LM3429_14 Datasheet, PDF (32/50 Pages) Texas Instruments – LM3429Q1 N-Channel Controller for Constant Current LED Drivers

LM3429
SNVS616F – APRIL 2009 – REVISED JANUARY 2010
Determine minimum allowable RMS current rating:
I_L-RMS =
I_LED
Dc
x
1+
1
12
x
¨¨©§'^iL
-PP ^x
I_LED
Dc¸¸¹·²
I_{L- RMS}
=
1A
0. 533
x
1+
1
12
x
¨¨©§⁴⁸⁵
mA x
1A
0.533_{¸¸¹·}²
I_L-RMS = 1.88A
The chosen component from step 4 is:
L1 = 33 PH
5. OUTPUT CAPACITANCE
Solve for C_O:
C_O =
I_LED x D
r_D x 'i_LED-PP x f_SW
1A x 0.467
C_O = _{1.95: x 50 mA x 700 kHz} = 6.84 PF
The closest standard capacitor is 6.8 µF therefore the actual Δi_LED-PP is:
'i_LED-PP
=
r_D
I_LED x D
x C_O x f_SW
'i_LED-PP
= _1.95:
1A x 0.467
x 6.8PF x 700
kHz
=
50
mA
Determine minimum allowable RMS current rating:
I_CO-RMS = I_LED x
D_{MAX = 1A x}
1- D_MAX
0.677
1- 0.677
=
1.45A
The chosen components from step 5 are:
C_O = 6.8PF
6. PEAK CURRENT LIMIT
Solve for R_LIM:
R_LIM
=
245 mV
I_LIM
=
245 mV
6A
=
0.041:
The closest standard resistor is 0.04 Ω therefore I_LIM is:
I_LIM
=
245 mV
R_LIM
=
245 mV
0.04:
=
6.13A
The chosen component from step 6 is:
R_LIM = 0.04:
7. LOOP COMPENSATION
ω_P1 is approximated:
1+D
Z_P1 = _{rD x CO}
1.467
=
1.95: x 6.8 PF
=
110k
rad
sec
ω_Z1 is approximated:
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