MSP430F56xx usb design, power source

Delared Delared

Expert 1945 points

Other Parts Discussed in Thread: MSP430F5659, MSP-EXP430F5529LP

Hi,

I'm designing a micro usb port on the MSP430F5659. I'm a little bit confused about the Vbus power source.

based on the application report "Starting a USB Design Using MSP430™ MCUs" there is a Schottky diode placed on the Vbus.

in page 17 I noted "The diode on VBUS is placed there to ensure compliance with the USB 2.0 specification's requirement
that the device never source current toward the host over VBUS"

however, this diode doesn't exist in the MSP-EXP430F5529LP_Schematic. so the MSP430 could be powered from the VBUS ?

could you please explain me if I need it form my design or not ?

over 10 years ago

0 Clemens Ladisch over 10 years ago

Guru 318740 points

... a scotchkey diode ...

Are you trying to power your device from a generator run by Walter Schottky rotating in his grave?

Anyway, on every MSP430 chip, VBUS is an input to the LDO. Furthermore, when powering the device from a battery or wall wart, this is likely to use VUSB, not VBUS.

As far as I can see, any circuit you're likely to use (and certainly the LaunchPad) doesn't have any current that could go from VBUS to the host.

0 Delared Delared over 10 years ago in reply to Clemens Ladisch

Expert 1945 points

Hi Clemens,

thanks for your reply,

Actually I'm using external power sources for both the MSP430 and the USB, my design is as follows:

- The MSP430 DVCC and AVCC are generated by an external LDO (3.3Volts)

- The VBUS(referenced V_USB in my design) is generated by an external 5Volts generator.

so, the MSP430 will be the host, the device that would be connected to the MSP430 through the USB port should be powered from the VBUS.

below my design for the MSP430 power supplies and the usb port. is it correct ? have I missed some thing?

Thank you.

0 Clemens Ladisch over 10 years ago in reply to Delared Delared

Guru 318740 points

An MSP430 cannot be a USB host. What is the purpose of the USB connection in your design?

0 Delared Delared over 10 years ago in reply to Clemens Ladisch

Expert 1945 points

I planned to use the usb port of the MSP430 to communicate with other usb devices ( MCU, sensers, etc).

0 Clemens Ladisch over 10 years ago in reply to Delared Delared

Guru 318740 points

USB does not have a peer-to-peer architecture. There is a strict division into hosts and devices, and MSP430 is a device, and must be connected to a host. (There is hardware that has OTG ports, which can be switched between host and device mode.)

0 Delared Delared over 10 years ago in reply to Clemens Ladisch

Expert 1945 points

I'm disappointed :(
I'll see hos to deal with that.
Thanks for your answer Clemens.

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MSP430F56xx usb design, power source