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*To*: "'Jack Andresen'" <jandresen@xxxxxxxxxx>*Subject*: RE: Potential heating problem with standard patch Cat5 panels*From*: Yair Darshan <YairD@xxxxxxxxxxxxxx>*Date*: Mon, 7 May 2001 23:53:17 +0200*Cc*: stds-802-3-pwrviamdi@xxxxxxxx*Sender*: owner-stds-802-3-pwrviamdi@xxxxxxxx

Jack, I understand your calculations, thanks. Is there any data for peak currents limited by time? Yair. > -----Original Message----- > From: Jack Andresen [SMTP:jandresen@xxxxxxxxxx] > Sent: ב מאי 07 2001 20:41 > To: Yair Darshan > Cc: stds-802-3-pwrviamdi@xxxxxxxx > Subject: Re: Potential heating problem with standard patch Cat5 > panels > > Yair, > > Correction: A 0805 SMT resistor is 2 X 1.6 mm, which translates to 79 X > 63 mils. > > If we assume that the effective convection/radiation area is only that > area (i.e., no conduction to the board nor to the traces) you have > .07/.005 or 14 watts/sq in. That would clearly burn up. Hence, you need > to take into account nearby conduction. If we allow .25 in. spacing per > device in an array and assume uniform conduction/radiation, we still get > .07/0625 or 1.1 watta/sq in. That translates to over 100 degrees C rise. > Still a problem. > > Concerning my numbers, I did make a mistake that I only realized when > trying to rationalize your numbers. I forgot that my model was for a > pair, yielding twice the wattage. Thus, my calculation should have shown > a 19 degree C rise. Still not a problem. > > Note. At 25 degree C a .1W/sq.in generates 15 degree C temperature rise > while 1W/sq.in. gives a 100 degree C rise > > Jack Andresen > ****************************** > Yair Darshan wrote: > > > > What is the worst case of the two cases: > > > > Case 1: PC board trace with 0.07W/inch generating 12C rise > > Case 2: 0.07W dissipated on 0805 SMT resistor rated to 125mW and its > area is > > 8mils x 5 mils. > > > > I know that case 2 is being used without failure reporting. Since in > case 2 > > the power density/area is much higher than case 1, it seems that it is > not a > > real problem. > > > > What others think about it? > > > > Yair. > > > > > > > > > -----Original Message----- > > > From: Jack Andresen [SMTP:jandresen@xxxxxxxxxx] > > > Sent: ?, ??? 03, 2001 11:21 PM > > > To: stds-802-3-pwrviamdi@xxxxxxxx > > > Subject: Potential heating problem with standard patch Cat5 > panels > > > > > > A customer mentioned panels burning up when one of his customers senr > > > power down the network.. I did some canculations and found a potential > > > problem. > > > > > > Jack Andresen << File: DTE power.doc >>

**Follow-Ups**:**Re: Potential heating problem with standard patch Cat5 panels***From:*Sterling Vaden

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