Why resistors array 22 Ohm (USB)

Other Hardware General Electronics
1

I noticed that in Arduino UNO, Leonardo, and so on, in the lines D +, D- of the USB connector, an assembly of 22 Ohm resistors array is used. Why are 2 resistors (number 1, 4) of array used, but 2 resistors (number 2, 3) of array are not used? Could the assembly of resistors array be replaced with two single resistors SMD 0402/0201 22 Ohm?

First, two separate resistors are lower-lower cost than a resistors array. Secondly, two separate resistors will take up the same space on the PCB. Thirdly, the Arduino UNO Wi-Fi uses 2 separate 22 ohm resistors. What will be the assumptions?

2

I see 2 resistors and 2 varistors for circuit protection, I think.
Show us on your schematic what you mean.

3

True (or maybe not!) and maybe the assembly cost of the board would fall by circa 0.1p.

Edit: as @EmilyJane has suggested maybe the arrays are cheaper, or were cheaper when the board design was commited.

4

Yes.

Maybe they found a huge quantity of surplus resistor arrays for cheap and the cost to pick and place one part instead of two added up to a cost savings that made sense for a large quantity of boards.
You should ask someone at Arduino since they are the only ones likely to know for sure.

Edit:
A quick check of Mouser shows that at 10,000 quantity, the resistor array is actually cheaper than two 22Ohm resistors.

5

Can it be tied to the characteristic impedance of the D+, D- circuits?
Array

6

A quick check of Mouser shows that at 10,000 quantity, the resistor array is actually cheaper than two 22Ohm resistors.

Does not sure. I have other data on TME.EU - array 0402 Royal Ohm=0.004$ (+10000), single resistor 0402 Royal Ohm=0.00055$ (+10000)

7

Time on the placement machine is shorter with one part. More efficient production.

8

We'll never really know. Design decisions have so many possible inputs it boggles the mind. Perhaps the assembler has other devices that use a ton of these arrays.

When looking a the cost of a single part ; I was told some time ago that the part costs less than the "installation". i.e. purchasing, inventory, handling etc.