FAN5330 Datasheet, PDF (7/10 Pages) Fairchild Semiconductor – High Efficiency Serial LED Driver with 30V Integrated Switch

Inductor Selection
The inductor parameters directly related to device performances
are saturation current and dc resistance. The FAN5330 oper-
ates 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 1.5A,
which is the threshold of the internal current limit circuit. 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 automatic turn-off of
the switching transistor, resulting in higher ripple and reduced
efficiency.
Some recommended inductors are suggested in the table
below:
Inductor
Value
10µH
10µH
10µH
Vendor
TDK
MURATA
COOPER
Part Number
Com-
ment
SLF6025&-100M1R0
LQH66SN100M01C Highest
Efficiency
SD414-100
Small Size
Brightness Control
1. Dimming Using PWM Logic Signal
A PWM signal applied to SHDN Table 5 on page 7 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 7. Adjusting the duty cycle from 0% to 100%
results in varying the LED’s current between I_MIN and I_MAX.
Where
I_MIN = _R--V---M-^F---_I-^B-_N-- and I_MAX = _R-----M----_I--_N-V----^F---R^B----_S----_E---_T--
FAN5330
SHDN
Table 1: Recommended Inductors
Capacitors Selection
For best performance, low ESR input and output capacitors are
required. Ceramic capacitors of C_IN = 4.7µF and C_OUT = 0.47µF
placed close to the IC pins, are required for optimum perfor-
mance. The capacitances (C_OUT) may be reduced to 0.1µF, if
higher ripple is acceptable. The output capacitor voltage rating
should be according to the V_OUT setting. Some capacitors are
suggested in the table below
Capacitor
Value
0.47µF
4.7µF
Vendor
Panasonic
Murata
Part Number
ECJ-3YB1E474K
GRM21BR61A475K
Table 2: Recommended Capacitors
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_OUT to GND,
even with the IC disabled, since the diode can be instantly dam-
aged by the excessive current.
Figure 5. Dimming Using a PWM Signal
FAN5330
FB
R_MIN
R_SET
Figure 6. Dimming Using a PWM Logic Signal
2. Dimming Using DC Voltage
An external adjustable DC voltage Table 7 on page 7 between
0V to 2V can control the LED’s current from 15mA to 0mA,
respectively.
FAN5330
FB
V_DC
1.6KΩ
90KΩ
5Ω
Figure 7. Dimming Using DC Voltage
7
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FAN5330 Rev. 1.0.1