I'm using the MAX5995B in a configuration very similar to the Reference Design 1266 (PoE++ MAX5995b with MAX5974A Flyback Converter).
I'm surprised by the temperature of the MAX995B chip. It's a QFN package soldered on an internal ground plane on my PCBA (even if this ground plane is not so large).
When I disconnect the output of the MAX5995B part of the circuit, I measure an average current of 7mA (variations from 5mA to 13mA), which seams to be equivalent to the current of the MPS feature since there is no load. In this situation I get a case temperature of 48°C (ambient is 25°C) which is, I think, a bit high.
When I connect a load (from 35mA and up to 160mA), There is a constant quiescent current into MAX5995B of about 13mA; which seams very high since the MPS feature should be off when sufficient current is provided to the load (over 28mA). The case of the MAX5995B is at about 65 to 70°C which is very high for such a chip which didn't do anything when the load is connected in a PoE system.
Here are some questions:
- Do you think these values are normal?
- My LED output is stuck at ground (same as reference design). Could it impact the quiescent current?
- Any idea, based on reference design, of what could impact quiescent current in active powering mode?
Thanks for help!
