How to do for the io pin of imx6Q when imx6q is powered off?

[翔李]

HI,

Now I use my imx6q-board for car production,I add a mcu-STM32F042G6U6 connecting to IMX6Q to monitor the car's battery power in for my board.The mcu's NRST pin connects to IMX6Q'S io,Now when MCU power off the IMX6Q,then MCU also  be disturbed and outputs wrong signal,it maybe come from the effect of imx6q's pin when it is powering off.

when it occurs,the NRST signal-R932 some times drop to 2.2V suddenly then rise up to 3.3v,some times keep all 3.3V right status.

So,what can I do for solving the problem? I want to know how to do to solve the disturb of imx6q and mcu?

Following is sch,Thanks.

[art]

According to the schematic you've provided, the IO pin of the i.MX6Q processor is always externally driven by the R929 pull-up resistor, even when the i.MX6Q processor is powered off. This situation is absolutely not allowed. No GPIO pins of the processor must be driven by any external voltage when the processor is powered off. When not powered, a GPIO buffer becomes non-functional and behaves randomly if driven by any external voltage. So, some isolation buffer circuit is required here between the MCU and the i.MX6Q processor.

Have a great day,
Artur

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[翔李]

Thanks.

1:Please recommend some isolation ic(1 chaneel and 8 channel style) name for me.Do you have sch for IMX connect to MCU or other externally circuit,give it to me,Thanks.

2:Can the NPN or PNP do isolate between IMX6Q-MCU?

3:what is the reason of behaves randomly-imx6q?Is it the sink current of the IMX6Q'S IO pin?So what is way to solve the problem？

[art]

Q. Can the NPN or PNP do isolate between IMX6Q-MCU?

A. What is the signal direction? Is it from i.MX6Q (GPIO output) to MCU (input)? If so, you can use a N-channel FET to isolate the signal. An external pull-down resistor on the FET's gate is required in that case.

Q. Is it the sink current of the IMX6Q'S IO pin?

A. Yes.

Q. So what is way to solve the problem?

A. The only way to fix the issue is to not drive a GPIO pin with any external voltage source when the processor is powered down.

Artur