Teensy 4.1 USB Host max. allowed Power (current)

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Hi Teensy team:

I am using a Teensy 4.1 and the USB-Host port to control a photo-camera.
All software works fine but now I remembered that the camera uses the USB plug to charge its battery, when its turned off.

I powered the teensy via its USB by an USB charger and power meter and connected the camera to the USB Host pins on the board.

In "working" mode ( camera turned on ) powerdissipation is ~110mA to 130mA.
3 seconds after turning the camrea off, powerdissipation turns up to ~550mA, this tells me that the camreas battery is charged through USB host port of the teensy.

so some questions:
- how much current can be drawn on the USB host for a longer time (hours) without getting heat problems.
- is there a way to limit current? else the USB-or teensy port might be damaged.

thanks in advance!
 
Teensy 4.1 has a TPD3S014 chip which limits the current. Scroll down to the schematic on the Teensy 4.1 page for details. But according to the TPD3S014 datasheet on page 5, the actual limit can be anywhere between 0.67 to 1.01 amp, with 0.85 being the typical expected at room temperature.
 
Thanks, Paul,
yep , the datasheet of the TPD3S014 is a bit confusing. I measured limitation to 500mA .. (no short)
But what I dont know: how long can the chip stand that current without cooling but everthing in a small housing? so some experance would be nice if there is any.
 
R_DS(on) is at most 154 milliohms, sounds like 0.04659 watts of heat with 550mA

The low end of the current limit is 0.65A so thermal shutdown should happen at 155C, that's pretty hot. The derating curve in the datasheet only tops out at T_J of 125C

I'm looking at a SOT-23-3 MOSFET datasheet with about 150 milliohm R_DS(on) and the derating curve for it says the T_A could be 120C with a maximum rated T_CH of 150C

You know... I bet you can leave it charging indefinitely. The thermal shutdown is auto resetting anyways, I mean... it's not a nice thing to do to just count on that, but depending on how serious your project is, you can just shuffle this problem under the rug.

My camera is pulling 1.5A at 5V while shutdown, 0.5A when ON but USB plugged into a QCport, and 0A when ON and PC remote control is active. If you are topping out at 550mA then I'm guessing it's a point-and-shoot
 
That sounds quite good - so thank you for the details having a look at that :)
I just was afraid because of this very very tiny circuit... but on the other hand, the cams circuit are not bigger in size.
 
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