Clarifications on measuring low current to M.2 port using power monitor IC on Jetson TX2

[Srilakshmi.Jayaprakash]

Hi Team,

I want to measure current on the M.2 port from a range of 0.5mA to 1A.
I am using the on board power monitors for the same.
I am reading the current value from
/sys/bus/i2c/drivers/ina3221x/0-0043/iio:device3/in_current2_input

I see that a 10mOhm resistor is used as sense resistance(R193 for Jetson TX2).
This results in current resolution of 4mA as the minimum step size of the INA3221 power monitor IC for the shunt voltages is 40uV.

I am planning to solder a 100mOhm resistor instead of 10mOhm so that I will be able to read lower currents upto 400uA.

What is the corresponding change I need to make if I replace the external shunt resistance to 100mOhmm so that I can read the current consumned by M.2 port directly from /sys/bus/i2c/drivers/ina3221x/0-0043/iio:device3/in_current2_input?

There is a configuration option for power monitors 0x40 and 0x41 at Linux_for_Tegra/sources/hardware/nvidia/platform/t18x/common/kernel-dts/t18x-common-platforms

1. Is there a similar configuration for 0x42 and 0x43?
2. Is there any other way to measure to measure lower currents other than replacing the series resistor?
3. Will the 100mV drop when 1A current passes through the sense resistor impact the M.2 connection?

Thanks and Regards
J Sri Lakshmi

[WayneWWW]

Hi,

The shunt -resistor could affect the critical current limit.

Critical Current Limit Jetson TX2

To clarify I would like to limit our inrush current to 3A when powering off a 12V battery. Does the 0.1638V change with a different input voltage? If not then I will just change the shunt resistance to 56 to acheive a critical current of 2925mA. I would have expected to need to edit “/sources/hardware/nvidia/platform/t18x/common/kernel-dts/t18x-common-platforms/tegra186-quill-p3310-1000-a00-powermon.dtsi” as with the TX1 but I suppose this “fragement-pmon” overides the other powermon file. T…

[Trumany]

We don’t have such support of custom usage of power monitor to measure other rails, as that are not validated.

[Srilakshmi.Jayaprakash]

Hi Trumany,

I am measuring current on the supported rail itself.
in_current2_input. (M.2 supply monitor on the power monitor having I2C address 0x43).

I am wanting to know the ways in which I can measure current in the range of 500uA.
Can the sense resistor be changed to 100mOhm?

Thanks and Regards
J Sri Lakshmi

[Srilakshmi.Jayaprakash]

Hi WayneWWW,

I looked through the post. It is talking about power monitors on 0x41 that affects inrush current.
My question was regarding the power monitor on 0x43 that measures the M.2 current. It will not affect inrush current, right?
Is there any problem the sense resistor corresponding to M.2 input. (R193 from the schemtics)
There should be a corresponding change in the software, if I make the hardware change on the carrier board. Where is such provision available for 0x43 power monitor?

Thanks and Regards
J Sri Lakshmi

[Trumany]

@Srilakshmi.Jayaprakash

Hi Trumany,

I am measuring current on the supported rail itself.
in_current2_input. (M.2 supply monitor on the power monitor having I2C address 0x43).

I am wanting to know the ways in which I can measure current in the range of 500uA.
Can the sense resistor be changed to 100mOhm?

Thanks and Regards
J Sri Lakshmi

It also depends on the power consumption of M.2 device. The shunt voltage of power monitor is 163.8mV in max, I’m afraid that 100mohm is too big as the current could be 2A in general.

[Srilakshmi.Jayaprakash]

I am connecting a wifi module to the M.2 port. The current consumption of the wifi module in my application won’t exceed 1A.

[Trumany]

So it would not exceed 163.8mV and you can try that, but we don’t have hardware experience can be shared on this kind of invalidated custom usage.

[Srilakshmi.Jayaprakash]

Ok. Got it. Thanks.