Current Carrying Capacity Analysis of TR42.7 update to IEEE802.3at

Transcription

1 IEEE80.3at Task Force Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007, Moterey CA Yair Darsha Micro semi/powerdsie Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 1

2 Objectives Aalyzig TR4.7 Test Results Derivig PD max power as fuctio of Ambiet temperature Derivig Deratig Curves Review of TR4.7 test results vs other stadards ad lab tests Summary ad Ope questios Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page

3 TR4.7 results Curret vs Temperature rise m ad b are the costats of the fittig fuctio dt=mi^+b Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 3 Temperature Rise [degc] Series1 Curret [A] Poly. (Series1)

4 TR4.7 results cot. 70mA at Ta=45degC while all wires i the cable are coductig i.e. 4 pairs-8 wires are carryig curret of 360mA per wire. Budle cosists of 100 cables Curret decreased to zero at 60degC as fuctio of I^. Max power at 100 cables is limited to ~5000W. 30W/P ad 60W/4P. Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 4

5 Focusig o CAT5E worst case results Curret vs Temperature rise Temperature Rise [degc] y =.045x x R = Curret [A] Series1 Poly. (Series1) Actual fittig fuctio should be mx^+bx+c to accout for resistace chages over temperature. See Aex A for Tr vs Curret equatio derivatio Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 5

6 Deratig Curve (Curret vs. Ambiet Temperature) 800 Deratig Curve I = T I [ma] C urret [A ] Temperature [degc] See aex C for deratig curve equatio Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 6

7 Data Summary Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 7

8 TR4.7 results vs others stadards ad tests Source TR4.7 1 Temperature Rise [degc] 6 Curret /Wire [ma] 75 5 NASA Others 3, Notes: 1,,3,4: See ERENCE slide for data source. 5: 75mA/wire as compariso poit was selected due to its presece i all sources Good correlatio betwee iputs, therefore techically we do have good ad reliable base lie. Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 8

9 Summary ad ope questios TR4.7 gave us its recommedatios: Ta=45degC i all pairs. Recommedatios are with good agreemet with other data sources Ope Questios Should the IEEE80.3at take desig margi? TR4.7 recommedatios are max limits of cablig ifrastructure IEEE should ot exceed this level.. Existig equipmet desiged for 40-50degC ambiet so cablig temperature may be at higher temperature. Should TR4.7 work icludes sufficiet margi to accout for actual higher cablig ambiet temperatures? Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 9

10 What ext? Questios, Discussio Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 10

11 Aex A - Temperature rise vs Curret Showig how Tr is a polyomial fuctio of the curret I, of the form mx^+bx+c which takes the copper resistace as fuctio of temperature as a variable too. Tr=Temperature rise i the ceter cable =Number of cables i a budle Theta_= Thermal resistace of cables budle P=Power dissipated per cable R=Cable resistace K=Copper coefficiet [1/degC] Rref = Cable resistace at Referece temperature Tref (1) Tr= P Θ () Tr = Θ (3) R= R (4) R= R (5= + 4) (6) (7) (8) Tr= Θ I + K R I Tr (1 K R R + K R Tr = Θ Θ Tr= 1 K R R I ( T Tr T Tr Θ I R Tr Θ ( R + K R Tr) + K R I I ) = Tr Θ ) = Θ = mx I I + bx R + C Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 11

12 Aex A1 Saity check for Aex A usig TR4.7 measuremets Performig Curve fit for the TR4.7 data by expressig Tr as a fuctio of I^. If Curve fit is of the form Y=mX^+b the plottig it as Tr =f(i^) would give liear curve otherwise it will be of the form Y=mX^+bX+C. Temperature Rise vs Curret Temperature Rise [degc] y =.1186x x R = Squared Curret [A] Series1 Poly. (Series1) Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 1

13 Aex A1 Saity check for Aex A cot. Eve if we will decide that measuremet poit #4 is a error ad we should take it out the the results will be: Temperature Rise vs Curret Temperature Rise [degc] y = x x R = Squared Curret [A] Series1 Poly. (Series1) We still have small effect of X^ however it is very close to liear equatio as expected Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 13

14 Aex B = PD iput voltage as fuctio of the curret Ppd=Power at PD iput Ppse=Power at PSE output Ipse=Ipd=Curret at PSE output Rcable=Cable resistace Assumig PD iput impedace is egative i.e. Ppd=Vpd*Ipd=Costat due to DC/DC coverter operatio Ppd=Ppse - Cable Loss Ppd=Vpse*Ipse-Ipse^*Rcable Vpd=Ppd/Ipd=Ppd/Ipse Example: For Vpse=50V, Ipse=70mA, Rcable=1.5 ohm, Ppd=9.5W, Vpd=41V Geeral case: Vpd 1, Vpse± = Vpse 4 Rcable Ppd UVLO deletes d solutio (the egative part) Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 14

15 Aex C Deratig Curve Equatio (1) () (3) (4) (7) (8) (9) (10) I (5) 45 t Tr= P Θ= I T = Tr Tr= T R Θ 60 45= 0.7 T Ta= I = Ta Ta I T Ta = = = R Θ I R Θ T Ta 15 R Θ= Practical assumptios:. Assumig thermal resistace is costat. 3. Assumig Cable resistace chage vs Temperature is small 4. For more accurate equatio see Aex A as example for equatio derivatio. Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 15

16 Refereces (1) TR4.7 Update to IEEE 80.3at - Curret Carryig Capacity of Cablig, () 80.3 PoEPlus Maximum Power, pdf (3) DC Curret vs. Temp Rise, (4) UTP Cable limits, Curret Carryig Capacity Aalysis of TR4.7 update to IEEE80.3at Ja 007 Page 16