USB - Battery Charing

Getting to the bottom of USB Battery Charging (了解 USB 电池充电的真相)

如今，几乎所有带电池的产品都被期望支持 BC1.2 USB 充电标准。

Today, almost every product with a battery is expected to support the BC1.2 standard for USB charging.

这对消费者来说是个好消息。USB Type-C® Power Delivery 目前支持高达 240W 的充电功率，并且向下兼容。BC1.2 定义的充电端口可使便携式设备吸收更多电流，这意味着充电速度更快。BC1.2 还为未来的快速充电技术奠定了基础。不过，这也意味着使用 USB Type-C 插座并支持 Power Delivery 的流行 USB-C 充电器和笔记本电脑的制造商必须确保其产品支持 BC1.2，并通过 BC1.2 认证测试。

That’s good news for consumers. USB Type-C® Power Delivery currently supports charging at up to 240W and is also downward compatible. The BC1.2-defined charging port enables portable devices to absorb more current, which means quicker charging. BC1.2 also lays the foundation for future quick charge technologies. However, it also means that manufacturers of popular USB-C chargers and laptops that use a USB Type-C receptacle and support Power Delivery, must ensure their products support BC1.2 and pass the BC1.2 test for certification.

本文旨在介绍 BC1.2 认证的基本操作原理和测试项目，帮助制造商减少设计中遇到的问题，顺利通过测试。

This article is aimed at providing an understanding of the basic operational principles and test items for BC1.2 certification, to help manufacturers reduce the problems encountered in design, and pass tests smoothly.

1，Introduction to BC 1.2 (BC 1.2 介绍)

基于 USB 2.0 的 Vbus 电源可提供 500mA 的最大供电电流。但是，移动电话等便携设备的充电时间较长。

A Vbus power supply based on USB 2.0 can provide a maximum supply current of 500mA. However, a portable device such as a mobile phone can take a long time to recharge.

2010 年 10 月发布的 USB-IF 电池充电 1.2 规范要求便携式设备在连接 USB 主机或集线器充电时吸收最大电流 1500mA（相当于 USB 2.0 的三倍）。这样，设备就能在原来三分之一的时间内完成充电。

The USB-IF’s Battery Charging 1.2 specification, which was issued in October 2010, requires portable devices to absorb a maximum current of 1500mA (equivalent to three times that of USB 2.0) during charging when connecting to a USB host or a hub. This enables the device to be recharged in a third of the original time.

便携式设备和 USB 主机或集线器都需要支持 BC1.2，通过检测 USB D+ 和 D- 触点来确认是否支持BC 1.2。一旦检测完成并确认支持 BC1.2，Vbus 就会提供 1500mA 的充电电流。

The portable device and USB host or hub both need to support BC1.2, which detects the USB D+ and D- contacts. Once this is complete and support for BC1.2 is confirmed, Vbus provides 1500mA current for recharging.

2，Charging capacity comparison (充电能力比较)

支持 BC1.2 的手机的充电能力会有所不同，这取决于手机是通过标准 USB3 端口（SDP）连接到笔记本电脑，还是通过支持 BC1.2 的 USB3（CDP）连接到笔记本电脑？

The charging capacity of mobile phones supporting BC1.2 varies, depending on whether they connect to laptops via standard USB3 ports (SDP) or laptops with USB3 supporting BC1.2 (CDP)?

当手机连接到带有标准 USB3 端口（不支持 BC1.2）的笔记本电脑时，最大可吸收电流为 900mA。

When the mobile phone connects to a laptop with standard USB3 ports (not supporting BC1.2), the maximum absorbable current is 900mA.

当手机已连接、未配置且未进入暂停状态时，最大可吸收电流为 100 mA。
当手机已连接、已配置且未进入暂停状态时，最大可吸收电流为 900 mA（USB 3.2 为 900 mA，USB 2.0 为 500mA）。
当手机已连接、已配置并进入暂停状态时，最大可吸收电流为 2.5 mA。

When the mobile phone is connected, unconfigured, and has not entered the Suspend state, the maximum absorbable current is 100 mA.
When the mobile phone is connected, configured, and has not entered the Suspend state, the maximum absorbable current is 900 mA (900 mA for USB 3.2, 500mA for USB 2.0).
When the mobile phone is connected, configured, and has entered the Suspend state, the maximum absorbable current is 2.5 mA.

根据规范，在未配置的情况下，如果便携式设备的电池处于 "死电 "或 "弱电 "状态，最大可吸收电流应为 100 mA。(弱电池状态意味着可以用最小的能量启动设备，而死机状态则意味着无法启动设备）。

According to the specification, without being configured, if the battery of a portable device is in the Dead or Weak state, the maximum absorbable current should be 100 mA. (a Weak battery state means the device can be started with the minimum of energy, while the Dead state means the device cannot be started)

SDP（标准下游端口）是指不支持 BC1.2 的标准端口。

SDP (Standard Downstream Port) refers to a standard port that does not support BC1.2

CDP（充电下游端口）是指支持 BC1.2 的标准端口。

CDP (Charging Downstream Port) refers to a standard port that supports BC1.2

不过，当手机连接到支持 BC1.2 的 USB3 笔记本电脑时，无需配置即可吸收 1.5 A 的最大电流。

However, when the mobile phone connects to the laptop with USB3 supporting BC1.2, it can absorb a maximum current of 1.5 A without being configured.

3，Common BC 1.2 types (常用BC 1.2 类型)

对于标准 USB 下游端口，Vbus 可提供 500mA （USB2.0）或 900mA （USB3.2）电流，而 BC1.2 充电端口可提供 1.5A 电流。BC1.2 充电端口还可分为支持 USB 数据的 CDP（充电下游端口）和用于充电的 DCP（专用充电端口）。

For standard USB downstream ports, Vbus can supply 500mA (USB2.0) or 900mA (USB 3.2), while a BC1.2 charging port can supply 1.5A. The BC1.2 charging port can also be divided into CDP (Charging Downstream Port) to support USB Data, and DCP (Dedicated Charging Port) for charging.

CDP（下游充电端口）：该 USB 端口具有更高的充电能力。它提供 USB 数据传输，还能为兼容 BC1.2 的设备提供最大 1.5 A 的电流。
DCP（专用充电端口）：该端口是一种不带 USB 数据传输功能的 CDP，可为 BC1.2 便携式设备提供 4.75V-5.5V 的电压和 1.5A 的充电电流。DCP 将在 D+ 和 D- 之间桥接一个电阻 R。
ACA（附件充电器适配器）： ACA 有一个用于充电的充电器端口、一个用于便携设备的 OTG 端口和一个用于其他设备的附件端口。ACA 可使便携设备在充电的同时连接其他设备。
ACA-Dock: ACA-Dock 有一个上游端口（Micro-A 插头）和多个或没有下游端口。当连接到 ACA-Dock 上游端口时，便携式设备可吸收的最大电流为 1.5 A。ACA 和 ACA-Dock 的最大区别在于 ACA 支持 OTG 端口，可以作为 A 设备或 B 设备连接便携设备。

CDP (Charging Downstream Port): This USB Port has a higher charging capacity. It offers USB data transmission and is also capable of supplying a maximum current of 1.5 A to a BC1.2 compatible device.
DCP (Dedicated Charging Port): A CDP without USB data transmission, this port can supply a voltage of 4.75V-5.5V and a charging current of 1.5A to a BC1.2 portable device. A DCP will have a resistance R bridged between D+ and D-.
ACA (Accessory Charger Adaptor): ACA has one Charger Port for charging, one OTG Port for a portable device and one Accessory Port for other devices. ACA enables the portable device to connect to other devices while being recharged.
ACA-Dock: ACA-Dock has one Upstream Port (Micro-A plug) and more than one or no Downstream Ports. The portable device can absorb a maximum current of 1.5 A when connected to an ACA-Dock Upstream Port. The biggest difference between ACA and ACA-Dock is that ACA supports an OTG Port and can connect to a portable device as an A-Device or a B-Device.

4，SDP, CDP and DCP Comparison （充电对比表）

5，Five Steps to Check for BC1.2 Charging Support （检查 BC1.2 充电支持的五个步骤）

支持 BC1.2 的手机如何知道自己连接的是支持 BC1.2 的 SDP、CDP 还是 DCP？图 1（如下）展示了一个简单的流程，图 2 则提供了更详细的说明。

How can a mobile phone that supports BC1.2 know whether it is connected to an SDP, a CDP or a DCP supporting BC1.2? Figure 1 (below) illustrates a simple flow, while Figure 2 offers a more detailed description.

图1：Simple Steps to Check for BC1.2 Charging Support (检查是否支持 BC1.2 充电的简单步骤)

图2： Detailed Steps to Check for BC1.2 Charging Support （检查是否支持 BC1.2 充电的详细步骤）

5.1 VBUS Detect (VBUS检测)：

手机连接到 USB 充电端口。当检测到 Vbus 电压大于内部有效电压阈值时，表示手机连接到了有效电路。

The mobile phone connects to a USB charging port. When it detects a Vbus voltage which is greater than the internal effective voltage threshold, it means that the mobile phone is connected to an effective circuit.

5.2 Data Contact Detect (DCD) （数据触点检测）：

手机检测所连接的充电端口是否支持 BC1.2。手机在 D+ 上输出电流（IDP_SRC），然后检测 D- 上的电压值，以确认 D+/D- 引脚是否成功连接。由于不要求手机支持 DCD，因此采用了另一种机制：手机将在一段时间（TDCD_TIMEOUT）后进入步骤 3 进行检测。DCD 的优点是，手机可以在判断连接成功后立即进入步骤 3 进行检测，从而减少等待时间。

The mobile phone detects whether the connected charging port supports BC1.2. The phone outputs current on D+ (IDP_SRC) and then detects the voltage value on D- to confirm whether the D+/D- pins are successfully connected. As the mobile phone is not required to support DCD, another mechanism is used: the mobile phone will enter Step 3 for detection after a period of time (TDCD_TIMEOUT). The advantage of DCD is that the mobile phone can enter Step 3 for detection immediately after judging that connection is successful, thus reducing waiting time.

判断适配器是否完全接入手机USB座子。判断完VBUS接入后，随后即是判断数据信号的连接是否到位。当Attached时，手机端的D+的IDP_SRC(大概10uA)打开，因为D+端接了一个电阻RDP_DWN(20K左右)下地，所以D+会存在一定的小电压200mV，当电压小于参考值时，说明USB接入良好。所以在波形上看D+最前端存在一个非常小的电压起伏。

然而DCD的检测并不是必须要执行，如果没有执行DCD的检测，协议会在VBUS有效后的T DCD_TIMEOUT开始执行后面的步骤(后面的波形是没有执行DCD检测的情况)。

5.3 Primary Detection（主要检测）：

手机会检测所连接的充电端口是否支持 BC1.2。也就是说，手机会检测所连接的是 SDP、CDP 还是 DCP。手机将在 D+ 上提供一个电压（VDP_SRC），然后比较 D- 上的 VDM 和 VDAT_REF。

The mobile phone detects whether the charging port connected supports BC1.2. That is to say, the mobile phone detects whether it is connected to an SDP, CDP or DCP. The mobile phone will supply a voltage (VDP_SRC) on D+ and then compare VDM and VDAT_REF on D-.

如果 VDM 大于 VDAT_REF，则可能连接的是 CDP 或 DCP，然后继续执行步骤 4。

如果 VDM 小于 VDAT_REF，则肯定连接的是 SDP，过程结束。

If VDM is greater than VDAT_REF, it may be connected to a CDP or a DCP, and proceed to Step 4 for

If VDM is less than VDAT_REF, it is definitely connected to an SDP and the process is complete.

5.4 Secondary Detection（二次检测）：

二次检测确认与手机连接的 BC1.2 充电端口是否支持 USB 数据传输（DCP 或 CDP）。手机将在 D- 端提供一个电压（VDM_SRC），然后比较 D+ 端的 VDP 和 VDAT_REF。

Secondary detection confirms whether the BC1.2 charging port connected to the mobile phone support USB Data transmission (DCP or CDP). The mobile phone will supply a voltage (VDM_SRC) on D-, and then compare VDP and VDAT_REF on D+.

a，如果 VDP 大于 VDAT_REF，则连接到 DCP。

b，如果 VDP 小于 VDAT_REF，则连接至 CDP

a. If VDP is greater than VDAT_REF, it is connected to a DCP

b. If VDP is less than VDAT_REF, it is connected to a CDP

5.5 ACA Detection (ACA检测)：

ACA 检测仅针对带有 Micro-AB 接口的便携式设备。便携式设备会检测是否连接到 ACA 充电端口，并确定设备类型。它主要通过检测 ID 引脚上的五个不同电阻来进行判断。

ACA Detection is conducted only for a portable device with a Micro-AB socket. The portable device detects whether it is connected to an ACA charging port and determines the device type. It mainly makes this determination by detecting the five different resistances on the ID pin.

6, How BC1.2 Mobile Phones Determine If They Are Connected via SDP, CDP or DCP

[ BC1.2 移动电话如何确定连接的是 SDP、CDP 或 DCP ]

6.1 Case (I) BC1.2 mobile phone connects to SDP (no BC1.2 support)

[ 第一种情况，BC1.2 移动电话连接到 SDP（不支持 BC1.2） ]

a. 手机（便携设备）连接至 SDP 并检测到与 VBUS 的连接（VBUS > VOTG_SESS_VLD）。

b. DCD 检测超时

c. 移动电话在 D+ 上提供电压 VDP_SRC (0.5V - 0.7V)，通过 SDP 上的 RDP_DWN (14.25 - 24.8kΩ)连接到地，然后比较 D- 上的 VDM 和 VDAT_REF。

如果 VDM（0V）小于 VDAT_REF（0.25V - 0.4V），则表示它已连接到 SDP，过程完成。

a. The mobile phone (Portable Device) connects to SDP and detects connection to VBUS (VBUS > VOTG_SESS_VLD)

b. DCD detection timeout

c. The mobile phone supplies a voltage VDP_SRC (0.5V - 0.7V) on D+, connects to ground via RDP_DWN (14.25 - 24.8kΩ) on SDP, and then compares VDM and VDAT_REF on D-

At this time, if VDM =0 V. If VDM (0V) is less than VDAT_REF (0.25V - 0.4V), it means it is connected to SDP, and that the process is complete

6.2 Case (II) BC1.2 mobile phone connects to CDP

[ 第二种情况，BC1.2 移动电话连接到 CDP ]

图4： Primary Detection, CDP and Secondary Detection, CDP

a. 手机连接到 CDP 并检测到 V BUS（V BUS > V OTG_SESS_VLD ）连接

b. DCD 检测超时

c. 初级检测（图 4 - 左）：手机在 D+ 上提供电压 VDP_SRC (0.5V - 0.7V)，并通过 CDP 上的 RDP_DWN (14.25 - 24.8kΩ) 与地连接

i. CDP 检测 D+=VDP_SRC (0.5V-0.7V)，然后启用 CDP 的 VDM_SRC (0.5V-0.7V)

ii. 如果手机检测到 D-=VDM_SRC (0.5V-0.7V)，大于 VDAT_REF (0.25V-0.4V)，则连接至 CDP 或 DCP

d. 二次检测（图 4 - 右）：手机在 D- 上提供一个电压 VDM_SRC（0.5V-0.7V）。

i. 此时，D+ ≈0 V，如果手机 DCP_DET 检测到 D+ 小于 VDAT_REF（0.25V-0.4V），则将其连接至 CDP。

ii. 然后，手机禁用 VDP_SRC 和 VDM_SRC，并将 D+ 和 D- 保持在低电位。

a. The mobile phone connects to CDP and detects a V BUS (V BUS > V OTG_SESS_VLD ) connection

b. DCD detection timeout

c. Primary detection (Figure 4 – left): The mobile phone supplies a voltage VDP_SRC (0.5V - 0.7V) on D+, and connects to ground via RDP_DWN (14.25 - 24.8kΩ) on CDP

i. CDP detects D+=VDP_SRC (0.5V-0.7V), and then enables VDM_SRC (0.5V-0.7V) of CDP

ii. If the mobile phone detects D-=VDM_SRC (0.5V-0.7V), greater than VDAT_REF (0.25V-0.4V), it is connected to CDP or DCP

d. Secondary detection (Figure 4 – Right): The mobile phone supplies a voltage VDM_SRC (0.5V-0.7V) on D-

i. At this time, D+ ≈0 V, if the mobile phone DCP_DET detects that D+ is less than VDAT_REF (0.25V-0.4V), it is connected to CDP

ii. Then the mobile phone disables VDP_SRC and VDM_SRC, and keeps D+ and D- at low potential

6.3 Case (III) BC1.2 mobile phone connects to DCP

[ 第三种情况，BC1.2 移动电话连接到 DCP ]

图5： Primary Detection, DCP and Secondary Detection, DCP

a. 手机连接到 DCP 并检测到 V BUS（V BUS > V OTG_SESS_VLD ）连接

b. DCD 检测超时

c. 初级检测（图 5 - 左）：手机在 D+ 上提供电压 VDP_SRC (0.5V-0.7V)，并通过 DCP 上的 RDCP_DAT (<200Ω) 连接到 D-

i. 如果手机检测到 D- ≈ VDP_SRC (0.5V-0.7V) 大于 VDAT_REF (0.25V-0.4V)，则连接至 CDP 或 DCP（RDCP_DAT 的最大压降为 200Ω x 175μA= 0.035V）

d. 二次检测（图 5 - 右）：手机在 D- 上提供电压 VDM_SRC (0.5V-0.7V)，通过 DCP 上的 RDCP_DAT (<200Ω) 连接到 D-，并启用 IDP_SINK (25μA -175μA)

i. 如果手机检测到 D+ ≈ VDM_SRC (0.5V-0.7V) 大于 VDAT_REF (0.25V-0.4V)，则将其连接至 DCP（RDCP_DAT 的最大压降为 200Ω x 175μA= 0.035V）。

ii. 然后，手机启用 VDP_SRC。

a. The mobile phone connects to DCP and detects to V BUS (V BUS > V OTG_SESS_VLD ) connection

b. DCD detect timeout

c. Primary Detect (Figure 5 – Left): The mobile phone supplies a voltage VDP_SRC (0.5V-0.7V) on D+, and connects to D- via RDCP_DAT (<200Ω) on DCP

i. If the mobile phone detects D- ≈ VDP_SRC (0.5V-0.7V) greater than VDAT_REF (0.25V-0.4V), it is connected to CDP or DCP (maximum voltage drop of RDCP_DAT is 200Ω x 175μA= 0.035V)

d. Secondary Detect (Figure 5 –Right): The mobile phone supplies a voltage VDM_SRC (0.5V-0.7V) on D-, connects to D- via RDCP_DAT (<200Ω) on DCP and enables IDP_SINK (25μA -175μA)

i. If the mobile phone detects D+ ≈ VDM_SRC (0.5V-0.7V) greater than VDAT_REF (0.25V-0.4V), it is connected to DCP (maximum voltage drop of RDCP_DAT is 200Ω x 175μA= 0.035V)

ii. Then the mobile phone enables VDP_SRC.

总结，根据波形总结，在识别阶段，Primary Detect由D+发起，Secondary Detect由D-发起。SDP DCP CDP三者在波形上的区别，SDP在Primary Detect就被识别，所有永远只有一次位于D+的高电平。DCP由于D+ D-被电阻短接在一起，所以D+与D-永远保持一样的电平状态，两次都位于高电平状态。CDP则是看为二者的波形中和，D+只存在一次高电平，D-存在两次高电平。

7，BC 1.2 Test Items (BC 1.2测试项)

BC1.2 测试的主要目的是确认 BC1.2 通信的正确性和 Vbus 电源的质量。

The BC1.2 test is conducted mainly to confirm correct BC1.2 communication and Vbus power supply quality.

7.1 CDP test items for certification (CDP 认证测试项目):

7.2 DCP test items for certification（DCP 认证测试项目）:

8，Conclusion （结论）

USB Type-C Power Delivery 的快速充电支持既能满足现代效率需求，又能向下兼容便携式设备。BC1.2 规定的充电端口允许便携式设备消耗更多电流，从而加快充电速度。通过了解 BC1.2 的基本工作原理和测试项目，制造商可以最大限度地减少设计问题，生产出符合现代市场需求的产品。

USB Type-C Power Delivery's fast charging support meets modern needs of efficiency while also providing downwards compatibility with portable devices. Having a charging port defined by BC1.2 allows portable devices to draw more current to facilitate faster charging. By understanding the basic operating principles and test items surrounding BC1.2, manufacturers can minimize design problems and produce products that are in line with modern market demands.

9，References （参考）