FAN5608 Fairchild Semiconductor, FAN5608 Datasheet - Page 5

• Manufacturer Part Number: FAN5608
• Description: Serial/Parallel LED Driver with Current-Regulated/ Step-Up DC/DC Converter
• Manufacturer: Fairchild Semiconductor

Block Diagram
FAN5608
Circuit Description
When the input voltage is connected to V
turned on, the bandgap reference acquires its nominal volt-
age and the soft-start cycle begins. Once “power good” is
achieved (0.5mA in the diodes), the soft-start cycle stops and
the boost voltage increases to generate the desired current
selected by the input control pins. If the second channel is
not selected, its output will go high to about V
diodes are turned off.
The FAN5608 DC/DC converter automatically adjusts its
internal duty cycle to achieve high efficiency. It provides
tightly regulated output currents for the LEDs. An internal
circuit determines which LED string requires the highest
voltage in order to sustain the pre-set current levels, and
adjusts the boost regulator accordingly.
REV. 1.0.3 6/28/04
A2
A1
B2
B1
V
IN
DAC2
DAC1
Note: In the 8-pin version (analog version only), pins B1 and B2 are omitted.
GND
BG
IN
pin, the system is
OSC
IN
, and the
START-UP
POWER GOOD
REF
REF CH1
REF CH2
DBB
To maintain the regulated current at the selected value, the
difference in the number of LEDs between branches should
not exceed one. If only one branch is used, another branch
should be disabled, connecting the corresponding DAC
inputs to low. If the output external capacitor is shorted, the
Schottky diode can be damaged, therefore such a condition
should be avoided.
LED Brightness Control
The control inputs are A1, B1 for CH1 and A2, B2 for CH2.
B1 and B2 are digital inputs, thus they require LOW (GND)
and HIGH (V
are connected to an external stable voltage source via an
external resistor, and B1 and B2 inputs are connected to
ground. The current flowing through the resistor is scaled by
a factor of approximately 1000.
COIL DRIVER
CC
) control signals. In analog mode, A1 and A2
LINEAR REGULATOR
LINEAR REGULATOR
W_OR
PRODUCT SPECIFICATION
IND
V
IND
CH2
CH1
OUT
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