lt3475efe-trpbf Linear Technology Corporation, lt3475efe-trpbf Datasheet - Page 10

• Manufacturer Part Number: lt3475efe-trpbf
• Description: Dual Step-down 1.5a Led Driver
• Manufacturer: Linear Technology Corporation

LT3475/LT3475-1
current have signifi cantly increased. Exceeding V
is safe if the external components have adequate ratings
to handle the peak conditions and if the peak inductor
current does not exceed 3.2A. A saturating inductor may
further reduce performance.
Inductor Selection and Maximum Output Current
A good fi rst choice for the inductor value is:
where V
f is the switching frequency and L is in μH. With this value
the maximum load current will be above 1.6A at all duty
cycles. The inductor’s RMS current rating must be greater
than the maximum load current and its saturation current
should be at least 30% higher. For highest effi ciency,
the series resistance (DCR) should be less than 0.15Ω.
Table 2 lists several vendors and types that are suitable.
For robust operation at full load and high input voltages
(V
higher than 3.2A.
10
APPLICATIONS INFORMATION
IN
L = (V
> 30V), use an inductor with a saturation current
(AC COUPLED)
500mV/DIV
F
OUT
is the voltage drop of the catch diode (~0.4V),
20V/DIV
1A/DIV
Figure 4. Operation above V
Ripple and Peak Inductor Current Increases
V
V
OUT
SW
I L
+ V
F
) •
1.2MHz
f
IN(MAX)
. Output
3475 F04
IN(MAX)
Table 2. Inductors
The optimum inductor for a given application may differ
from the one indicated by this simple design guide. A larger
value inductor provides a higher maximum load current, and
reduces the output voltage ripple. If your load is lower than
the maximum load current, then you can relax the value of the
inductor and operate with higher ripple current. This allows
you to use a physically smaller inductor, or one with a lower
DCR resulting in higher effi ciency. In addition, low inductance
may result in discontinuous mode operation, which further
reduces maximum load current. For details of maximum
output current and discontinuous mode operation, see Linear
Technology’s Application Note 44. Finally, for duty cycles
greater than 50% (V
is required to avoid sub-harmonic oscillations:
PART NUMBER
Sumida
CR43-3R3
CR43-4R7
CDRH4D16-3R3
CDRH4D28-3R3
CDRH4D28-4R7
CDRH6D26-5R0
CDRH6D26-5R6
CDRH5D28-100
CDRH5D28-150
CDRH73-100
CDRH73-150
CDRH104R-150
Coilcraft
DO1606T-332
DO1606T-472
DO1608C-332
DO1608C-472
MOS6020-332
MOS6020-472
DO3316P-103
DO3316P-153
L
MIN
= (V
OUT
VALUE
(μH)
+ V
3.3
4.7
3.3
3.3
4.7
5.0
5.6
3.3
4.7
3.3
4.7
3.3
10
15
10
15
15
10
10
15
OUT
F
) •
/V
IN
800kHz
> 0.5), a minimum inductance
I
1.44
1.15
1.10
1.57
1.32
2.20
1.30
1.10
1.68
1.33
1.30
1.10
2.00
1.50
1.80
1.50
RMS
(A)
2.0
3.1
3.9
3.1
f
0.086
0.109
0.063
0.049
0.072
0.032
0.036
0.048
0.076
0.072
0.130
0.050
0.100
0.120
0.080
0.090
0.046
0.050
0.038
0.046
DCR
( )
HEIGHT
(mm)
3.5
3.5
1.8
3.0
3.0
2.8
2.8
3.0
3.0
3.4
3.4
4.0
2.0
2.0
2.9
2.9
2.0
2.0
5.2
5.2
3475fb