Problem with TI TMS320DM6446 and crystal not starting

KJ · 2009-08-15T18:55:01+00:00

Has anyone had any difficulties with the crystal used for the USBperipheral interface on the TMS320DM6446 not starting up? The leadingproduction board failure that our board supplier reports is that thisparticular crystal circuit is not staring, sometimes replacing thecrystal 'fixes' the board, sometimes not. Based on what we've seen sofar it doesn't appear to be a generic 'crystal not starting problem',but seems to be quite specific to the TI part.I was just wondering if anyone here has happened to encountered thisproblem. Details for those interested are listed below.Kevin Jennings===============Details of the design:- Crystal circuit layout is reasonable, the crystal and caps arelocated close to the 6446, short traces.- The 6446 has two crystal input circuits, one to drive the processorcore, the other is strictly for USB. We're not observing any problemswith the crystal used to drive the processor core, only the USB one.- There are a total of four crystals on the board, they're all thesame supplier (different frequencies only). The other three crystalsdo not have any reported startup issues.- Per the TI spec, both the 'processor core crystal' and 'USB crystal'I/O pins are powered from the same supply voltage (DVdd18). There isnothing indicating that the DVdd18 supplies are in any way segregatedfor the USB pins, so it would seem that since one crystal circuitworks and the other one doesn't that it wouldn't likely be a powersupply issue (speculating).- The TI part in question is TMS320DM6446ZWT. Pins 'F18' (name M24XI)and 'F19' (M24XO) are the 'USB crystal' pins in question.- The USB crystal that won't start is CITIZEN AMERICA CORP.CS10-24.000MABJ-UT- The crystal capacitor load is spec'ed at 18pF which is implementedon the board with two 33pF caps, allowing for ~3pF of straycapacitance.Some other observations:- Most boards do not exhibit this problem. However, of the boardsthat end up in the 'not working' pile, the crystal not starting is themost frequently...

Aug 15, 2009 20 Replies

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KJ 17 years ago

For the benefit of those who do a web search and hit on this problem...the crystal not starting was due to software not enabling the interface.

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Problem with TI TMS320DM6446 and crystal not starting

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