We have the MP8009 as PoE DCDC in our design.
We now want to use the AUX input additionally. In the DevKit and sample schematics a variant is shown to use 48V for AUX input.
We want to use lower voltage AUX, e.g. down to 24V. We understand the datasheet in a way, that from 8,5V AUX operation shall be possible and we have to implement the voltage divider at the AUX pin in a way to level that between -2,3V and -6,5V from Vxx/Aux-Imput to bring the converter into the right mode. We modified the voltage divider on the Evalution board in that way but are not able the use lower voltages than approx. 32V with load connected.
Are there any additional application notes or samples for other AUX voltages than the 48V sample?
HI tiemo.krueger,
Can you confirm that your VDD-VUX > 2.3V and VDD-VSS > 8.5V? Otherwise, the AUX will not be swapped over. For assistance with choosing the resistor values, you can use the equation below:
Where:
Regards,
Vinh Tran