LM3429 datasheet(21/50 Pages) TI1

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ILED

ROV1

ROV2

RSNS

OVP

LM3429

nDIM

VIN

PGND

DAP

GATE

COMP

CSH

RCT

HSN

HSP

CIN

CBYP

RLIM

CCMP

RCSH

RUV2

RUV1

RHSN

RHSP

AGND

RUVH

PWM

RFS

CFS

COV

VIN

VCC

LM3429

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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 (CIN),

the recirculating diode (D1), the N-channel MosFET (Q1), and the sense resistor (RLIM). In the LM3429 boost and

buck-boost regulators, the discontinuous current flows through the output capacitor (CO), D1, Q1, and RLIM. 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 (VIN < VO)

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