Question, eMMC supply voltage change

[SLICE]

Dear team,

I would like to ask about changing supply voltages, 3.3/1.8V, of eMMC with i.MX6SX.

This inquiry is related to the following post.

https://community.nxp.com/thread/452620

The customer understand that SD3 or SD4 can be used for eMMC connection and they want to add the feature of supply voltage change of eMMC for their board.

In the case of using SD3 port for connecting to eMMC, my customer has a concern on the deviation of the timing between a changing the voltage of eMMC power supply and a changing i.MX6SX’s internal operation voltage.

If the deviation exists, they believes that SW needs to know when the voltage change has been completed.

(1)

Are there any ways to detect the voltage change of eMMC has been actually completed?

(2)

In the case of using SD4 port;

Can I understand that the timing deviation such as above does not occur by using SD4_VSELECT pin for changing eMMC voltage?

Thanks,

Miyamoto

[weidong_sun]

Hello Miyamoto,

     You misunderstood my meaning , For your application, you should connect eMMC chip to SD3 port, because voltage of SD3 port can be selected by BOOT_CFG2[1] when booting board.

Before booting board, we can set LCD1_DATA09 pin to be High or Low, telling ROM code in processor what voltage for eMMC device will be supplied. You can also use the feature to control what voltage will supply eMMC device through external circuit of voltage selection.

    See below, whichi is a part of schematic of i.MX6SX evk:

NVCC_HIGH & NVCC_LOW are power input pins of SD3, so ROM CODE can select 3.3V or 1.8V to be SD3 IO power, but there is only one power input for SD4 port, NVCC_SD4, we can't use 3.3V and 1.8V at the same time to be power input for SD4. Even if you add an external swtching circuit for 3.3V or 1.8V, and using SD4_VSELECT to switch them, you can't also realize your solution, see below:

If we use SD4_VSELECT pin to control voltage selection, before booting, we should set boot configuration select pins(LCD pads, see last page of i.mx6sx evk schematic), and tell ROM code what level will be output on SD4_VSELECT(KEY_ROW1), BUT there is no LCD pin for the configuration. So there is no way to control output(High or LOW) of SD4_VSELECT, then if we use the SD4_VSELECT, how to switch voltage between 3.3V and 1.8V?

    This is the reason why SD3 port is recommended to your application.

Have a great day,
TIC   Weidong Sun

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[SLICE]

Hello weidong.sun‌

Thanks for your kindly explanation!

We understand that using SD3 is good, because;

- As for SD3, when boot-up, changing 3.3/1.8V can be done by setting BOOT_CFG pins.

- As for SD4, one cannot specify VSELECT at boot-up and the supply voltage to eMMC is unknown.

Please give your answer to the following original question.

In the case of using SD3 port for connecting to eMMC, my customer has a concern on the deviation of the timing between a changing the voltage of eMMC power supply and a changing i.MX6SX’s internal operation voltage.

Are there such deviation?

If so, the customer thinks that they can use SD4 with connecting external pull-down via 10K Orm to SD4_VSELCT.(supply voltage of eMMC will be 3.3V)

Is it true?

Thanks,

Miyamoto

[SLICE]

Hello weidong.sun‌

I am still waiting for your comment!

Thanks,

Miyamoto

[weidong_sun]

Hello Masamichi,

    Sorry for my late reply!  I asked for help form i.MX Expert team on the question, and got their reply , see below:

-------------------------------------------------------------------

1. In normal use case, you just need fixed the eMMC VCCQ (with NVCC_SDx) in 1.8V. Add the voltage selection is not necessary.

2. In case use SD3 port to connect eMMC

    Usually, use SD3 port connect to SD Card is recommended. (SD Card doesn't need VCCQ switching)

    You can use BOOT_CFG2[1] to controls the NVCC_SD3 default voltage value, but you need use GPIO to controls the external power switch for VCCQ in eMMC side (please make sure the default voltage values are same)

    And you need add some delay time in SD driver when switching the bus voltage.

3. In case use SD4 port to connect eMMC

    Please add an external power switch (1.8/3.3V) to supply "NVCC_SD4" in MX6SX and VCCQ in eMMC, and use SD4_VSELECT pin to controls the external power switch.

    And you need add external pull up/down resistor for SD4_VSELECT (KEY_ROW1) to define the default value to controls the external power switch to output 3.3V in default.

-----------------------------------------------------------

Have a nice day!

Best Regards,

Weidong Sun