Jetson/Jetson TK1 Power

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Revision as of 04:27, 13 June 2014 by Shervin.emami (talk | contribs) (Limiting power use: Rephrased it a little)
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Jetson TK1 power draw

The Tegra K1 SOC is aimed at tablets and thus typically uses between 2W to 6W of power during normal use, but this varies greatly depending on how much you manage to push the 4 CPU cores, 192 GPU cores, DRAM, camera ISP and codec hardware to their limits. That is just for the SOC, so clearly the Jetson TK1 board requires a lot more power than this if you will also use various expansion ports & accessories.

The absolute max power draw of Jetson TK1 if you push everything to the limit and use every port including SATA and PCIe is 4.8A @ 12V (60W). So you can probably get by with smaller 20W or 40W power supplies if you don't use too many accessories, while a 60W power supply will ensure you never have any lack of power onboard.

Replacing the fan with a heatsink

The Jetson TK1 board comes with a large 12V fan+heatsink combo (using 0.4W) attached to the SOC, to ensure the board is always safe to touch by humans even when running the CPU & GPU at max performance for long durations. But some users may want to remove the fan and replace it with a passive heatsink, to reduce power or to get rid of the fan noise. The fan+heatsink is clearly much larger than it needs to be, so it can be replaced by a small fan or large heatsink without a reduction in performance or safety.

The Tegra K1 SOC is designed for tablets that use a small heatsink or heatspreader plate, thus clearly it doesn't require a powerful fan. But tablets aren't expected to run at full performance for long periods, and you also can't touch the SOC of a tablet with your bare fingers, so NVIDIA decided to use a large surplus fan for Jetson TK1. If you wish to replace the fan with a heatsink, take into account that if you will be pushing the SOC to its limits for long durations, the SOC might be using upto 15W of power that you must dissipate with a large heatsink and/or external fan and/or attaching a heatspreader to the metal case of your overall device, otherwise the internal Tegra thermal management may reduce the performance to ensure it won't overheat.

It hasn't been tested by NVIDIA, but rough estimatations suggest that a 1.5" x 1.5" x 0.8" Aluminium heatsink (such as an Aluminium Malico MBH33002 or Copper Malico CMBA054949 north-bridge heatsink) would allow pushing Tegra K1 to it's limits for long durations while not getting hot enough for the SOC to reduce the performance or burn human skin.

Limiting power use

Note: Debugfs and non-upstream sysfs nodes aren't guaranteed to remain unchanged in future releases.

Reducing power if display isn't required

Turning off the HDMI port can slightly reduce the power usage of the board. Run this as root (such as by running "su" before and then "exit" after):

echo -1 > /sys/kernel/debug/tegra_hdmi/hotplug
echo 4 > /sys/class/graphics/fb0/blank

Restricting to low-power core only

Restricting the CPU to the low-power companion core can significantly reduce peak power (if running on a power-limited battery pack, for example). The 5th companion core in Tegra K1 is still a Cortex-A15 core with NEON and 32KB L1 cache and 512KB L2 private cache, but obviously at lower performance than the 4 main cores. To use just the low-power core, run this as root:

echo 0 > /sys/devices/system/cpu/cpuquiet/tegra_cpuquiet/enable
echo LP > /sys/kernel/cluster/active

Powering the Jetson TK1 board with a battery

The Jetson TK1 accepts a standard 2.1mm DC barrel plug and is rated for 12V DC input, but will actually work with any input voltage between 9.5V to 13.5V. Note that SATA disks require a fairly precise 12V, so you shouldn't be using voltages at those ranges if you will use SATA hard drives. It is known that the Jetson TK1 board won't turn on at less than 9.5V and it will likely be damaged at 16V or above. It may also be possible to power the Jetson TK1 board somewhere in the 13.5V to 16V range but NVIDIA has not tested this.

Since Jetson TK1 needs a voltage between 9.5V to 13.5V, there are several options for powering the Jetson TK1 by batteries:

Direct connection to a rechargeable battery pack

A battery pack made of several battery cells in series to have roughly 12V can power the Jetson TK1 board directly without a step-up or step-down converter. However the voltage output of a battery varies quite a lot when it is fully charged compared to fully drained, so you need to make sure the voltage will always be within the recommended voltage range. Several battery options are:

  • Lithium Ion or Lithium Polymer: Any large 3S rechargeable Lithium battery pack (3 x Li-Ion or Li-Po cells in series) can power a Jetson TK1. Because a Li-Ion/Li-Po "3.7V" rechargeable battery is usually near 3.7V on average but actually gives 4.2V when charged and around 3.3V when discharged. (The battery is likely to be damaged whenever it falls below 3.0V per cell). Thus an "11.1V" battery made from 3 Li-Ion/Li-Po cells gives 9.9V - 12.6V. An example of a 3S battery pack is Turnigy 3S 2200mA for $8.50, and battery chargers include the popular Turnigy Accucell-6 for $23.
  • Nickel-Cadmium or Nickel-Metal-Hydride: 10 x rechargeable NiCad or NiMh AA or AAA batteries can power a Jetson TK1. Because a NiCad or NiMh AA "1.2V" rechargeable battery gives about 1.3V when fully charged and drops to about 1.0V when consumed. Thus 10 NiCad/NiMh cells gives 10V - 13V. Note that a non-rechargeable AA battery gives 1.5V per cell whereas a rechargeable AA gives 1.2V per cell, so if you want to use non-rechargeable consumable batteries for some reason then you should use 8 x AA instead of 10 x rechargeable AA batteries.

Step-down voltage regulator

A voltage regulator can produce a stable 12V DC voltage from a higher voltage, thus allows some battery options:

  • Lead-Acid (car battery): A car battery is roughly 12V but the actual voltage can reach upto 14.4V. So if you want to plug the Jetson TK1 into your car battery then it is highly recommended to use a 12V voltage regulator to ensure the voltage to the board will not be too high. You should also use a fuse to ensure nothing catches on fire if there is a short-circuit! You could even use a 24V truck battery if your voltage regulator allows it.

DC-DC step-up converter with a single-cell battery

A DC-DC step-up converter can convert a low voltage into a stable 12V DC thus allows using a single-cell battery. Some suitable step-up converters range from a 20W step-up converter for $4 (that might be enough for some use cases but not others) to a 60W step-up converter for $14 (that is always able to push Jetson TK1 to its full limits). Both of these step-up converters will work from a single LiIon/LiPo battery cell or a few AA batteries or a 5V USB portable charger. (Note that most USB portable chargers can only produce 5W to 10W, so are unlikely to power the whole Jetson TK1 board unless if you replace the fan, don't run intensive code, and disable many ports).