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LM3404: LM3404

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Part Number:LM3404

Hi everybody from Italy

As you can see in the linked messages -I'm tryng to drive a Cree COB led with the TI LM3404.

At the beginning I received help from Mr. Irvin and - thanks to this - I was able to realize an excel spreadsheet and afterwards a pr ototype which you can see down here

The schematics were realized according to the one in the LM3404 datasheet page 23.

The components were chosen basing on the following calculations as in the pages 24, 25 and 26 of the same datasheet:

Input voltage:24Vin [Volt]1,34E-10cost
LED forward voltage:17,5V0 [Volt]0,4inductor ripple curront increase
LED current: 0,65IL [Amp]0,1ΔiF
Switching frequency:3,00E+05Fsw [Hz]2,25rD
RON =V0/(1.34 E-10*Fsw)440298,5075RON  [Amp]442000Ron comm
fSW =V0/1.34E-10*RON298845,1408Fsw comm  [Hz]
tON = 1.34E-10*(RON/VIN)2,46783E-06ton  [sec]  
ΔiL = 0.4 *If0,26ΔiL  [Amp]
LMIN = ((VIN - VO)*tON)/ΔiL 6,35942E-05
LMIN [H]
6,20E-05H L  comm
ΔiL= ((VIN - VO)*tON)/Ltip 0,266685215[Amp]6,10E-05H L  comm
ΔiL= ((VIN - VO)*tON)/LMax 2,71E-01[Amp]6,30E-05H L  comm
ΔiL= ((VIN - VO)*tON)/LMin 2,62E-01[Amp]
IL(peak)=IL+0,5*ΔiLMax7,86E-01[Amp]
ΔiL(led short)= ((VIN - 0,2)*tON)/LMin 9,47E-01[Amp]
IL(peak )=IL+0,5*ΔiLMax7,86E-01
Rsns=(0,2*L)/((If*L)+(V0*tsns)-(((Vin-V0)/2))*ton)0,345146642ohm0,3ohm 
Zc=(ΔiF*rD)/(ΔiLiF)1,349849775ohm
C0=1/(2*PI*Zc*fSW)3,95E-07F0,33uF
D=tON/(tON+toff-min)0,891611971
if=0,2/(Rsns-((Vf+0,2)*tsns)/(C0+(ΔiL typ/2)))0,666685343
Id=if*D0,594424633
Pd=0,3*Id0,17832739

The other integrated circuits that you can see realize a PWM dimming controller and other functions.

The Item is perfect and now a new lamp it is hanging from my lab ceiling.

The only problem that sticks to my mind is that - despite the expected current was 650 mA - the real measured current is 480 mA as you can see in the multimeter down here.

So I realized another prototype by changing the starting data as you can see in the next spreadsheet.

Input voltage:24Vin [Volt]1,34E-10
LED forward voltage:17,5V0 [Volt]0,4
LED current: 0,8IL [Amp]0,1
Switching frequency:3,00E+05Fsw [Hz]2,25
RON =V0/(1.34 E-10*Fsw)440298,5075RON  [Amp]442000Ron comm
fSW =V0/1.34E-10*RON298845,1408Fsw comm  [Hz]
tON = 1.34E-10*(RON/VIN)2,46783E-06ton  [sec]  
ΔiL = 0.4 *If0,32ΔiL  [Amp]
LMIN = ((VIN - VO)*tON)/ΔiL 5,16703E-05
LMIN [H]
5,12E-05H L  comm
ΔiL= ((VIN - VO)*tON)/Ltip 0,322939128[Amp]5,12E-05H L  comm
ΔiL= ((VIN - VO)*tON)/LMax 3,23E-01[Amp]5,12E-05H L  comm
ΔiL= ((VIN - VO)*tON)/LMin 3,23E-01[Amp]
IL(peak)=IL+0,5*ΔiLMax9,61E-01[Amp]
ΔiL(led short)= ((VIN - 0,2)*tON)/LMin 1,15E+00[Amp]
IL(peak )=IL+0,5*ΔiLMax9,61E-01
Rsns=(0,2*L)/((If*L)+(V0*tsns)-(((Vin-V0)/2))*ton)0,279882681ohm0,274ohm
Zc=(ΔiF*rD)/(ΔiLiF)1,009244104ohm
C0=1/(2*PI*Zc*fSW)5,28E-07F0,47uF
D=tON/(tON+toff-min)0,891611971
if=0,2/(Rsns-((Vf+0,2)*tsns)/(C0+(ΔiL typ/2)))0,729943435
Id=if*D0,650826305
Pd=0,3*Id0,195247891
Cin3,85599E-06

I increased the led current from 650 mA to 800 mA hoping to obtain 700/750 mA  in the prototype.

The result was miserable:

As you switch on the circuit on - the current starts growing from 400 mA to 500 mA in five minutes; then The  LM4036 becomes hot and the Led starts blinking with a connected current fluctuation.

The LM quickly dies.

I'm wondering if I should settle for this results and give up the idea to get at least 700 mA or someone of you can "LED me to this LED (COB LED)"

I recall that the mentioned COB LED is a CREE  XLamp CXA1507-0000-000F0YE435F .

Best regards from Italy.

Federico Polidori


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