- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄384596 > LM25007 (National Semiconductor Corporation) 42V, 0.5A Step-Down Switching Regulator PDF資料下載
參數(shù)資料
| 型號(hào)： | LM25007 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 42V, 0.5A Step-Down Switching Regulator |
| 中文描述： | 42V的0.5A的降壓型開(kāi)關(guān)穩(wěn)壓器 |
| 文件頁(yè)數(shù)： | 9/12頁(yè) |
| 文件大?。?/td> | 615K |
| 代理商： | LM25007 |
Over-Voltage Comparator
The over-voltage comparator is provided to protect the out-
put from overvoltage conditions due to sudden input line
voltage changes or output loading changes. The over-
voltage comparator monitors the FB pin versus an internal
2.875V reference. If the voltage at FB rises above 2.875V
the comparator immediately terminates the buck switch on-
time pulse.
ON Time generator and Shutdown
The on-time of the LM25007 is set inversely proportional to
the input voltage by an external resistor connected between
RON/SD and VIN. The RON/SD terminal is a low impedance
input biased at approximately 1.5V. The current through the
resistor and into the RON/SD pin is approximately propor-
tional to Vin and used internally to control the on-timer. This
scheme of input voltage feed-forward hysteretic operation
achieves nearly constant operational frequency over varying
line and load conditions. The on-time equation for the
LM25007 is :
Ton = 1.42 x 10
-10
x R
ON
/ V
IN
The RON/SD pin of the LM25007 also provides a shutdown
function which disables the regulator and significantly de-
creases quiescent power dissipation. By pulling the pin be-
low 0.7V activates the low power shutdown mode. The V
IN
quiescent current in the shutdown mode is approximately
100μA internal to the LM25007 plus the current in the R
ON
resistor. See
Figure 3
Current Limit
The LM25007 contains an intelligent current limit off-timer
intended to reduce the foldback characteristic inherent with
fixed off-time over-current protection. If the current in the
Buck switch exceeds 725mA the present cycle on-time is
immediately terminated (cycle by cycle current limit). Follow-
ing the termination of the cycle a non-resetable current limit
off timer is initiated. The duration of the off time is a function
of the external resistor (RCL) and the FB pin voltage. When
the FB pin voltage equals zero, the current limit off-time is
internally preset to 17μs. This condition occurs in short cir-
cuit operation when a maximum amount of off-time is re-
quired.
In cases of overload (not complete short circuit) the current
limit off-time is reduced as a function of the output voltage
(measured at the FB pin). Reducing the off-time with smaller
overloads reduces the amount of foldback and also reduces
the initial start-up time. The current limit off time for a given
FB pin voltage and R
CL
resistor can be calculated by the
following equation:
Toff = 10
-5
/ (0.59 + (V
FB
/ 7.22 x 10
-6
x R
CL
))
Applications utilizing low resistance inductors and/or a low
voltage drop rectifier may require special evaluation at high
line, short circuit conditions. In this special case the preset
17μs (FB = 0V) off-time may be insufficient to balance the
inductor volt*time product. Additional inductor resistance,
output resistance or a larger voltage drop rectifier may be
necessary to balance the inductor cycle volt*time product
and limit the short circuit current.
N - Channel Buck Switch and
Driver
The LM25007 integrates an N-Channel Buck switch and
associated floating high voltage gate driver. The gate driver
circuit works in conjunction with an external bootstrap ca-
pacitor and an internal high voltage diode. The bootstrap
capacitor is charged by V
CC
through the internal high voltage
diode. A 0.01uF ceramic capacitor connected between the
BST pin and SW pin is recommended.
During each cycle when the Buck switch turns off, the SW
pin is approximately 0V. When the SW pin voltage is low, the
bootstrap capacitor is charged from Vcc through the internal
diode. The minimum off timer, set to 300ns, ensures that
there will be a minimum interval every cycle to recharge the
bootstrap capacitor.
20165507
FIGURE 3. Shutdown Implementation
L
www.national.com
9
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM25007MM | 42V, 0.5A Step-Down Switching Regulator |
| LM25007MMX | 42V, 0.5A Step-Down Switching Regulator |
| LM25007SD | 42V, 0.5A Step-Down Switching Regulator |
| LM25007SDX | 42V, 0.5A Step-Down Switching Regulator |
| LM25010 | 42V, 1.0A Step-Down Switching Regulator |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM25007_08 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:42V, 0.5A Step-Down Switching Regulator |
| LM25007_11 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Boot Capacitor Regulation in LM25007 Constant-On-Time (COT) Converter |
| LM25007EVAL | 功能描述:電源管理IC開(kāi)發(fā)工具 LM25007 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM25007MM | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM25007MM/NOPB | 功能描述:直流/直流開(kāi)關(guān)調(diào)節(jié)器 42V,0.5A STEP-DOWN SWITCHING REG RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開(kāi)關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。