FAN5606 Fairchild Semiconductor, FAN5606 Datasheet - Page 4

• Manufacturer Part Number: FAN5606
• Description: Serial LED Driver with Current-Regulated/ Step-Up DC/DC Converter
• Manufacturer: Fairchild Semiconductor

FAN5606
4
Block Diagram
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.
The FAN5606 DC/DC converter automatically adjusts its
internal duty cycle to achieve high efficiency. If the output
external capacitor is shorted, the Schottky diode can be dam-
aged, therefore such a condition should be avoided.
LED Brightness Control
The inputs A and B can be digitally controlled LOW (GND)
and HIGH (V
nected to an external stable voltage source via an external
resistor and B input is connected to ground. The current
flowing through the resistor is scaled by a factor of approxi-
mately 1000.
V
A
B
IN
CC
) signals. In analog mode, A input is con-
DAC
GND
BG
IN
pin, the system is
OSC
START-UP
POWER GOOD
REF
DBB
Digital Control
The FAN5606’s digital decoder allows selection of the fol-
lowing modes of operation: OFF, 5mA, 10mA, 20mA per
branch.
Analog Control with PWM
In analog control mode, the LED current can go up to 25mA.
Input A is used to control the LED currents. Input B should
be connected to GND (logic level "0"). An external resistor
(R) is connected from A to a stable voltage source (V
NAL
the formula or the graph below:
I
I
AMPLIFIER
LED
) to control the LED current, I
LED
A
B
=
COIL DRIVER
OFF


V
-----------------------------------------
V
0
0
OUT
External
R
5mA
1
0
–
LINEAR REGULA TOR
V
Ref
10mA


×
0
1
PRODUCT SPECIFICATION
LED
Multiplication Ratio
. The I
20mA
REV. 1.0.2 5/14/04
1
1
LED
is given by
IND
CAT
EXTER-