參數(shù)資料
型號(hào)： LT1578IS8-2.5
廠(chǎng)商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS
中文描述： SWITCHING REGULATOR, 240 kHz SWITCHING FREQ-MAX, PDSO8
封裝： 0.150 INCH, PLASTIC, SO-8
文件頁(yè)數(shù)： 14/28頁(yè)
文件大?。?/td> 286K
代理商： LT1578IS8-2.5
14
LT1578/LT1578-2.5
APPLICATIO
S I
N
FOR
ATIO
U
boost capacitor. This normally means that peak BOOST
pin voltage is equal to input voltage plus output voltage,
but when the boost diode is connected to the regulator
input, peak BOOST pin voltage is equal to twice the input
voltage. Be sure that BOOST pin voltage does not exceed
its maximum rating
For nearly all applications, a 0.33
μ
F boost capacitor works
just fine, but for the curious, more details are provided
here. The size of the boost capacitor is determined by
switch drive current requirements. During switch on time,
drain current on the capacitor is approximately I
OUT
/50. At
peak load current of 1.25A, this gives a total drain of 25mA.
Capacitor ripple voltage is equal to the product of on time
and drain current divided by capacitor value;
V = (t
ON
)(25mA/C). To keep capacitor ripple voltage to
less than 0.5V (a slightly arbitrary number) at the worst-
case condition of t
ON
= 4.7
μ
s, the capacitor needs to be
0.24
μ
F. Boost capacitor ripple voltage is not a critical
parameter, but if the minimum voltage across the capaci-
tor drops to less than 3V, the power switch may not
saturate fully and efficiency will drop. An approximate
formula for absolute minimum capacitor value is:
W
U
–
+
–
+
2.42V
0.4V
GND
V
SW
LT1578
INPUT
R
FB
R
HI
1578 F04
OUTPUT
SHDN
STANDBY
IN
TOTAL
SHUTDOWN
3.5
μ
A
R
LO
C1
+
Figure 4. Undervoltage Lockout
C
I
V
V
)
f V
( )
V
MIN
OUT
OUT
IN
OUT
=
(
)(
)
(
/
/
50
3
f = Switching frequency
V
OUT
= Regulated output voltage
V
IN
= Minimum input voltage
This formula can yield capacitor values substantially less
than 0.24
μ
F, but it should be used with caution since it
does not take into account secondary factors such as
capacitor series resistance, capacitance shift with tem-
perature and output overload.
SHUTDOWN FUNCTION AND
UNDERVOLTAGE LOCKOUT
Figure 4 shows how to add undervoltage lockout (UVLO)
to the LT1578. Typically, UVLO is used in situations where
the input supply is current limited or has a relatively high
source resistance. It is particularly useful for input sup-
plies with foldback current limiting. A switching regulator
draws constant power from the source, so source current
increases as source voltage drops. This looks like a
negative resistance load to the source and can cause the
source to current limit and latch under low source voltage
相關(guān)PDF資料
PDF描述
LT1578C CAP 22UF 50V ELECT TG SMD
LT1578CS8 CAP 47UF 50V ELECT TG SMD
LT1578CS8-2.5 CAP 10UF 63V ELECT TG SMD
LT1578I CAP 22UF 63V ELECT TG SMD
LT1578 1.5A, 200kHz Step-Down Switching Regulator(1.5A, 200kHz，步降開(kāi)關(guān)穩(wěn)壓器)
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