TUSB8040A / USB_VBUS pin

Toshiyuki

Other Parts Discussed in Thread: TUSB8040A, TUSB8041

Hi,

In our customer's application, VBUS is not directly applied to the TUSB8040A. If they are using a 3.3V signal, what should be the resistance value instead of 90.9k||10k ?

Best Regards,

Kato

over 11 years ago

0 JMMN over 11 years ago

TI__Guru 60870 points

Hello Kato,

You can use something like 90.9K/16K if the VBUS input is 3.3V. Please note that tying VBUS permanently high may lead to interoperability issues. The USB specification requires that VBUS go low when the upstream port is disconnected. For example, if VBUS remains high and the host is removed during a low power state, the TUSB8040A may not realize the host is removed and when it is re-attached will expect to see resume instead of new enumeration.

JMMN

0 Toshiyuki over 11 years ago in reply to JMMN

Mastermind 7075 points

JMMN - san,

Thank you for the reply.I understood tying VBUS permanently high may lead to interoperability issues.

So, could we realize new enumeration by using USB controller device ?

*the lower illustration

Best Regards,

Kato

0 JMMN over 11 years ago in reply to Toshiyuki

TI__Guru 60870 points

Hi Kato-san,

Yes, that solution would work. The resistor values would need to be modified if the VBUS input is changed from 5.0V to 3.3V. For 5.0V we use 90.9K and 10K, for 3.3V you could use 90.9K and 16K (or similar).

Regards,

Julie

0 Toshiyuki over 11 years ago in reply to JMMN

Mastermind 7075 points

Julie - san,

I have additional question.

I confirmed USB controller device(uPD720202) PPON1 signal has VOH=3.2V(min), VOL=0.1V(max).

Is there any problem for our proposal ?

Best Regards,

Kato

0 JMMN over 11 years ago in reply to Toshiyuki

TI__Guru 60870 points

Hi Kato-san,

The proposal looks good.

Regards,

JMMN

0 Toshiyuki over 11 years ago in reply to JMMN

Mastermind 7075 points

Julie - san,

Thank you for the reply. If we connect PPON1 to USB_VBUS as post proposal figure, it seems that USB_VBUS is exceeded ABSOLUTE MAXIMUM RATINGS 1.2V. Is my understanding correct?

Best Regards,

Kato

0 JMMN over 11 years ago in reply to Toshiyuki

TI__Guru 60870 points

Hi Kato-san,

I missed that on the previous figure, the resistor divider needs to be placed to shift the voltage. For a 3.3V voltage, use a 90.9K resistor and a 16K resistor.