We are now in an era of global wireless Internet, and there is almost nothing more important than keeping mobile phones or mobile Internet devices in power at all times. With the continuous expansion of functions on portable and handheld devices, the designers of battery chargers IC are also facing severe challenges. High resolution screens, greater storage capacity and new devices on the device all increase the battery load, which requires not only a better battery charging technology, but also an efficient power management capability.
Reducing power consumption to extend battery life has been the source of handheld power management. However, consumers are now expecting the charging efficiency of the battery charger, hoping to shorten the charging time of the equipment. The new generation of charger is designed to replace the traditional linear charger with the switch charger. In addition to providing the high efficiency of the traditional linear charger, the greatest advantage is to improve the power supply. The charging current for the supply. When the USB port is powered off, the available current is limited to less than 500mA, and this advantage is particularly important. Higher current means shorter charging time, which is completely in line with the needs of consumers.
Nowadays, most handheld devices use two kinds of battery chargers, one is a linear charger and the other is a switching charger. The linear charger has a long history. The charging mode is simple and effective, the noise is very small, and there are not many external components. However, with the increasing complexity of portable devices and the emergence of new functions, the demand for high-capacity batteries is more intense. The disadvantage of a linear charger is that the power is too large, especially when the device is used at the side of the charge, when the heat generated may damage the system or battery.
The switch charger or switch mode battery charger IC is available. It can use as little power as possible to provide higher current for the battery. From past experience, this kind of IC usually has some noise problems. In addition, the previous generation of switching chargers also need some external components.
However, the advantage of switch battery topology is also obvious. These advantages include higher efficiency and lower power consumption, and shorter charging time. Such devices can also be recharged using higher input voltages, using lower cost non voltage adapters. The charging current from the current limiting current source can also be improved.
Switch charger usually produces noise when running at light load, especially in the pretreatment process. With the reduction of noise, the switch charger will enter the pulse skipping mode. In the pulse hopping mode, the PWM frequency changes asynchronously. The current battery charger IC, which can provide high charge current when using switch charger, has very small heat impact on the system, and switching to linear charger in low current charging mode to reduce noise. The PWM switch mode charger, which provides a linear mode, can achieve high efficiency under full current (fast charging) conditions. Switch charger can use PWM switching regulator to control constant current charging up to 2A. When the battery is in the preconditioning process and the constant pressure peak (taper) charging mode is quickly finished, the device automatically converts to the linear mode to reduce the noise and use the switch mode to speed up the charging. Once the charging current value is lower than 300mA, the linear mode will start completely, and the noise generated by the switching converter will be eliminated.
But now charging technology has developed further. For example, a single node lithium ion / polymer battery charger for a new handheld device has a charge current of up to 1A, with advanced electric full display functions and a full charge system monitoring system. The 100mA/500mA charging current setting that meets the USB standard helps to achieve programmable precharge and fast charging. Many products also have battery temperature monitoring function to ensure safe charging.
Intersil and other companies are developing a new generation of charger IC technology. These fully integrated solutions are very suitable for compact applications, and can also provide charging control functions for high-power applications. At present, the accuracy of charging voltage can reach 0.5%, which is greatly improved compared with 1% in previous years. The switching frequency is up to 3MHz, and the new type of switch charger can provide up to 2A charging current. The latest application example is ISL9220, which is suitable for one and two lithium ion batteries.
In addition, the new design can also limit leakage. At present, the typical leakage current is less than 0.5uA without adding input power. Moreover, these improvements can also be used in smaller packages, such as 4mm x 4mm QFN or 2mm * 2mm CSP, to save the design space of handheld devices.
The latest battery charger IC can also monitor input voltage, battery voltage and charging current. When any of the three parameters exceeds a specified limit, the IC will turn off the internal N channel MOSFET, so that the charging system stops charging the battery. Using these important devices can improve efficiency flexibly, which is essential for sustained growth, mobile expansion and handheld products.