2 UBS-PD versus Non-USB-PD

USB Power Delivery (USB-PD) is a charging protocol that allows USB port to deliver more power to the load, provide faster charging speed and powering up more end equipment. USB-PD allows USB-C® port to vary the output voltage other than 5V. With higher voltage, higher power can be delivered.

Table 2-1 shows the evolution of USB-PD standards. With the USB-PD 3.1/3.2, output voltage is supported up to 48V and output current is supported up to 5A. With up to 240W power handling capability, a USB-C port can charge a load much faster.

The USB-PD operates based on the load requirement. When the equipment such as a phone is plugged into a power adapter USB-C port, a negotiation process happens. The power adapter (source) and the phone (sink) negotiate the voltage and current level that source can provide and the sink can take. Then, the source modifies the USB-C port output voltage to the corresponding level. And, then the charge happens. Through this process, the output voltage of the USB-C port can vary between 5V to the maximum voltage. According to Figure 2-1, for a 65W USB-PD adapter, the maximum voltage supported is 20V.

When designed for USB-PD application, UCG2882x receives a feedback signal through an optocoupler. The feedback signal is generated by the secondary side USB-PD controller, which controls the output voltage level. As shown in Figure 2-2, the USB-PD controller connected with USB-C port generates the feedback signal through the integrated control loop.

When designed with non-USB-PD applications, the output voltage is fixed. A TL431 is often used to close the output voltage regulation loop. The TL431 generates the feedback signal and transfers the signal back to UCG2882x through an optocoupler. This implementation is illustrated in Figure 2-3.