I.MX6ULL heat issue

[carotte]

Hi,

We've recently received the first iteration of a custom I.mx6ull board, and noticed that the processor is running significantly hotter compared to the eval board.

The eval board idles at around 37°C, whereas our board idles at around 60°C.

Some changes of the custom board include:

- eMMC on board

- VDD SOC fixed at 1.5V

I think the latter might explain a slightly higher temperature, but not to this extent.

I have another suspicion of what might be going on. All the tamper pins are grounded. I did try to initialise them to 0 in the iomux, but that doesn't seem to make a difference.

On another board, I have removed the balls of the tamper pads for them to become floating. This board seems to run much cooler at around 50°C

It seems that I haven't modified the devicetree correctly, since otherwise I would not expect a temperature difference between the two. 

/ {
....
	disable_tamper {
		pinctrl-assert-gpios = <
			&gpio5 0 GPIO_ACTIVE_LOW 
			&gpio5 1 GPIO_ACTIVE_LOW 
			&gpio5 2 GPIO_ACTIVE_LOW 
			&gpio5 3 GPIO_ACTIVE_LOW 
			&gpio5 4 GPIO_ACTIVE_LOW 
			&gpio5 5 GPIO_ACTIVE_LOW 
			&gpio5 6 GPIO_ACTIVE_LOW 
			&gpio5 7 GPIO_ACTIVE_LOW 
			&gpio5 8 GPIO_ACTIVE_LOW 
			&gpio5 9 GPIO_ACTIVE_LOW
		>;
		pinctrl-0 = <&pinctrl_tamper>;
	};
};
.....
&iomuxc {
	pinctrl-names = "default";

	pinctrl_tamper: tampergrp {
		fsl,pins = <
			MX6ULL_PAD_SNVS_TAMPER0__GPIO5_IO00	0x80000000
			MX6ULL_PAD_SNVS_TAMPER1__GPIO5_IO01	0x80000000
			MX6ULL_PAD_SNVS_TAMPER2__GPIO5_IO02	0x80000000
			MX6ULL_PAD_SNVS_TAMPER3__GPIO5_IO03	0x80000000
			MX6ULL_PAD_SNVS_TAMPER4__GPIO5_IO04	0x80000000
			MX6ULL_PAD_SNVS_TAMPER5__GPIO5_IO05	0x80000000
			MX6ULL_PAD_SNVS_TAMPER6__GPIO5_IO06	0x80000000
			MX6ULL_PAD_SNVS_TAMPER7__GPIO5_IO07	0x80000000
			MX6ULL_PAD_SNVS_TAMPER8__GPIO5_IO08	0x80000000
			MX6ULL_PAD_SNVS_TAMPER9__GPIO5_IO09	0x80000000
		>;
	};
.....
};

Any help or suggestions would be greatly appreciated!

[turker]

Did you measure the surface temperature of the chips? Do they differ as well?

[carotte]

@turker Yes they do.

On the EVK the surface temperature of the processor is around 33°C, whereas on the custom board it is 47°C.

[art]

It is not recommended to ground the unused tamper or I/O pins since it really
can cause extra current leakage and extra processor heating. Better is to leave
them unconnected and configure as pulled-up GPIO inputs in software. Actually,
this is the default out-of-reset state for most of the I/O pins, so, you can
just do nothing with them in software.

[carotte]

Any ideas ?