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LMZ modules: Output caps on opposite side of PCB?
Is it acceptable practice to put the output capacitor of an LMZ1420x module on the opposite side of the PCB? If so, are there any PCB thickness limitations and recommended number and size of vias?
There is nothing wrong with putting the output caps on the back side of the PCB; However you should really control the schematic net connections such that the current leaving the VOUT pin of the module goes through the PCB in a via(s) that does not yet connect to the VOUT plane. The current path should go from VOUT all the way to the output capacitor terminal and then be distribute to the loads. This will provide the quietest VOUT possible by forcing the output current to go past the capacitor terminal first. For 0.62" thick PCB my associate says that 1A per 12 mil via is a rule of thumb to go by. So more than 3 vias for a 3A device. Larger vias can support more current especially if you plug them with solder. Thicker boards will need a larger hole to support 1A per via.
On the other hand, the input capacitor should really be adjacent to the VIN and PGND since this has fast discontinuous current steps.
Let us know if you need further clarification.
Alan Martin TI/SVA
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