AM3354: USB_VBUS cannot reach 5V

Eddie Koh

Part Number: AM3354

Generic question: What can cause USB1-VBUS to rise to 3.3V only? It doesn't rise to 5V, leading to AM3354 disabling (toggling) VBUS.

Customer had rectified the schematic mistakes from this previous post. They still see a smaller set of units failing, with 3.3V observed at USB1-VBUS.

e2e.ti.com/.../2333479

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

The USB experts have been notified. They will respond here.

0 -DK- over 7 years ago

TI__Mastermind 27890 points

Hi Eddie,
DRVVBUS typically controls a 5V load switch. Is that the case here?
In the cases where 3.3V is observed on VBUS, is it steady or does it pulse?

0 Eddie Koh over 7 years ago in reply to -DK-

TI__Genius 10635 points

Hi -DK-,

It pulses as captured in the image below:

0 -DK- over 7 years ago in reply to Eddie Koh

TI__Mastermind 27890 points

Eddie,

Please answer my question about DRVVBUS. Is it controlling a 5V load switch?

Typically we see two causes for VBUS pulsing:

USB OTG SRP is active. The controller is configured in USB Dual-Role mode rather than Dedicated USB Device or Dedicated USB Host and is actively trying to establish a session. This is normal behavior.
The VBUS load switch is in OC mode and the customer OS is actively enabling/disabling DRVVBUS as a result. Please monitor DRVVBUS to see if it pulses in concert with VBUS.

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AM3354: USB_VBUS cannot reach 5V