usb bus power burning out chips?

slcott

I have a design that integrates a propeller programmer onto the board so that one only needs a USB cable to reprogram my board. The USB bus power is powering other components on the board and there only is a also decoupling capacitor, 0.1 uF. There is also a tri-m power supplying 5V to the rest of the board as well. I'm finding that two of my chips are burning out, a micromega fpu and 24 bit ADC and I suspect it is the USB bus power that is to blame. The micromega is powered off a 3.3 V voltage regulator and the ADC is powered directly off the 5V supply lines.

I've read about overcurrent or overvoltage events when plugging into a USB cable. There are various designs I have come across that call for ferrite beads or zener diodes or even pmos transistors to attenuate, chop, or turn off spikes in the power that may be destroying these ICs. Does anyone have any experience with this?

slcott

Pictured is one of the chips on my board that keeps dying, the ADC. You can see that it is powered directly off the USB power.

Phil Pilgrim (PhiPi)

Have you even looked at the FTDI documentation as it pertains to bus-powered devices? If you have, you've obviously ignored it at your peril. If you have not, please do. It contains a wealth of information. Some of it is wrong, however. This thread will help with some of its deficiencies:

http://forums.parallax.com/showthread.php?p=699564

-Phil