FAN5611 Fairchild Semiconductor, FAN5611 Datasheet - Page 8

• Manufacturer Part Number: FAN5611
• Description: Low-Dropout LED Drivers for White/ Blue or any Color LED
• Manufacturer: Fairchild Semiconductor

FAN5611/FAN5612/FAN5613/FAN5614
In some cases, there is already a voltage bus in the system,
which can be utilized. Due to the ultra-low voltage drop of
the FAN561X series of LED drivers to drive high V
or blue LEDs. The V
the highest V
Where V
Key advantages:
• No boost circuit needed for LCD or keyboard backlight
• Driver utilizes the existing bus
• Ultra-low voltage drop provides the full 20mA LED
Example 3: Drive white, blue, red, amber LEDs
string
Assuming boost circuit, or existing voltage bus, the
FAN561X series of LED drivers can be used to drive a whole
string of LEDs and flexible brightness control - analog
and/or PWM.
Where V
8
V
– V
– V
– V
– V
current at the lowest possible voltage level.
– V
– V
– V
CONTROL
ENABLE
V
CONTROL
DROP
F (at 20mA)
IN (at 20mA)
IN (at 5mA Typical)
DROP
IN_MIN
IN _MAX
IN
IN
V
IN
R
I
SET
SET
= Existing bus = 3.3V to 4.3V
= Existing bus, boost voltage
< 0.3V
< 0.3V
F
ENABLE
V
= N × V
in the circuit.
IN
= N × V
CTRL
ON/OFF
I4
R
I
< 3.3V to 4.0V (High V
SET
SET
=V
IN
DROP
FAN5613
I3
F
needs to be only 300mV higher than
~ 3.3V
F
GND
+ V
CTRL
ON/OFF
+ 5.5V
I4
+ V
DROP
I2
F
= 3.6V to 4.3V
I3
I1
FAN5613
GND
F
'N' number of LEDs Per Branch
)
I2
F
I1
white
Key advantage:
• No need for current matching resistors and discrete
LED Brightness Control
All of the FAN561X LED Drivers feature analog and PWM
controls to give designers flexible brightness control. These
control methods can be applied to the circuit in two different
ways, to provide more flexibility than any other solution. To
determine the value of R
under the Typical Performance Characteristics section.
1. FAN5611
- Analog
Set V
- PWM
V
2. FAN5612
- Analog
Set V
- PWM - 1
V
I
I
LED
LED
CONTROL
CONTROL
transistor for brightness control
– Amplitude sets maximum LED current
– Pulse width controls between 0 and maximum
V
V
CONTROL
CONTROL
=
=
CONTROL
CONTROL
200
-------------------------------------------------------------------------
200
-------------------------------------------------------------------------
= PWM
= PWM
×
×
ENABLE
(3V
(
(
V
V
and R
V
and R
V
)
IN
CONTROL
CONTROL
R
I
SET
IN
R
I
SET
SET
SET
R
R
SET
SET
SET
SET
ON/OFF
CTRL
SET
CTRL
for LED current
for LED current
I4
I3
–
–
, use the “I
V
V
CTRL
CTRL
I3
FAN5612
PRODUCT SPECIFICATION
FAN5611
)
)
GND
GND
I2
SET
I2
vs. V
REV. 1.0.4 6/4/04
I1
CTRL
I1
” graph