參數(shù)資料
型號: LT1578CS8-2.5
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: CAP 10UF 63V ELECT TG SMD
中文描述: SWITCHING REGULATOR, 240 kHz SWITCHING FREQ-MAX, PDSO8
封裝: 0.150 INCH, PLASTIC, SO-8
文件頁數(shù): 26/28頁
文件大?。?/td> 286K
代理商: LT1578CS8-2.5
26
LT1578/LT1578-2.5
Ripple Current in the Input and Output Capacitors
Positive-to-negative converters have high ripple current in
both the input and output capacitors. For long capacitor
lifetime, the RMS value of this current must be less than
the high frequency ripple current rating of the capacitor.
The following formula will give an approximatevalue for
RMS ripple current. This formula assumes continuous
conduction mode and a arge nductor value Small induc-
tors will give somewhat higher ripple current, especially in
discontinuous mode. The exact formulas are very com-
plex and appear in Application Note 44, pages 30 and 31.
For our purposes here, a simple fudge factor (ff) is added.
The value for ff is about 1.2 for load currents above 0.38A
(in continuous conduction mode) and L
10
μ
H. It in-
creases to about 2.0 for smaller inductors at lower load
currents (in discontinuous conduction mode).
Capacitor
ff I
V
V
OUT
OUT
IN
I
RMS
=
( )(
)
ff = Fudge factor (1.2 to 2.0)
APPLICATIO
S I
FOR
ATIO
U
W
U
U
Diode Current
Average diode current is equal to load current. Peak diode
current will be considerably higher.
Peak diode current:
Continuous
(
I
V
V
V
V
V
L f V
( )( )
V
Discontinuous
V
L f
( )( )
OUT
IN
OUT
IN
IN
(
OUT
+
IN
OUT
OUT
Mode
Mode =
2 I
OUT
=
+
)
+
(
)(
)
)
(
)(
)
2
Keep in mind that during start-up and output overloads,
the average diode current may be much higher than with
normal loads. Care should be used if diodes rated less than
1A are used, especially if continuous overload conditions
must be tolerated.
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