- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385481 > LM3478 (National Semiconductor Corporation) High Efficiency Low-Side N-Channel Controller for Switching Regulator PDF資料下載
參數(shù)資料
| 型號： | LM3478 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | High Efficiency Low-Side N-Channel Controller for Switching Regulator |
| 中文描述： | 高效率低側N溝道開關穩(wěn)壓器控制器 |
| 文件頁數(shù)： | 15/21頁 |
| 文件大?。?/td> | 624K |
| 代理商： | LM3478 |
Typical Applications
(Continued)
If V
L
(t) is constant, di
L
(t)/dt must be constant. Hence, for a
given input voltage and output voltage, the current in the
inductor changes at a constant rate.
The important quantities in determining a proper inductance
value are I
L
(the average inductor current) and
i
L
(the
inductor current ripple). If
i
is larger than I
, the inductor
current will drop to zero for a portion of the cycle and the
converter will operate in discontinuous conduction mode. If
i
is smaller than I
, the inductor current will stay above
zero and the converter will operate in continuous conduction
mode. All the analysis in this datasheet assumes operation
in continuous conduction mode. To operate in continuous
conduction mode, the following conditions must be met:
I
L
>
i
L
Choose the minimum I
to determine the minimum L. A
common choice is to set
i
to 30% of I
. Choosing an
appropriate core size for the inductor involves calculating the
average and peak currents expected through the inductor. In
a boost converter,
and I
L_peak
= I
L
(max) +
i
L
(max),
where
A core size with ratings higher than these values should be
chosen. If the core is not properly rated, saturation will
dramatically reduce overall efficiency.
The LM3478 can be set to switch at very high frequencies.
When the switching frequency is high, the converter can be
operated with very small inductor values. With a small induc-
tor value, the peak inductor current can be higher than the
output currents, especially under light load conditions.
The LM3478 senses the peak current through the switch.
The peak current through the switch is the same as the peak
current calculated above.
PROGRAMMING THE OUTPUT VOLTAGE AND OUTPUT
CURRENT
The output voltage can be programmed using a resistor
divider between the output and the feedback pins, as shown
in
Figure 10
. The resistors are selected such that the voltage
at the feedback pin is 1.26V. R
F1
and R
F2
can be selected
using the equation,
A 100pF capacitor may be connected between the feedback
and ground pins to reduce noise.
The maximum amount of current that can be delivered at the
output can be controlled by the sense resistor, R
. Current
limit occurs when the voltage that is generated across the
sense resistor equals the current sense threshold voltage,
V
SENSE
. Limits for V
SENSE
have been specified in the elec-
trical characteristics. This can be expressed as:
I
sw(peak)
*
R
SEN
= V
SENSE
V
SENSE
represents the maximum value of the control signal
as shown in
Figure 2
. This control signal, however, is not a
constant value and changes over the course of a period as a
result of the internal compensation ramp (see
Figure 3
).
Therefore the current limit will also change as a result of the
internal compensation ramp. The actual command signal,
V
, can be better expressed as a function of the sense
voltage and the internal compensation ramp:
V
CS
= V
SENSE
(D
*
V
SL
)
V
is defined as the internal compensation ramp voltage,
limits are specified in the electrical characteristics.
The peak current through the switch is equal to the peak
inductor current.
I
sw(peak)
= I
L
+
i
L
Therefore for a boost converter
Combining the three equation yields an expression for R
SEN
L
www.national.com
15
相關PDF資料 |
PDF描述 |
|---|---|
| LM3478MM | High Efficiency Low-Side N-Channel Controller for Switching Regulator |
| LM3478MMX | High Efficiency Low-Side N-Channel Controller for Switching Regulator |
| LM3485 | Hysteretic PFET Buck Controller |
| LM3485MM | Hysteretic PFET Buck Controller |
| LM3485MMX | Hysteretic PFET Buck Controller |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM3478_09 | 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 |
| LM3478EVAL | 功能描述:BOARD EVALUATION LM3478 RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - DC/DC 與 AC/DC（離線）SMPS 系列:- 產(chǎn)品培訓模塊:Obsolescence Mitigation Program 標準包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓撲結構:升壓 頻率 - 開關:3MHz 板類型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
| LM3478EVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 EVAL BOARDFOR LM3478 RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM3478MA/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| LM3478MAX/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
發(fā)布緊急采購，3分鐘左右您將得到回復。