str73xF PLL Limitation

[javida14]

Posted on July 13, 2006 at 20:25

str73xF PLL Limitation

[javida14]

Posted on July 08, 2006 at 15:10

I'm looking at ARMs for my next project. The STR736F series could work for me (4-UARTS and 72-IO in the 100-pin package). In the documented titled STR73xF under ''Know Limitations'', it states the ''PLL may not work properly'' at 55 degree C and above. This part is spec'ed at +85 or +105 degree C.

This makes this part virtually un-usable in an outdoor application. I would like to see some comments especially from ST. I planning on using a crystal and the PLL to run the part at or near maximum rated clock speed. The upper clock rate will be adjusted depending on CPU utilization.

[kaouther]

Posted on July 13, 2006 at 14:11

Hello,

There is a misunderstanding with the limitation known in the STR730 datasheet. This limitation is only for PLL Free running mode. Please do not confuse PLL and PLL Free running mode. The product works as specified at +85 or +105°C depending on part number and up to 36MHz. There is no limitation to run the product at the maximum speed and in HIGH temperature up to 105°C. The “PLL free running mode� is used to provide a back-up clock source when the reference clock signal disappears and then the system will continue to run with a valid clock provided by the PLL. In the datasheet “limitation known� section, it is mentionned as a workaround that it is recommended to use the internal RC oscillator as a backup clock source rather than the PLL free running mode. More details about PLL Free running mode are available on the STR730 reference manual available on the web site. http://www.stmcu.com/familiesdocs-86.html#Reference%20Manual Hope this clarify the confused info. Regards.

[javida14]

Posted on July 13, 2006 at 20:25

I just received the same feedback from a ST FAE. Thanks for your response. At this point, I'll start looking at the part in more detail.

Thanks