參數(shù)資料
型號: LTC3419EDD-1#TR
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 1.2 A DUAL SWITCHING CONTROLLER, 2250 kHz SWITCHING FREQ-MAX, PDSO8
封裝: 3 X 3 MM, PLASTIC, MO-229WEED-1, DFN-8
文件頁數(shù): 16/16頁
文件大?。?/td> 264K
代理商: LTC3419EDD-1#TR
LTC3419
9
3419f
A general LTC3419 application circuit is shown in Figure 1.
External component selection is driven by the load require-
ment, and begins with the selection of the inductor L. Once
the inductor is chosen, CIN and COUT can be selected.
Inductor Selection
Although the inductor does not inuence the operat-
ing frequency, the inductor value has a direct effect on
ripple current. The inductor ripple current ΔIL decreases
with higher inductance and increases with higher VIN or
VOUT:
Δ=
I
V
fL
V
L
OUT
O
OUT
IN
( )
11
Accepting larger values of ΔIL allows the use of low
inductances, but results in higher output voltage ripple,
greater core losses, and lower output current capability.
A reasonable starting point for setting ripple current is
40% of the maximum output load current. So, for a 600mA
regulator, ΔIL = 240mA (40% of 600mA).
The inductor value will also have an effect on Burst Mode
operation. The transition to low current operation begins
when the peak inductor current falls below a level set by
the internal burst clamp. Lower inductor values result in
higher ripple current which causes the transition to occur
at lower load currents. This causes a dip in efciency in
the upper range of low current operation. Furthermore,
lower inductance values will cause the bursts to occur
with increased frequency.
Inductor Core Selection
Different core materials and shapes will change the size/cur-
rent and price/current relationship of an inductor. Toroid
APPLICATIONS INFORMATION
Figure 1. LTC3419 General Schematic
or shielded pot cores in ferrite or permalloy materials are
small and do not radiate much energy, but generally cost
more than powdered iron core inductors with similar
electrical characteristics. The choice of which style induc-
tor to use often depends more on the price versus size
requirements, and any radiated eld/EMI requirements,
than on what the LTC3419 requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3419 applications.
Table 1. Representative Surface Mount Inductors
MANU-
FACTURER
PART NUMBER
VALUE
MAX DC
CURRENT
DCR
HEIGHT
Taiyo Yuden
CB2016T2R2M
CB2012T2R2M
CB2016T3R3M
2.2μH
3.3μH
510mA
530mA
410mA
0.13Ω
0.33Ω
0.27Ω
1.6mm
1.25mm
1.6mm
Panasonic
ELT5KT4R7M
4.7μH
950mA
0.2Ω
1.2mm
Sumida
CDRH2D18/LD
4.7μH
630mA
0.086Ω
2mm
Murata
LQH32CN4R7M23
4.7μH
450mA
0.2Ω
2mm
Taiyo Yuden
NR30102R2M
NR30104R7M
2.2μH
4.7μH
1100mA
750mA
0.1Ω
0.19Ω
1mm
FDK
FDKMIPF2520D
4.7μH
3.3μH
2.2μH
1100mA
1200mA
1300mA
0.11Ω
0.1Ω
0.08Ω
1mm
TDK
VLF3010AT4R7-
MR70
VLF3010AT3R3-
MR87
VLF3010AT2R2-
M1R0
4.7μH
3.3μH
2.2μH
700mA
870mA
1000mA
0.28Ω
0.17Ω
0.12Ω
1mm
VIN
RUN2
RUN1
LTC3419
VFB2
SW2
SW1
MODE
VFB1
CF2
CF1
GND
VIN
2.5V TO 5.5V
VOUT2
VOUT1
3419 F01
R4
R2
R3
R1
L2
L1
COUT2
COUT1
C1
Input Capacitor (CIN) Selection
In continuous mode, the input current of the converter is a
square wave with a duty cycle of approximately VOUT/VIN.
To prevent large voltage transients, a low equivalent series
resistance (ESR) input capacitor sized for the maximum
RMS current must be used. The maximum RMS capacitor
current is given by:
II
VV
V
RMS
MAX
OUT
IN
OUT
IN
()
Where the maximum average output current IMAX equals
the peak current minus half the peak-to-peak ripple cur-
rent, IMAX = ILIM – ΔIL /2. This formula has a maximum at
VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case
is commonly used to design because even signicant
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