So, I was looking at redoing my power supply for my circuit.
Now, I am not sure if switching frequency matters much, as I am only going to be operating Logic Gates (74HC) and LED's with this circuit.
The LM2596s-adj is just too big. It works, and works fine, but I am trying to make the PCB smaller, therefore, I need to look for a smaller alternative.
I need to produce ~5.3v to compensate for voltage drop I will have along the wiring going to the switches I have. In addition to that, I also need to produce a flat out 5v output from the PCB to run other things. The voltage supplied to the PCB will be from a WalWart that is 7.2v-24v output, depending on which is on hand at the time.
I was thinking maybe a 1.0A-1.5A max load on the 5.3v, and a max load of 1.0A-1.5A on the 5v at any given time. Most likely, the load will be half that amperage.
The circuit I have could have 42 LED's on at a given time, they don't all draw the 20mA though, but if I calculate at 20mA each, that is 840mA current draw for the circuit, not taking into account the draw for the sensors or the logic gates, which I don't think is much. The sensors draw 25mA each, but they will NEVER be on at the same time. So worse case scenario, the circuit will draw less than 1A at a given time.
It would be nice to fine a small footprint that has 2 outputs that can achieve that.
For the 5v output, I was thinking maybe this chip....
http://www.mouser.com/ds/2/631/ACT4088_Datasheet-345917.pdf but it doesn't show anything about the recommended land pattern. How do I figure that out? Which pin should I extend the copper out for heat dissipation and vias through to copper side?
I am not sure what chip can use for the 5.3v.
It looks like the ACT4088 can also do adj. Using the formula 49900/((5.3/.81)-1)=9002 So using a 49.9K resistor for RFB1 as the data sheet suggests, that would make RFB2 a 9k resistor. Or am I limited to voltages out BELOW 5volts with this chip?
If this chip works, I think I can get the overall footprint fairly small for 2 of these chips, both operating at a different voltage output, as it looks like it only uses surface mount components, i.e. ceramic capacitors.
If this would work, I could run two of these chips and be okay.
Any suggestions? Maybe a different chip? Would this chip be sufficient enough to do both outputs?
If you think this chip will work, what is the recommendation for footprint/placement of components for heat dissipation and optimal operation? The data sheet was vague on that.
All the datasheet size is
PC Board LayoutThe high current paths at G, IN and SW should be
placed very close to the device with short, direct
and wide traces. The input capacitor needs to be as
close as possible to the IN and G pins. The external
feedback resistors should be placed next to the FB
pin. Keep the switch node traces short and away
from the feedback network and use shielded
inductors.
That ACT4088 seems like a nice chip. It is small, works off SMD ceramic caps, internal start, thermal shutdown, and enable pin.