Today it's the turn of the power supply. There may be a number of issues: - the TPS76301 data sheets shows 1 uF input caps but clarifies that no or only >= 47 nF caps are needed. They recommend larger caps if there are large transients and the regulator is several inches from the power supply.
We have 100 nF. Given that our (external) power supply is very far away, perhaps C234 and C145 should be increased ? U23 is also far from C154, which may double as buffer for the 5 V rail. - U12 drops 5-1.8 = 3.2 V. If we assume the "High K" scenario with an ambient temperature of 70 C, then we can burn 305 mW. The maximum current would thus be 305/3.2 = 95.3 mA 1V8 feeds (only) the video decoder, and there the digital core and the PLL. Depending on what it does, the core's typical current is specified as 90-106 mA and the PLL's as 11-12 mA. Thus we have Iout(max) = 95 mA vs. Iin(typ) = 118 mA. Should we worry ? - the fuses (F2 and F3) may be a bit weak: at 60 C, their hold current is only 1.5 A, which we could exceed on both 5 V rails if high-current USB devices are connected. Not sure if we have much of a choice, though. Incorrectly regarded as goof: - TI show on the first page of the PTH04000W data sheet that Rset should be rated at 0.1 W. Our Yageo RC0402FR-072K32L only does 1/16W. But TI relent to 0.05 W on page 7. - Werner _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode
