USB VBus Detect for AM335x

Lee HSIN WEI

Dear all,

I want to know that how many long time when the VBUS < 4.4V, before USB generate a Vbus error interrupt .

Base on AM335x Datasheet,

"After 100 ms, if it does not see the voltage on the USBX_VBUSIN pin to be within a Vbus Valid range (>= 4.4V), it will generate a Vbus error interrupt. "

But i measure is different, I confuse on the result.

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

Please provide more details - what do you measure, how do you measure this?

0 peaves over 9 years ago in reply to Biser Gatchev-XID

TI__Guru 62855 points

Please note: VBUS valid is false when VBUS is less than 3.3 volts, true when greater than 4.4 volts, and undetermined between 3.3 and 4.4 volts. So you may need to reduce the voltage applied to VBUS below 3.3 volts to trigger the interrupt.

Regards,
Paul

0 Lee HSIN WEI over 9 years ago in reply to Biser Gatchev-XID

Prodigy 30 points

I use oscilloscope to measure the 5V of VBUS, and when the USB IST receive the vbus error interrupt then i pull a GPIO to high.

After the measure, i found the time is 20ms, between vbus under 4.4V to GPIO is high. So i confuse on the spec of 100ms.

0 -DK- over 9 years ago in reply to Lee HSIN WEI

TI__Mastermind 27890 points

The 100ms number is for VBUS rise to =>4.4V after session start, not the time between VBUS fall and VBUS_ERROR. I've reviewed the available documentation and do not find that the latter (VBUS <4.4 to VBUS_ERROR interrupt time) is characterized. Logically, this time would depend greatly on system loading so it makes sense that a time is not provided.

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USB VBus Detect for AM335x