Customer wants to convert Vin = 10.8V to 13.2V to Vout = 9V using multiple TL1963A. Output load = 1.2A. Tambient = 45degC.
One approach is to cascade two TL1963A LDOs (in KTT package) in series to share the power dissipation. Both LDOs would share a thermal pad on the topside of the board just large enough to encase the two packages. The pad would have about 20 thermal vias down to layer 7 of an 8 layer board. Layer 7 is almost all ground plane (>2500 sqmm).
An alternate approach would be to use three TL1963A devices in parallel to share the load. All three would handle the full In/Output drop, but would output to different circuits so no load ballast is required. Each LDO would handle about 400 mA load current. Topside thermal pad would be just large enough to hold all three LDOs.
Which approach would we recommend? Customer would like to get away with just two LDOs for area reasons. Seems like using three LDOs would reduce junction temp of the LDOs, but may be largest solution considering size of device and needed input/output caps.
Its not clear how to model the thermal plan of the PCB. Will the thermal vias be enough to keep the topside thermal pad at a reasonable temp?