Switching Regulator IC, 5V output, in Parallel with Aux USB supply.

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dan_bat2

Joined Jan 1, 2018
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I've had an issue in the past (not medical, I'll keep to the topic) whereby a switching regulator output was becoming a sink while a USB device was attached. It could of been particular to that IC, the TL2575HV-5, or perhaps it's the nature of switching regulators reliant on freewheeling diode and an inductor? The current seemed to be flowing back through coil (hot). I may have had the orientation of the catch diode wrong, however, I don't think that was the case because the regulator worked fine the rest of the time.

The circuit I have is being powered from a DC source up to 65V. I require 5V (100mA) and 3.3V (500mA) both for the digital circuitry beyond.
I've discovered the MAX5035 (MAX5035BASA+) switching regulator, 5V output, which I could potentially power the 5V components with, then simply a 3.3V REG1117 linear regulator afterwards.

I would like to power the 3.3V components with auxilliary USB as an option, most simply done would be to connect the USB 5V and the switching reg's output together. Has anyone experienced an issue doing this? If so, what's the workaround? How stable is the switching reg's output? Good enough for amplifiers with gain of 100 outputting 4.5V?

The MAX5035 datasheet illustrates the 5V output clearly. Would connecting 5V here to USB 5V cause any issues? This I would like to know.

I think the safest solution might be to switch down to around 6.5V, then linear to 5V and 3.3V. External USB 5V definitely won't go back through the linear reg.
Would be efficient to keep component numbers down by other means perhaps.. Hmm..
 
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