Influence of internal resistance of USB data cable on charging current

Influence of internal resistance of USB data cable on charging current

Mobile phone and tablet Charger interface for USB interface, the use of the adapter through the power of the USB cable and ground to form a loop to charge the phone, if the quality of the data line, the resistance of the line is large, charging current in the data line pressure drop will become larger. The input voltage on the power management chip that arrives at the phone or tablet is lowered. The software detects the input voltage of the pmic. If the voltage is below 4.7V, the charge current will be reduced. Prevent charging current too general adapter burnt out. For example, the maximum charging current of the Sony Lt26ii is 1300ma, which means that if the adapter can supply a current greater than 1300ma and the battery is not in power, the charge current is 1300ma.

If the resistance of the data cable is too large, although the adapter can provide charging current greater than 1300ma, but due to the presence of the internal resistance of the data line, the charge current multiplied by the data line's internal resistance is the data line pressure drop. The pmic voltage to reach the phone is the output voltage of the adapter minus the voltage drop of the data line, it is not 5V, if less than 4.7V, the phone's software will be the charging current one step lower, to ensure that the pmic input voltage greater than 4.7V.

So if you want to charge your phone fast, reach the maximum charging current of your phone. To meet the following two conditions at the same time.

The first condition is that the output power of the adapter is sufficient, the output 5V DC voltage should be stable;

The second condition is that the internal resistance of the data line is small, that is, the copper core of the data line to be thick, the length of the line is not too long, so that the pressure drop in the data line is small.