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USB3320, external REFCLK and suspend / resume

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timistof
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2019/06/20 14:32:06 (permalink)
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USB3320, external REFCLK and suspend / resume

I'm using an external oscillator to supply REFCLK to the USB3320 in a bus powered usb device. To support peripheral suspend / resume, the MCU connected to the USB3320 has to disable this clock in order to meet the maximum 2.5 mA usb suspend current, since the oscillator uses about 4 mA when kept running.
Maybe I'm missing something from the datasheet, but how exactly is the PHY supposed to notify the MCU about a resume command if REFCLK is stopped? Doesn't it need it for that?
Or does the resume current limitation imply that an external oscillator is off the menu and I should just use the XO instead?
post edited by timistof - 2019/06/20 16:02:21
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    timistof
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    Re: USB3320, external REFCLK and suspend / resume 2019/06/24 15:11:40 (permalink)
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    After a more thorough inspection of the ULPI protocol, I found that in low power mode, the usb linestate is reflected on the ULPI databus. When the host issues a resume and a linestate change / interrupt occurs on the UPLI bus, the MCU sees this, re-enables refclk, wakes up the PHY and resumes operation.
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