LM3429_14 Datasheet, PDF (27/50 Pages) Texas Instruments – LM3429Q1 N-Channel Controller for Constant Current LED Drivers

LM3429
www.ti.com
Buck
T=
T_U0
x
¨¨©§¹⁺
Z^s_P1¸¸¹·
x
1
¨¨©§¹⁺ Z^s_P2¸¸¹·
x
¨¨©§¹⁺
Z^s_P3¸¸¹·
SNVS616F – APRIL 2009 – REVISED JANUARY 2010
(60)
Boost and Buck-boost
¨¨©§^1- _Z^s_Z1¸¸¹·
T = T_U0 x _{¨¨©§1+ ZsP1¸¸¹· x ¨¨©§1+ ZsP2¸¸¹· x ¨¨©§1+ ZsP3¸¸¹·}
(61)
8. INPUT CAPACITANCE
Set the nominal input voltage ripple (Δv_IN-PP) by solving for the required capacitance (C_IN):
Buck
I_LED x (1 - D) x D
C_IN = _{'VIN-PP x fSW}
(62)
Boost
3009_'i4_L-P4_P
C_IN = _{8 x 'VIN-PP x fSW}
(63)
Buck-boost
30_IL0_ED9_x4_D
C_IN = _{'VIN-PP x fSW}
(64)
Use D_MAX to set the worst case input voltage ripple, when solving for C_IN in a buck-boost regulator and D_MID = 0.5
when solving for C_IN in a buck regulator.
The minimum allowable RMS input current rating (I_CIN-RMS) can be approximated:
Buck
I_{CIN- RMS} = I_LED x D_MID x (1-D_MID)
(65)
Boost
'i_L-PP
I_CIN-RMS =
12
(66)
Buck-boost
D_MAX
I_CIN-RMS = I_LED x _1-DMAX
(67)
9. NFET
The NFET voltage rating should be at least 15% higher than the maximum NFET drain-to-source voltage (V_T-
MAX^):
Buck
V_{T - MAX} = V_{IN - MAX}
(68)
Boost
V_{T - MAX} = V_O
(69)
Copyright © 2009–2010, Texas Instruments Incorporated
Product Folder Links: LM3429
Submit Documentation Feedback
27