FAN5606 Fairchild Semiconductor, FAN5606 Datasheet - Page 6

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

FAN5606
6
PWM Control
3. A and B are PWM. I
Notes:
4. Proportionally select the duty cycle to achieve a typical LED current between 1mA to 4mA.
5. Maximum PWM frequency can be up to 30KHz.
6. Proportionally select the duty cycle to achieve a typical LED current between 1mA and 19mA.
Applications Information
Inductor Selection
The inductor is one of the main components required by the
boost converter to store energy. The amount of energy stored
in the inductor and transferred to the load is controlled by the
regulator using PWM and pulse skipping techniques. In most
cases, the FAN5606 operates the inductor in discontinuous
conduction mode.
To ensure proper operation of the current regulator over the
entire range of conditions, the inductor should be selected
based on the maximum required power (P
mum input voltage (V
where units of L, V
respectively and F = 0.4 is a factor depending upon the
FAN5606 architecture.
A Input (PWM)
B Input (PWM)
LED CURRENT
IN
IN
, and P
L
(Continued)
0mA
).
<
LED
(
-------------------------- -
V
P
IN
OUT
(Average) =
OUT
)
2
are in µ H, Volt, and Watt,
×
Duty Cycle
Duty Cycle
1KHz
1KHz
F
30%
30%
I
LED
OUT
δ
(Average) = 0.3 x 20mA = 6mA
x 20mA, where
) and the mini-
δ
is Duty Cycle.
The above relation is applicable up to P
L = 4.3 µΗ , or greater. The peak current in the inductor is:
where T
driving upto 6 LEDs, type QTLP670CiW is L = 6.8 µ H rated
at minimum 0.5A.
Low ESR capacitors should be used to minimize the input
and output ripple voltage. Use of C
C
capacitor are recommended.
A larger value input capacitor placed as close as possible to
FAN5606 may be needed to reduce the input voltage ripple
in noise sensitive applications. An additional LC filter
between the battery and the FAN5606 input can help to fur-
ther reduces the battery ripple to the level required by a par-
ticular application.
OUT
= 4.7µF/25V type X5R/X7R multi layer ceramic
ON_Max
= 1.25 µ S. The recommended inductor for
I
I
LED
Duty Cycle
Duty Cycle
=
1KHz
1KHz
70%
70%
(Average) = 0.7 x 20mA = 14mA
T
------------------------------------------------- -
ON_Max
L
×
V
PRODUCT SPECIFICATION
IN
IN_Max
= 4.7µF/6.3V and
OUT
REV. 1.0.2 5/14/04
= 0.6W and
OFF