I don't know this for certain but I suspect the issue comes down to having a voltage from the PIC landing on the FTDI chip when it is de- energized. Many times the specs will limit an input voltage to some low value over Vcc but don't really discuss what happens when Vcc is 0 or undefined. --- In piclist@picl..., "tadaosystems" <flipflops67@h...> wrote: > I've successfully used a bootloader in combination with an FTDI 232BM > USB chip for simple serial communication to the PC, but I have a few > questions about how best to power it. > > The application in question is battery powered, so I want to conserve > as much as possible. Can I power the PIC off the battery, and use the > power rail coming from the USB port with a ferrite bead to run the > FTDI chip? Most examples show the entire circuit either powered by > the battery, or by the USB port, which isn't quite what I need. > > If it is not possible to have the USB port power the FTDI chip while > the battery powers the PIC, what about powering the FTDI chip right > off one or two of the PIC ports? I believe the normal current draw of > an FTDI 232BM is less than 25 mA at all times. > > I understand you can put the FTDI chip to "sleep", but I would rather > not have it draw any current since it will rarely be used.

I've successfully used a bootloader in combination with an FTDI 232BM USB chip for simple serial communication to the PC, but I have a few questions about how best to power it. The application in question is battery powered, so I want to conserve as much as possible. Can I power the PIC off the battery, and use the power rail coming from the USB port with a ferrite bead to run the FTDI chip? Most examples show the entire circuit either powered by the battery, or by the USB port, which isn't quite what I need. If it is not possible to have the USB port power the FTDI chip while the battery powers the PIC, what about powering the FTDI chip right off one or two of the PIC ports? I believe the normal current draw of an FTDI 232BM is less than 25 mA at all times. I understand you can put the FTDI chip to "sleep", but I would rather not have it draw any current since it will rarely be used.