FAN5343UMPX データシートの表示（PDF） - Fairchild Semiconductor

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FAN5343UMPX

6-LED Series Boost LED Driver with Integrated Schottky Diode and Single-Wire Digital Interface

Fairchild Semiconductor 

Functional Description

Overview

The FAN5343 is an inductive current-mode boost serial

LED driver that achieves LED current regulation by

maintaining 0.25V across the RSET resistor. The current

through the LED string (ILED) is therefore given by:

ILED

=

0.25

RSET

(1)

The voltage VOUT is determined by the the sum of the

forward voltages across each LED, plus the voltage

across RSET, which is always 250mV.

UVLO and Soft-Start

If EN has been LOW for more than 1ms, the IC may

initiate a “cold start” soft-start cycle when EN rises,

provided VIN is above the UVLO threshold.

Digital Interface

The FAN5343 implements a single-wire digital interface to

program the LED brightness to one of thirty two (32) levels

spaced in linear steps. With this single-wire solution, the

FAN5343 does not require the system processor to

constantly supply a signal to drive the LEDs.

Digital Dimming Control

The FAN5343 starts driving the LEDs at the maximum

brightness level. After startup, the control logic is ready to

accept programming pulses to decrease the brightness level

by the positive edges applied to the EN pin. Figure 14

illustrates the digital pulse dimming control for the FAN5343.

Over-Current and Short-Circuit Detection

The boost regulator employs a cycle-by-cycle peak inductor

current limit of ~750mA to protect the switching elements and

the device itself from being damaged.

Over-Voltage / Open-Circuit Protection

If the LED string is open circuit, FB remains at 0V and the

output voltage continues to increase in the absence of an

Over-Voltage Protection (OVP) circuit. The FAN5343’s OVP

circuit disables the boost regulator when VOUT exceeds 24.5V

and keeps the regulator off until VOUT drops below 22.5V.

Thermal Shutdown

When the die temperature exceeds 150°C, a reset occurs and

remains in effect until the die cools to 125°C; at which time, the

circuit is allowed to begin the soft-start sequence.

Figure 14. Digital Pulse-Dimming Control Diagram

© 2009 Fairchild Semiconductor Corporation

FAN5343 • Rev. 1.0.4

8

www.fairchildsemi.com

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