Hi.
I am building a PSU board for an application with 3 different Vouts.
My input will be either 12vdc or 24vdc in an industrial environment (aka noisy).
I use:
- one TPS54331 to feed ~3.8volts at 600~900mA
- one TPS54331 to feed ~5ish volts to two devices (one router @ 500mA and one RaspberryPi @ 300mA) and charge up two supercaps in series (2x 50F/2.7V = 25F/5.4V).
-and finally one TPS61200 to power Pi from the supercaps for some time if 12/24v power fails.
So far only the 3.8v part works as supposed to.
Here is the schematic and layout of the 5V circuit.
I have the following problem(s) with the rest of my circuit. When I power the circuit the router powers up immediately, after the supercaps charge to (around) 1V the RaspberryPi boots and the caps keep charging until they reach 1.6~1.8V and then they stop. Also then, the Pi starts to reboot due to insufficient power(current?). If I disconnect the Pi for 2~3 seconds and the supercaps charge above 2V and reconnect the Pi they keep charging but the Pi also keeps rebooting and after a random amount of time the router hangs too (probably from bad power source).
If I power only the Pi it works without a problem.
To test the "UPS" function I remove the 12/24v supply and the Pi hangs from insufficient power(current) and starts rebooting. The supercaps discharge slowly but I measure at the TPS61200 output 3.6V~4.8V (the Pi usually hangs at 3.8V from the tests I have done with a variable DC/DC).
I have built with some cheap chinese DC/DC's and the same caps 10 working units.
So to the Questions...:
-Is my setup doable, at all, with these IC's? or I have to search for another solution?
-Is TPS61200 limiting the current output for some reason? (thermal protection due bad PCB layout?)
-Is so important the PCB layout (I haven't really cared for it in the handmade test PCBs) that may be the cause of my problems?
-Does someone have any suggestions to make about my design?
-Why the inductors buzz so much?
G.Ph.
Edited to change the images to the correct ones.