Exhibition Reminder: 2019 (Autumn) USB PD & Type-C Asia Expo
(Register in advance to receive a free value 199 yuan conference magazine on-site!)
Recently, the Raspberry Pi 4 Model B was officially released, providing comprehensive upgrades in processing power, communication methods, and external interfaces, bringing good news to embedded developers. After receiving the product, many developers excitedly began to try it out. However, they found serious problems with the design specifications of the USB-C interface.
Figure 1 Raspberry Pi 4 with USB-C Interface
Through practical testing, it was found that the USB-C interface on the Raspberry Pi 4 has its CC1 and CC2 connected together, sharing a 5.1k pull-down resistor to ground.This design seems very clever; the control of the USB-C interface is made extremely simple, requiring only a 5.1k pull-down resistor. When the external USB-C cable does not contain an Emark chip, it can work normally. This type of USB-C cable has its CC2 floating, only CC1 is connected to the opposite end, so when this cable connects to the Raspberry Pi 4B’s USB-C interface, it perfectly conforms to the design specifications of the Sink end, where CC1 has a 5.1k pull-down resistor to ground.
Figure 2 Connection status of Raspberry Pi 4B using a cable without Emark chip
However, the USB TYPE-C specification also stipulates a type of cable with an Emark chip, which has a 1K pull-down resistor on CC2 to inform the DFP side’s CC identification chip to provide VCONN Source on CC2. Once connected to such a cable, the Raspberry Pi 4 Model B will encounter serious problems. Because CC1 and CC2 are connected together, they will be in parallel with the 1K pull-down resistor on the cable, forming an impedance smaller than 1k, thus meeting the connection specifications of the USB-C specification for Audio Adapter Accessory Mode, leading the power supply side to mistakenly identify it as an analog headphone device, thus refusing to supply power.
Figure 3 Connection status of Raspberry Pi 4B using a cable with Emark chip
From the above figure, we can see that the 1k resistor on the Emark cable causes CC1 to fail to establish a connection, and the parallel connection of the 1k resistor and the 5.1k resistor leads the Raspberry Pi 4B to be recognized as an Audio Adapter Accessory Mode. The solution to this problem is also very simple; just connect a 5.1K resistor to ground independently on CC1 and CC2. This point can be searched in the author’s original article from 2015, “Do You Really Need a TYPE-C Chip?”. This article provides three principles and two implementation methods for determining whether a system needs to use a USB-C control chip.
The design of the Raspberry Pi 4B’s USB-C interface is actually a beginner-level design, as this interface is only used for 5V power supply and USB 2.0 communication, without complex audio, video, or USB 3.0 functions. In actual embedded development, the function of a USB-C interface may be much more than this. Below, we will elaborate on three points: high power supply, high-speed signal transmission, and dual C port DRP control.
First, there is a need to use the USB-C interface to obtain power supply voltages of 9V/12V/15V/20V. Many embedded systems have very complex functions, and a mere 5V power supply cannot meet the requirements. In this case, simply setting a 5.1k pull-down resistor on CC1 and CC2 is not enough; it is necessary to use a USB PD control chip, preferably one that can flexibly configure various voltage USB PD control chips, such as LDR6015 and LDR6021. In some system designs, there is even a desire for the USB PD control chip to automatically determine the highest power level of the adapter so that the power supply can directly supply the highest power to the embedded system; in this case, the LDR6015Max can be used, which does not require any control and can directly obtain the highest power.
Second, there is a need to use the USB-C interface for high-speed video signal transmission application development. The USB-C interface can simultaneously support 10G/b USB 3.1 Gen2 data transmission and 4K high-definition video transmission. However, to allow the Sink end to enter DP ALT mode, a USB PD Controller is required, such as LDR6282. This type of USB PD control chip acts as a traffic manager, configuring the high-speed differential pair pathways in the USB-C cable through USB PD communication, allowing data signals and video signals to adapt to the appropriate differential pair.
Third, dual C port DRP function control; many embedded applications not only use a single USB-C port but may also have two USB-C ports, one for power supply and the other for high-speed data and video signal transmission. However, during user use, it is uncertain which of the two ports will be plugged in for power or multimedia devices, so it is necessary to meet the dual C port blind plug identification and control. The most typical application is USB-C interface displays and projectors. This belongs to relatively complex USB PD control functions. Currently, only LDR6282 on the market can meet this demand.
Figure 4 USB PD chip LDR6282 for dual C port DRP control
In summary, we can see that for embedded systems where the USB-C interface is only used for power supply and debugging functions, there is no need to use any chip control; just pull down a 5.1k resistor to ground independently on CC1 and CC2. For embedded designs that require high power supply or high-definition video transmission functions, it is necessary to use USB PD control chips.
Warm Reminder
Charging Head Network
Will be held on August 23 in Shenzhen, China
Exhibition Area Layout (3rd Floor):
Exhibition Area Layout (1st Floor):
Partial Exhibitors Preview:
Area A (Fully booked)
Honsen Precision (Booth A01), Cypress (Booth A02), Nanjing (Booth A03), Beiqi Technology (Booth A04), Tongjia Technology (Booth A05), Jixiang Tengda (Booth A06), Yujin Electronics (Booth A07), Innoscience (Booth A08), Chipmore (Booth A09), Maorui Chip (Booth A10), Power Integrations (Booth A11), Fuman Electronics (Booth A12), ABOV (Booth A13), Yifeng Precision (Booth A14), Huake Long (Booth A15), Tianyu Technology (Booth A16), Suxin Micro (Booth A17), Baoli Micro (Booth A18), Weifeng Electronics (Booth A19), Yifan Micro (Booth A20), Yijichip (Booth A21), Shounoxin (Booth A22), Likun Technology (Booth A23), Green Gem (Booth A24), Kunxing (Booth A25), Kangyuan (Booth A26), Qinheng (Booth A27), Hengtai Ke (Booth A28), Dongke (Booth A29), UL (Booth A30), Jindao Micro (Booth A31), Zhirong (Booth A32)
Area B (Fully booked)
Huinengtai (Booth B01), Wanjingyuan (Booth B02), Taipusheng (Booth B03), Weice (Booth B04), Angshengda (Booth B05), Weimeng (Booth B06), Xinsi Bao (Booth B07), Chipeng (Booth B08), Jingtou (Booth B09), DIODES (Booth B10), Yanjiji (Booth B11), Chuangwei Technology (Booth B12)
Area C (Only 1 seat left)
World (Booth C01), Junkaida (Booth C02), Renyue (Booth C03), Youwei (Booth C04), Deyue Technology (Booth C05), Bo Wen Chuang Yi (Booth C06), Jinshengxin (Booth C07), Runshi Technology (Booth C08), Deli Hua (Booth C10), Ximiyaer (Booth C11)
Area D (Hot Registration)
Yichong Semiconductor (Booth D01), Jiayi (Booth D02), Wanguo Semiconductor (Booth D03), Tail Certification Center (Booth D11)
Area E (Only 2 seats left)
Yongming (Booth E01), Nami (Booth E03), Nami (Booth E04), Nami (Booth E05), Guojin Shen Electronics (Booth E07)
Area F (Hot Registration)
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