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When using the TUSB1210 in a Host Application where the connecting client does not need VBUS, only DP and DM communcations, can the VBUS and ID pins on the TUSB1210 IC remain NCs?
ID pin is used to determine of the TUSB1210 is in host or peripheral mode. In OTG applications, this is handled by the cable. For permanent host applications, then ID must be grounded.
The VBUS pin of the TUSB1210 is not needed in stand-alone host mode. However, your system is required per the USB spec to be a power supplier on the VBUS line.
dear sir, in our design (based on OMAP3630 + TUSB1210), the only usb device, an on-board wcdma modem module, is separately powered and needs only D+/D- communication with TUSB1210. According to your answer, my understanding is that we can leave VBUS and CPEN pins floating, is that correct?
I'm also wondering how to handle TUSB1210 VBUS pin in this situation. A 10K pullup to 5V rail gives a VBUS pin voltage of ~2.2V. What exactly is the VBUS pin doing, and how should it be terminated if not connected to a supply? (we float CPEN, ID is grounded, this is a special embedded controller application.)
Please find VBUS connection recommendations and background information below which I hope will answer your question.
Best regards,
Peter CONSIDINE
(TUSB1210, TUSB1211 design lead)
Q: How should VBUS be connected?
ANSWER:
- TUSB121x does not strictly require VBUS to function.
A Host controller Link may require VBUS detection via ULPI RxCmd (see ULPI V1.1 specification standard P16 Table7) if it is using CPEN (TUSB1210) or PSW (TUSB1211) to enable an external supply on VBUS pin. Otherwise it may not be required.
A Device controller Link will require VBUS detection via ULPI RxCmd in order to detect a host connection.
Therefore whether or not VBUS pin of TUSB121x needs to be connected to the USB connector depends on the Link controller requirements, not TUSB121x.
HS Host Link Controller: (embedded in OMAP3, etc)
USBHOST only requires s/w based Port Power to start functioning and detect device connection.
VBUS is outside scope of EHCI Host Controller, hence needs to be managed externally.
- If VBUS detection is not required by the link then:
VBUS (input pin): Recommended to tie to GND if unused. However leaving VBUS floating is also acceptable since internally there is an 80kohm resistance to ground.
- If VBUS detection is required by the link but VBUS pin is not connected to TUSB121x then:
It should be possible for software to “create” VBUS presence signal by setting ULPI bits: USEEXTERNALVBUSINDICATOR = 1, INDICATORPASSTHRU = 1, INDICATORCOMPLEMENT = 1. See ULPI specification Ver1.1 Table13, Figure45. (We verified this functionality is working in TIF MIS lab)
- Note that connecting VBUS to VBAT pin is not recommended as VBAT cannot be guaranteed to be > VA_VBUS_VLD comparator level (4.65Vmin).
