5v power availability on TX2 Developer Kit Carrier Board


Short version: I’d like to know how much current is safe to draw from the 5v supply on the TX2 Developer Kit carrier board, and what’s the best way to do it?

Long version:

I am using the Jetson TX2 Developer Kit Carrier Board, and I have added a PCIe USB 3 card to have an additional USB 3 bus. This is working, but these cards typically have a power connector where you can provide a 5v source for additional power to make available to the connected USB devices, which I would like to do as I have several fairly power-hungry devices to connect (and I would like to avoid a self-powered USB hub for logistical reasons if possible).

It looks like there are several places where 5v/gnd are available, especially on the “GPIO Expansion Header J26” and the “Expansion Header J21”. I’m hoping I can use those 5v sources to power the card, but I do not want to risk drawing too much power and browning out any other systems. (Or perhaps there are better places to access the 5v supply?)

In the “Jetson TX1/TX2 Developer Kit Carrier Board Specification” document I see that the Main 5V supply (VDD_5V0_IO_SYS) can source 7000ma (Table 35).

The VDD_5V0_IO_SYS header pins (2 on J21 and 1 on J26) are listed as having a “Current Capability” of 1A, with this note: “This is current capability per power pin” (Tables 16 and 22).

Would it be correct to assume that 3A is the maximum I can draw at 5v, and I should do it by connecting to all 3 pins (and 3 of the gnds)? Or is there a way to draw more current? Or, is that 7A already mostly allocated to other uses, and I should be drawing significantly less than 3A?

Thanks for any help and information!!

Hi, you can use that three pins for 5V supply, and each is up to 1A capability. The output capability of 5V DC-DC (tps53015) is up to 8A, you can estimate the total power consumption accordingly.

Great, thank you for the quick response!

Relatedly, do you know the current limit on the USB 3 port of the carrier board? I see that the limit for USB_VBUS is maintained by a RT9715 chip, but without knowing the chip suffix (e.g. RT9715A, RT9715C, etc.) it looks like there is a fairly broad range of possible limits (1A - 2.5A).

Also, as I add my devices to the 5V supply, I am monitoring my current usage with this command:

cat /sys/devices/3160000.i2c/i2c-0/0-0042/iio_device/in_current1_input

(rail_name_1 at that address reports VDD_5V0_IO_SYS)

Is that a proper way to monitor this usage? The values appear to be in milliamps, although they are a bit lower than I would have expected. Should I treat this monitor as fairly accurate, e.g., if I keep the output safely below 8000 I am OK?

Thank you for your help!

The load switch of vbus is APL3511CBI-TRG, you can find its character by google.

For the command, it is just for reading the value of current, not to monitor. Please refer to the power monitor guide for detail: https://developer.nvidia.com/embedded/dlc/jetson-tx1-tx2-voltage-current-config

Hi Trumany,

Thanks for your response!

In the “Jetson TX2 Developer Kit Carrier Board” I’m looking at (20190408), the two USB ports are using different load switches:

USB 2.0 Micro AB, VDD_VBUS_CON, is using APL3511CBI-TRG
USB 3.0 Type A, USB_VBUS, is using RT9715

From (Figure 21, and/or Table 32)

The full product number is given for the APL3511CBI-TRG, but only the partial number is given for the RT9715 (no suffix indicating current limit). Do you have the full part number of the RT9715 used on the USB 3.0 USB_VBUS? Or, is my datasheet old and both ports are using an APL3511CBI-TRG?

Thanks for your help!!

Please refer to the BOM of carrier board in DLC which indicate both are APL3511CBI-TRG.

Hi Trumany,

Perfect! Thank you, that clears it up for me!


For anyone finding this thread, the APL3511CBI-TRG lists:
Recommended Output Current: 0-1A
Current Limit Threshold: Min 1.1A, Typical 1.5A, Max 1.9A
Short Circuit Output Current: 0.8A

Nice! Thanks for your sharing!