LM3429_14 Datasheet, PDF (21/50 Pages) Texas Instruments – LM3429Q1 N-Channel Controller for Constant Current LED Drivers

LM3429
www.ti.com
SNVS616F – APRIL 2009 – REVISED JANUARY 2010
Discontinuous currents are the most likely to generate EMI, therefore care should be taken when routing these
paths. The main path for discontinuous current in the LM3429 buck regulator contains the input capacitor (C_IN),
the recirculating diode (D1), the N-channel MosFET (Q1), and the sense resistor (R_LIM). In the LM3429 boost and
buck-boost regulators, the discontinuous current flows through the output capacitor (C_O), D1, Q1, and R_LIM. In
either case, this loop should be kept as small as possible and the connections between all the components
should be short and thick to minimize parasitic inductance. In particular, the switch node (where L1, D1 and Q1
connect) should be just large enough to connect the components. To minimize excessive heating, large copper
pours can be placed adjacent to the short current path of the switch node.
The RCT, COMP, CSH, IS, HSP and HSN pins are all high-impedance inputs which couple external noise easily,
therefore the loops containing these nodes should be minimized whenever possible.
In some applications the LED or LED array can be far away (several inches or more) from the LM3429, or on a
separate PCB connected by a wiring harness. When an output capacitor is used and the LED array is large or
separated from the rest of the regulator, the output capacitor should be placed close to the LEDs to reduce the
effects of parasitic inductance on the AC impedance of the capacitor.
Basic Topology Schematics
BOOST REGULATOR (V_IN < V_O)
L1
V_IN
C_IN
R_T
R_HSN
1
V_IN
LM3429
14
HSN
C_CMP
2
COMP
13
HSP
R_HSP
R_CSH
3
CSH
12
IS
C_T
4
RCT
5
AGND
11
V_CC
C_BYP
10
GATE
D1
C_FS
R_FS
I_LED
R_SNS
C_O
Q1
R_UV2
R_UV1
R_UVH
PWM
6
OVP
7
nDIM
Q3
DAP
9
PGND
8
NC
R_LIM
R_OV2
C_OV
R_OV1
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