I have sampled a TPS54531 from Texas Instruments to build a 5V car adapter. I have used their WEBENCH online deisgner for the 5A version.
Input 8 to 16V, output 5V at 5A (adertised).
I have made my PCB, adapted some values in order to use what I had handy in my drawers and ended up with a 5.02V source.
I have only tested it at 2A
(I do not have a bigger power load) and here is how it performed at different input voltages.
At 9V input, the drawn current was 1.6A.
At 12V input, the drawn current was 1A.
At 14.5V input, the drawn current was 0.86A - this is the closest to the car normal voltage (while engine running)
At 16V input, the drawn current was 0.75A.
The top view of the (19x40mm) PCB:
This show you the modifications I made. The rest of them are as required. The Coicraft coil is amazingly small. The diode gets warmer in time.
Ripple at no load:
And at 2A loading:
LE: I decided to give a try to the 1.2R / 10W resistor. This is the output (at 4A, 5.001V from 5.02V):