Other Parts Discussed in Thread: TPS54560, , TPS23861, TPS23861EVM-612, TIDA-01463
We've had a board developed for us that uses TPS2372 as the PD interface. This then supplies power to a tps54560 switcher set to supply 12V at 2A. 3x MR16 LED bulbs are to be connected to the output of the PCB. There is also a switch circuit to allow the LED bulbs to be turned on/off. The MR16 bulbs used are 5W LED bulbs that can work on either 12V AC or DC (constant voltage). I expect that within the bulb, there is circuitry to drive the LED with constant current and also allow dimming.
Having received the PCB's for test, i have noticed the following -
- If i supply 48V through the input RJ45 from a PSU, on pins 1,2 and 3,6, then I can turn 3x bulbs on/off without issue.
- If i connect the PCB to our PoE PSE (based on tps23861) then i can only load with 1x LED bulb. Any more than 1x LED bulb results in the light initially turning on then it turns off immediately, so a brief flash.
- I have repeated (2) using the TI tps23861evm-612 eval board with the same result.
- Repeating (2) & (3) with the TI PoE commander software monitoring the PSE, i dont see any fault flags for Icut which is set for 110-686mA. Are there anyother registers i should pay attention to?
- I have replaced the LED bulbs with a DC load set to drawn 2A at 12V. This works and i see the power draw expected when i turn the output on/off.
In (2), (3), (4) and (5) the PCB correctly classifies as class 4 and is confirmed as such with the PoE commander software. Even when the bulbs are switching off in (2) and (3) the classification is never re-done.
Could you suggest where to look for the source of the turn off in (2) and (3). To me, the PSE is supplying power correctly as the PCB classifies and maintains this, plus there is no error flag in PoE commander.
I believe that the tps2372 might be causing the blip, but i need to investigate further tomorrow, but i cant explain why all is well in scenario (1).