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TUSB320: TUSB320 VTH_DFP_CC_USB Range

Part Number: TUSB320
Other Parts Discussed in Thread: , ESD441

Tool/software:

Hello , for TUSB320 and similar parts, VTH_DFP_CC_USB is listed in the datasheet Rev F as from 1.51V to 1.64V. 

I also see the default pullup current of 80uA +/- 20%. 

If I understand right, the part is looking for the 5.1k +/- 20% pulldown in the cable, however this will result in a voltage of only about 400mV? Perhaps I am missing something in this analysis, is this the correct setup for detecting a UFP (for example, a USB flash drive) attach? 

  • Hi Raiyan,

    VTH_DFP_CC_USB are not the voltage thresholds on the CC lines. These are the voltage thresholds that the TUSB320LAI internal current source is pulling from when advertising DFP mode. The actual CC voltage detection levels will align with the USB C spec:

    is this the correct setup for detecting a UFP (for example, a USB flash drive) attach? 

    Yes if you want to attach devices (UFP) to the Type-C port, then you should configure the TUSB320LAI as a DFP. You cannot attach a UFP to another UFP or the connection will fail.

    Best,

    Shane

  • Thanks for the reply Shane. Got it, those are not the right voltage limits for this setup. If I'm understanding right then the voltage range would just be the range made by the 80uA +/- 20% into the 5.1K +/- 20%. 

  • Hi Raiyan,

    You're correct. Since the TUSB320LAI uses a current source instead of a pullup resistor, we are providing the 80uA/180uA/330uA required to advertise as a DFP. If you multiply the current by the UFP pulldown (5.1K) you would get the voltage threshold on the CC line.

    Best,

    Shane

  • Is there any published upper voltage limit for the UFP attach ?

    Reason I ask is we are investigating ESD mitigations for the CC pins, we are seeing damage to the DRP mode switching on these pins with our current TVS and surge protection devices. We want to know if there is a maximum value of series resistor for filtering that could be used , that wouldn't affect the DRP functionality. 

  • The CC pins should not go above 6V or damage can occur:

    If you're seeing ESD damage on the CC pins the ESD diode + series resistor combination could work. You'd want a diode that ideally clamps around 6V. The closest one I can think of that we offer is ESD441 which clamps at 7.6V. 

    Since the UFP pulldowns are relatively large, I figure using a 10ohm series resistor would be ok for CC negotiation. Since we do not have test data on this, I recommend starting with 10 ohms and reducing or increasing the value as needed.

    Best,

    Shane