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Dimmable Buck LED Driver - AC Mains or DC Input LED

Driver

ISL1903

The ISL1903 is a high-performance, critical conduction mode

(CrCM), single-ended buck LED driver controller. It may be used

with DC input converters, but also supports single-stage

conversion of the AC mains to a constant current source with

power factor correction (PFC). The ISL1903 supports buck

converter topologies, such as isolated forward converters or

non-isolated source return buck converters. Operation in CrCM

allows near zero-voltage switching (ZVS) for improved

efficiency while maximizing magnetic core utilization.

The ISL1903 is compatible with both leading and trailing edge

modulated AC mains dimmers. It provides all of the features

required for high-performance dimmable LED ballast designs.

Applications

• Industrial and commercial LED lighting

• Retrofit LED lamps with triac dimming

• Universal AC mains input LED retrofit lamps

• AC or DC input LED ballasts

Features

• Excellent LED current regulation over line, load, and

temperature

• 0 - 100% dimming with leading-edge (triac) and

trailing-edge dimmers

• Power factor correction for up to 0.995 power factor and

less than 20% harmonic content

• Critical conduction mode (CrCM) operation for

quasi-resonant high efficiency performance

• Supports Universal AC Mains Input

• Configurable for PWM or DC current dimming control of

LEDs

• Monitors FET switching current for load regulation

• Supports isolated and non-isolated buck topologies

• Closed loop soft-start for no overshoot

• OFFREF feature to set dimming off-point to improve fixture

performance matching

• -40°C to +125°C operation

• Pb-free (RoHS compliant)

FIGURE 1A. BOOST-RETURN (BUCK) TOPOLOGY

FIGURE 1B. CURRENT vs AC CONDUCTION ANGLE

FIGURE 1. ISL1903 APPLICATION PERFORMANCE

12

EMI Filter

AC Mains

8

13

3

DHC

6

7

DELADJ

GND

VREF

IOUT

OUT

OC

FB

ISL1903

VDD

CS+

5

14

1

4

10

RAMP

16

9

VERR

AC

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

CONDUCTION ANGLE (%)

September 20, 2012

FN8285.1