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Question, i.MX28 PSWITCH characteristic and recovery mode

Question asked by AVNET JAPAN FAE (team share account) on Dec 1, 2014
Latest reply on Dec 2, 2014 by Artur Petukhov

Dear team,


I would like to ask about the PSWITCH of i.MX28 and recovery mode.


The reference manual of i.MX28 says as follows.

“There is an integrated 5-KΩ resistor that can be switched in between the VDDXTAL pin and PSWITCH. If enabled using HW_RTC_PERSISTENT0_AUTO_RESTART, then the device immediately begins the power-up sequence after power-down.”

Can I understand that one can control the internal connection between PSWITCH and VDDXTAL?

And can the switch be enabled only by using HW_RTC_PERSISTENT0_AUTO_RESTART?



When PSWITCH was fed from external on my customer’s board, they saw the actual voltage of PSWITCH was lower than the calculated voltage from external register value. PSWITCH seems to have internal impedance.

And they saw when PSWITCH pin was pulled down to GND with 100Kohm register, the voltage of PSWITCH was 0V. In this case, PSWITCH seems not to have internal impedance.

In datasheet(IMX28CEC Rev.3) at the footnotes of Table-11, it is said as follows.

“PSWITCH acts like a high impedance input (>300 kΩ) when the voltage applied to it is less than 1.5V. However, above 1.5V it becomes lower impedance.”

Can I understand the phenomenon the customer saw is caused by the impedance change of PSWITCH?



The question from my customer is;

When does the sampling of PSWITCH voltage to decide whether i.MX28 enters into recovery mode start? After the release of reset? Or before the release of reset?

I believe it must be done after the release of reset, right?