Jetson TX2 GPIO power off state?

Autonomous Machines Jetson & Embedded Systems Jetson TX2
1

Hello,

I am using an GPO to enable/disable an IC which has an active low enable signal. My system is powered by a battery. When the TX2 is OFF I have that GPO connected to a 10k pull up (to keep my IC in an disabled sate when the TX2 is OFF) to a 1V8 (which is always on even when TX2 is OFF) .

Question is in the OFF state looks like the TX2’s GPO is pulling down the I/O line. My 10K pull up seems too weak and I read 0.34V on that I/O. Looks like there is a pull down on the GPIO in the OFF state. Why is this? What is the GPIO state of the TX2 in the OFF condition? Should it be High-Z?

4

Which GPIO pin do you mean and how did you configure that pin in pinmux?

5

@Trumany We’re using a custom carrier board and are needing to set GPIO3_PN.02 high when the Jetson is off.

The relevant device tree entry is:

gpio@2200000 {
    led-drv {
        gpio-hog;
        gpios = <TEGRA_MAIN_GPIO(N, 2) GPIO_ACTIVE_LOW>;
        output-high;
        label = "led-drv";
        status = "okay";
    };
};

We’re able to control the state of the GPIO correctly when the power is on, however we need it to be HIGH when power is off, while it seems to always be LOW when powered off.

6

I am a little confused, as you know the pin can’t be high by itself when power is off. Meanwhile it has default pull-down to GND which will work during power off.

7

Hi @Trumany , I’m working on this with @dhrumil44 Thanks for your responses so far.

We just wanted to clarify whether there’s any way to configure a pin to by high when the Jetson is powered off but still connected to battery? (ie. Make high the default state of the pin when powered off?)

Or is this not something which can be controlled?

8

Hi, you can try some pins powered by VDDIO_AO / VDDIO_AO_HV. You can find below pins in pinmux sheet. Not sure if that can fit your requests.

AO pins
AO pins1068×557 225 KB

9

Thanks @Trumany I think I understand now.

To clarify, the pins on the VDDIO_AO / VDDIO_AO_HV power rails can be high while the system is off, while the power rail our pin is using (VDDIO_UARTCAM) can only be low when the Jetson is not running, is that correct?

10

This is correct! @Trumany @jeremypd5mf looks like the pin we are using (GPIO1 , on Pin F7) is not part of the VDDIO_AO / VDDIO_AO_HV and we cannot change this as the hardware is already built.

Regardless we are okay if we can not pull the pin high when the system is OFF (we have another power rail we can pull this up to).

The problem is that on this GPIO pin its Pulling this pin LOW (looks like there is a strong ~1K pull down to GND so when we pull up the pin using another power rail using a 10K resistor the pin is still LOW because of that strong pull down). Why is this? Is this for protection? Ideally one would assume in an OFF state the GPIO pins would be high impedance/floating (or open drain).

We are wondering if there is anyway to NOT pull down the GPIO LOW when the system is OFF.

11

If the system power supply is not unplugged, you can try the pins on the VDDIO_AO / VDDIO_AO_HV power rails as said, not sure if that can work certainly for your case. The default pull down of pins on other power domains won’t be changed since the pins are not power supplied.

12

@Trumany Thanks for all the suggestions! We have found a solution thanks!

13

@Trumany just for curiosity, do you know what protection circuit the Jetson uses on its GPIO pins?

Is it something similar to the image below?

image

14

Hi, could you share what the solution is?

For GPIO info, you can refer to the Tegra X2 Series SoC Technical Reference Manual doc in DLC.

15

@Trumany , we realize the GPIO pin we are using most likely has protection circuit as shown in my previous post (see image with 2 diodes). The solution to keep the voltage rail “HIGH” after shutting down the Jetson TX2 module is to pull up that GPIO pin to another another always on voltage rail with a 10K resistor. This way during normal operation GPIO works normally but during shutdown the GPIO is kept high.

Alternate solution if you do not have a another always on voltage rail is to use the GPIO pins on VDDIO_AO / VDDIO_AO_HV as @Trumany suggested. We have not tested this though.

16

Thanks, but still a little confused, as you said below:

Seems it is same to your first post:

Why is the result different?

17

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