Simplify The Charging Process Of Lithium-ion Batteries With An Independent Power Manager

- May 29, 2020-

Consumer demands for miniaturization, low cost of battery-powered handheld devices, and ease of use by accepting multiple input power supplies pose many challenges to system design engineers. These challenges can be effectively solved with the powerpath battery manager series, which has independent autonomous operating features and is able to efficiently perform seamless switching between multiple power sources (such as car adapters, FireWire inputs, AC adapters, USB ports, and the battery itself) management. For system design engineers of battery-powered handheld devices today, some of the important challenges they faced including minimizing power consumption, maximizing efficiency, simplifying design, and reducing costs.


Many portable battery-powered electronic products today can obtain power from AC adapters, car adapters, USB ports, or lithium-ion / polymer batteries. However, autonomous management of power path control between these different power sources is extremely technically challenging. All along, designers have tried to adopt a "discrete" way to accomplish this function, that is, using a large number of MOSFETs, operational amplifiers and other discrete components, but encountered hot swapping and influx that may cause major system problems current problems. Recently, even discrete IC solutions use multiple chips to implement a practical solution, and integrated power manager ICs can easily solve these problems. In addition, the IC's autonomous operation also eliminates the need to add an external microprocessor for charge termination, which further simplifies the design.


When using, for example, FireWire, unregulated high-voltage (> 5.5V) AC adapters and car adapters, the voltage difference between the adapter's voltage source and the battery in the handheld device is very large. Therefore, linear chargers may not be able to solve the problem of high power consumption, but ICs using switch-mode topologies can improve efficiency and alleviate thermal management issues. It is worth noting that when using USB, lithium-ion / polymer batteries or an adapter with an input lower than 5.5V to supply power, a linear charger / power manager is a more suitable choice.


Powerpath Control

The device with powerpath control function can power itself from USBVBUS or AC adapter power supply, and charge its single cell. In order to ensure that a fully charged battery is in an unused state when it is connected to the bus, the IC directly supplies power to the load through the USB bus instead of obtaining power from the battery. Once the power supply is removed, the current will flow from the battery to the load through an internal low-loss ideal diode, thereby minimizing voltage drop and power consumption.


Features of Powerpath Control:

1. Get power from USB power supply, AC adapter or battery;

2. Transfer power to an application circuit connected to the OUT pin and a battery connected to the BAT pin (assuming that an external power supply is connected instead of the battery)

3. The battery charging current will be adjusted to ensure that the sum of the charging current and the load current does not exceed the set USB input current limit;

4. The AC adapter current can be connected to the output (load side) through an external device (such as a power Schottky diode or FET);

5. With a unique function, you can use the output of the AC power supply to charge the battery while supplying power to the load;

6. The load on the OUT pin can get the USB input current first.


Ideal Diode

When the output / load current exceeds the input current limit or the input power is removed, a low-loss ideal diode will supply power from the battery. Powering the load through an ideal diode (rather than directly connecting the load to the battery) keeps a fully charged battery fully charged before the external power supply is removed. Once the external power supply is removed, the output voltage drops until the ideal diode is forward biased. The forward-biased ideal diode will then supply the output power from the battery to the load. The forward voltage drop of an ideal diode is much lower than that of a traditional diode, and its reverse leakage current is also smaller. The small forward voltage drop reduces power consumption and self-heating, thereby extending the life of the battery.