UCC28881: UCC28881 quiescent current: <125 μA, what needs to be debugged?

Hello Eagle,

Thank you for your interest in the UCC28881 and TIDA-01097.

The TIDA-01097 reference design is designed for operation on 110Vac. To operate from 230Vac, the input stage components need to be rated for the higher peak voltage. Also the transformer needs to be redesigned.

The quiescent current of TIDA-01097 is <125uA under no load conditions at 110Vac. After a redesign for 230Vac, it may be difficult to achieve <125uA at 230Vac, because other leakage currents and losses are higher than with 110Vac.
When your 5V output is loaded to 400uA (2 mW), conversion efficiency is low. The TIDA-01097 design guide shows efficiency is about 14% for a 0.45mA load before the LDO (page 19). Using that as a guide, 2mW/0.14 = ~14mW input power for a 155Vdc input.

To scale this to a 230Vac input, I would estimate that the 14mW increases to 16mW to account for AC to DC rectification losses and apply a 0.1 power factor (estimate) to arrive at 160mVA at 230Vac. This equates to 0.696mA rms input current, which is over 5X your target.
This tells me that you cannot have a 400uA load on 5V output and expect to get anywhere near 125uA input current at 230Vac, even after optimizing. I suggest to reconsider your target of <125uA, and see if a higher input current with lower output load can be acceptable.

It is not clear if <125uA can be achieved at 230Vac with no load on the output, but it may be possible. You'll have to test your board in that condition. Make sure that all of the components for the design are chosen for lowest possible leakage current at high voltage.

Regards,
Ulrich