LM5116 andTPS54386 both sides of PC board

Ed Wilinski

Other Parts Discussed in Thread: TPS54386, LM5116

Hi, I'm trying conserve board space so that my end product will be small I would like to have it a little bigger than a 4.3LCD display. We are usning the LM5116 and TPS54386 to step down our input voltage to 12 volts with the LM5116 and using the TPS54386 to give our main 3.3V supply and 3.8volt supply for our cell modem.

With both power supplies on the same side it's taking a 1.7inches by 1.7 inches of PC board space.

My question can 2 switching regulators be on opposite sides of the board above each other for example the LM5116 is on the Bottom side and the TPS54386 on the top side?

Can the support components for these IC's be on both the top and bottom instead of the same side and which components have to be on the same side?

Thanks,

over 10 years ago

0 JohnTucker over 10 years ago

TI__Guru**** 191445 points

In general you can place circuits on opposite sides of the PCB. You will need to be careful of thermal performance. Both of these ICs use exposed thermal pads for heat dissipation. these pads need to be connected to GND copper fills or planes. So for your case, you will probably need a 4 layer PCB with an internal GND plane. You will likely not want to place the two ICs directly opposite each other as there will be thermal vias required. As far as the external components are concerned, it is acceptable to place them on the opposite side from the IC. the primary exception to this is the input bypass capacitors. I highly recommend they be placed on the same side as close to the IC VIN and GND pins as possible. I usually try to place and rout the output circulating current path (IC SW node, output inductor, output capacitors and return to IC GND) on the same side as well but I have seen many successful designs where they are placed on the opposite side to save board space. From a noise perspective, the critical signals are the SW nodes and feedback paths. Keep the SW traces short and rout FB traces well away from them.