Question, i.MX28 power block

[Aemj]

Hi All,

My customer is developing their i.MX28 custom board.

As for the power supply, they want to use VDD5V for normal operation.

And when the VDD5V is lost, i.MX28 has to continue to work with DCDC_BAT input for system shutdown operation. After the shutdown operation, i.MX28 should be powered-off.

For the above operation, the customer is considering how they should construct the power block including register setting.

Their understanding is as below.

Are those correct?

(1)

When PSWITCH is pulled-up, i.MX28 will go into re-boot after VDD5V is lost whether HW_POWER_RESET_PWD_OFF bit is 0.

In this case, to power-off i.MX28, one has to clear PWD_OFF bit and then set PWD bit.

(2)

When PSWITCH is pulled-down, i.MX28 will go into power-off right after VDD5V is lost if HW_POWER_RESET_PWD_OFF is cleared.

In this case, one has to clear PWD_OFF bit after the necessary processing when VDD5V is lost to make i.MX28 power-off.

Please show me how they should construct the power block and the register settings.

Thanks,

Miyamoto

[art]

The case 2 you've listed seems to be the most appropriate one. PSWITCH should be

pulled down with a weak (e.g. 100kOhm) resistor with some shunt capacitor in

parallel, as it is done on the i.MX28 EVK reference board. Also, an optional

pushbutton that pulls PSWITCH up to VDDXTAL voltage can be provided. It might be

useful for some "emergency start" function.

Regarding the schematics of the power supply and PSWITCH/RESET sections, please

ask the customer to exactly follow the i.MX28 EVK board design that can be found

on the NXP web site (check the "Schematics" section):

http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/i.mx-applications-process...

Regarding the register settings for the Power Supply module, ask the customer to

exactly follow the ones, provided by the L2.6.35_1.1.0 Linux BSP. The BSP source

code and demo images can also be found on the link above (check the "Board

Support Packages" section).

Have a great day,
Artur

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[Aemj]

Hi Artur,

Thanks for your answer.

Could you show me the reason why (2) is better than (1)?

Thanks,

Miyamoto

[art]

The Case 2 is better than Case 1 since it provides more stable PSWITCH environment and prevens wrong PSWITCH triggering.

Best Regards,

Artur