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| R&S RTB2004 front USB 5V power output? |
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| langwadt:
--- Quote from: nctnico on October 02, 2024, 06:46:03 pm --- --- Quote from: tooki on October 02, 2024, 06:35:23 pm --- --- Quote from: nctnico on October 02, 2024, 06:29:36 pm ---The 100mA max. really is a deprecated part of the standard for a long time. --- End quote --- Well that is certainly a bold claim. I don't think it's correct, though. --- End quote --- Lets put it differently: try and find a USB port which enforces it... I have never found a USB port which doesn't deliver less than 500mA. It just causes the user grief to limit the current based on negotiation at the cost of extra parts and software. It never made sense to negotiate power at this level. Maybe the very, very first USB host ports had variable current limiting but I guess they found out quickly that it wasn't a good idea. --- End quote --- I had a laptop eons ago it definitely didn't have any current limiting, if you shorted Vbus you got a scream from the supply and instant reset of the PC negotiating the the current limit sorta makes sense when you have a bus powered hub, if you have a five port hub with four devices using 100mA each and the plug in something that needs 500mA should you deny that or crash all five devices because the hub can only deliver 500mA in total? |
| tooki:
--- Quote from: nctnico on October 02, 2024, 06:46:03 pm --- --- Quote from: tooki on October 02, 2024, 06:35:23 pm --- --- Quote from: nctnico on October 02, 2024, 06:29:36 pm ---The 100mA max. really is a deprecated part of the standard for a long time. --- End quote --- Well that is certainly a bold claim. I don't think it's correct, though. --- End quote --- Lets put it differently: try and find a USB port which enforces it... I have never found a USB port which doesn't deliver less than 500mA. It just causes the user grief to limit the current based on negotiation at the cost of extra parts and software. It never made sense to negotiate power at this level. Maybe the very, very first USB host ports had variable current limiting but I guess they found out quickly that it wasn't a good idea. --- End quote --- I guess you've never used an unpowered USB 1.1/2.0 hub. It has 500mA for the whole hub and all unpowered downstream devices. But you also seem to mistakenly think that it's the host's responsibility to enforce the negotiated current. It isn't. It's the device's responsibility to obey. If it doesn't follow this, it's noncompliant. A port can be designed to protect itself, and that's OK. I've never heard of the protection being variable, but I have seen hosts that shut down the port if a device pulls more than the port's maximum current. --- Quote from: nctnico on October 02, 2024, 06:46:03 pm ---Also, there are dual-use ports for both data and charging (Charging Downstream Port) defined in the USB battery charging standard. --- End quote --- That is true, but so what? I am discussing the port on the RTM2004, not every type of USB port that exists in the universe. --- Quote from: nctnico on October 02, 2024, 06:46:03 pm ---The whole USB power delivery situation is a huge mess; better design something that has wide margins for as long as it doesn't make attached devices go up in smoke. --- End quote --- Well, find a time machine and tell early-90s Intel that USB will become the dominant DC charging port. Back when they designed it, nobody even distantly envisioned it as a de-facto DC power supply standard. The little bit of power envisioned was just a courtesy so small gadgets wouldn't need a separate power supply. Remember, it was conceived as a replacement for the keyboard and mouse ports, the serial port, and the printer port. Every other application basically got tacked on later. And of those original applications, only the keyboard and mouse ports had power at all. So the original power architecture was designed for that kind of thing. The 500mA power level was itself generous overkill for all the original applications. At the time, storage devices and the like were envisioned to use FireWire, which had up to 1.5A of power (at 9-30V), though actual available power varied wildly by system. It's so easy to forget that USB only accidentally became the de-facto DC power supply standard (and later still a de-jure one in the EU!), since it's now everywhere. Had we known that back then, we doubtless would have designed it differently. But it's disingenuous to decry as poor the decisions made ages ago in a context where those decisions absolutely made sense. |
| tooki:
--- Quote from: langwadt on October 02, 2024, 07:16:52 pm --- --- Quote from: nctnico on October 02, 2024, 06:46:03 pm --- --- Quote from: tooki on October 02, 2024, 06:35:23 pm --- --- Quote from: nctnico on October 02, 2024, 06:29:36 pm ---The 100mA max. really is a deprecated part of the standard for a long time. --- End quote --- Well that is certainly a bold claim. I don't think it's correct, though. --- End quote --- Lets put it differently: try and find a USB port which enforces it... I have never found a USB port which doesn't deliver less than 500mA. It just causes the user grief to limit the current based on negotiation at the cost of extra parts and software. It never made sense to negotiate power at this level. Maybe the very, very first USB host ports had variable current limiting but I guess they found out quickly that it wasn't a good idea. --- End quote --- I had a laptop eons ago it definitely didn't have any current limiting, if you shorted Vbus you got a scream from the supply and instant reset of the PC negotiating the the current limit sorta makes sense when you have a bus powered hub, if you have a five port hub with four devices using 100mA each and the plug in something that needs 500mA should you deny that or crash all five devices because the hub can only deliver 500mA in total? --- End quote --- I've seen both Mac and Windows machines that displayed a message that a USB port has been shut down because too much power was drawn. Definitely better than just resetting!!! :( |
| gdr771:
--- Quote from: skander36 on October 02, 2024, 06:47:24 pm ---Micsig DP10013 tested with RTB2002 works without problems. Maybe you have Micsig DP1500 from description. --- End quote --- Micsig completely redesigned the probe into a two-part device but used the exact same model number. I have the new version shown in the attached photo. Which version do you have? |
| gdr771:
Here's a capture of the inrush in question. Channel C2 is the 5V line from the USB port. C3 is the voltage drop across a 0.1-ohm 5% 5W resistor in series on the ground line scaled for current. I confirmed the scaling by comparing the DC steady-state draw against both a Fluke 87 and a Siglent SDM3045X meters. You can see the initial inrush at plug-in isn't bad at all: Then, after about 1 second there is a second inrush around 2.5A, which lasts for a millisecond: That's when the Micsig probe resets, and the whole process starts over again, resetting every second. |
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