FAN5608_06 FAIRCHILD [Fairchild Semiconductor], FAN5608_06 Datasheet - Page 5

• Manufacturer Part Number: FAN5608_06
• Description: Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

© 2006 Fairchild Semiconductor Corporation
FAN5608 Rev. 1.0.5 • 8/8/06
Electrical Specifications
Recommended operating conditions and component values are per the Figure 18 test circuit. Typical values are at
25°C and V
Notes:
3.
4.
Circuit Description
When power is applied to the V
enabled, the bandgap reference acquires its nominal
voltage (1.2V), and the soft-start cycle begins. Once
“power good” is achieved (when 0.5mA voltage flows
through the LEDs), the soft-start cycle stops, and the
boost voltage increases to generate the current selected
by the input control pins (A1, A2, B1, B2).
If CH1 is not selected, the CH1 output pin is HIGH, its
output measurement is approximately equal to V
and its LEDs are OFF. The FAN5608 provides tightly
regulated output currents for the selected LED’s
channel. An internal feedback loop determines which
LED string requires the highest output voltage to sustain
the pre-set current. It also adjusts the boost regulator
based on CH1 and CH2 feedback voltage and A1, A2,
B1, B2 input settings. System efficiency decreases if the
channels’ strings of LEDs have different forward voltage.
If one channel is used, the other channel should be
disabled by connecting the corresponding DAC inputs to
logic LOW. If the external output capacitor V
shorted to GND, the internal Schottky diode can be
damaged, a condition which should be avoided.
Parameter
Supply current in OFF mode
LED current accuracy
Current matching
Switching frequency
Internal reference voltage, V
Current multiplication ratio
Power efficiency (AVG)
Input A1, A2 threshold
Input B1, B2 threshold
Input A1, A2 current
Input B1, B2 current
Current matching is the absolute value of the difference in current of the two LEDs channels, divided by the
average current in the two channels.
Power efficiency is the ratio between the electrical power to the LEDs and the total power consumed from the
input power supply. Although this definition leads to a lower value than the boost converter efficiency, it more
accurately reflects the system performance in an application.
IN
=3.6V. Boldface indicates specifications over ambient operating temperature (-40°C to +85°C).
(3)
(4)
A
A input LOW, B input LOW
A input HIGH, B input HIGH
A input HIGH, B input HIGH
Analog Control Mode
V
Digital Control Mode
Analog Control Mode
Digital Control Mode
Digital Control Mode
Digital Control Mode
IN
IN
pin, the system is
> 3V
Conditions
OUT
OUT
is
,
5
LED Brightness Control
The control inputs are A1 and B1 for CH1 and A2 and
B2 for CH2. B1 and B2 are digital inputs that require
LOW (GND) and HIGH V
mode, A1 and A2 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
approximately 1000.
LED dimming can be controlled with static or dynamic
inputs from CH1 and CH2. CH1 and CH2 outputs are
driven directly by A1, B1 and A2, B2 inputs, respectively.
Either channel can be configured as analog or digital.
Inputs A1 and A2 are analog inputs that can be
connected to an external regulated voltage source,
which can be calculated by:
where current multiplication ratio is according to the
Electrical Specifications table.
Inputs B1 and B2 are digital inputs and can only be set
by external logic of “0” (LOW) or “1” (HIGH).
V
V
A
A
HIGH
HIGH
= V
=0
LOW
LOW
the
IN
resistor
0.6 x V
V
Min.
IN
850
18
0
0
-0.7
IN
is
IN
scaled
Typ.
1000
control signals. In analog
500
0.1
1.2
1.2
20
80
50
0.3 x V
by a
Max.
1150
0.6
0.1
0.1
V
V
80
22
1
3
IN
IN
www.fairchildsemi.com
IN
factor
Units
EQ 1
KHz
mA
µA
µA
µA
%
%
V
V
V
of