Question Regarding Page 4 of F28069 Controller Card Schematic

John Westmoreland43

Other Parts Discussed in Thread: TMS320F28069

Hello,

I have a design with the TMS320F28069 - and am using the Control Card as a reference - (ISO version) -

I have a question regarding page 4 of the attached schematic - 0363.F2806XISO-CONTROLCARDR0.3-SCH.pdf

If the 5V0 source is generated from the Control Card Docking Station - and the USB MICRO AB is plugged in -
and U200 is 'ON' - (D200 will be on if VBUS > +5V + Vf D200) - doesn't this cause a short of the USB VBUS voltage
and +5V?

I have one of these boards - so I can do some testing on my own - but I wanted to ask how this is supposed to work - I can imagine the algorithm is something like this: (I haven't reviewed the firmware) -

Voltage on VBUS_DET?
If yes - do not enable USB_ENA, if no - enable U200.

Is there a requirement on the '069's USB Bus to always have a VBUS voltage present once the USB module is enabled?

Thanks!
johnw

over 12 years ago

0 John Westmoreland43 over 12 years ago

Guru 13945 points

And - in a related question - why weren't the ESD diodes used as suggested in the tech reference:

Thanks,
johnw

0 John Westmoreland43 over 12 years ago in reply to John Westmoreland43

Guru 13945 points

Here is a snippet from my current schematic:

Regards,
johnw

0 John Westmoreland43 over 12 years ago in reply to John Westmoreland43

Guru 13945 points

Oh - the diagram - it is referring to the internal ESD diodes in the '069 to clamp the voltage - correct?

0 ChrisClearman over 12 years ago in reply to John Westmoreland43

TI__Guru** 119680 points

jonw,

I've asked Brett to comment on this topic, he owns the controlCARDs. He's back in the office tomorrow.

0 John Westmoreland43 over 12 years ago in reply to ChrisClearman

Guru 13945 points

Chris,

OK - I also have been asking about the max freq the HRCAP module can handle - I think it is ~ 17.15 MHz - would
be great to get an answer on that one.

Thanks For Your Help,
johnw

0 Brett Larimore over 12 years ago in reply to John Westmoreland43

TI__Guru 57255 points

John,

Sorry for any delay. I kept trying to get to this post as I was out.

External Diodes on USB: The diagram shown refers to the internal diodes in the MCU. That may be adequate. However, it is good practice to have extra protection. External ESD diodes would probably be preferred and especially on this line. Putting ESD diodes on DM and DP are also not bad ideas just make sure that you use a USB diode rated to the USB speed you wish to use so that the diodes don't load the line.

Is there shorting between USB power and the docking station power: They are shorted when EPEN is high (the MCU is trying to be the host) and ID is low (the OTG cable is telling the MCU that it is the USB device). In general, the type of USB you want to use (OTG, host or device) will determine the best hardware implementation. The implementation shown in the controlCARD should work for all, but may be more than necessary in many circumstances.

Thank you,
Brett

0 John Westmoreland43 over 12 years ago in reply to Brett Larimore

Guru 13945 points

Brett,

OK - thanks for the detailed answers.

Regards,
johnw

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Question Regarding Page 4 of F28069 Controller Card Schematic