How to terminate PSWITCH of iMX280 (VDD5V only)

[hikaruuruno]

Hello all,

Should we leave PSWITCH floating, or pull it down with weak registor (ca. 100k-ohm) in case off VDD5V source only configuration?

On the one hand, Item 19 of i.MX_HW_DESIGN_CHECKLIST_v1.2 mentions "It can be left floating."

On the other hand, Yuri Muhin's reply to a question was "PSWITCH should be pulled down."

(https://community.nxp.com/message/452203)

Which is true and why?

*Following is the background.*

We are having a problem with our custom board.

The board is 5V source only configuration and PSWITCH is left floating as mentioned in the design checklist.

There was no problem when we evaluated the board alone.

However, when we embedded the boards in an apparatus, some of the boards started to malfunction.

In the serial log of the malfunctioning one, a line "pswitch goto suspend" appears frequently.

So we assumed that PSWITCH is affected by the noise from the apparatus, and the same symptom could be reproduced without apparatus when we soldered a 4-inch wire to PSWITCH.

Now, we need to modify the board to be noise-proof. We also need to know why the method is appropriate.

Please help us.

(part of the log)

[    4.100000] pswitch goto suspend

[    4.100000] PM: Syncing filesystems ... done.

[    4.130000] Freezing user space processes ...

[    4.210000] UBIFS: recovery needed

[    4.310000] UBIFS: recovery completed

[    4.310000] UBIFS: mounted UBI device 0, volume 0, name "rootfsA"

[    4.320000] UBIFS: file system size:   24887296 bytes (24304 KiB, 23 MiB, 196 LEBs)

[    4.330000] UBIFS: journal size:       9023488 bytes (8812 KiB, 8 MiB, 72 LEBs)

[    4.330000] UBIFS: media format:       w4/r0 (latest is w4/r0)

[    4.340000] UBIFS: default compressor: lzo

[    4.340000] UBIFS: reserved for root:  0 bytes (0 KiB)

[    4.350000] VFS: Mounted root (ubifs filesystem) on device 0:13.

[    4.360000] devtmpfs: mounted

[    4.370000] Freeing init memory: 140K

[    4.430000] (elapsed 0.29 seconds) done.

[    4.430000] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.

[    4.450000] Suspending console(s) (use no_console_suspend to debug)

[    4.460000] PM: suspend of devices complete after 9.437 msecs

[    4.470000] PM: late suspend of devices complete after 0.687 msecs

[    4.470000] wakeup irq = 6

[    4.480000] PM: early resume of devices complete after 0.468 msecs

[art · Accepted solution]

Of course, PSWITCH should not be left floating to improve its noise immunity. In 5V only power configuration, the application of VDD5V voltage is treated as power-on event itself, so, generally, PSWITCH is not required to generate a power-on event in that case. So, it can be pulled down to GND to improve the noise immunity.

Have a great day,
Artur

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[hikaruuruno]

Hi Autur,

I have one more question right now.

Does setting HW_POWER_RESET_PWD_OFF prevent the current "pswitch goto suspend" situation?

Thank you,

Hikaru

[art]

Yes, this is correct. However, when operating in highly noisy environments, software may have no time to set this bit before the PSWITCH initiated power down occurs. So, it is still better to use the hardware solution, i.e. pull PSWITCH down to GND.

Artur

[hikaruuruno]

Hi Autur,

Thank you for your replies.

They are very helpful.

Best regards,

Hikaru

[hikaruuruno]

Hi Artur,

Thank you for your reply.

Let me confirm something.

So in case of 5V only configuration;

1.PSWITCH "can be" left floating but it's not recommended.

2.PSWITCH works as power-down trigger.

To prevent unwanted power-down, it's better be pulled down.

Is my understanding right?

Thank you,

Hikaru

[art]

Yes, this is correct.

Artur