imx28 Brownout GPIO behavior

[franzforstmayr]

Dear all,

Our IMX28 switches off in an brownout condition. I have an 47k Pullup from a GPIO to VDDIO. When VDDIO begins to sink due to the VBATT brownout, i can see an instant drop of 1V over the resistor, which means, there's an 20µA current flowing in the GPIO. Is there any specification about this behavior.

Is there any way to recognise the brownout moment by hardware?

yours

Franz

[igorpadykov]

Hi Franz

in general VDDIO brownout can be configured with

register HW_POWER_VDDIOCTRL,  BO_OFFSET value. However

I do not think that such small 20µA current flowing in the GPIO

may cause VDDIO brownout. It may be recommended to pay more attention

to VBATT voltage and probably add there capacitor.

Best regards

igor

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[franzforstmayr]

Hi Igor,

i think we talk from different things.

We set the brownout to 2.4V, in normal usecase there's a 4V LDO which is charging an electrolyt capacitor on VBATT. In an Powerloss event, the electrolyt capacitor can supply the imx28 for about 50ms, to save our data.

So the brownout is ok in this case, it's a result of the discharging capacitor.

In brownout condition VDDIO, (3.25V in our case) begins to decrease slowly, in the same moment, there's a current of about 10µA (Sorry, i had a false voltage value yesterday) flowing into the input pin.

Green: VDDIO

Blue: LCD_D02/ETM_DA2/GPIO1_2

As you can see, there's an instant drop of 0,5V, so there's a current of 10µA.

The blue signal is directly pulled directly to VDDIO, no other connections on my application.

Is it possible, that the gate keepers draw the current at first moment after reset?

[igorpadykov]

Hi Franz

so issue is not observed with disconnected GPIO1_2 ?

~igor

[franzforstmayr]

Hi,

i can see this behavior on every pin with an pullup resistor.

With an pulldown resistor it's not visible of course.