FAN5333B Fairchild Semiconductor, FAN5333B Datasheet - Page 8

• Manufacturer Part Number: FAN5333B
• Description: The FAN5333B is a general-purpose LED driver that features Fixed-Frequency Mode operation and an integrated FET switch
• Manufacturer: Fairchild Semiconductor

FAN5333A/FAN5333B Rev. 1.0.1
Inductor Selection
The inductor parameters directly related to device performances
are saturation current and dc resistance. The FAN5333A/
FAN5333B operates with a typical inductor value of 10µH. The
lower the dc resistance, the higher the efficiency. Usually a
trade-off between inductor size, cost and overall efficiency is
needed to make the optimum choice.
The inductor saturation current should be rated around 1A, in
an application having the LED current near the maximum cur-
rent as indicated in “Typical Performance Characteristics”. The
peak inductor current is limited to 1.5A by the current sense
loop. This limit is reached only during the start-up and with
heavy load condition; when this event occurs the converter can
shift over in discontinuous conduction mode due to the auto-
matic turn-off of the switching transistor, resulting in higher rip-
ple and reduced efficiency.
Some recommended inductors are suggested in the table
below:
Capacitors Selection
For best performance, low ESR input and output capacitors are
required. Ceramic capacitors of C
placed as close to the IC pins, are required for the maximum
load(65mA). For the lighter load ( 20mA the capacitances may
be reduced to C
if higher ripple is acceptable. The output capacitor voltage rating
should be according to the V
suggested in the table below.
Diode Selection
The external diode used for rectification is usually a Schottky
diode. Its average forward current and reverse voltage maxi-
mum ratings should exceed the load current and the voltage at
the output of the converter respectively. A barrier Schottky diode
such as BAT54 is preferred, due to its lower reverse current over
the temperature range.
Care should be taken to avoid any short circuit of V
even with the IC disabled, since the diode can be instantly dam-
aged by the excessive current.
Inductor
Capacitor
Value
10µH
10µH
10µH
Value
0.47µF
10µF
1µF
Table 2: Recommended Capacitors
Table 1: Recommended Inductors
IN
Vendor
COOPER
MURATA
= 4.7µF and C
TDK
Panasonic
Vendor
Murata
Murata
SLF6025&-100M1R0
OUT
LQH66SN100M01C
Part Number
OUT
setting. Some capacitors are
SD414-100
IN
= 0.47µF or even to 0.1µF,
= 10µF and C
GRM21BR61E105K
GRM21BR61A106K
ECJ-3YB1E474K
Part Number
OUT
Efficiency
OUT
Highest
Com-
ment
Small
Size
to GND,
= 1µF
8
Brightness Control
1. Dimming Using PWM Logic Signal
A PWM signal applied to SHDN Table 5 on page 8 can control
the LED’s brightness in direct dependence with the duty cycle.
The maximum frequency should not exceed 1kHz to ensure a
linear dependence of the LED’s average current. The amplitude
of the PWM signal should be suitable to turn the FAN5333 ON
and OFF.
Alternatively, a PWM logic signal can be used to switch a FET
ON/OFF to change the resistance that sets the LED’s current
Table 6 on page 8. Adjusting the duty cycle from 0% to 100%
results in varying the LED’s current between I
Where
2. Dimming Using DC Voltage
An external adjustable DC voltage Table 7 on page 8 between
0V to 2V can control the LED’s current from 15mA to 0mA,
respectively.
Figure 6. Dimming Using a PWM Logic Signal
5
Figure 5. Dimming Using a PWM Signal
Figure 7. Dimming Using DC Voltage
I
1.6K
MIN
FAN5333A
=
FB
-------------
R
V
FAN5333
R
MIN
FB
MIN
90K
FB
and I
V
DC
FAN5333
R
SHDN
MAX
SET
15
=
------------------------------- -
R
MIN
4.7K
V
FAN5333B
MIN
FB
R
FB
SET
www.fairchildsemi.com
and I
90K
MAX
V
.
DC