Question, i.MX28 PSWITCH handling

[Aemj]

Hi all,

I would like to ask about PSWITCH handling of i.MX28.

My customer is facing the issue that i.MX280 cannot startup on their two proto boards out of 30 boards.

They are using i.MX280 with 5V power supply pin opened, and feeding 3.3V to Battery pin.

To enable internal DC/DC, PSWITCH is connected to VDDXTAL directly to set PSWITCH to mid-level.

In i.MX28 datasheet, it is described as below.

“A MID LEVEL PSWITCH state can be generated by connecting the VDDXTAL output of the SoC to PSWITCH through a switch.”

(1)

Is it possible to connect PSWITCH to VDDXTAL always?

For test, they cut the connection between PSWITCH and VDDXTAL and changed the connection of PSWITCH as below.

Then they saw i.MX28 could boot-up normally.

But when they removed the capacitor from above circuit, i.MX28 could not boot-up(DC/DC did not start).

It seems that the rise of PSWITCH voltage needs delay.

(2)

Are there any requirements on the power-up sequence of PSWITCH?

Thanks,

Miyamoto

[Yuri]

Hello,

According to the i.MX28 Design Checklist, linked below,

it is not recommended to connected PWITCH to VDDXTAL directly,

as it cannot be asserted when asserting RESETN.

https://community.freescale.com/docs/DOC-98792

Have a great day,
Yuri

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[Aemj]

Hi Yuri,

Thanks for your reply and sorry for my late response.

Is it possible to feed about 1V to SPWITCH during asserting RESETN?

Thanks,

Miyamoto

[Yuri]

Yes.

~Yuri.