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參數(shù)資料
| 型號(hào)： | LT3837IFE#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 110 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16 |
| 文件頁數(shù)： | 7/28頁 |
| 文件大?。?/td> | 247K |
| 代理商： | LT3837IFE#TRPBF |
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LT3837
15
3837fc
APPLICATIONS INFORMATION
tight coupling usually increases primary-to-secondary
capacitance and limits the primary-to-secondary break-
down voltage, so it isn’t always practical.
Primary Inductance
The transformer primary inductance, LP, is selected based
on the peak-to-peak ripple current ratio (X) in the trans-
former relative to its maximum value. As a general rule,
keep X in the range of 50% to 70% ripple current (i.e., X =
0.5 to 0.7). Higher values of ripple will increase conduction
losses, while lower values will require larger cores.
Ripple current and percentage ripple is largest at minimum
duty cycle; in other words, at the highest input voltage.
LP is calculated from:
L
VDC
fX
P
V
P
IN MAX
MIN
OSC
MAX
IN
IN MAX
= () =
()
2
D
DC
Eff
fX
P
MIN
OSC
MAX
OUT
()2
where:
fOSC is the OSC frequency
DCMIN is the DC at maximum input voltage
XMAX is ripple current ratio at maximum input voltage
Continuing with the 9V to 3.3V example, let us assume a
10A output, 9V to 18V input power with 88% efciency.
Using X = 0.7, and fOSC = 200kHz:
P
A
W
DC
NV
V
IN
MIN
IN MAX
OUT
=
=
+
33 10
88
37 5
1
.
%
.
()
==
+
=
()
1
3
18
33
35 5
18
0 355
200
0
2
.
.%
.
L
V
kHz
P
7
737 5
78
.
W
H
=μ
Optimization might show that a more efcient solution
is obtained at higher peak current but lower inductance
and the associated winding series resistance. A simple
spreadsheet program is useful for looking at tradeoffs.
Transformer Core Selection
Once LP is known, the type of transformer is selected.
High efciency converters use ferrite cores to minimize
core loss. Actual core loss is independent of core size for
a xed inductance, but decreases as inductance increases.
Since increased inductance is accomplished through
more turns of wire, copper losses increase. Thus trans-
former design balances core and copper losses. Remem-
ber that increased winding resistance will degrade cross
regulation and increase the amount of load compensa-
tion required.
The main design goals for core selection are reducing
copper losses and preventing saturation. Ferrite core mate-
rial saturates hard, rapidly reducing inductance when the
peak design current is exceeded. This results in an abrupt
increase in inductor ripple current and, consequently, out-
put voltage ripple. Do not allow the core to saturate! The
maximum peak primary current occurs at minimum VIN:
I
P
VDC
X
now
DC
PK
IN
IN MIN
MAX
MIN
MA
=+
()
:
1
2
X
IN MIN
OUT
MIN
NV
V
X
V
=
+
=
+
=
1
3
9
33
52 4
.
.%
()
IIN MIN
MAX
OSC
P
IN
DC
fL
P
kH
()
.
()
=
()
2
90 52
200
zzH
W
.
.
7 8
37 5
0 380
μ
=
Using the example numbers leads to:
I
W
V
A
PK =+
=
37 5
9
0 524
1
0 380
2
947
.
.
Multiple Outputs
One advantage that the yback topology offers is that ad-
ditional output voltages can be obtained simply by adding
windings. Designing a transformer for such a situation is
beyond the scope of this document. For multiple windings,
realize that the yback winding signal is a combination of
activity on all the secondary windings. Thus load regulation
is affected by each windings load. Take care to minimize
cross regulation effects.
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| LT3844EFE#PBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
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