I am trying to thread a needle here and realize that I will likely not be within worst case prameters for a limited run of parts. I am designing a circuit that will be connected to USB Host ports that are already in the field. It will only be connected to our USB port, not any port in general. The question is whether I should set the circuit to run slightly above the minimum current limit threshold or slightly above the minimum overcurrent pulse width. As presently designed the worst case load will be 636 mA baseline with peaks to ~1.1 amp for 1.1 msec at 5 msec intervals. By making adjustements in the power circuitry I can get the baseline current below 600 mA, but the overcurrent pulse gets higher in amplitude up to 1.5 amps. The TPS2074 sepcifies 1 msec as its minimum delay and 600 mA as its lowest current limit. The TUSB2046 indicates that it has "noise filtering" but has no specificaiton on it.
I have measured 2 msec delay of the TUSB2046 on three units. If that was the value for every unit in the field I would be OK, but don't want todepend on that test alone for making more units. I would like to have a specification Ican work from. Is there a range of filter times designed into the TUSB2046B that will reject pulses of say1 to 4 msec or is it 2 +/-0.2 msec or is there a specification? On a related part,is there a distribution of expected current levels for the overcurrent trippoint of the TPS2074? I tested three and found it to be 1.1A. The specified range is 600mA to 1.2A (typical 900 mA). Is the 600 mA level only reached at extremetemperature? Is there a range at 40 degC that I could expect? Is there anyquality data that might indicate the likelihood of a 600 mA threshold partbeing encountered?
First the USb power specs are for maximum currents seen, a bus-powered USB peripheral or hub is never allowed to utilize more than 500mA peak current to be considered compliant withthe USB spec. I am guessing you are ignoring these guidelines, but given that the host system may not be tolerant of this, it could be an issue.
The noise filtering on the TUSB2046B is with respect to the DP/DM lines and is to address "babble" of a "lost" downstream device. The TUSB2046B downstream ports do not "touch" the downstream VBus.
I am somewhat confused on your scenario. You are building a hub board that features the TUSB2046B and the TPS2074. When you say the worst case load will be 636mA, are you referring to what the host port will see or what the downstream port of the TUSB2046B/TPS2074 combo will see?
We do not have the data that you are requesting for the TUSB2046B.
The TPS2074 would need to be requested in the Power Interface Forum.
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