LP5907: Questions of LP5907

Hi Jimmy,

This looks like the device is cycling in and out of thermal shutdown. What is the load current? The DQN package has relatively poor thermal characteristics because of its small size, so it cannot handle a lot of power dissipation. Also, what does the load current look like? Is it closer to a constant DC load, or is it pulsed or something like that? 

Regards,

Nick

Hi Nick,

load current is light load condition.

Thanks a lot!

Jimmy

Hi Jimmy,

How light is light? Can you provide a current in Amperes? Otherwise we can't do any calculations. 

Thanks,

Nick

Hi Nick,

Thanks for your great support!

 current is 10~20mA. 

Many Thanks,

Jimmy

Hi Jimmy,

I see the picture of the board, but I can't see what the surrounding copper looks like. Can you share the layout for the LDO? I think this is a thermal issue, so I want to verify the layout. How many layers is the board?

What does the load waveform look like? Is it 10-20mA DC or is it more of a pulsed load? 

Thanks,

Nick

Hi Nick,

please refer below, thanks a lot!

Many Thanks,

Jimmy

Hi Jimmy,

This layout looks fine for thermals with this relatively light loading. Can you please provide waveforms showing the load current, input voltage, and output voltage, zoomed in to one of the output voltage drops? If it is not possible (or overly difficult) to get the current waveform, then at least a zoomed-in waveform of the input and output voltage will be helpful. 

Regards,

Nick

Hi Jimmy,

On second thought, I wonder if the fact that the ground pour is somewhat pinched off is limiting the heat spreading. Do they have a thermal imaging gun to help here? I ask because the waveforms that we have look exactly like thermal shutdown cycling. 

Regards,

Nick