USB charging method having protection function

1. A USB charging method having a protection function, the USB charging method comprising:

a) providing a source device and a sink device interconnected with each other through a USB Type-C interface supporting USB PD standard;

b) detecting a configuration channel (CC) pin of a USB Type-C connector of the sink device;

b1) providing an initial power option list to the sink device, wherein the initial power option list only comprises an initial voltage/current combination;

b2) receiving, from the sink device, a request for the initial voltage/current combination;

b3) transmitting, to the sink device, an Accept signal in response to the request for the initial voltage/current combination;

b4) switching the source device to a supply voltage that satisfies the initial voltage/current combination;

b5) transmitting a Power Supply Ready (PS_Rdy) signal to the sink device; and

b6) providing, according to the switched supply voltage, an initial power to the sink device, wherein the initial power corresponds to the initial voltage/current combination;

c) obtaining a plurality of working voltage/current combinations of the sink device, wherein the plurality of working voltage/current combinations comprise at least a value of a best working voltage;

d) generating a power option list comprising all voltage/current combinations supported by the source device;

e) adjusting, according to the best working voltage, the power option list to generate an adjusted power option list, comprising:

e1) if the best working voltage does not exceed a sum of 5V and a tolerance, and if the working current is less than 3 A, adjusting the power option list to comprise a 5V/3 A combination;

e2) if the best working voltage does not exceed a sum of 12V and the tolerance, and if the working current is less than 3 A, adjusting the power option list to comprise the 5V/3 A combination and a 12V/3 A combination;

e3) if the best working voltage does not exceed a sum of 15V and the tolerance, and if the working current is less than 3 A, adjusting the power option list to comprise the 5V/3 A combination, the 12V/3 A combination and a 15V/3 A combination; and

e4) if the best working voltage does not exceed a sum of 20V and the tolerance, and if the working current is less than 2.25 A, adjusting the power option list to comprise the 5V/3 A combination, the 12V/3 A combination, the 15V/3 A combination and a 20V/2.25 A; and

f) transmitting the adjusted power option list to the sink device.

2. The USB charging method in claim 1 , wherein the power option list comprises a 5V/3 A combination; a 12V/3 A combination; a 15V/3 A combination; and a 20V/2.25 A combination.

3. The USB charging method of claim 1 , wherein the initial voltage/current combination is a 5V/3 A combination.

4. The USB charging method of claim 1 , wherein the step d, the voltage of each voltage/current combination in the adjusted power option list does not exceed a sum of the best working voltage and a tolerance.

5. The USB charging method of claim 4 , wherein the tolerance is 0.5V.

6. The USB charging method of claim 1 , wherein step d) further comprises a step d5) adjusting the power option list to comprise a secure voltage/current combination if the best working voltage exceeds the sum of 20V and the tolerance.

7. The USB charging method of claim 6 , wherein the secure voltage/current combination is a 5V/3 A combination.

8. The USB charging method of claim 1 , wherein the tolerance is 0.5V.

9. The USB charging method of claim 1 , wherein the source device is a power supply and the sink device is a laptop computer.