FAN5341 Fairchild Semiconductor, FAN5341 Datasheet - Page 8

• Manufacturer Part Number: FAN5341
• Description: Fan5341 Series Boost Led Driver With Integrated Schottky Diode And Single-wire Digital Interface
• Manufacturer: Fairchild Semiconductor

© 2009 Fairchild Semiconductor Corporation
FAN5341 • Rev. 1.0.0
Circuit Description
Overview
The FAN5341 is an inductive current-mode boost serial
LED driver that achieves LED current regulation by
maintaining 0.253V across the R
through the LED string (I
The voltage V
voltages across each LED, plus the voltage across R
which is always 253mV.
Driving Five LEDs in Series
FAN5341 can drive five LEDs in series but, the forward
voltage (V
remains under the over-voltage specification of 18.9V.
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 V
above the UVLO threshold.
Digital Interface
The FAN5341 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
I
LED
=
. 0
R
SET
F
253
) of the LED MUST be less than 3.5V such that it
OUT
is determined by the sum of the forward
LED
) is therefore given by:
SET
Figure 14. Digital Pulse-Dimming Control Diagram
resistor. The current
IN
SET
(1)
is
,
8
FAN5341 does not require the system processor to
constantly supply a signal to it to drive the LEDs.
Digital Dimming Control
The FAN5341 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 number of positive edges applied to the EN pin.
Figure 14 shows the digital pulse dimming control.
Over-Current and Short-Circuit Detection
The boost regulator employs a cycle-by-cycle peak inductor
current limit of ~750mA.
Over-Voltage / Open-Circuit Protection
If the LED string is an open circuit, FB remains at 0V and
the output voltag continues to increase in the absence of an
over-voltage protection (OVP) circuit. The FAN5341’s OVP
circuit disables the boost regulator when V
18.9V and continues to keep the regulator off until V
drops below 18.1V.
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.
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OUT
exceeds
OUT