System and method for externally controlling the charging of a battery powered device
A system and method for externally controlling the charging of a battery powered mobile computing device includes a charging unit configured to be electrically coupled to the mobile computing device to charge a battery therein. The charging unit comprises a charger configured to operate in a first mode to provide a constant charge current to the battery to be charged and to operate in a second mode to provide a constant charge voltage to the battery to be charged and where the switch from the first mode to the second mode occurs when the voltage at the battery a predefined threshold voltage. The charger including an offset compensator configured for applying an offset voltage to the measured output of the charger to maintain the charger in the first mode to compensate for voltage drops between the charger and the battery thereby allowing the battery voltage to reach the threshold voltage.
1. A charging unit for charging a rechargeable battery on a mobile computing device, the charging unit to be electrically coupled to the mobile computing device, the charging unit comprising:
a charging circuit comprising a charger configured to output a voltage and electrical current to the rechargeable battery of the mobile computing device external to the charging unit, the charging circuit configured to receive a measurement of the voltage received at the rechargeable battery as reported by the mobile computing device, the charger configured to charge the rechargeable battery in a first mode wherein a constant charge current is applied to the rechargeable battery until a predefined threshold voltage is obtained at the rechargeable battery and to then operate in a second mode wherein a constant charge voltage is applied to the rechargeable battery until the rechargeable battery is charged; and
an offset compensator configured to apply an offset voltage to a measurement of the output voltage of the charger to compensate for voltage drops in the charge path between the charger and the rechargeable battery determined from the measurement of the voltage received by the rechargeable battery as reported by the mobile computing device thereby allowing the voltage of the rechargeable battery to reach the threshold voltage before entering the second mode.
2. The charging unit of claim 1 , wherein the offset voltage is related to a difference between the measured voltage received by the rechargeable battery and the predefined threshold voltage.
3. The charging unit of claim 1 , wherein the charger is configured to poll a power processor associated with the rechargeable battery across a digital communication path for receiving battery parameters in response to the polling.
4. The charging unit of claim 3 wherein the battery parameters include at least the predefined threshold voltage and the defined charge current.
5. A method for charging a rechargeable battery in a mobile computing device from an external charging unit, the charging unit configured to be temporarily electrically coupled to the mobile computing device, the method comprising:
operating in a first mode wherein a constant predefined charge current is supplied to the rechargeable battery until the voltage received at the rechargeable battery as reported by the mobile computing device temporarily electrically coupled to the charging unit is at least equal to a predefined threshold voltage for the rechargeable battery;
during operation in the first mode, measuring the output voltage of the charging unit to determine if the output voltage of the charger is at least equal to the predefined threshold voltage for the rechargeable battery and, if the output voltage is at least equal to a predefined threshold voltage for the rechargeable battery, determining if the charge current has decreased;
if the charge current has decreased, obtaining from a power processor of the mobile computing device a measurement of the voltage received at the rechargeable battery and, if the voltage received at the rechargeable battery is less than the predefined threshold voltage, then applying an offset voltage to the measurement of the charger output voltage to compensate for voltage drops between the output of the charger and the voltage received by the rechargeable battery;
if the charge current has decreased and the voltage received at the rechargeable battery is at least equal to the predefined threshold voltage, operating the charger in a second mode wherein a constant charge voltage is applied to the rechargeable battery; and
when in the second mode the charge current falls below a predefined minimum, deciding the rechargeable battery is charged.
6. The method of claim 5 wherein battery parameters are obtained by the charger from a power processor associated with the rechargeable battery.
7. The method of claim 6 wherein the battery parameters include at least the predefined threshold voltage and the predefined charge current.
8. The method of claim 5 wherein the offset voltage is related to a difference between the voltage received by the rechargeable battery as reported by the mobile computing device and the predefined threshold voltage.
9. The method of claim 5 , further comprising polling the power processor across a digital communication path between the charger and the mobile computing device for receiving the battery parameters in response to the polling.