Questions related to USB in STM32F429

[MLaso]

Is this possible to use internal USB OTG HS PHY in FS mode in STM32F429NI with 1.8V VDD? Internal USB OTG FS PHY needs VDD>2.7V. USB OTG HS in HS mode needs external PHY connected via ULPI. Would OTG HS PHY in FS mode work with VDD = 1.8V?

[Khouloud GARSI]

Hi @MLaso​ ,

First of all, let's be clear about some aspects: The STM32F429 MCU have two USB 2.0 OTG interfaces:

* USB 2.0 FS device/host/OTG controller with on-chip FS PHY

* USB 2.0 FS/HS device/host/OTG controller, integrating the transceivers for FS operations, and featuring an ULPI for HS operations.

So, there is no internal HS PHY for this MCU. If you need HS operations, you should connect an external PHY device to the ULPI.

If what you meant is , that you need to use the USB OTG HS interface in FS mode,then this is possible since an internal FS PHY is already implemented.

Now regarding power, USB is functional only for operating voltage ≥ 2.7 Volts. And in order to use the MCU when the operating voltage VDD is below 2.7 V, the MCU should have a VDDUSB pin.

Only when this pin is available, the MCU can be powered with the minimum specified supply voltage, while an independent 3.3 V power supply can be connected to VDDUSB and power the USB block.

However, on the STM32F429 device, this pin is not available. Thus, using this MCU and if you will use USB, VDD should be ≥ 2.7 Volts.

Please also note that,when the USB operating voltage is below 3.0 V (and of course ≥ 2.7 V), the electrical signals will not be compliant with the USB2.0 Full speed specification, and, consequently,

some tests needed to get the USB certification (such as the eye diagram test) will not pass. 

In other words, the USB is operational, but the customer cannot get the USB certification.

Khouloud.

[MLaso]

Hi Khouloud,

Thank you very much for fast and detailed answer!

Yes, my question was about using integrated transceiver for FS operations from USB 2.0 FS/HS device/host/OTG controller. I would like to use this integrated transeciver for communication with GSM module in FS mode, and to use the same controller but with external ULPI transceiver to communicate with PC in HS mode. The challenge is that I would like to use VDD = 1.8V. If I understand your answer correctly - it is not possible?

I have read in datasheet that "USB is functional only for operating voltage ≥ 2.7 Volts", but I am not sure what exactly does this mean in case I would like to use VDD=1.8V.

Will both controllers (FS and FS/HS) work at 1.8V, but internal FS transceivers will not work -> I can work only with external ULPI transceiver for HS mode?

Controllers will not work at 1.8V -> Not possible to use USB at all (even with external ULPI transceiver)?

Which of above understanding is correct?

Thanks & regards!

Maciej

[Khouloud GARSI]

Hi Maciej,

I have added my answers below each of your feedback:

*Thank you very much for fast and detailed answer!

-> You're always welcome 😉

*Yes, my question was about using integrated transceiver for FS operations from USB 2.0 FS/HS device/host/OTG controller. 

I would like to use this integrated transceiver for communication with GSM module in FS mode, and to use the same controller but with external ULPI transceiver to communicate with PC in HS mode. The challenge is that I would like to use VDD = 1.8V. If I understand your answer correctly - it is not possible?

 -> Indeed, using the STM32F429, it's not possible to use USB when VDD is 1.8V because there no dedicated VDDUSB on this product to power the USB block (For USB applications, the operating voltage should be between 3.0 and 3.6 V)

*I have read in datasheet that "USB is functional only for operating voltage ≥ 2.7 Volts", but I am not sure what exactly does this mean in case I would like to use VDD=1.8V.

 -> The datasheet says that the USB transceiver functionality is ensured down to 2.7 V, but the full-speed electrical characteristics are degraded in 2.7 to 3.0 V voltage range. That means that for USB transceivers, the operating voltage should be between 3.0 and 3.6 V. But, in case the USB voltage is below 3V and above 2.7 V, ST guarantees that the PLL generates correctly the 48 MHz and that the analog transceivers are functional. However, the electrical signals will not be compliant with the USB specification: Some tests will fail when trying to get the USB certification.

*Will both controllers (FS and FS/HS) work at 1.8V, but internal FS transceivers will not work -> I can work only with external ULPI transceiver for HS mode?

-> As explained above, for USB transceivers, the operating voltage should be between 3.0 and 3.6 V. Thus, both controllers could not be used when VDD=1.8V.

*Controllers will not work at 1.8V -> Not possible to use USB at all (even with external ULPI transceiver)?

-> Correct! 

What you should know is that this MCU is able to work when VDD=1.8V but you can not use USB applications in this condition.

Khouloud.

[Khouloud GARSI]

Hi @MLaso​ ,

I have edited your inputs: I have proposed a meaningful, short title and kept the same description of your initial question inside the body of the request. It's the proper way to add a post on the forum 😊

Khouloud.

[MLaso]

OK Khouloud, thanks a lot!

[Tesla DeLorean]

Will also note that if you run the F429 at 180 MHz, you'd have to use an external PHY for USB, as you can't generate the required 48 MHz clock locally. You'd need to clock the part at 168 MHz, or 96 MHz, etc.

[Khouloud GARSI]

Welcome!

[MLaso]

Hi, one more thing in this topic - I have found such information in datasheet (pictures below).

It looks that USB OTG HS (controller only; not FS transceivers) should work with VDD=1.8V. So it should be possible to use USB HS only (with external transceiver via ULPI) at 1.8V. Am I right?

[MLaso]