Design Points of USB Cables for High-Current PD Power Adapters

With the rapid popularization of USB PD fast charging on mobile devices such as laptops and mobile phones, we have learned that many high-current PD power adapters will be equipped with a USB-C adapter equipped with an Electronic label chip (eMarker chip) and a current level of 5A. USB-C cable.

foreword

With the rapid popularization of USB PD fast charging on mobile devices such as laptops and mobile phones, we have learned that many high-current PD power adapters will be equipped with a USB-C adapter equipped with an electronic label chip (eMarker chip) and a current level of 5A. USB-C cable.

The EN 61000-3-2 standard stipulates that electronic products with an input power of more than 75W must have a power factor correction (PFC) function, so the traditional AC-DC power adapter generally has an output rated power of 65W. In this way, the input power can be controlled within 75W to save the cost of the PFC circuit. With the rise of PD fast charging, many PD power adapters follow this power level and make a rated power output of 65W. In this way, when the 20V Voltage is output, the rated output current is 3.25A. For the introduction of related products, see “Separation of Line Body: Dismantling of Xiaomi USB-C Power Adapter (65W) CDQ07ZM” and “Talking about a Huawei 65W PD Charger”.

USB Type-C specifies the occasions where the eMarker chip is mounted, as shown in Table 1. The rated output current of the 65W power adapter is 3.25A, a cable with a current rating of 5A must be used, and an eMarker chip must be installed. Even without considering the requirements of USB3.1 high-speed signal transmission, cables with a current level of 5A must be equipped with eMarker chips. It should be noted that if the cable is not equipped with an eMarker chip, even if the power adapter can output power of 65W or more, the device can only draw with a maximum current of 3A and a maximum power of 60W, and the power adapter still cannot reach the output power of 65W. Require.

Design Points of USB Cables for High-Current PD Power Adapters

Table 1. The USB Type-C specification specifies the occasions where the eMarker chip is mounted

The following describes the design points of USB2.0 USB-C cables equipped with eMarker chips for high-current PD power adapters. The 5A current level USB3.1 high-speed cable can also be used for the same charging occasion, but the cost is much more expensive, which is not within the scope of this article.

Line Voltage Drop Specifications for USB-C Cables

The USB Type-C specification defines the maximum voltage drop when current flows through a USB-C cable. Including all voltage drops on the USB-C male and USB-C female connectors, the maximum voltage drop on the GND line is 250mV and the maximum voltage drop on VBUS is 500mV when the cable flows through the rated current. For cables with a current rating of 5A, the line impedance is lower than that of ordinary cables with a current rating of 3A due to the larger transmission current. The longer the cable length, the thicker the wire size is chosen to reduce the line impedance. For many cables with a wire length of 1.5m, GND and VBUS are both connected by two wires with a wire size of AWG22.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 1. Line Voltage Drop Limits for USB-C Cables

Choice of eMarker Cable Architecture

The first eMarker cable architecture: one Paddle Card (commonly known as USB-C connector) is equipped with an eMarker chip, while the other Paddle Card does not have an eMarker chip, as shown in Figure 2. The VCONN power supply of the two Paddle Cards is connected by a single wire. So a USB2.0 cable with this architecture has a total of six wires: GND, VBUS, D+, D-, CC, and VCONN. The VCONN power supplies on both sides are isolated from each other on the eMarker chip to prevent two VCONNs from being driven by voltages at the same time and colliding on the VCONN wires. One cable only needs one eMarker chip, which is more cost-effective and is the mainstream choice.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 2. Schematic diagram of only one eMarker chip mounted on one Paddle Card

The second type of eMarker cable architecture: one eMarker chip is mounted on each of the two paddle cards, as shown in Figure 3. The USB2.0 cable of this architecture has a total of five wires: GND, VBUS, D+, D-, CC. Therefore, only two eMarker chips are required for a single cable. Although one wire is saved, the cost is still more expensive.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 3. A schematic diagram of one eMarker chip mounted on each Paddle Card

Selection of eMarker Chips

There are two core points in choosing eMarker chips: one is “small” and the other is “big”.

“Small” refers to the small size of the eMarker chip. The mainstream Paddle Cards are all in the direction of miniaturization, so that the cables produced will be more beautiful and the cost will be lower. At the same time, for the convenience of PCB circuit layout, the eMarker chip size is often required to be smaller, and the 2mm x 2mm DFN package is an ideal choice.

“Large” means that the tube spacing of the eMarker chip is large. In the USB cable industry, the paddle card is generally produced by the connector manufacturer first, and then sold to the cable manufacturer to make the finished cable. The Paddle Card processed by the connector manufacturer must ensure a very high yield, otherwise it will reduce the yield of the cable and bring additional costs to the cable manufacturer. After the conventional Paddle Card without eMarker chip is patched, it can be directly tested by a test instrument with a USB-C port and then provided to cable manufacturers to make a finished product. On the Paddle Card with eMarker chip, the VCONN pin that is not connected to the USB-C male header cannot be tested by a test instrument with a USB-C port. However, manufacturers of test fixtures are often reluctant to develop test instruments specially designed for Paddle Cards with eMarker chips because the positions of the outgoing pads of each VCONN are different and cannot achieve universal design. Chips with 0.65mm tube spacing can achieve almost 100% chip yield rate, which can omit the VCONN outgoing pad test link, and will not reduce the yield of the cable. In contrast, for a certain brand of WLCSP package, the patch failure rate has been maintained at about 2%-4%, and these costs are directly passed on to consumers through cable manufacturers.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 4. Physical photo of Paddle Card

In addition to the above two points, passing USB PD3.0 certification, supporting multiple programming and programming locking are also important factors for choosing eMarker chips. It is worth mentioning that Hynetek’s eMarker chip has emerged. With its good design and excellent quality, it is favored by many international famous brands, and it is a banner of domestic chips.

Hardware Design of Paddle Card

The definition of the USB-C male header of USB2.0 is shown in Figure 5. Except for A1, A4, A5, A6, A7, A9, A12, B1, B4, B5, B9 and B12, all other pins are empty.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 5. USB2.0 male header definition

The reference schematic diagram of the USB-C cable equipped with the eMarker chip is shown in Figure 6. It contains two Paddle Cards: Plug A and Plug B. Plug A is equipped with an eMarker chip, and Plug B is not equipped with an eMarker chip. Plug A and Plug B are connected by six wires.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 6. Reference schematic diagram of USB2.0 cable with eMarker chip

The outgoing lines of the Paddle Card can be divided into three categories, with a total of six lines:

・USB2.0 data cable D+/D-.

・Type-C communication lines CC and VCONN.

・ Power supply VBUS and ground GND, transmit 5A current.

Some cables do not transmit USB2.0 data, as long as they transmit 5A current. The outgoing line of such a cable only needs four lines of VBUS, GND, CC and VCONN.

PCB design points of Paddle Card:

・ Use ordinary FR4 material PCB material, it is recommended to use four-layer PCB to meet the current transmission level of 5A. The second and third layers of the inner layer take VBUS and GND respectively.

・ According to the specifications of the male header, the thickness and tolerance of the PCB meet the design requirements.

・ Place the lead pad on the Top layer. The eMarker chip and the resistive container are placed on the bottom layer of the Bottom.

・ Consider impedance matching for D+/D- traces, parallel and equal-length traces.

・ Control the length and width of the PCB, the recommended size is 8.4mm x 6mm.

Programming and testing of eMarker chips

The YG-508H writer is a high-performance, user-friendly eMarker writer, as shown in Figure 7. YG-508H can support offline programming and online programming two programming modes. The friendly graphical user interface can help users to quickly complete the programming configuration. The configured settings can be saved on the computer for the next call, or downloaded to the programmer for offline programming.

A good feature of YG-508H is to support offline automatic programming. In offline mode, as long as the operator inserts the Paddle Card or finished cable, no additional operations are required, the YG-508H will automatically complete the programming and prompt the operator to pull out the Paddle Card or finished cable with a prompt tone. Because the programming time is very short, the programming efficiency is very high.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 7. YG-508H programmer software interface

The finished cable with eMarker chip can use YG-620 Type-C data comprehensive tester to complete various functional tests, including conventional USB-C cable functional test and eMarker chip test. There are two Type-C female sockets on the tester. Insert the male heads at both ends of the cable to be tested into the two female sockets, and start the test program to complete the test of the finished cable. Figure 8 is a photo of the YG-620 Type-C data synthesis tester testing the finished cable. Figure 9 shows the corresponding test results.

Design Points of USB Cables for High-Current PD Power Adapters

Figure 8. Photo of YG-620 Type-C data cable integrated tester testing cable

postscript

The design and processing of USB-C cables, especially high-frequency and high-speed cables, seem to be simple, but actually require very professional knowledge and skills. It is not easy to do well, and many details need to be considered to make the product well. This article focuses on the design points of cable electronics, and the content is relatively shallow. I hope to attract more professionals to participate in the exchange and jointly develop the USB-C cable industry.

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