Separating high- and low-power ground-planes
This board will not work...

There are no capacitors on the input and output of your DC-DC !

Come on... Considering the huge size of the inductor, and the fact there are ACS711-25, it's at least 10 amps... Please, please, please. Stick a healthy amount of ceramics, plus some low-ESR bulk caps both at the input and at the output.

Consider this:


Q3 OFF, Q4 ON, I(L)=5A
Q3 turns on, Q4 turns OFF
Inductor current must now go somewhere (in the output)
However, there are no caps. This means the current must go into the inductance of the wires...
L1 will generate enough voltage at the output to force its current wherever it has to go.
All components at the output will blow.


Now, layout. I'll start with the MOSFET drivers.

You want the current loops to be small to ensure fast and clean switching, without ringing. For U4 driver and Q1/Q2 FETs, loops are:


Q2 turn-on: GND-C15-U4.VCC-U4.BG-Q2.G-GND
Q2 turn-off: GND-U4.GND-U4.BG--Q2.G-GND
Q1 turn-on: U4.TS-C14-U4.Boost-U4.TG-Q1.G-Q1.S-U4.TS
Q1 turn-off: U4.TS-U4.TG-Q1.G-Q1.S-U4.TS


Also C14 charging loop should be optimized:


GND-C15-D1-C14-Q2-GND


Layout error: these loops are quite long, and they run over  splits in the ground plane. Gate drivers are not sensitive analog opamps! You can locate them close to the FETs, with short traces for gate drive... and optimize decoupling caps placement! (I see a split in GND plane between your decoupling caps GND and the chip's GND)...

----------------------- EDIT

Your Hall current sensor is isolated, which means you should reference its output to signal ground, not noisy power ground. Also check if it needs a decoupling cap.

Also, its output is centered on VCC/2, which is your 3V3. If this 3V3 is different from the one used in the micro, you will have DC offset.

MCP604 does not have rail to rail input, which might be incompatible with ACS711 output voltage.

Did you check the MOSFET thermal dissipation?

80V FETs seem a bit high for automotive use. Perhaps you could get better RdsON*Qg with 40-60V FETs?

Can't find datasheet for STPS2105 diode.

Look at C9-10-11-12-13, why are your decoupling caps clumped together in a corner of the board, instead of close to the chips they're supposed to decouple?

Schematic says U2=LT1764EQ, which is not the 3V3 part. Also, do you need big expensive LT LDO here? 

Placement of GND vias for capacitors C3, C8 is... uhhhh... are there even any GND vias?

But... This kind of DC-DC is DIFFICULT to pull off. This is really really NOT the kind of circuit you want to do for your first PCB! There are so many mistakes here... and every time I look at it I find more... and it's normal since this is your first PCB, as you say.

There is no way a beginner will succeed on this kind of design. I'm not trying to bash you or insult you, OK? But you risk burning tons of parts, wasting a week in frustration, and it will probably not work.

There is also the fact that this is PWM-controlled, so a software bug can make your FETs explode. And you didn't choose the easiest package to desolder...

I strongly suggest you seek help from someone qualified who can look over your shoulder and help you, this will avoid lots of butthurt.