Problem with driving a circuit using boost converter from Li-ion Battery

[nitish111]

Hi All,

I have a device that runs on 9V battery. It consumes about 100 mA @ 8.5 V. I am trying to replace 9V battery with rechargeable Li - ion battery (1 cell nominal 3.7 V). I have connected Li-ion battery to input of LT3580 (schematic attached). The circuit works fine when the load is not connected. The output of LT3580 is around 9.56 V. When I connect the load output voltage of LT3580 drops to battery voltage. According to data sheet this configuration should give me around 500 mA but I am not getting expected output. 

http://cds.linear.com/docs/en/datasheet/3580fg.pdf

[bktemp]

It sounds like current limit is tripping to early, maybe a bad pcb layout?

[sanwal209]

are you using the right inductor? There are few mentioned in datasheet

[nitish111]

Thanks for the reply. Here is my PCB layout. All traces are 10 mil. Do you think there is a problem?

I took a inductor I had handy with me. I will order inductors specified in datasheet. Any other suggestions?

[bktemp]

The layout is most likely the problem.
Look at page 15 in the datasheet. It describes all important traces: The switching node must have short and thick traces, much shorter than your ones. Compare the high frequency switching path between your layout and the layout in the datasheet.

[Neilm]

Thanks for the reply. Here is my PCB layout. All traces are 10 mil. Do you think there is a problem?

I took a inductor I had handy with me. I will order inductors specified in datasheet. Any other suggestions?

Calculate the current that is flowing in the inductor. If you don't know the parameters of what you have it could easily be saturating. Be aware that manufacturers all specify the current capability of their inductors in different ways, some might say the value has reduced by 5%, others use 10%. 10mil sounds a bit thin for this but I would not expect this failure mode.