Choosing the Right USB Charger for Multiple Devices

Choosing the Right USB Charger for Multiple Devices

The USB port on most laptops and computers doubles as a 5-volt power source for handheld electronics like cell phones and personal digital assistants (PDA).usb charger To charge these devices, they simply plug into a usb charger. USB chargers are available in a wide variety of amp outputs to meet the charging needs of various electronic devices. The higher the output, the faster the device charges. Choosing the right usb charger for multiple devices is important to avoid overcharging or damaging them with too much current.

Most USB chargers rely on a microcontroller to communicate with the host system and determine if the cable is plugged in correctly. This process is called enumeration and configuration. Several different methods are used, depending on the microcontroller and charger interface IC. Some microcontrollers use an internal microprocessor to perform enumeration and configuration, while others have a dedicated IC such as the MAX8900 that manages these tasks.

Depending on the design, either the microcontroller or the charging IC can also make decisions about the current to draw from the USB host interface. These decisions can be based on the results of enumeration and configuration, or a combination of enumeration and configuration plus user-set current limits. For example, if the IC detects that the cable is not a USB battery charger, it might set the current to 500mA to prevent overcurrent and damage to the connected device.

Some non-compliant USB device designs ignore certain portions of the specification and rely on their own methods for power control. These include keyboard lights, fans and mug coolers that draw power from the USB hub, and battery chargers. These devices may draw too much current and cause the computer to shut down, or they might damage the circuitry by overdrawing power. Adding a simple power detection scheme can help to address these problems.

USB On-the-Go (OTG) is a special feature that allows two USB devices to connect together, with one acting as the "host" for the other. This is similar to the way a desktop PC can act as an external hard drive for a mouse or keyboard, which is why most USB OTG cables have a fifth pin that enables this functionality.

Many of the latest USB cables and receptacles support USB Power Delivery, which provides for a higher wattage to offer quicker recharge times or to charge larger devices. This protocol requires a compatible device and a USB charger that supports it, and it can reduce the amount of heat generated by the charging circuit. However, the higher wattage also means the charger itself must be able to deliver it. In order to take advantage of USB Power Delivery, the charger must implement a number of additional protocols, including programmable power supply (PPS) and channel configuration (CC) pins. This increases the complexity of the charger, and can increase its cost as well. However, it is a necessary feature for enabling fast, reliable charging for a wide variety of mobile devices.