Hi all,
I am working on a project that will connect via USB to two computers. In regular operation either or both of the ports will have power coming through them. If only one is powered, regardless of which one it is, the entire circuit needs to use the same power. My current plan is to send the incoming +5V line from each port through a selector/combiner. I could do this with a diode or, but I don't really want that voltage drop. I have found the TI TPS2115A (https://www.digikey.ca/en/products/detail/texas-instruments/TPS2115APWR/652785 ) which I believe would also work. I'm curious if there's another solution using discrete MOSFETs (or anything really) that might be a better option. Thanks! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
On 14 Jun 2020 at 15:41, Josh Koffman wrote:
> Hi all, > > I am working on a project that will connect via USB to two computers. > In regular operation either or both of the ports will have power > coming through them. If only one is powered, regardless of which one > it is, the entire circuit needs to use the same power. > > My current plan is to send the incoming +5V line from each port > through a selector/combiner. I could do this with a diode or, but I > don't really want that voltage drop. I have found the TI TPS2115A > (https://www.digikey.ca/en/products/detail/texas-instruments/TPS2115APWR/652785 > ) which I believe would also work. > > I'm curious if there's another solution using discrete MOSFETs (or > anything really) that might be a better option. Hi Josh, The functional block diagram in the TI datasheet shows how they chose do it... In essence 2 x internal N-Ch MOSFETs. First off it requires a charge pump to get high side drive. Then you start considering protection requirements (ULVO, thermal, reverse conduction, cross conduction) and pretty soon the supporting circuitry and control logic gets quite complex. Hence the specialised chip... hard to do better with discrete components. I had wondered if a simple circuit with 2 x P-Ch MOSFET's might work, thinking an extension of the 1 x P-Ch MOSFET circuit sometimes used for reverse battery protection with minimum voltage drop. Seems there would be issues with both on at the same time... in which case you may as well just have a wire connecting the 2 x USB's together (and I'm sure you want something better than that). Two x Schottky diodes is hard to beat if you can tolerate some voltage drop. -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
On Sun, Jun 14, 2020 at 5:23 PM Brent Brown <[hidden email]> wrote:
> The functional block diagram in the TI datasheet shows how they chose do it... In > essence 2 x internal N-Ch MOSFETs. First off it requires a charge pump to get high > side drive. Then you start considering protection requirements (ULVO, thermal, > reverse conduction, cross conduction) and pretty soon the supporting circuitry and > control logic gets quite complex. Hence the specialised chip... hard to do better with > discrete components. > > I had wondered if a simple circuit with 2 x P-Ch MOSFET's might work, thinking an > extension of the 1 x P-Ch MOSFET circuit sometimes used for reverse battery > protection with minimum voltage drop. Seems there would be issues with both on at > the same time... in which case you may as well just have a wire connecting the 2 x > USB's together (and I'm sure you want something better than that). > > Two x Schottky diodes is hard to beat if you can tolerate some voltage drop. Hi Brent, I agree about the chip, it seems to be an easy to implement way of managing this. I admit, part of me just didn't want to have to create a new part in Eagle! I'd prefer to avoid connecting the two USBs together. Seems like it's a recipe for damaging a computer someday. Agreed on the diodes. It's where I first went, and might not be too bad. I do have a 7 segment driver (HT16K33) and some WS2812 LEDs on the 5V rail though, so I'd have to do some tests to make sure I am not too low for them. Thanks! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
Free forum by Nabble | Edit this page |