LM3530 datasheet(38/50 Pages) TI1

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ILED

GND

LM3530

Up to 40V

Paracitic

Circuit Board

Inductances

Current through

inductor

Pulsed voltage at SW

Voltage Spike

LCD Display

SDA

SCL

OVP

COUT

Current through

Schottky Diode and COUT

2.7V to 5.5V

10 k:

Affected Node

due to capacitive

coupling

Cp1

Lp1

Lp2

Lp3

VLOGIC

IAVE = IIN

IPEAK

VOUT + VF Schottky

LM3530

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

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10 Power Supply Recommendations

The LM3530 operates from a 2.7-V to 5.5-V input voltage. The 500-kHz switching frequency for the boost can

lead to ripple voltage on the input voltage rail. To minimize this, the input to the inductor should be well bypassed

with a 1-µF (min) ceramic bypass capacitor (see Output Capacitor Selection).

11 Layout

11.1 Layout Guidelines

The LM3530 contains an inductive boost converter which detects a high switched voltage (up to 40 V) at the SW

pin, and a step current (up to 900 mA) through the Schottky diode and output capacitor each switching cycle.

The high switching voltage can create interference into nearby nodes due to electric field coupling (I = CdV/dt).

The large step current through the diode and the output capacitor can cause a large voltage spike at the SW pin

and the OVP pin due to parasitic inductance in the step current conducting path (V = Ldi/dt). Board layout

guidelines are geared towards minimizing this electric field coupling and conducted noise. Figure 56 highlights

these two noise generating components.

Figure 56. LM3530 Boost Converter Showing Pulsed Voltage At SW (High Dv/Dt) and

Current Through Schottky and COUT (High Di/Dt)

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