Datasheet

LT3469
6
3469f
OPERATIO
U
transient response, however, more output capacitance can
help limit the voltage droop on V
CC
during transients.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER PHONE URL
Taiyo Yuden 408-573-4150 www.t-yuden.com
AVX 843-448-9411 www.avxcorp.com
Murata 814-237-1431 www.murata.com
Kemet 408-986-0424 www.kemet.com
Inrush Current Considerations When Hot Plugging
When the supply voltage is applied to V
IN
, the voltage
difference between V
IN
and V
CC
generates inrush current
flowing from the input through the inductor, the SW pin,
and the integrated Schottky diode to charge the output
capacitor. Care should be taken not to exceed the LT3469
maximum SW pin current rating of 1A. Worst-case inrush
current occurs when the application circuit is hot plugged
into a live supply with a large output capacitance. The
typical application circuit will maintain a peak SW pin
current below 1A when it is hot plugged into a 5V supply.
To keep SW pin current below 1A during a hot plug into
a 12V supply, 4.7Ω must be added between the supply
and the LT3469 input capacitor. During normal operation,
the SW pin current remains significantly less than 1A.
Layout Hints
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are made
3469 F04
–
+
C
BOOST
R2
R1
V
OUT
g
m
INPUT
Figure 4. Boosting the Bandwidth of the g
m
Amplifier
with Capacitance On the Inverting Input
simply an amplified version of the difference between the
feedback voltage and the reference voltage of 1.23V. In
this manner, the error amplifier sets the correct peak
current level to keep the output in regulation. If the error
amplifier’s output increases, more current is delivered to
the output; if it decreases, less current is delivered. The
switching regulator provides the boosted supply voltage
for the g
m
amplifier.
Inductor Selection
A 47µH inductor is recommended for most LT3469 appli-
cations. Some suitable inductors with small size are listed
in Table 1. The efficiency comparison of different induc-
tors is shown in Figure 5.
Table 1. Recommended Inductors
CURRENT
DCR RATING
PART NUMBER (Ω) (mA) MANUFACTURER
LQH32CN470 1.3 170 Murata
814-237-1431
www.murata.com
CMD4D11-470 2.8 180 Sumida
847-545-6700
www.Sumida.com
LBC2518T470M 1.9 150 Taiyo Yuden
408-573-4150
www.t-yuden.com
Capacitor Selection
The small size of ceramic capacitors makes them ideal for
LT3469 applications. X5R and X7R types are recommended
because they retain their capacitance over wider voltage and
temperature ranges than other types such as Y5V or Z5U.
A 1µF input capacitor is sufficient for most LT3469 appli-
cations. A 0.22µF output capacitor is sufficient for stable
LOAD CURRENT (mA)
0
40
EFFICIENCY (%)
50
60
70
5
10
15 20
3469 F05
25
80
90
45
55
65
75
85
30
V
IN
= 12V
V
OUT
= 35V
MURATA LQH32CN470
SUMIDA CMD4011-470
TAIYO YUDEN LBC2518T470M
Figure 5. Efficiency Comparison of Different Inductors