OVER VOLTAGE DETECTOR WITH STAND-BY MODE
Publication Date: 2003-Apr-15
The IP.com Prior Art Database
Key words: battery life, leakage current, phone and charger Problem The over voltage protection integrated circuit (OVIC) is powered by an adapter or battery BATT+ coupled to an external bus called EXT.B+, which is further coupled to pin VCC of the OVIC, FIG. 1. A gate of transistor Q1 is controlled by both an over voltage event at pin IN of the OVIC and a logic signal coupled to pin CNTRL. When the phone is removed from the cradle, the battery BATT+ provides power for the phone. However, when the phone is removed from the cradle, a leakage current ICC develops across Q1’s internal body diode from the battery BATT+ to the pin VCC of the OVIC. This shortens the battery BATT+ life. FIG. 2 includes a CCCV charger embodiment with transistor Q2 and the required electrical coupling from the EXT. B+ to pins VCC, ISNS and VSNS of the CCCV charger and pin OUT to a gate of transistor Q2. The leakage problem presented above is aggravated by an additional leakage current ISS2 across transistor Q2’s internal body diode, because now there are two leakage currents ISS1 and ISS2. This results in even a shorter battery BATT+ life. Prior Art Prior art resolves the current leakage problem by adding components in the charging path, such as a Schottky diode or a PMOS transistor. However, the addition of such components in the charging path causes an increase in power dissipation and affects the phone performance as well. Solution FIG. 3 includes a new standby mode coupled to the CNTRL pin of the OVIC from the PMU and is characterized by a substantial reduction in leakage current. The standby mode functions by biasing the PMOS transistor in the forward direction and is implemented by a voltage comparator that compares input and battery voltages when the adaptor/charger is disconnected from the phone. The standby method reduces leakage currents without the power dissipation from components added in the leakage path as in the prior art. The standby method can be implemented at a low cost and substantially improves battery life.