Zhiyuan Electronics Releases USB-PD Fast Charge Test Solution

USB-PD (Power Delivery) is a USB type-c based power supply standard with a maximum power of 100W. Although USB-PD fast charging is getting hotter, there is no testing tool for fast charging in the industry. ZLG Zhiyuan Electronics officially released the USB-PD test solution and provided free home test!

Type-c is a form of USB interface that can be inserted without regard to both sides. It supports USB standard charging, data transmission, video transmission, audio transmission, display output and other functions. Support for USB-PD can achieve up to 100W power supply. The USB-PD involved in this article communicates via type-c's "Configure Channel Pin CC" (Figure 1).

Figure 1 Type-C interface and socket pin function definition

The USB standard charging power is relatively small. When the USB host and device support USB-PD, the maximum power can reach 20V@5A (Table 1).

Table 1 USB power supply standard

The USB-PD physical layer uses single-line communication (Type-C configuration channel CC). In order to enhance the anti-interference ability and equalize the DC component, when transmitting protocol data, the physical layer first converts the data using 4b/5b encoding, and then uses the bi-phase tag. The code (BMC) performs a second conversion on the data stream and finally outputs the signal to the CC line.

The process of receiving is opposite to the process of sending. The specific process is shown in Figure 2. The sender or receiver is typically a USB PD controller or microprocessor. When analyzing the USB-PD protocol, only the signals transmitted on the CC line can be analyzed, and the analysis process is similar to the behavior of the receiver.

Figure 2 USB-PD communication process

Since USB-PD broke out in 2017, there are no relevant test analysis tools in the industry. At present, when engineers analyze USB-PD, they need to manually print out the entire communication process waveform. Through violent analysis and reverse decoding with the protocol, the process is very painful! The picture below shows the analysis method that the Zhiyuan Electronic Promotion Team saw when visiting a company.

Figure 3 USB-PD printing analysis live shot

Use a conventional oscilloscope to analyze it by the following methods (Figure 4): BMC decoding, 5b4b conversion, and then get the raw data of the communication, and finally consult the USB PD specification to parse out the "Good CRC" information frame (the handshake command in USB PD communication). How much hardship and helplessness this contains.

Figure 4 USB-PD manual analysis

· Connect the oscilloscope probe to the CC line of Type-C;

· Use deep storage to sample all data in the power-on process for a few seconds;

· Then open the USB-PD protocol decoding plugin, and the analysis can be completed in a few seconds.

Figure 5 shows the communication waveform of the USB PD charger with the device after power-on. From the event list in Figure 5, it can be seen intuitively that the charger can provide 5V@3A, 9V@3A and 15V@3A. Power supply capacity, the charger can output a maximum of 45W.

Figure 5 ZDS4054 Plus USB-PD protocol analysis

Figure 6 uses the "Accept" frame as an example to describe the four processes of the internal analysis of the oscilloscope.

1 BMC decoding the signal on the CC line (hopping to logic "1", not jumping to logic "0") to get the bit stream;

2 Combine the bit rate into a 5B code;

3 Convert the 5B code to 4B code to get the original protocol data in nibble (hexadecimal);

4 The original data is parsed according to the USB PD protocol and translated into plain text that can be easily understood (exportable web report or CSV file).

Figure 6 USB-PD decoding process analysis

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