TOP245 audible noise

Posted by: alex_power on 01/18/2010

We can not continue using the TOP242 with the premature overtemp protection on my aplication PCB, but I think we can use a more power TOP to avoid the problem. So, we have bought some TOP245 units from Mouser and now we are trying to use it: the temperature test is OK, but we have a terrible audible noise around 4kHz. On the past, we have had also audio noise designing the TOP242 application, but we solved all problems. Now, we can not solve it. I attach the application schematic. We have changed the inductor, up to 1mH and we have used tantalum capacitors, but it don´t solve the problem. We have a comsumption around 170mA on the +15V supply. What do you suggest? We can down more the inductance value to try solve the problem?

Thanks in advance.

Comments

Hi,

Please let us know if connecting the "M" pin to the "S" pin solves the issue.

Regards

PI-Sarek

Hi,

Connecting M to S we reduce the noise, but not totally. We have a high 2kKz ripple on the output, which is the noise we heard in the coil and the PCB. Using a 1mH, we reduce this ripple, but we continue hearing a higher frequency noise. If we mount the inductance at 90º in the PCB (it is an open core, horizontal, parallel to the PCB), we reduce also the level of the noise significantly.

Why we have this great 2kHZ ripple using the 3.32mH inductance? How we can reduce this ripple to avoid heard it? The problem is we used a TOP242 for a compsution around 175mA in the +15V output, and now we have to use the TOP245 for the same compsuntion, and we have the noise due to the ripple. The regulation using the same TOP242 values are bery bad.

Thanks.

Alex

Hi,

I suggest you send us a screen shot of the output ripple. This will help us understand the problem.

Regards

PI-Sarek

Hi,

it is a continuous 1Vpp 2kHz ripple in the output which you can heasd directly in the coil. At this moment I can not take a picture. Changing the inductance to 1mH this ripple dissapears but we have a high frequency noise. We have solved the problem using a diferent coil. Initially we used a coil like this:

http://es.farnell.com/murata-power-solutions/13r105c/inductor/dp/1710434

and we have the noise, but changing it to a inductance like this:

http://es.farnell.com/epcos/b82144b1105j000/inductor-axial-1000uh-0-28a/dp/1644311?Ntt=1644311

we solved totally the noise problem. Any problem to use this inductance type? Do you have any experience?

Thanks in advance.