Products > Test Equipment
R&S RTB2004 front USB 5V power output?
tooki:
--- Quote from: gdr771 on October 01, 2024, 01:00:52 am ---The RTB2004 front USB port can supply 500mA without breaking a sweat, but a >2A inrush of the 2024 Micsig DP10013 probe that occurs ~1sec after power-up causes a voltage dip to <1V for a couple of msec. This causes the Micsig to reset before the voltage can recover. Rinse & repeat.
I don't know what the USB spec is, so I can't say if the RTB2004 supply is too weak or if the Micsig probe is too sensitive.
--- End quote ---
The RTB2004 is behaving correctly. A USB device (that isn't using USB Power Delivery or Battery Charging protocols) must draw only 100mA without performing power negotiation. If power negotiation succeeds, then it may begin to draw up to 500mA for USB 1.1 and 2.0, and (IIRC) 900mA for USB 3.
Many "dumb" gadgets just pull from USB ports without negotiating, but this isn't really allowed.
It's common for USB hosts to protect their ports with overcurrent protection devices, be it something like a polyfuse, or (what is more likely in this case because it happens so quickly) some kind of active protection.
So Micsig kinda messed up by drawing so much power.
nctnico:
Not quite. A dedicated charging port can supply several amps without any form of negotiation. Also, USB spec say that a capacitance of up 10uF should be tolerated on a USB device.
The 100mA max. really is a deprecated part of the standard for a long time. If you want to design a somewhat useful USB port on a device, make sure it can supply somewhere between 500mA and 2A and that it allows the rush-in current from a 10uF capacitor (which some margin).
The MicSig device is only at fault if the capacitance exceeds 10uF.
tooki:
--- Quote from: nctnico on October 02, 2024, 06:29:36 pm ---Not quite. A dedicated charging port can supply several amps without any form of negotiation. Also, USB spec say that a capacitance of up 10uF should be tolerated on a USB device.
--- End quote ---
But the RTB2004 does not have a dedicated charging port. It has a normal USB port, which is what my statements are about. No need to be a pedantic whataboutist.
--- 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.
--- Quote from: nctnico on October 02, 2024, 06:29:36 pm ---If you want to design a somewhat useful USB port on a device, make sure it can supply somewhere between 500mA and 2A and that it allows the rush-in current from a 10uF capacitor (which some margin).
The MicSig device is only at fault if the capacitance exceeds 10uF.
--- End quote ---
I suppose.
But I kinda trust R&S to have been more fastidious about standards-compliance than Micsig, if I had to make a guess as to who messed up.
nctnico:
--- 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.
Also, there are dual-use ports for both data and charging (Charging Downstream Port) defined in the USB battery charging standard. 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.
skander36:
Micsig DP10013 tested with RTB2002 works without problems.
Maybe you have Micsig DP1500 from description.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version