Why is current limiter U9 using resistors R32, R34, R37 with a total resistance of 1.7 kOhm (see diagram)? In the U9 datasheet, the resistance of the Rset should be 2.1 kΩ to limit the current to 0.5 A for USB (see graph)
This is to provide a slight increase in the nominal current limit since the tolerance of the IC is high and with the nominal value the current limit could be less than 0.5A.
Thanks for the answer. However, the USB standard provides for a maximum power of 2.5W at 500mA (see below from Wikipedia). With a resistor Rset of 1.7 kOhm, the maximum current is approximately 650mA (page 19 of datasheet SLG59H1341C). At a voltage of 5V, the power is 5 * 0.65 = 3.25W, which does not comply with the USB standard. What arguments will you have?
That is power used by a device. Where does it say that a host port cannot be able to provide more power?
No one tightly obeys that spec, anyway. The usual current-limiting solution is a 500mA polyfuse, which will probably not open (or at least, take quite some time to open) at 650mA.
I'm a bit impressed that the Arduino has something more complex than that!