Hi,
I want to build up a sepic converter with the lm3481, but it din t work. I used the Webbenchdesigner (Vin=6.5V-18V, Vout=15V, Iout=1.4A).
So I ordered the parts of the bom and built up the schematic on a stripboard. At the first start up I used a load with 100 Ohm in order that the output power was by 10 % of the complete output power. You can see a picture of an oszi screenshut of this constellation.
On CH1 is the outputvoltage visible. The voltage level, beside the peaks by switching, is ok. On CH2 describes the Isense pin (PIN1 lm3481), CH3 the gate voltage (DR pin) and CH4 the voltage over the inductor Lout.
Suspicious are the high peaks at the Isense pin (nearly 500mV) on CH2. According to the maximum ratings of the data sheet lm3481 the voltage range is limited by -0.4V to 500mV.
If I increase the output power (40% of the max. output power, load = 27 Ohm) a noise of the lm3481 is herable. After a short while (1 min) the lm3481 is destroyed or doesn t work any more. The peaks on the Isense pin also increases up to 1V. I guess that the high peaks on the Isense pin destroy the component. I tried to dissipate the peaks by using a diode to ground, but the after this modification the outputvoltage breaks down.
My question is what causes this high peaks or is it maybe a complete different problem that the component is destroyed. I red in the data sheet that I should keep the AC current loops as small as possible (loop between MOSFET, DIODE and CAPACITOR). I don t use a pcb, so my loop is comperatively quite big. Can this be the reason for the peaks?
I would be very glad if somebody can help me!
Best wishes
Florian
