LM1086ILD-3.3/NOPB Operation

[drkidd22]

Hello,

I'm using an LM1086ILD-3.3/NOPB to power a pic. The input is 5V, I had to solder wires to the pads due to a bad foot print layout, but I noticed that if I only use the bottom center pad as the output the voltage will not be 3.3V with load or no load, it was more like anywhere from .8V to 1.1V. I then soldered the rest of the output pads and tied them together to the bottom center output one with 30AWG wire. This fixed the issue for me and everything is working fine with a load or no load. I'm curious to find out why it worked this way. Any insight will be appreciated.

 

[bountyhunter]

The center pad is the substrate of the die. The other Vout pads may have sense leads bonded to them. The data sheet does not have any info on it, but it is always advisable to tie all pins together of the same type.

 

[Rich D.]

I have seen more than a few chip specs that state that some ground points are for heat sink attachments, while others are tied to the ground circuit's current paths.

In some cases multiple ground points are designed specifically to tie together external to the chip. There may be a small conduction path or leakage from multiple ground pins, but a better conductive path is usually needed for correct operation.

My general rule-of-thumb concerning ground connections: All or nothing. Do not even bother to try to run a chip without all grounds tied together in some way unless you have a specific strategy that requires splitting them up.