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Charge Pump Whistle (ST662/MAX662)

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harvie

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Hello,
i've designed circuit using ST662 charge pump IC (5V to 12V; 30mA; 400kHz; Clone of MAX662) and the first prototype PCB we've assembled produces slight audible whistling under load. (We are using it to provide 12V supply for small OLED display, which draws around 20mA).
I've gone for charge pump design, since i was thinking that no inductor coil = no possibility of whistling. No i am bit disappointed.

Is this normal? Is there something that i can do about this?
 

Hi,

Ceramics capacitors have piezo effect. They generate noise when voltage varies.
Try different types, diiferent voltage, different ceramics.

If this does not help, use foil capacitors or do a PCB redesign and turn/move the capacitor.

Klaus
 

is the load a pulsating load - if so this could easily be the source of the whistle - does it do it with a steady DC load ?

else your power source to the charge pump may be doing something funny ...? you need a scope to check these things ...
 

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