I have a design where I am using the LM2594HV-12V. The load current is approximately 200mA with a short (500uS) startup peak of 295mA. input voltage is 48Vdc and output voltage is 12V. Below a measurement taken when using a lab supply to provide the 12V to make sure I know the correct 12V load current. The LM2594HV however won't startup and seems to be in some sort of overcurrent protection mode.
Current requirement (measurent when using the lab supply at 12V to verify load current the LM2594HV will need to provide):
Schematic of the LM2594HV:
PCB layout (2-layer):
Measurement taken at pin8 of the LM2594HV (using 31Vdc input - lab supply won't go up to 48V). Note: this cycle repeats at approx 7Khz and regulated ouput voltage remains at 2.95Vdc (won't rise to 12V).
Startup behaviour:
I can get the switcher to work if I reduce the input voltage to 15Vdc and lower the load current to 45mA (board is also powering external peripherals that I can disconnect to lower current consumption):
But even when using an input voltage of 15V and a load current of 45mA, the switcher gets a lot warmer that I expected (+70degC) while the inductor remains cool:
So I'm a little puzzled as to what I am doing wrong? A far as I can see I calculated the correct inductor (also tested with smaller and larger inducators but same results), the feedback line is as short as possible, unused pins are also connected to coper area to provide cooling, load current and supply voltage are within specs, ...
