2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

8

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Freewheeling-Diode Selection

For stability and best efficiency, a low forward-voltage

drop diode with fast reverse-recovery time and low

capacitance is recommended. A Schottky diode is a

good choice as long as its breakdown voltage is high

enough to withstand the maximum operating voltage.

PCB Layout Guidelines

Careful PCB layout is critical to achieve low switching

losses and stable operation. Use a multilayer board

whenever possible for better noise immunity. Minimize

ground noise by connecting high-current ground

returns, the input bypass-capacitor ground lead, and

the output-filter ground lead to a single point (star

ground configuration). In normal operation, there are two

power loops. One is formed when the internal MOSFET

LED load, the inductor, the internal MOSFET, and GND.

The other loop is formed when the internal MOSFET is

load, the inductor, and the freewheeling diode. Minimize

each loop area to reduce noise interaction.

better noise immunity, a Kelvin connection between CS

t

t

t2

ΔI

t1

AVG. LED

CURRENT

HYSTERETIC

MODE

Figure 2. Current-Regulator Operation