LT3492 LINER [Linear Technology], LT3492 Datasheet - Page 10

• Manufacturer Part Number: LT3492
• Description: Triple Output LED Driver with 3000:1 PWM Dimming
• Manufacturer: LINER [Linear Technology]

LT3492
Table 1. Ceramic Capacitor Manufacturers
Inductor Selection
Inductor value is selected based on switching frequency
and desired transient response. The data sheet applica-
tions show appropriate selections for a 1.3MHz switching
frequency. Proportionately higher values may be used if a
lower switching frequency is selected.
Several inductors that work well with the LT3492 are listed
in Table 2. However, there are many other manufacturers
and devices that can be used. Consult each manufacturer
for more detailed information and their entire range of
parts. Ferrite core inductors should be used to obtain the
best effi ciency. Choose an inductor that can handle the
necessary peak current without saturating, and ensure that
the inductor has a low DCR (copper-wire resistance) to
minimize I
shield should be used to prevent noise radiation and cross
coupling among the three channels.
Diode Selection
The Schottky diode conducts current during the interval
when the switch is turned off. Select a diode V
for the maximum SW voltage. It is not necessary that
the forward current rating of the diode equal the switch
current limit. The average current, I
is a function of the switch duty cycle. Select a diode with
forward current rating of:
where I
If using the PWM feature for dimming, it is important to
consider diode leakage, which increases with the tem-
perature from the output during the PWM low interval.
Therefore, choose the Schottky diode with suffi cient low
leakage current at hot temperature. Table 3 shows several
Schottky diodes that work well with the LT3492.
APPLICATIONS INFORMATION
10
I
F
Taiyo Yuden
= I
VENDOR
Murata
Kemet
AVX
TDK
L
L
is the inductor current.
• (1 – D)
2
R power losses. An inductor with a magnetic
Ceramic
Ceramic
Ceramic
Ceramic
Ceramic
TYPE
F
, through the diode
X5R, X7R
X5R, X7R
X5R, X7R
X5R, X7R
X5R, X7R
SERIES
R
rated
Table 3. Schottky Diodes
PART NUMBER
ZETEX
ZLLS350
ZLLS400
DIODES
B1100
ROHM
RB160M-60
Undervoltage Lockout
The LT3492 has an undervoltage lockout circuit that
shuts down all the three converters when the input volt-
age drops below 2.1V. This prevents the converter from
switching in an erratic mode when powered from a low
supply voltage.
Programming the LED Current
An important consideration when using a switch with a
fi xed current limit is whether the regulator will be able to
supply the load at the extremes of input and output voltage
range. Several equations are provided to help determine
Table 2. Surface Mount Inductors
PART NUMBER
Sumida
CDRH4D28
CDRH5D28
CooperET
SD20
SD25
Taiyo Yuden
NP04SZB
TDK
VLF5014A
Würth Electronics
7447789133
Coilcraft
M556132
VALUE
(μH)
15
22
33
15
22
33
15
22
15
22
33
22
V
100
R
40
40
60
(V)
(Ω MAX)
0.1655
0.2053
0.2149
0.149
0.122
0.189
0.180
0.210
DCR
0.32
0.46
0.24
0.19
I
I
0.38
0.52
RMS
F
1.0
1.0
0.76
0.75
1.25
1.12
1.11
0.95
0.77
0.97
0.51
1.22
1.45
(A)
0.9
(A)
W × L × H (mm3)
5.0 × 5.0 × 3.0
6.0 × 6.0 × 3.0
5.0 × 5.0 × 2.0
5.0 × 5.0 × 2.5
4.0 × 4.0 × 1.8
4.5 × 4.7 × 1.4
7.3 × 7.3 × 3.2
6.1 × 6.1 × 3.2
PMDU/SOD-123
PACKAGE
SOD523
SOD323
SIZE
SMA
3492f