i.MX 6DL LDO_USB & LDO_2P5 configuration

[masahirokiniwa]

Hi, 

We have an issue about USB connection as below.

Could you tell us the suggested configuration range of LDO_USB and LDO_2P5?

(Currently BSP provided their values LDO_USB = 3.2V and LDO_2P5 = 2.5V, but we would like to know your suggested range of them for tuning them.)

If do you know the same issue and solution for it, could you tell us them?

<issue>

Sometimes i.MX cannot recognize the USB hub.

In this case, i.MX couldn't keep the USB specification Twidch (max 100us) in reset Hand shake protocol.

i.MX over the above time (USB Hub stop the CHIRP K, and i.MX start the CHIRP K.).

We checked the i.MX configuration and its time, and found below result.

<result>

1. When we down the LDO_USB voltage, its time is decreased.

2. When the deference of voltage LDO_USB and LDO_2P5 is small, the USB connection will be stable.

<Environment>

MPU : MCIMX6U5EVM10AC

USB Hub : USB2514B-I/M2

OS : Linux 3.14.52 (fsl-yocto-3.14.52_1.1.0)

Best regards,

M.Kiniwa

[weidong_sun]

Hello M.Kiniwa,

     PMU_REG_3P0 is USB LDO, which is used to supply USB PHY. it's output range is :

for i.MX6 processors , the output voltage should be less than 3.3V,  so We usually set this voltage to 3.0V and LDO 2P5 to 2.5V.

Have a nice day!
BR,

Weidong

[masahirokiniwa]

Hi Weidong,

Thank you for your reply.

Did you find the issue same as above?

If you have other solution for its timing issue, could you tell me it?

Best regards,

M.Kiniwa

[weidong_sun]

Hello Masahiro,

    >>Did you find the issue same as above?

    I have never heard the issue, and up to now there are no customer's feedback on above issue.

   >> test it.

    Because i.mx6q/d/dl/s adopts similar design architecture, and they use the same USB IP, so I tested on the customized i.mx6q board. The USB HUB chip is USB2514, and all the extended USB interfaces are normal.

  So the problem you encountered is a very strange phenomenon, which also confuses me.

  Could you tell me what output voltages of USB_LDO and LDO_2P5 can make your USB HUB stable?

Have a nice day!

BR,

weidong

[masahirokiniwa]

Hi weidong.sun,

I confirmed your question.

In this application, USB HUB use other 3.3V power line, so it doesn't use both USB_LDO and LDO_2P5.

And both USB _LDO and LDO_2P5 are supplied only for i.MX 6DL.

We have two additional question as below.

1. Can you tell me the reason why there is a difference between your recommendation USB_LDO=3.0V and the NXP original BSP setting USB_LDO=3.2V ?

2. Can I set the output voltage of USB_LDO down and/or the output voltage ofLDO_2P5 up to make the differential voltage of them smaller?

Is it out of your recommend if I set  USB_LDO=3.0V, LDO_2P5=2.6V ?

If I change the output voltage of LDO_2P5, is there any impact to other module inside CPU that I must take care ? 

Best regards,

M.Kiniwa

[weidong_sun]

Hi, M.Kiniwa,

>>1. Can you tell me the reason why there is a difference between your recommendation USB_LDO=3.0V and the NXP original BSP setting USB_LDO=3.2V ?

For i.MX6, USB_LDO should be less than 3.3V.  So 3.2V is no problem.

>>2. Can I set the output voltage of USB_LDO down and/or the output voltage ofLDO_2P5 up to make the differential voltage of them smaller?

--USB_LDO: yes, you can.  the Min value is 2.625V,  max is 3.4V.

--LDO_2P5:  you should pay attention to it's input voltage(2.8V ~3.3), Output should be less than Input.  it's the Min value is 2.10, nominal is 2.5V, even max is 2.875V, if you make it higher,  not more than 2.75V.

>>Is it out of your recommend if I set  USB_LDO=3.0V, LDO_2P5=2.6V ?

the setting is no problem.

>>If I change the output voltage of LDO_2P5, is there any impact to other module inside CPU that I must take care ?

There is no effect if you tune the LDO, 2.6V is within the range allowed.

Have an nice day!

BR,

Weidong

[masahirokiniwa]

Hi weidong.sun,

Thank you for your answer.

I have an additional question as below.

I have found the source code change the USB_LDO to 3.2V from default 3.0V in the original BSP released by NXP as below.

I understood USB_LDO should be less than 3.3V, and 3.2V is within the range allowed. 

But is there any particular reason why BSP change the voltage to 3.2V, not use the default value 3.0V? 

http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/tree/drivers/usb/phy/phy-mxs-usb.c?h=imx...

Best regards,

M.Kiniwa

[masahirokiniwa]

Hi weidong.sun,

Did you check my question?

Could you tell me the reason why the USB_LDO is changed in the BSP?

https://community.nxp.com/message/1248794?commentID=1248794#comment-1248794 

Best regards,

M.Kiniwa