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參數(shù)資料
| 型號： | LTC3544BEUD#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 2700 kHz SWITCHING FREQ-MAX, PQCC16 |
| 封裝： | 3 X 3 MM, PLASTIC, MO-220WEED-2, QFN-16 |
| 文件頁數(shù)： | 2/18頁 |
| 文件大?。?/td> | 288K |
| 代理商： | LTC3544BEUD#TR |
LTC3544B
0
3544bfb
applicaTions inForMaTion
The basic LTC3544B application circuit is shown on the
first page of this data sheet. External component selec-
tion is driven by the load requirement and begins with the
selection of L followed by CIN and COUT.
Inductor Selection
For most applications, the value of the inductor will fall in
the range of 1H to 10H. Its value is chosen based on the
desired ripple current. Large inductor values lower ripple
current and small inductor values 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 for the 300mA regulator is
ΔIL = 120mA (40% of 300mA).
ΔI
L
V
L
OUT
IN
= ( )( )
1
–
(1)
TheDCcurrentratingoftheinductorshouldbeatleastequal
to the maximum load current plus half the ripple current
to prevent core saturation. Thus, a 360mA rated inductor
should be enough for most applications (300mA + 60mA).
For better efficiency, choose a low DCR inductor.
Inductor Core Selection
Different core materials and shapes will change the
size/current and price/current relationship of an induc-
tor. Toroid or shielded pot cores in ferrite or permalloy
materials are small and don’t radiate much energy, but
generally 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.
sizerequirementsandanyradiatedfield/EMIrequirements
than on what the LTC3544B requires to operate. Table 1
shows typical surface mount inductors that work well in
LTC3544B applications.
Table 1. Representative Surface Mount Inductors
PART NUMBER
VALUE
(H)
DCR
(
Ω MAX)
MAX DC
CURRENT (A) W
× L × H (mm3)
Sumida
CDH2D09B
10
6.4
4.7
3.3
0.47
0.32
0.218
0.15
0.48
0.6
0.7
0.85
3.0
× 2.8 × 1.0
Wurth
TPC744029
10
6.8
4.7
3.3
0.50
0.38
0.210
0.155
0.50
0.65
0.80
0.95
2.8
× 2.8 × 1.35
TDK
VLF3010AT
10
6.8
4.7
3.3
0.67
0.39
0.28
0.17
0.49
0.61
0.70
0.87
2.8
× 2.6 × 1.0
CIN and COUT Selection
In continuous mode, a worst-case estimate for the input
current ripple can be determined my assuming that the
source current of the top MOSFET is a square wave of duty
cycle VOUT/VIN, and amplitude IOUT(MAX). To prevent large
voltage transients, a low ESR input capacitor sized for the
maximumRMScurrentmustbeused.ThemaximumRMS
capacitor current is given by:
I
V
RMS
OUT MAX
OUT
IN
OUT
IN
(
)
(
)
–
This formula has a maximum at VIN = 2VOUT, where IRMS
= IOUT/2. This simple worst-case condition is commonly
used for design. Note that the capacitor manufacturer’s
ripple current ratings are often based on 2000 hours of
life (non-ceramic capacitors). This makes it advisable to
further de-rate the capacitor, or choose a capacitor rated
at a higher temperature than required. Always consult the
manufacturer if there is any question.
The selection of COUT is driven by the required effective
series resistance (ESR). Typically, once the ESR require-
ment for COUT has been met, the RMS current rating
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