Help with using a boost converter

Thread Starter

Vanush

Joined Apr 19, 2008
46
Hi,
I'm trying to use a FAN5331 boost converter (www.fairchildsemi.com/ds/FA/FAN5331.pdf) but cannot get it working no matter what I try. I've followed the recommended schematic, layout as much as possible.

Here's my schematic (note that the VIN and enable pins are swapped on this schematic):



Here's my layout:



Here's what I get on the switching node (SW to GND)



Note that 1.6 MHz is the switching frequency of this device, and that Vpp/2 in this picture is approximately what my output should be.

Here's what I get on the output node (VOUT to GND)



PCB



As my output should be Vout = 1.23*(1 + (150/39)), I should expect 6v on that output. But I don't get htat :(!! If anyone has an idea of what I should loook into, that would be good.
 

DickCappels

Joined Aug 21, 2008
10,138
From the scope shot, it looks like your output is shorted. Could it have something to do with the grounded lead of D201? (I would check one with an ohmmeter to make sure).
 

Thread Starter

Vanush

Joined Apr 19, 2008
46
Actually after I posted this thread, I tested the polarity of the diode (BAT54) and found that it was the opposite polarity than I expected: the manufacturer that given me a variation (BAT54A) with the anode and cathode pins swapped. It's quite ridiculous, since I ordered the correct one. I have been messing around with this for many months, many PCB's, many components! Utterly ridiculous! :rolleyes:
 
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