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參數(shù)資料
| 型號(hào)： | ML4894 |
| 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(bǔ)償控制器（5.9V～15V到5V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(bǔ)償控制器（高于全?15V的到5V的變換）） |
| 文件頁(yè)數(shù)： | 8/10頁(yè) |
| 文件大?。?/td> | 246K |
| 代理商： | ML4894 |
ML4894
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
(
IN
IN
IN
(
)
(
)
)
(
)
+
-
1
2
5
5
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 ML4894.
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)
LAYOUT
A typical application circuit is shown in Figure 6.
Proximity of passive devices and adequate power and
ground planes are critical for reliable operation of the
circuit. In general, use the top layer for the high current
connections and the bottom layer for the quiet
connections such as GND, feedback and current sense.
Some more specific guidelines follow.
1. The connection from the current sense resistor to the
I
SENSE
pin should be made by a separate trace and
located as close to the lead of the resistor as possible.
The trace length from the sense resistor to the ML4894
should be kept as short as possible and away from
switching components and their traces.
2. The trace lengths from the buck regulator’s input
capacitor to the switching MOSFET, from the MOSFETs
to the inductor, from the synchronous rectifier MOSFET
to the sense resistor, and from the inductor to the output
capacitor should all be as short as possible.
3. The high current ground paths need to be kept separate
from the signal ground paths. The GND connection
should be made at a single-point star ground. It is very
important that the ground for the ML4894 GND pin be
made using a separate trace.
4. Concentrating on keeping the current sense and high
current connections short as well as keeping the
switching components and traces away from the
sensitive analog components and traces during layout
will eliminate the majority of problems created by a
poor layout.
5. The V
REG
and bypass capacitor needs to be located
close to the ML4894 for adequate filtering of the IC’s
internal bias voltage.
6. Remote sensing the output for improved load regulation
can be implemented with the ML4894. The output can
be remote sensed by using the top of the external
resistor divider as the remote sense point.
DESIGN CONSIDERATIONS
(Continued)
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ML4895 | Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的同步補(bǔ)償控制器（5.9V～15V到2.5V～4V變換）) |
| ML4900 | High Current Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的大電流同步補(bǔ)償控制器（5V到2.1V～3.5V變換）) |
| ML4901 | High Current Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的大電流同步補(bǔ)償控制器（12V到2.1V～3.5V變換）) |
| ML4902 | High Current Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的大電流同步補(bǔ)償控制器（5V到1.8V～3.5V變換）) |
| ML4903 | High Current Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的大電流同步補(bǔ)償控制器（12V到1.8V～3.5V變換）) |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ML4894ES | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Fairchild Semiconductor Corporation 功能描述: |
| ML4894ES/4895ES WAF UP | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| ML4895 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Synchronous Buck Controller |
| ML4895ES | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Fairchild Semiconductor Corporation 功能描述: |
| ML4895ESX | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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