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參數(shù)資料
| 型號： | ML4895 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的同步補償控制器（5.9V～15V到2.5V～4V變換）) |
| 中文描述： | 同步降壓控制器，用于直流/直流轉(zhuǎn)換（用于直流/直流變換的同步補償控制器（高于全?15V的到為2.5V?4V變換）） |
| 文件頁數(shù)： | 8/10頁 |
| 文件大?。?/td> | 248K |
| 代理商： | ML4895 |
ML4895
8
The worst case power dissipation for the N-MOS switch
occurs at the maximum input voltage and is determined
using:
P
I
R
N MOS
-
RMS OFF
(
DS ON
(
=
)
)
2
(11)
INPUT CAPACITOR SELECTION
The choice of the input capacitor is based on its ripple
current and voltage ratings rather than its capacitance
value. The input capacitor should be a low ESR type and
located as close to the source of the P-MOS switch as
possible. The input capacitor’s ripple current is determined
by the load current and input voltage, with the worst case
condition occurring at V
IN
= 2 x V
OUT
:
I
I
I
V
V
V
V
RMS C
SENSE MAX
L MAX
(
OUT
IN
OUT
IN
IN
(
)
(
)
)
(
)
+
-
1
2
D
1
6
(12)
The capacitor’s voltage rating is based on the maximum
input voltage, V
IN(MAX)
. Capacitor manufacturers
typically recommend derating the capacitor voltage
rating by 20% to 50% for aluminum electrolytic types and
50% to 70% for tantalum types.
In high current applications it may necessary to add a
small 100nF ceramic capacitor to bypass the V
IN
pin of
the ML4895.
OUTPUT CAPACITOR SELECTION
The output capacitors determine the loop stability and the
output ripple voltage. Use only low ESR capacitors
intended for switching power supply applications, such as
AVX TPS, Sprague 593D, Sanyo OS-CON, or Nichicon PL
series. To ensure stability, the minimum capacitance
value is given by:
C
V
t
R
OUT
OUT
ON MAX
(
SENSE
43
)
(13)
The maximum ESR value can be estimated using:
ESR
V
I
L MAX
D
(
OUT
D
)
(14)
The selected capacitor must meet both the capacitance
and ESR requirements. As a final check, make sure the
output capacitor can handle the ripple current, I
RMS
:
I
I
RMS
L MAX
12
D
(
)
(15)
OUTPUT VOLTAGE
The output of the buck converter is adjustable and can be
set to any voltage between 2.5V and 4V by connecting a
resistor divider to the feedback pin as shown in Figure 1.
The resistor values R1 and R2 can be calculated using the
following equation:
V
V
R
R2
R2
OUT
=
+
250
.
1
(16)
The value of R2 should be 475k
W
or less to minimize bias
current errors.
It is important to note that the accuracy of these resistors
directly affects the accuracy of the output. Use precision
resistors and set the nominal voltage approximately 1% to
2% high in order to make up for the load regulation. This
offset results in the best overall output accuracy over line
and load.
DESIGN CONSIDERATIONS
(Continued)
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相關代理商/技術參數(shù) |
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|---|---|
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| ML4895ESX | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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