eMMC深入浅出第六章 eMMC时序第一节 eMMC电源完整性

Section 1 eMMC Power Integrity

第一节 eMMC电源完整性

Power is so important that it could bring some unexpected consequence once not handled properly. Before starting the power topic, we need first clarify some concepts. What are VCC VCCQ VDD VSS? To knowing better what they are, we need start from semiconductor basic unit MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

电源是如此重要，如果没有处理好会带来不可预料的后果。我们开始电源话题之前，我们先要澄清一些概念。什么是VCC VCCQ VDD VSS？要更好的知道他们是什么，我们需要从半导体的基本单元MOSFET（金属氧化物半导体场效应管）说起。

In MOSFET, there are three gates, Control Gate, Source Gate and Drain Gate. Source Gate is where to provide negative electrons or positive holes, that is why we call it source. Electrons or Holes are drained at Drain Gate, and these activities are through the channel in the silicon substrate that is opened by providing high voltage to the Control Gate. Usually, Drain Gate is also connected with High Voltage as Control Gate, and Source Gate is connected to the low voltage Ground. Now we have the names VCC for voltage on Control Gate, VDD for voltage on Drain Gate, which both represent high voltage. While VSS is for the voltage on Source Gate, similar to GND (Ground voltage).

在MOSFET中，有三个极，栅极，源极和漏极。源极是提供负电子或者正空穴的，这是我们为什么称他为源极。电子或者空穴在漏极耗尽，这些动作通过给栅极加高电压打开的硅衬底的隧道来实现。通常，漏极也和栅极一样会连接到高电压，源极会连接到低电压地。所以我们现在给栅极电压命名VCC，漏极为VDD，都表示高电压。而VSS是源极的电压，和GND（低电压）类似。

The last one is VCCQ. Letter Q is usually to represent the data lines in the digital circuit, like DQ (Data lines), so VCCQ is the Power supply for the signals lines（generally we call them I/O）. Specifically, VCC is for the NAND Falsh in the eMMC device, VCCQ is for the controller in the eMMC device which provide the I/O interface. Both NAND Flash and eMMC device controller are composed by MOSFET, but with different semiconductor lithography process technology.

最后一个是VCCQ。字母Q通常代表数字电路里的数据线，比如DQ（数据线），所以VCCQ就是信号线（统称为I/O）的供电电压。特别注意，VCC是给eMMC器件的NAND闪存供电，VCCQ是给提供I/O接口的eMMC器件的控制器供电的。NAND闪存和eMMC器件控制器都是由MOSFET构成，只不过是用了不同的半导体制程技术。

There is a range for each of the power supply. For the high voltage 3.3V, range is from 2.7V to 3.6V. For the low voltage 1.8V, range is from 1.7V to 1.95V. Since 1.2V voltage on VCCQ is not used until now, just neglect it. Nevertheless, remember the lower voltage is for the higher I/O speed, since eMMC bus frequency is up to 200Mhz in the last specification and no update for 6 years, this is the reason why 1.2V voltage is not used.

每一个电压都有一个范围。高电压3.3伏的范围是2.7伏到3.6伏。低电压1.8伏的范围是1.7伏到1.95伏。由于1.2伏VCCQ到现在也没有用，就不用管他了。但是，记得更低的电压是为了更高的I/O速度，因为eMMC总线的频率在最后一版规范里最高只到200Mhz，六年都没有更新了，所以1.2伏电压没有使用。

The power ramp-up time tPRUH（time of PoweR Up High voltage 3.3V）and tPRUL （time of PoweR Up Low voltage 1.8V）are the two criteria of the power timing we could get from eMMC specification, they are quite easy to meet since the unit is millisecond. In the next sub topic of PI, we need to talk about something that we really need to take care about but often be neglected.

电源上电时间tPRUH（3.3伏高电压上电时间）和tPRUL（1.8伏低电压上电时间）是我们可以从eMMC规范中得到的两个电源时序指标，他们因为单位是毫秒所以非常容易达到。在下一个PI的子话题里面，我们需要聊一聊那些我们真正需要关心的但是经常被忽视的事。

Rule number one, during the power ramp-up and power down, no any host command input is allowed. Because eMMC device is not ready during Power ramp-up and It could not guarantee to complete the Host command during power down. Before power down, there should be CMD6 with Power Off Notification either SHORT or LONG argument if PoN supported by eMMC device.

第一条规则，在上电和下电过程中，不允许有主机的任何命令。因为eMMC器件在上电过程中没有准备好，在下电过程中也不能保证完成主机命令。在下电之前，如果eMMC支持PoN，需要有CMD6带SHORT和LONG参数的下电提示。

Rule number two, only VCC could be cut off when eMMC device enter Sleep state, VCCQ should be kept on for receiving of wakeup command. Before VCC being cut off and eMMC device goes into sleep, need CMD6 with Power Off Notification SLEEP argument and CMD5 for sleep, then CMD7 for deselecting the eMMC device.

第二天规则，在eMMC器件进入休眠状态，只能切断VCC，VCCQ需要保持以用来接收唤醒命令。在VCC被切断以及eMMC进入睡眠状态之前，需要用CMD6带下电提示睡眠的参数，以及CMD5睡眠，然后用CMD7来取消选择eMMC器件。

Rule number three, when either VCC or VCCQ is below 0.5V for more than one millisecond except in the sleep state, eMMC device will return to Pre_Idle state.

第三条规则，除了睡眠状态之外，不论是VCC或是VCCQ低于0.5伏超过1毫秒，eMMC器件会回到预闲置状态。

Rule number four, remember to check if the VCC and VCCQ are within the operating range during both the eMMC bus idle time and active time. Why? Because voltage is the reflection of the power consumption. When doing the read and write operations, so called eMMC bus active time, we could check if there is drop on the VCC and VCCQ power trail to know the current provided by the host is enough or not.

第四条规则，记得要在eMMC总线闲置或者活跃状态都要检查VCC和VCCQ是否在操作范围之内。为什么？因为电压手机是电源消耗的反应。当做读和写的操作时，也就是eMMC总线的活跃时，我们可以通过检查VCC和VCCQ电源线上有没有电压降来了解主机提供的电流是否足够。