Voltage regulation circuit 12V to 5V in 5A range

[Ioannis]

The LCD datasheets note that the backlight is 5v at 90mA, isn't it?

So I understand that no current liminting resistor is necessary, as it is included on the LCD board.

Ioannis

[richard]

So I understand that no current liminting resistor is necessary, as it is included on the LCD board

you may be correct but that does not explain why the backlights cause so much noise.
it would be a 2 minute job to apply 5v to the backlight and measure the current .[i would used a cc regulated ps just in case]
i have never come across an lcd of that type with anything onboard to limit led current.

[Ioannis]

i have never come across an lcd of that type with anything onboard to limit led current.

Well, there are not many but they exist. I use them all the time to avoid external resistors.

If the datasheet marks it as 5V then the LCD includes the limiting resistor. Otherwise they note 4 or 4.2 volts at specific current and specific resistor for 5V supply.

Ioannis

[Demon]

I've put on hold debugging/testing LCDs, ADC and whatnot until I get a handle on power regulation.

Thanks to Ioannis, the datasheet for the TPS voltage regulators led me to TI's WEBBENCH; that tool is just remarkable for the newb like me. I've spent the last 2 days playing with various ICs, checking their availability on JLCPCB and such.

The 2 best features has to be that Alternate and Simulate features; you can chose equivalent parts that are no available at JLCPCB, and see exactly what the output ripple will look like.

I've narrowed down my choice to a TPS56637. I can run 5V @ 5A using 7V to 12V at 11.4mV Vout Peak-Peak; it can do more, but the output ripple degrades as you push it.

This is awesome because it gives me a wider range of power supply adapters. I was initially fixated on running on 9V to limit heat from conventional voltage regulators.

The datasheet even gives a very detailed PCB layout:



Thanks mucho Ioannis!

[Ioannis]

You are most welcome! Thats what friends are for, right?

The selected TPS is difficult to handle by hand. Needs heatsinking on the PCB by special design. I do understand why you selected this one over the TPS565208, that is super easy to handle.

Amazing chips TI has...!

Ioannis

[Demon]

Y...The selected TPS is difficult to handle by hand. Needs heatsinking on the PCB by special design. I do understand why you selected this one over the TPS565208, that is super easy to handle.

Amazing chips TI has...!

Ioannis

Definitely, that's why I did my best to mimic the "suggested" layout I posted above. I figure there's countless hours or even days put into that design.

I came up with this 4-layer PCB, top layer:




Both inner layers are identical:




And the bottom layer:




I did my best to use the same outlines, but I didn't have identical sized components, so I had to make due.
- Rpg goes to VCC on the datasheet drawing, but goes straight to 5Vout on the generated schematic.
- they have a single Cin cap, but mine is split into 2 using alternate parts.
- my inductor seems to be twice as large as theirs.

Also, the Webench schematic for 7-12Vin to 5A-5Vout didn't have these resistors:
- Rmode
- Renb
- Rent
So I don't have that trace from PGND going up to VIN.

The last thing I have to adjust is the copper layers; I remember reading something about needing 2 ounces top and bottom, and 1 ounce inners (or something like that - got reading to do).

Looks like this in 3D:

[Demon]

ARGH! Of course it's only now that I notice Webench generated a layout specifically for that schematic.




I couldn't find any mention of copper thickness in the datasheet. No mention in the Evaluation Board for the TPS56637, but it does have a much nicer layout with A LOT MORE cooling holes and a wider area.




I must have read about the copper thickness in the datasheet for another TPS. I just can't remember which cause I looked at so many.


EDIT: No mention of copper in their Quick Reference Guide:

https://www.ti.com/lit/an/slva958b/slva958b.pdf