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參數(shù)資料
| 型號： | LM3477MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High Efficiency High-Side N-Channel Controller for Switching Regulator |
| 中文描述： | 1 A SWITCHING CONTROLLER, 575 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | MSOP-8 |
| 文件頁數(shù)： | 13/23頁 |
| 文件大?。?/td> | 815K |
| 代理商： | LM3477MM |
Functional Description
(Continued)
calculations for minimum inductance and necessary slope
resistance R
SL
are carried out based on this resonant peak-
ing.
Start-up/Soft-start
The LM3477/A incorporates an internal soft-start during
start-up. The soft-start forces the inductor current to rise
slowly and smoothly as it increases towards the steady-state
current. This technique is used to reduce the input inrush
current during soft-start. The soft-start functionality is effec-
tive for approximately the first 5ms of start-up.
Note:
The LM3477/A will not start-up if the output voltage is being held up
externally by more than 200mV.
If the slope resistor R
is used, the LM3477/Amay need up to 100 mA
of pre load to successfully start up.
Short Circuit Protection
When the voltage across the sense resistor (measured as
the V
I
differential voltage) exceeds V
, short-circuit
current limit gets activated. In the short-circuit protection
mode, the external MOSFET is turned off. When the short is
removed, the external MOSFET is turned on after five
cycles. The short circuit protection voltage V
is specified in
the
ELECTRICAL CHARACTERISTICS
section. V
SC
is
lower in the LM3477A than in the LM3477.
Shutdown
The compensation pin (Pin 2) of LM3477/A also functions as
a shutdown pin. If a low signal (refer to the
ELECTRICAL
CHARACTERISTICS
for definition of low signal) appears on
the COMP/SD pin, the LM3477/A stops switching and goes
into a low supply current mode. The total supply current of
the IC reduces to less than 10μA under these conditions.
Figure 5
shows different implementations of the shutdown
function.
Design Section
General
Power supply design involves making tradeoffs. To achieve
performance specifications, limitations will be set on compo-
nent selection. The LM3477/A provides many degrees of
flexibility in choosing external components to accommodate
various performance/component selection optimizations. For
example, the internal slope compensation can be externally
increased to allow smaller inductances to be used. The
design procedures that follow provide instruction on how to
select the external components in a typical LM3477/A buck
circuit in continuous conduction mode, as well as aid in the
optimization of performance and/or component selection.
See
Figure 6
for component reference and typical circuit.
The LM3477/A may also be designed to operate in discon-
tinuous conduction mode.
Programming the Output Voltage
The output voltage can be programmed using a resistor
divider between the output and the feedback pins, as shown
in
Figure 6
. The resistors are selected such that the voltage
at the feedback pin is 1.27V. R
FB1
and R
FB2
can be selected
using the equation:
V
OUT
= 1.27
*
(1+ R
FB1
/R
FB2
)
Calculating the Duty Cycle
In buck converter applications, the duty cycle of the
LM3477/A may be calculated as:
Where
V
D
= forward drop of the power diode
)
0.5V
V
Q
= V
DS
of the MOSFET when it is conducting
)
I
OUT
*
R
DSON
V
SN
= Voltage across the sense resistor = I
OUT
x R
SN
20003325
20003326
FIGURE 5. Implementing Shutdown in LM3477
200033M8
FIGURE 6. LM3477 Buck Converter Reference
Schematic
L
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13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3477MM | 制造商:Texas Instruments 功能描述:SWITCH CONTROLLER SMD 3477 MSOP8 |
| LM3477MM/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3477MMX | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3477MMX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3478 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Efficiency Low-Side N-Channel Controller for Switching Regulator |
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