i.MX28 hangs on unplugging the wallsocket

[rpjknoop]

We have a custom board with u-boot and Linux running. We run using the 5V-only option.

We have a Gold-Cap connected to the BATTERY pin, we use the application note from Freescale for this.

When we disconnect the external power supply by removing the power cord, all goes well.

When we disconnect the external power supply by unplugging the wall socket, the i.MX28 does not start anymore.

The difference is due to the capacitors in the power supply, it caused the 5VDC to slowly drop when being unplugged.

What we see is:

- when we enable power again, we see that the gold-cap is being drained.

- the 4V2 power supply is zero.

We can only restart the i.MX28 by removing power and discharging the Gold-Cap.

So we get a lock-up when the 5V is slowly dropping (1 sec.) and the i.MX28 seems to want to use the BATTERY as power supply.

We used u-boot (when it boots) to check the several registers but all seem to be OK. The HW_POWER_DCDC4P2 register is configured so it will use the DCDC_4P2 as the power source.

What can cause that the 4P2 power supply is not present after a slow drop of the 5V?

And how can we fix this without having to drain the gold-cap.

Thanks in advance.

[igorpadykov]

Hi Richard

recommended schematic in case of 5V sags in attached

file "RESET CIRCUIT OPTIONS" or similar can be implemented

in external power supply. When processor hangs, 4P2 power supply

may not present because it is turned on by software.

Best regards

igor

[rpjknoop]

Hi Igor,

thanks for your reply. We will look into this.

Do you know in what state the i.MX28 is, when it fails to start-up?

Why does draining the gold-cap help?

I just try to understand how this is happening.

Best regards,

Richard

[igorpadykov]

Hi Richard

one can check where processor fails adding printfs

to  bootlets sources (like init-mx28.c):

1. ./ltib -m prep -p imx-bootlets

This command will put imx-bootlets source codes in the folder --

ltib/rpm/build/

2. modify sources

3. ./ltib -m scbuild -p  imx-bootlets

This command will build new images.

Usually issues with enablement DCDC4P2 (gold-cap)

are related to erratum 5837.

Best regards

igor

[rpjknoop]

Hi Igor,

we are using bitbake/open embedded.

You mention errata 5837. I am looking for a "spl_power_init.c" (5V-Only) where this work-around is already applied. No need to do the job twice.

Do you know where I can find this? The current u-boot sources does not seem to contains this work-around.

Best regards,

Richard

[igorpadykov]

Hi Richard

work-around is impemented for i.MX28 EVK reference board.

For any other board parameters defined in errata 5837

should be adjusted according to board specific. Also

there are other brownout levels for other power supplies -

they should be checked for brown-out conditions too.

All these levels may vary from one board to another.

~igor