TUSB320: VBUS_DET resistance

Brian,

Can you tell me why 920k-ohm is the max. When I checked in the EVM schematics, you placed on 1M-ohm.

Thank you very much.

Tow question.

What kind of failure or issue will be expected if VBUS detect threshold become lower.

How do we calculate VBUS detect threshold voltage. Do we calculate by RVBUS and 95k-ohm RVBUS_PD.

best regards,

VBUS detect threshold voltage is Vbus *  95k/( 95k+1M).

I didn't see any issue there that's why they put 1M on schematic.

Regards.

Brian

Thanks you.

The reason of this question is to use a cheaper resister due to his multi-source policy. The other CC controller device does not need VBUS_DET resistance in his use case of 5V VBUS whereas TUSB320 is necessary. It is important for him for saving cost as well, so he requests a cheaper resistance such as E24 series or less. 

Would you also give him a suggestion about VBUS detection voltage criteria. If he takes 1M-ohm RVBUS and VBUS=5V, VBUS_THR is 0.4V.

Best regards,

VBUS detection voltage criteria is 300mv +-5%. above 350mv will be safe.

Regards,

Brian

Thank you for your help.

Let me recap RVBUS criteria.

VBUS_THR should be set as low as 300mV+/-5%, higher than 350mV is safe. RVBUS minimum resistance should be defined by this number.

RVBUS maximum resistance must be defined by not exceeding VBUS_DET > 4V abs max rating including the VBUS overshoot.

If you have something to add or correct, please suggest him.

best regards,

sorry for confusion, the threshold on data sheet (4v) is the voltage from Vbus , not the voltage on pin.

Regards,

Brian

Thank you very much.

I have imagined following configuration, so the max RVBUS should be defined VBUS_DET voltage exceeded 300mV +/-5% threshold.

Please let me know, if my understanding is incorrect.

best regards,

Correct, this circuit will help to understand.

Hello,

Ever since we could explain the VBUS DET configuration and 1M-ohm RVBUS would work, the customer still has some questions about RVBUS specification shown in below.

- why do we define RVBUS 855k-ohm(min), 887k-ohm(typ), 920k-ohm(max) in the spec.

- If we can guarantee 1M-ohm RVBUS or incorrect spec, does TI have a plan to revise RVBUS specification.

-  what is the differences or gap between VBUS_THR=300mV +/-5% and RVBUS specification in below.

best regards,

Toshiro:

       Value of resistor just determines at what VBUS voltage the TUSB320 will detect its presence/absence.  A larger value resistor means TUSB320 will detect VBUS presence/absence at a higher voltage. 

      TI have no plan to revise RVBUS specification if 1Mohm  works fine.

Regards,

brian

Hi Brian,

I understood RVBUS resistance should be defined by the VBUS voltage either absence or present. Does this RVBUS specification maybe come from what we did in the validation process, which means we tested the product performance in this condition.

I also understood we have no plan to revise RVBUS specification.

Best regards,