Buck

Hi,

I’m trying to incorporate the ISL9120 in to my product. I built some prototype breakout boards to test the device and understand more about it, but I cant seem to get them to work.

I am using the fixed 3.3v version of the device. I had 5 boards made and they all seem to do the same thing. They give me 3.3v output when Vin is above 4.5v (4.5v to 5.5v), but then the output drops proportionally, as Vin is reduced, roughly Vout = Vin -1.0v below 4.5v all the way down to 2.0v.

It’s like the boost circuit isn’t working, just the buck circuit?

The circuit is so simple, I don’t think I have made a mistake.

Any ideas why its behaving like it is?

Circuit diagram, board layout and component specs below.

Thanks.

Jon.

C1 = 10V 10uF X5R ±10% 0603 Multilayer Ceramic Capacitor (Samsung CL10A106KP8NNNC)

C2 = 6.3V 22uF X5R ±20% 0603 Multilayer Ceramic Capacitor (Samsung CL10A226MQ8NRNC)

L1 = 3.18A 1uH ±20% 1008 Power Inductor (Inpaq WIP252012P-1R0ML)