Part Number:TMS320C6678
Hi,
My customer is using C6678 on their custom board and seeing boot failure. And that seems to depend on CVDD voltage after VID has been validated during the power cycle. They are using LM10011 with DC/DC circuit on their custom board to provide SmartReflex CVDD voltage. They have cross-checked this issue on some boards. Please find the following matrix:
Board | VID | DC/DC output | DSP boot ok or not
--------------------------------------------------------------------
#1 | +1.052V | +1.050V | OK
#2 | +0.965V | +0.955V | NG (OK 2/10 power cycle)
#3 | +1.103V | +1.100V | OK
If you see #2, VID indicated 0.965V for CVDD and actually DC/DC circuit provided 0.938V (measured near by C6678) . This is actually lower than 0.965V because some voltage drop was seen in power distribution path between C6678 and DC/DC circuit. Please note, this does not still violate C6678 data sheet spec --- It says CVDD min value for operating condition is SRVnom × 0.95 (In this case, 0.965×0.95 = 0.917V), so even if we use 0.938V for CVDD, that should be ok in theory. But in this condition, they actually only saw 2 times boot success per 10 power cycles...
Now they tried to fix this voltage drop in power distribution path to provide more accurate value (0.965V), and then the board#2 boot failure has been disappeared.
Can you comment for this phenomenon ? Is CVDD min really SRVnom × 0.95 ?
Best Regards,
NK