Forum Post: RE: LM5116 Layout

Hi,

i've moved adjustable resistor from top to feedback. Problematic oscillations (250Hz) probably were caused by switching between internal regulator VCC and external source from VCCX. I've measured sawtooth signal at VOUT with maximum at 4.5V with load resistance approximately 1 Ohm. When i moved VCCX from VOUT to GND, oscillations dissapeared. During tests i had SPD30N03 as top FET, next i've changed it to IRFR540Z. Some test vith 30V VIN looks good, but when i've set VIN at 45V, chip stop working, draws ~30mA,  VOUT ~ 0V, no signals at HO, very low signal at LO and internal regulator provides VCC only ~4.4V with following waveform:

 

Have anybody idea, what i've done wrong ?

Thanks
Michal Dudka