參數(shù)資料
型號(hào): LTC3406ES5-1.2#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 1.3 A SWITCHING REGULATOR, 1800 kHz SWITCHING FREQ-MAX, PDSO5
封裝: PLASTIC, SOT-23, 5 PIN
文件頁(yè)數(shù): 10/12頁(yè)
文件大小: 228K
代理商: LTC3406ES5-1.2#PBF
7
LTC3406-1.2
340612fa
APPLICATIO S I FOR ATIO
WU
UU
The basic LTC3406-1.2 application circuit is shown in
Figure 1. External component selection is driven by the
load requirement and begins with the selection of L fol-
lowed by CIN and COUT.
Inductor Selection
For most applications, the value of the inductor will fall in
the range of 1
H to 4.7H. Its value is chosen based on the
desired ripple current. Large value inductors lower ripple
current and small value inductors result in higher ripple
currents. Higher VIN or VOUT also increases the ripple
current as shown in equation 1. A reasonable starting point
for setting ripple current is
IL = 240mA (40% of 600mA).
= ()( )
I
fL
V
L
OUT
IN
1
(1)
The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 720mA rated
inductor should be enough for most applications (600mA
+ 120mA). For better efficiency, choose a low DC-resis-
tance inductor.
Inductor Core Selection
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy mate-
rials are small and don’t radiate much energy, but gener-
ally cost more than powdered iron core inductors with
similar electrical characteristics. The choice of which style
inductor to use often depends more on the price vs size
requirements and any radiated field/EMI requirements
than on what the LTC3406-1.2 requires to operate. Table
1 shows some typical surface mount inductors that work
well in LTC3406-1.2 applications.
Table 1. Representative Surface Mount Inductors
PART
VALUE
DCR
MAX DC
SIZE
NUMBER
(
H)
(
MAX) CURRENT (A) W × L × H (mm3)
Sumida
1.5
0.043
1.55
3.8
× 3.8 × 1.8
CDRH3D16
2.2
0.075
1.20
3.3
0.110
1.10
4.7
0.162
0.90
Sumida
2.2
0.116
0.950
3.5
× 4.3 × 0.8
CMD4D06
3.3
0.174
0.770
4.7
0.216
0.750
Panasonic
3.3
0.17
1.00
4.5
× 5.4 × 1.2
ELT5KT
4.7
0.20
0.95
Murata
1.0
0.060
1.00
2.5
× 3.2 × 2.0
LQH3C
2.2
0.097
0.79
4.7
0.150
0.65
CIN and COUT Selection
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle VOUT/VIN. To prevent large
voltage transients, a low ESR input capacitor sized for the
maximum RMS current must be used. The maximum
RMS capacitor current is given by:
C
required I
I
VV
V
IN
RMS
OMAX
OUT
IN
OUT
IN
()
[]12/
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT/2. This simple worst-case condition is com-
monly used for design because even significant deviations
do not offer much relief. Note that the capacitor
manufacturer’s ripple current ratings are often based on
2000 hours of life. This makes it advisable to further derate
the capacitor, or choose a capacitor rated at a higher
temperature than required. Always consult the manufac-
turer if there is any question.
The selection of COUT is driven by the required effective
series resistance (ESR).
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