PMP22170: iM PMP22170 I NEED BOTH ISOLATED OUTPUT.

The optimal way to accomplish two isolated outputs would be to use an optocoupler feedback on the isolated output which has the highest power level. This would provide perfect regulation on that one output and reasonable regulation on the second (lower power) output under cross regulation conditions.

If an opto is not possible, cross regulation becomes a difficult issue when the primary side voltage has little to no loading (PSR) and the secondaries are heavily loaded because transformer leakage inductance degrades the output voltage regulation. In the PMP22170 reference design, the 5V output is primary side referenced and helps (to some extent) with regulation on the much higher output power isolated 10V output.

For two isolated output voltages, I recommend loading the primary regulated voltage as much as possible and tightly couple the two isolated output transformer windings. If one Gnd is common between the two isolated outputs, then create a tapped secondary where the lower output voltage is part of the higher outputs winding. This should improve output voltage extremes and cross regulation compared to two individual secondary windings.

Depending on the current/power levels, it may make sense to set the isolated output voltages higher, and use linear regulators for one or both output. This provides excellent output voltage regulation because of the LDOs, but will reduce efficiency and may create thermal challenges. If the loads are well balanced and do not vary a lot, this can be a good solution.

Consider contacting the local Texas Instruments Application Field Engineer (AFE) to discuss the specifics of your design.